How the German cockroach conquered the world

DNA study implicates medieval warfare and colonial trade.

German cockroach extract prevents IL-13-induced CCL26 expression in airway epithelial cells through IL-13 degradation

Inhaled aeroallergens can directly activate airway epithelial cells (AECs). Exposure to cockroach allergens is a strong risk factor for asthma. Cockroach allergens mediate some of their effects through their serine protease activity; protease activity is also a major contributor to allergenicity. The Th2 cytokine interleukin-13 (IL-13) induces upregulation of the eosinophil chemotactic factor CCL26. CCL26 induces eosinophil migration in allergic inflammation. In this work, we studied the effect of cockroach proteases on IL-13-induced effects. Immersed cultures of the human bronchial epithelial cell line BEAS-2B and air-liquid interface (ALI) cultures of primary normal human bronchial epithelial (NHBE) cells were stimulated with IL-13, Blattella Germanica cockroach extract (CE), or both. IL-13-induced genes were analyzed with qRT-PCR. IL-13 induced upregulation of CCL26, periostin, and IL-13Rα2 in bronchial epithelial cells which were decreased by CE. CE was heat-inactivated (HICE) or pre-incubated with protease inhibitors. HICE and CE preincubated with serine protease inhibitors did not prevent IL-13-induced CCL26 upregulation. CE-degraded IL-13 and specific cleavage sites were identified. CE also decreased IL-4-induced CCL26 upregulation and degraded IL-4. Other serine proteases such as bovine trypsin and house dust mite (HDM) serine proteases did not have the same effects on IL-13-induced CCL26. We conclude that CE serine proteases antagonize IL-13-induced effects in AECs, and this CE effect is mediated primarily through proteolytic cleavage of IL-13. IL-13 cleavage by cockroach serine proteases may modulate CCL26-mediated effects in allergic airway inflammation by interfering directly with the pro-inflammatory effects of IL-13 in vivo.

Oral toxicity of an artificial sweetener sucralose on the German cockroach (Blattodea: Ectobiidae) and its impact on water balance and gut microbiome

Artificial or non-nutritive sweeteners are indigestible by most animals. Some sweeteners are orally toxic to insects and have received recent interest as potential safe insecticides due to their low mammalian toxicity. In this study, we investigated the oral toxicity of sucralose on insecticide-susceptible and resistant German cockroaches, Blattella germanica (L.). In a nonchoice test, we evaluated 5, 10, and 20% sucralose solutions. Depending on the cockroach strains, mean mortality ranged from 62.5 to 92.5%, 15 to 55%, and 2.5 to 27.5% for 20, 10, and 5% sucralose, respectively. Next, we measured the impact of a 20% sucralose treatment on water loss rates in the cockroach strains. All strains lost 23.0-30.29% of body water by 6 d. Dehydrated cockroaches were more prone to be killed by sucralose than nondehydrated ones. Lastly, we evaluated the effect of 20% sucralose treatment on gut bacterial composition and found the diversity of gut bacteria in treated cockroaches was significantly reduced after 3 days, implicating a rapid change in the alimentary environment.

Behavioral responses of field-collected German cockroaches to pyrethroids and pyrethroid-formulated insecticides

BACKGROUND

Pyrethroids are synthetic insecticides with low mammalian toxicity and broad-spectrum activity across insects. One major challenge with pyrethroids is their perceived repellency. This perception can influence decisions made by pest control operators, especially when insecticides are used to reduce insect entry into or movement within structures. One major indoor pest that has been repeatedly shown to be repelled by some pyrethroids is the German cockroach, Blattella germanica. However, most experiments evaluating pyrethroid repellency in the German cockroach have used end-point assays, which do not provide information on the movement that led to the final position. Therefore, we evaluated the kinetic behavioral response of field-collected German cockroaches to five pyrethroid-based products and their active ingredients (A.I.) in open behavioral arenas using advanced video tracking software. In addition, in an effort to compare our free-moving experiments with end-point assays, we evaluated sheltering behavior using two-choice harborage arrestment assays where German cockroaches were provided a choice between pyrethroid-treated and untreated shelters.

RESULTS

All pyrethroid-formulated products and their respective A.I.'s failed to affect field-collected German cockroach movement behavior in free-moving assays, while positive controls (DEET, corn mint oil) resulted in reduced time spent by German cockroaches in treated areas. However, despite their willingness to move over pyrethroids-treated surfaces, field-collected German cockroaches displayed a reduced propensity to arrest on pyrethroids treated tents.

CONCLUSION

While most pyrethroids/pyrethroid-formulated products affected German cockroach arrestment, pyrethroids and pyrethroid-formulated products failed to change German cockroach movement behavior in free-moving assays. These results indicate the pyrethroids tested act as contact irritants rather than true-spatial repellents on field-collected German cockroaches. This distinction is critical to refining pest management strategies involving pyrethroids. © 2023 Society of Chemical Industry.

Intestinal pathogens detected in cockroach species within different food-related environment in Pudong, China

Cockroaches are considered mechanical transmitters of infectious diseases, posing a threat to human health. This study assessed the potential of cockroaches in food-related environments to mechanically transmit intestinal pathogens. Cockroaches captured with traps were placed together into a low temperature refrigerator at - 80° for 2 h. Standard taxonomic keys and Fluorescent quantitative PCR techniques were applied for species identification and digestive tract etiological examination. A total of 360 cockroach traps were placed, with a positive rate of 20.8%, and 266 cockroaches were captured. In general, compared with other places and areas, the degree of infestation of cockroaches was more serious in catering places and kitchens. Blattella germanica were most found in catering places (40.2%), followed by Periplaneta fuliginosa in schools (22.2%). According to the life stage, among the 128 cockroach samples, 23 were positive for nymphs and 13 were positive for adults. There were statistically significant differences in the intestinal pathogen detection rates between nymphs and adults (P < 0.05). A total of eight intestinal pathogens were detected, and enterovirus infections were the main ones, with sapovirus being the most detected in Blattella germanica or nymph. Shiga toxin-producing Escherichia coli (STEC) was the most frequently isolated bacterium. Blastocystis hominis had the highest isolation rate. In contrast, 12 diarrhoeal disease pathogens were isolated, and the viruses and bacteria with the highest frequencies were norovirus and E. coli, respectively; no parasites were found. Blattella germanica and Periplaneta fuliginosa in food-related environments can act as potential vectors for the spread of intestinal pathogens and may pose a significant threat to public health.

A new amber representative of the genus Ectobius Stephens, 1835 (Blattodea: Ectobiidae) from Storeblt (Denmark)

A new fossil cockroach, Ectobius danekrae sp. nov., is described on the basis of a single male adult individual from late Eocene Danish amber. This is the third representative of the genus Ectobius Stephens, 1835 from Eocene ambers. The new species exhibits plesiomorphic characters of small right stylus and subsymmetrical claws, compared to the known fossil and living species of the genus. The references to Ectobius balticus (Germar et Berendt, 1856) and Margattea Shelford, 1911 sp. presence in Danish amber are insufficient.

Descriptions of new species and new records of water bugs (Hemiptera: Heteroptera: Gerromorpha & Nepomorpha) from southeastern Brazil

Although most of the diversity of true bugs (Hemiptera: Heteroptera) is terrestrial, over 550 species of water bugs (Heteroptera: Gerromorpha, Leptopodomorpha & Nepomorpha) have been recorded from Brazil alone. Southeastern Brazil, composed of the states of Esprito Santo, Minas Gerais, Rio de Janeiro and So Paulo, is the best studied region of the country, but there are still knowledge gaps in the area. Here, two new species are described from Esprito Santo: Hydrometra ruschii Cordeiro, Rodrigues & Moreira, sp. nov. and H. tuberculata Cordeiro, Rodrigues & Moreira, sp. nov. (Gerromorpha: Hydrometridae). Furthermore, new records from southeastern Brazil are provided for 78 species of water bugs, of which 19 are firstly recorded from Esprito Santo, four from Minas Gerais, eight from Rio de Janeiro, and seven from So Paulo.

Differential development and survival of Blattella asahinai and Blattella germanica (Blattodea: Ectobiidae) at six constant temperatures

The Asian cockroach, Blattella asahinai Mizukubo, is a peridomestic nuisance pest in the southeastern United States. Blattella asahinai is the closest relative to Blattella germanica (L.), the German cockroach, one of the most prolific and widespread domestic pests. Because these two species live in different habitats, they are expected to have differential development patterns reflecting environmental adaptations. Development of B. asahinai and B. germanica cockroach nymphs were observed at six constant temperatures ranging from 10 to 35 °C. At 10 °C and 15 °C, all nymphs died in the first instar, but B. germanica nymphs survived longer (10 °C: 12.9 d; 15 °C: 42.9 d) than B. asahinai nymphs (10 °C 8.2 d; 15 °C 18.4 d) at both temperatures. At 20 °C, 25 °C, and 30 °C, B. asahinai consistently had more instars and longer stadia than B. germanica. At 35 °C, only B. germanica was able to complete nymphal development; cannibalism among B. asahinai nymphs during molting was often observed at this temperature. The results for B. asahinai corroborated previously estimated growth patterns. The lower nymphal development threshold was 14.1 °C for B. germanica and 13.7 °C for B. asahinai. Comparing the development of B. germanica directly with its closest relative reveals specific physiological adaptations that B. germanica has developed for the indoor biome.

Survival of Salmonella Typhimurium in the hemolymph of the German cockroach vector is limited by both humoral immune factors and hemocytes but not by trehalose metabolism

The German cockroach (Blattella germanica) has been linked to transmission of Salmonella enterica serovar Typhimurium (S. Typhimurium), but infection dynamics within this vector are poorly characterized. Our recent work has focused on S. Typhimurium infection in the cockroach gut. However, microbial dissemination to the hemolymph is an essential aspect of many vector-borne pathogen transmission cycles and could potentially contribute to S. Typhimurium colonization of cockroaches. Therefore, the goal of this study was to examine the ability of S. Typhimurium to disseminate, survive, and proliferate in the hemolymph of cockroaches after oral infection. We detected only low numbers of bacteria in the hemolymph of a minority of insects (~26%) after oral infection. Further, S. Typhimurium was unable to survive overnight in cell-free hemolymph. Several hypotheses to explain the inability of S. Typhimurium to colonize hemolymph were tested. First, we investigated the ability of S. Typhimurium to metabolize trehalose, the primary sugar in hemolymph. S. Typhimurium grew efficiently in vitro using trehalose as a sole carbon source and mutant strains lacking trehalose metabolism genes exhibited no growth deficiencies in media mimicking the composition of hemolymph, suggesting that trehalose metabolism ability is not a factor involved in restricting survival in hemolymph. On the other hand, heat-inactivated cell-free hemolymph was permissive of S. Typhimurium growth, demonstrating that survival in hemolymph is limited specifically by heat-labile humoral factors. The involvement of cellular immune responses was also investigated and cockroach hemocytes in culture were observed to internalize S. Typhimurium within 1 h of exposure. Most hemocytes harbored few to no bacteria after 24 h, indicating that hemocyte responses are additionally involved in clearing infection from the hemolymph. However, dense intracellular clusters of S. Typhimurium were observed sporadically, suggesting a small subset of hemocytes may serve as reservoirs for bacterial replication. Together, our results reveal that a minute proportion of ingested S. Typhimurium is able to escape the cockroach gut and enter the hemolymph, but this systemic population is limited by both humoral effectors and hemocytes. Thus, we conclude that invasion of the hemolymph appears minimally important for colonization of the cockroach vector and that colonization of the gut is the main driver of vector-borne transmission. Our insight into the antimicrobial mechanisms of cockroach hemolymph also highlights the strong ability of these prevalent pests/vectors to cope with frequent infectious challenges in septic habitats.

A study of allergen detection panel in Guangzhou, southern China based on real-world data from the past 7 years

This study aims to reduce the cost of allergen testing for Guangzhou, China by limiting the number of allergens for which patients are tested, and provide a testing panel to improve diagnostic and therapeutic efficiency. This retrospective study of real-world data from 2012 to 2019 included 39,570 patients with suspected allergies in Guangzhou, southern China. All the patients were tested for one or more of the following allergens serum specific immunoglobulin E (sIgE): Dermatophagoides pteronyssinus, Dermatophagoides farinae, cat dander, dog dander, Artemisia vulgaris, Aspergillus fumigatus, Alternaria alternata, Blattella germanica, egg whites, milk, wheat, peanuts, soybeans, Cancer pagurus, and Penaeus monodon by PhadiaCAP 1000. Totally, only the positive rates of allergens sIgE in D. farinae, D. pteronyssinus, milk, egg whites, B. germanica, C. pagurus, A. alternata, and P. monodon were > 10%, the other allergens were between 4-7%. Moreover, among the allergic diseases, dust mites exhibited the overall highest positive rate, followed by milk and B. germanica. In children, milk was the main allergen, whereas in adults, mites, cockroaches, shrimp, and crab allergens had higher positive rates. The optimal scale analysis shows that the multiple sensitization classification of patients can be divided into three categories: I D. farinae and D. pteronyssinus; II. C. pagurus, P. monodon, and B. germanica; III. Milk and egg whites. Generally, a panel including 4 allergens can detect > 90% of the potential allergy in this local population. In Guangzhou, southern China, D. farinae, milk, B. germanica, and A. alternata as a panel screening allergy for suspected allergic patients was suggested base on this study.

Route of pesticide spread on the body surface of Blattella germanica (Linnaeus): a NanoSuit-energy dispersive X-ray spectroscopy analysis

Numerous studies have focussed on the mechanisms of entry of pesticides into insect body parts such as oral intake, penetration through the integument of the body wall, and inhalation through spiracles. However, little is known about how insecticides spread to the points of entry or the paths on the body surface that are used to reach the target sites. In this study, elemental signals of pesticide-mimicking test solutions were tracked and their routes of spreading in experimental insects (Blattella germanica L.) were investigated using NanoSuit (a method of surface modification) and energy dispersive X-ray spectroscopy, combined with high-resolution scanning electron microscopy. When the test solution initially adhered to the dorsal and/or ventral body surface, it tended to spread horizontally to reach lateral plates. Whereas, when the solution directly adhered to the anterior side of the lateral plates, it spread to posterior segments. In this case, however, spreading in the opposite direction (i.e., the solution directly adhered to the posterior side of the lateral plates) was interrupted at a boundary erected by different groups of fine structures; each protrusion was large, and the arrangement was rather dense in the posterior segments. Morphological features of these fine structures and chemical characteristics of the hydrophobic surface substances potentially regulate the strength of the capillary force, which determines pesticide spreading.

The prevalence of Wolbachia in multiple cockroach species and its implication for urban insect management

Cockroach management relies heavily on the use of conventional insecticides in urban settings, which no longer provide the anticipated level of control. Knowledge of cockroach endosymbionts, like Wolbachia, might provide novel avenues for control. Therefore, we screened 16 cockroach species belonging to 3 families (Ectobiidae, Blattidae, and Blaberidae) for the presence of Wolbachia. We mapped the evolution of Wolbachia-cockroach relationships based on maximum likelihood phylogeny and phylogenetic species clustering on a multi-loci sequence dataset (i.e., coxA, virD4, hcpA, and gatB) of Wolbachia genes. We confirmed the previous report of Wolbachia in 1 Ectobiid species; Supella longipalpa (Fab.), and detected the presence of Wolbachia in 2 Ectobiid species; Balta notulata (Stål) and Pseudomops septentrionalis Hebard, and 1 Blaberid species; Gromphadorhina portentosa (Schaum). All cockroach-associated Wolbachia herein detected were clustered with the ancestor of F clade Wolbachia of Cimex lectularius L. (bed bugs). Since Wolbachia provision C. lectularius with biotin vitamins that confer reproductive fitness, we screened the cockroach-associated Wolbachia for the presence of biotin genes. In toto, our results reveal 2 important findings: (i) Wolbachia is relatively uncommon among cockroach species infecting about 25% of species investigated, and (ii) cockroach-associated Wolbachia have biotin genes that likely provide nutritional benefits to their hosts. Thus, we discuss the potential of exploring Wolbachia as a tool for urban insect management.

Insecticide resistance and its potential mechanisms in field-collected German cockroaches (Blattodea: Ectobiidae) from Thailand

We investigated insecticide resistance profiles of field populations of the German cockroach, Blattella germanica (L.), collected from central regions of Thailand. Seven strains (PW, RB, MTH, MTS, TL, AY, and SP) were evaluated with diagnostic doses (DD; 3 × LD95 generated from a susceptible strain) of deltamethrin, fipronil, and imidacloprid using topical assays and compared with a susceptible strain (DMSC). Results showed fipronil (2-27% mortality), deltamethrin (16-58% mortality), and imidacloprid (15-75% mortality) resistance in the field strains. Synergism studies with piperonyl butoxide (PBO) and S,S,S-tributyl phosphorotrithioate (DEF) in combination with the DD of insecticides significantly increased (P < 0.05) mortality of the test insects of the field strains suggesting the involvement of P450 monooxygenase and esterase pathways of detoxification. Gel bait evaluations demonstrated that all field-collected strains were resistant to Maxforce Forte (0.05% fipronil), Maxforce Fusion (2.15% imidacloprid), and Advion Cockroach Gel Bait (0.6% indoxacarb) with mean survival times ranging from 1.87-8.27, 1.77-11.72, and 1.19-3.56 days, respectively. Molecular detection revealed that the Rdl mutation was completely homozygous in all field-collected strains except in the PW strain. Field-collected strains were screened for 3 voltage-gated sodium channel (VGSC) mutations associated with pyrethroid resistance. The L993F mutation was present in 5 strains, but no C764R and E434K mutations were detected.

Cockroaches as Trojan Horses for Control of Cockroach Aggregations With Baits

Gel bait formulations of insecticides have been shown to be highly effective in managing German cockroach (Blattella germanica L. [Blattodea: Ectobiidae]) populations. Three potential reasons for this are high palatability of baits, the use of slow-acting insecticides, and their horizontal transfer within aggregations, a phenomenon known as 'secondary mortality'. Our objective was to determine whether horizontal transfer can go beyond secondary, to tertiary and quaternary effects, and to compare various gel baits with different active ingredients. We fed adult females a bait and recorded their bait consumption, moribundity, and mortality. Groups of first instars were then exposed to the dead females and their feces, secondary mortality was quantified, and a new cohort of nymphs was then exposed to the feces and dead nymphs (for tertiary mortality); this process was repeated for quaternary mortality. This design did not distinguish among the major mechanisms of horizontal transfer of insecticides, namely coprophagy and contact with feces, exposure to regurgitated fluids, and cannibalism and necrophagy of nymphs. All the tested baits caused 100% mortality of the adult females that directly fed on the bait and high secondary mortality (average of >85%) within 48 hr. Baits containing either dinotefuran, emamectin benzoate, fipronil, or indoxacarb caused tertiary mortality (average of 15-70%), but only the fipronil and indoxacarb baits caused some quaternary mortality. The relative importance of secondary, tertiary, and quaternary transfer of the active ingredient remains to be determined in field populations of the German cockroach.

Glucose- and disaccharide-containing baits impede secondary mortality in glucose-averse German cockroaches

Glucose aversion in the German cockroach, Blattella germanica (L.), results in behavioral resistance to insecticidal baits. Glucose-averse (GA) cockroaches reject foods containing glucose, even in relatively low concentrations, which protects the cockroaches from ingesting lethal amounts of toxic baits. Horizontal transfer of baits and the resulting secondary mortality have been documented in German cockroaches, including in insecticide resistant strains. However, the effects of the GA trait on secondary mortality have not been investigated. We hypothesized that ingestion of insecticide baits that contain glucose or glucose-containing disaccharides would result in behaviorally relevant glucose levels in the feces, possibly deterring coprophagy by GA nymphs. We fed adult female cockroaches hydramethylnon baits rich in either glucose, fructose, sucrose, or maltose and compared secondary mortality of GA and wild-type (WT) nymphs via coprophagy. When adult females were fed baits containing glucose, sucrose, or maltose and their feces offered to nymphs, secondary mortality was significantly lower in GA nymphs than in WT nymphs. However, survival of GA and WT nymphs was similar on feces generated by adult females fed fructose bait. Analysis of feces indicated that disaccharides in baits were hydrolyzed into glucose, some of which was excreted in the feces of females that ingested the bait. Based on these results, we caution that baits containing glucose or glucose-containing oligosaccharides may impede cockroach interventions; while GA adults and large nymphs avoid ingesting such baits, first instars reject the glucose-containing feces of any WT cockroaches that consumed the bait.

Development of a cockroach (Blattella germanica) qPCR for the objective measurement of exposure at home

Cockroach allergens have a greater impact on asthma morbidity than those from dust mites, cats, and dogs. The American cockroach (Periplaneta americana) and the German cockroach (Blattella germanica) are most frequently responsible for sensitization. The worldwide prevalence of allergic sensitization has been estimated at 2 to 26 % and is influenced by unfavorable socioeconomic conditions. Exposure is generally measured by determining antigen levels in dust or through insect trapping. We developed a real-time quantitative PCR (qPCR) method to provide an objective measurement of B. germanica levels in dwellings. The specificity of the qPCR primers and TaqMan® hydrolysis probe was validated in silico with 18S rRNA sequences. No amplification was observed for other species of cockroaches, with the exception of Blattella nipponica, which is not common indoors. From 2018 to 2021, exposure to B. germanica was detected and quantified in 27 of 389 dwellings in Bourgogne-Franche-Comté (mean = 333.8; median = 9.1 and maximum = 5304 copy number equivalents) and in 236 of 3193 ELFE cohort dwellings in mainland France in 2011 (mean = 15.6; median < 1 and maximum = 1275 copy number equivalents). The distribution of dwellings testing positive for cockroaches (7 %) differed among the 12 regions of France: <1 % in two regions, between 1 and 5 % in eight regions, 16.5 % in two regions and 35 % around Paris. Exposure measurements by the EDC sampling and qPCR methods are effective ways to assess the exposure to cockroaches in dwellings. A knowledge of the level of exposure to cockroaches is particularly important for asthmatic patients, particularly those not allergic to other common antigens.

Impacts of Bioassay Type on Insecticide Resistance Assessment in the German Cockroach (Blattodea: Ectobiidae)

The German cockroach, Blattella germanica (L.), is one of the most critical urban pests globally due to the health risks it imposes on people, such as asthma. Insecticides are known to manage large cockroach population sizes, but the rapid rate at which they develop resistance is a continuing problem. Dealing with insecticide resistance can be expensive and time-consuming for both the consumer and the pest management professional (PMP) applying the treatment. Each cockroach population is unique because different strains have different insecticide susceptibilities, so resistance profiles must be considered. This study addressed the above issue in a controlled laboratory setting. Cockroach strains from Indianapolis, Indiana, Danville, Illinois, and Baltimore, Maryland, USA were used. Four insecticide active ingredients (AIs) most used by consumers and PMPs were selected for testing in vial bioassays to establish resistance profiles. Next, no-choice and choice feeding assays with four currently registered bait products were performed to assess the impacts of competing food and circadian rhythms on bait resistance levels. The results indicate that emamectin benzoate (Optigard) was the most effective AI in causing the highest mortality in all strains in vial and no-choice bioassays; whereas, the other AIs and products were more impacted by resistance. The results acquired from these studies can help develop rapid tests for use by PMPs based on the no-choice feeding assay while also adding more information supporting current resistance and cross-resistance evolution theories.

Experimental evaluation and structure-activity relationship analysis of bridged-ring terpenoid derivatives as novel Blattella germanica repellent

Cockroaches are urban pests that are very difficult to control. Using repellents is a green, safe and effective strategy for their control. In order to find novel cockroach repellents, the repellent activity of 45 bridged-ring terpenoid derivatives synthesized from β-pinene against Blattella germanica was tested. The relationship between the molecular structure of these bridged-ring terpenoid derivatives and their repellent activity against Blattella germanica was also analysed. The results show that some of the bridged-ring terpenoid derivatives exhibit good repellent activity against Blattella germanica, and six compounds (RR = 60.44-87.32%) show higher repellent activity against Blattella germanica than DEET (RR = 54.77%), making them promising for development as new cockroach repellents. Quantitative structure-activity relationship (QSAR) analysis revealed that the HOMO-1 energy, Kier and Hall index (order 2), Balaban index, and relative positive charged surface area of bridged-ring terpenoid derivatives have effects on repellent activity against Blattella germanica. The present study may provide a theoretical basis for the high-value use of β-pinene and can be helpful to the development of novel repellents against Blattella germanica.

Microbe-mediated activation of indoxacarb in German cockroach (Blattella germanica L.)

The German cockroach (Blattella germanica L.) is a major urban pest worldwide and is notorious for its ability to detoxify and resist insecticides. German cockroaches have generalist feeding habits that expose them to a range of potential hazardous substances and host a wide variety of unique microbial species, which may potentially facilitate unique detoxification capabilities. Since field German cockroach populations are routinely exposed to both bait and spray insecticide treatments, we hypothesized whether these unique gut microbes might play roles in toxicological processes of the host insect. The goals of this research were to understand the metabolic processes inside the German cockroach gut after treatment with kanamycin, a broad-ranging antibiotic, and indoxacarb, an oxadiazine pro-insecticide used in cockroach bait products. In these experiments, two resistant cockroach strains were obtained from field populations in Danville, IL and compared to a susceptible laboratory strain that had no previous exposure to insecticides (J-wax). Roaches provided kanamycin-infused water had lower median mortality to indoxacarb compared to the control treatment in feeding bioassays regardless of strain, but in vial (surface contact) bioassays, only susceptible cockroaches experienced a shift in mortality apparently due to their greater susceptibility. When frass extracts of indoxacarb-fed cockroaches were analyzed, less of the active, hydrolytic metabolite DCJW (N-decarbomethoxyllated JW062) was produced relative to the parent compound indoxacarb with the antibiotic KAN. This result was further corroborated by hydrolase activity assays of whole homogenized cockroach guts. Taken together these results provide novel evidence of microbe-mediated pro-insecticide activation in the cockroach gut.

Comparative Insecticide Uptake Characteristics of Chlorfenapyr Suggests an Additional Reason Why Bed Bugs (Hemiptera: Cimicidae) are so Difficult to Control

Insecticides interact with biochemical sites, disrupting homeostasis, leading to moribundity and death. Considering this process of intoxication, investigating insecticide uptake ensures an understanding of exposure profile. This study evaluated insecticide uptake by bed bugs, Cimex lectularius L., as affected by time and formulation, and a comparative uptake by German cockroaches, Blattella germanica (L.). Insects exposed to chlorfenapyr residues from two Phantom insecticide formulations (i.e., Aerosol and Suspended Concentrate (SC)) were solvent extracted and analyzed by GC-ECD. Chlorfenapyr uptake by bed bugs significantly increased with time, but the rate of external chlorfenapyr adsorption between the two formulations was not significantly different. However, initial exposure and uptake to the aerosol-treated versus SC-treated surfaces were significantly greater by 2.7x. Absorption-rates of chlorfenapyr residues inside the insect, associated with internal insect tissues or exoskeleton-bound, were significantly lower compared with external adsorption, with aerosol and SC formulations accumulating at 4.8x and 14.4x less, respectively. An unexpected formulation effect occurred with aerosol-treated papers and aging of residues. A reformulation of the aerosol provided a greater adsorption of chlorfenapyr at 19.1x that of the original formula after 2 hr. External versus internal uptake of chlorfenapyr by cockroaches was inverse to that seen in bed bugs, with greater chlorfenapyr absorption. Obstructing cockroach mouthparts prevented an internal uptake of chlorfenapyr and provided a similar exposure profile to bed bugs. This work demonstrates a need to evaluate insecticide uptake with formulation and insect morphology to maximize dose, especially in such a morphologically and environmentally isolated insect as the bed bug.

Combined metabolic and target-site resistance mechanisms confer fipronil and deltamethrin resistance in field-collected German cockroaches (Blattodea: Ectobiidae)

Despite insecticide resistance issues, pyrethroids and fipronil have continued to be used extensively to control the German cockroach, Blattella germanica (L.) (Blattodea: Ectobiidae) for more than two decades. We evaluated the physiological insecticide resistance in five German cockroach populations collected from 2018 to 2020 and measured the extent of metabolic detoxification and target-site insensitivity resistance mechanisms. Topically applied doses of the 3 x LD₉₅ of deltamethrin, fipronil, DDT, or dieldrin of a susceptible strain (UCR, Diagnostic Dose) failed to cause >23% mortality, and the 10 x LD₉₅ of deltamethrin or fipronil failed to cause >53% mortality. All field-collected strains possessed a combination of metabolic and target-site insensitivity mechanisms that cause reduced susceptibility. Elevated activities of esterase and glutathione S-transferase were measured, and the synergists piperonyl butoxide or S,S,S-tributyl phosphorotrithioate increased topical mortality up to 100% for deltamethrin and 93% for fipronil 10 x LD₉₅. The target-site mutations L993F of the para-homologous sodium channel and A302S of the GABA-gated chloride channel associated with pyrethroid and fipronil resistance, respectively, were found at ~80-100% frequency in field populations. Pyrethroid and fipronil spray formulations also were ineffective in a choice box assay against field-collected strains suggesting that these treatments would fail to control cockroaches under field conditions.

Prevalence of Cockroaches, Bed Bugs, and House Mice in Low-Income Housing and Evaluation of Baits for Monitoring House Mouse Infestations

Pests are frequently found in homes, especially in apartment buildings in low-income communities. We investigated the prevalence and patterns of pest infestations in low-income communities in four cities (Jersey City, Linden, Paterson, Trenton) in New Jersey, USA. Resident interviews, visual inspections, and the placement of monitors were used to identify pest infestations. A total of 1,753 apartments from 19 buildings or building complexes were accessed. The infestation rates of cockroaches, bed bugs (Cimex lectularius L.), and house mice (Mus musculus domesticus Schwarz and Schwarz) were 37, 9, and 20%, respectively. Among apartments with cockroaches, 97.8, 2.5, and 0.8% had German cockroach [Blattella germanica (L.)], American cockroach [Periplaneta americana (L.)], and Oriental cockroach (Blatta orientalis L.), respectively. The percentage of residents who were aware of the presence of cockroaches, bed bugs, and house mice was 70.8, 55.3, and 56.8%, respectively. The prevalence of pest infestation was associated with resident ethnicity and gender. Among 856 interview responses, 78% implemented methods themselves to control pests in their homes in the past six months. Chocolate spread detected 99% of house mouse infestations and was much more sensitive than three commercial blank baits. Significant differences were also observed in the feeding preference of the three commercial blank baits.

Feeding Behaviour of a Pyrethroid-Resistant Strain of the German Cockroach Blattella germanica (Linnaeus, 1767)

Many authors report biological differences among insecticide-resistant pest species, mainly associated with parameters of life history, but only a few studies approach differences at the behavioural level. Feeding behaviour in Blattella germanica (L.) is modulated by the detection of chemical volatiles emitted from food sources in order to be located a long-median distance, and also by the physicochemical properties of food. This work aimed to study the differences in the feeding behaviour of a susceptible and a pyrethroid-resistant strain of B. germanica, in the location and exploitation of a food source. Resistant males showed a lower performance in the feeding behaviour compared to susceptible males. Particularly, the time taken to locate the source was significantly higher in the resistant individuals, suggesting a lower capacity in the detection of food odours. In addition, although the Intake rate was negatively related to the stiffness of food for both strains, resistant individuals showed a lower intake rate compared to susceptible ones, when exploiting a food source of the same stiffness. In a control context, the phenotypic characteristics associated to feeding of pyrethroid-resistant individuals could induce a behavioural resistance mechanism caused by a reduction in the amount of toxic gel bait ingested. If that is the case, resistance of this strain would not be associated to physiological changes affecting the toxicity of the active principle of gel baits, but to a lower efficacy of these products against resistant individuals due to less amount of gel consumed, generating control problems of this pest.

Reduced Susceptibility Towards Commercial Bait Insecticides in Field German Cockroach (Blattodea: Ectobiidae) Populations From California

Gel bait insecticides have been extensively used to manage the German cockroach, Blattella germanica (L.) (Blattodea: Ectobiidae), but issues with reduced effectiveness of such formulations are becoming increasingly common. We collected five field strains of German cockroaches in California and evaluated them against five commercial bait products [Maxforce FC Magnum (0.05% fipronil), Maxforce Impact (1% clothianidin), Advion Evolution (0.6% indoxacarb), Optigard (0.1% emamectin benzoate) and Siege (2% hydramethylnon)]. Increased survivorship and incomplete mortality towards all baits were recorded in the field strains. We assessed susceptibility to the active ingredients fipronil, clothianidin, indoxacarb, abamectin, hydramethylnon, and deltamethrin using topical bioassays with diagnostic doses (3 × LD95 and 10 × LD95) developed from the UCR susceptible strain. Low mortality was registered when tested with the 3 × LD95's of deltamethrin (0%), fipronil (0-3%), and clothianidin (13-27%); low to moderate mortality when treated with the 3 × LD95 of indoxacarb (13-63%), and moderate to high mortality after treatment with the 3 × LD95 of abamectin (80-100%) and hydramethylnon (70-83%). The mortality of all strains remained low after treatment with the 10 × LD99 of deltamethrin (0-20%) and low to moderate with fipronil (20-70%). We found negative correlations (P < 0.05) between Advion Evolution mean survival time and indoxacarb 10 × LD95 mortality and between Maxforce Impact and clothianidin 10 × LD95 mortality. These findings demonstrate multiple resistance towards all tested commercial bait insecticides except Optigard, suggesting the effectiveness of avermectin products in resistance management programs.

Characterization of the pyrethroid resistance mechanisms in a Blattella germanica (Dictyoptera: Blattellidae) strain from Buenos Aires (Argentina)

The use of chemical insecticides is the main control method for Blattella germanica worldwide. The prolonged and frequent use of insecticides produced the selection of insecticide-resistant individuals. The German cockroach is one of the most widespread urban pests in Argentina. In the last decades, resistance monitoring studies in this country demonstrated that there is a high prevalence of pyrethroid-resistant populations of B. germanica in the field. In this work, we studied the resistance mechanisms of a field-collected strain of B. germanica at toxicological, enzymatic, and molecular levels. A resistance ratio of 100 was obtained for the resistant strain when it was exposed to β-cypermethrin. The pretreatment with specific synergists (piperonyl butoxide and triphenyl phosphate) led to a significant increase in the toxicity of the pyrethroid, suggesting an involvement of oxidases and esterases in the detoxification of this insecticide. Moreover, esterase and oxidase activities in the resistant strain were 1.5-fold and 2-fold higher respectively, compared to the susceptible individuals. On the other hand, the voltage-gated sodium channel gene of the resistant cockroaches did not show nucleotidic substitutions in the domain II which are associated to knockdown resistance in this species. These results suggest that the main mechanism of resistance of the studied cockroaches' strain is metabolic, mainly due to an increase in the activity of oxidase and esterase enzymes. The results of this work in addition to other reports found in literature show that the extended use of a single active principle for cockroach control promotes the development of resistance leading to control failure in the field. In contrast, integrated pest management strategies include the use of different control tools in addition to chemical insecticides, which delay the appearance of resistance increasing the efficacy of pest control.

Comparison of Diet Preferences of Laboratory-Reared and Apartment-Collected German Cockroaches

The German cockroach, Blattella germanica (L.) (Blattodea: Ectobiidae), is a common pest of human-built structures worldwide. German cockroaches are generalist omnivores able to survive on a wide variety of foods. A number of studies have concluded that laboratory-reared B. germanica self-select diets with an approximate 1P:3C (protein-to-carbohydrate) ratio. We predicted that field-collected insects would exhibit more variable dietary preferences, related to the wide-ranging quality, quantity, and patchiness of foods available to them. We compared diet self-selection of B. germanica within apartments and in the laboratory by offering them a choice of two complementary diets with 1P:1C and 1P:11C ratios. We observed high variation in the population-level self-selection of these diets among individual apartment sites as well as among various life stages tested in laboratory-based assays. Significant differences between populations in various apartments as well as between populations maintained in the laboratory suggested that factors beyond temporary food scarcity influence diet choice. Nevertheless, we found significant correlations between the amounts of diets ingested by cockroaches in apartments and cockroaches from the same populations assayed in the laboratory, as well as between males, females, and nymphs from these populations. These findings suggest that females, males, and nymphs within apartments adapt to the local conditions and convergently prefer similar amounts of food of similar dietary protein content.

Laboratory and Field Evaluations of Food-Based Attractants for Monitoring German Cockroaches

Sticky traps are standard tools for monitoring German cockroaches (Blattella germanica L.); however, because they lack an attractant, their ability to catch cockroaches is by chance and largely dependent upon the location of placement and length of time they are left in place. Currently, highly effective and economical cockroach attractants are not available. Food-based attractants have the potential to be employed in sticky traps and enhance their effectiveness on trapping German cockroaches. We conducted laboratory and field experiments to evaluate the effectiveness of novel food-based attractants. Laboratory results showed that sticky traps containing the following attractants: apple oil, blueberry oil, orange oil, or their combination, fish oil, peanut butter, Roach lure tablet, and bacon extract had significantly higher trap catch compared to those traps that do not contain an attractant. Apple plus blueberry oil mixture and Roach lure tablet enhanced the trap catch by ≥ 103%, and bacon extract enhanced the trap catch by 92% in the field assays. Apple plus blueberry oil mixture and Roach lure tablet were the most promising attractants based on laboratory and field experiments. Apple plus blueberry oil mixture aged for 2 wk was as attractive to German cockroaches as fresh mixture.

The cys-loop ligand-gated ion channel gene superfamilies of the cockroaches Blattella germanica and Periplaneta americana

BACKGROUND

Cockroaches are serious urban pests that can transfer disease-causing microorganisms as well as trigger allergic reactions and asthma. They are commonly managed by pesticides that act on cys-loop ligand-gated ion channels (cysLGIC). To provide further information that will enhance our understanding of how insecticides act on their molecular targets in cockroaches, we used genome and reverse transcriptase polymerase chain reaction (RT-PCR) data to characterize the cysLGIC gene superfamilies from Blattella germanica and Periplaneta americana.

RESULTS

The B. germanica and P. americana cysLGIC superfamilies consist of 30 and 32 subunit-encoding genes, respectively, which are the largest insect cysLGIC superfamilies characterized to date. As with other insects, the cockroaches possess ion channels predicted to be gated by acetylcholine, γ-aminobutyric acid, glutamate and histamine, as well as orthologues of the drosophila pH-sensitive chloride channel (pHCl), CG8916 and CG12344. The large cysLGIC superfamilies of cockroaches are a result of an expanded number of divergent nicotinic acetylcholine receptor subunits, with B. germanica and P. americana, respectively, possessing eight and ten subunit genes. Diversity of the cockroach cysLGICs is also broadened by alternative splicing and RNA A-to-I editing. Unusually, both cockroach species possess a second glutamate-gated chloride channel as well as another CG8916 subunit.

CONCLUSION

These findings on B. germanica and P. americana enhance our understanding of the evolution of the insect cysLGIC superfamily and provide a useful basis for the study of their function, the detection and management of insecticide resistance, and for the development of improved pesticides with greater specificity towards these major pests. © 2020 Society of Chemical Industry.

Effects of novaluron ingestion and topical application on German cockroach (Blattella germanica) development and reproduction

BACKGROUND

Insect growth regulators disrupt insect development and reproduction. Chitin synthesis inhibitors (CSIs) allow the insect to grow normally, but because chitin is an essential component of the cuticle, formation of a new cuticle and ecdysis are prevented and the insect dies. CSIs can also kill embryos by disrupting their normal development. We evaluated the potential utility of novaluron in bait formulations against the German cockroach (Blattella germanica L.).

RESULTS

The minimum novaluron intake that interfered with molting and reproduction was assessed by exposing nymphs and adult females to novaluron. Results showed that 1 day of feeding on 0.1% novaluron was sufficient to disrupt molting in nymphs and prevent adult females from developing viable oothecae. The long-term effects on gravid females were investigated by feeding females 0.1% novaluron for different 5-day intervals during successive stages of gestation. Results demonstrated that gravid females fed novaluron during any period of gestation were able to produce viable eggs. To determine if ingestion of novaluron affected mating success and fertility of adult males, males were fed novaluron and then allowed to mate with untreated virgin females. Males that fed on novaluron successfully mated, and the females produced viable oothecae. Finally, direct comparisons revealed that novaluron is equally effective by ingestion and topical application.

CONCLUSIONS

Novaluron caused mortality in nymphs and interfered with ootheca production in adult females, but only before they formed an ootheca. It successfully reduced German cockroach populations in cages and has potential to be incorporated in cockroach baits.

Boric acid was orally toxic to different instars of Blattella germanica (L.) (Blattodea: Blattellidae) and caused dysbiosis of the, gut microbiota

Boric acid, a well-established chemical insecticide, has a good control effect on various types of cockroaches. In this study, we investigated the oral virulence effect of boric acid on German cockroach (Blattella germanica) of various instars and characterized its effect on the gut microbiota by high-throughput sequencing technology. The results of an oral toxicity test showed that the toxicity of boric acid was positively correlated with its concentration and negatively correlated with the instar of cockroach nymphs. The 1-3 instar nymphs showed the strongest sensitivity to boric acid, which exhibited a median lethal time of only 3.16 d, while the 6-7 instar nymphs showed the weakest sensitivity, and exhibited a median lethal time of 10.15 d. There was no significant difference between male and female insects regarding their sensitivity to boric acid. Oral treatment of boric acid resulted in severe dysbiosis in cockroaches, the relative abundances of Bacteroides, which can degrade a variety of complex macromolecules, and Enterococcus, which can inhibit pathogenic microorganisms, were significantly reduced, while the relative abundance of the opportunistic pathogenic bacterium Weissella was significantly increased. It was speculated that dysbiosis of gut microbiota might accelerate the toxicity of boric acid on German cockroaches.

Effects of Antibiotics on the Dynamic Balance of Bacteria and Fungi in the Gut of the German Cockroach

The German cockroach, Blattella germanica (L.) (Blattaria: Blattidae) harbored diverse microorganisms in the digestive tract, including bacteria, fungi, viruses, archaea, and protozoa. This diverse community maintains a relatively stable balance. Some bacteria have been confirmed to play crucial roles in the insect's physiology, biochemistry, and behavior. Antibiotics can effectively eliminate bacteria and disrupt the balance of gut microbiota, but the time-course of this process, the structure of the new microbial community, and the dynamics of re-assemblage of a bacterial community after antibiotic treatment have not been investigated. In the present study, antibiotic (levofloxacin and gentamicin) ingestion reduced bacterial diversity and abundance in the cockroach gut. Within 14 d of discontinuing antibiotic treatment, the number of culturable gut bacteria returned to its original level. However, the composition of the new bacterial community with greater abundance of antibiotic-resistant Enterococcus and Dysgonomonas was significantly different from the original community. Network analysis showed that antibiotic treatment made the interaction between bacteria and fungi closer and stronger in the cockroach gut during the recovery of gut microorganisms. The study on the composition change, recovery rules, and interaction dynamics between gut bacteria and fungi after antibiotic treatment are helpful to explore gut microbes' colonization and interaction with insects, which contributes to the selection of stable core gut bacteria as biological carriers of paratransgenesis for controlling Blattella germanica.

Screening of the Repellent Activity of 12 Essential Oils Against Adult German Cockroach (Dictyoptera: Blattellidae): Preparation of a Sustained Release Repellent Agent of Binary Oil-γ-CD and its Repellency in a Small Container

Cockroaches are important sanitary pests and very difficult to control worldwide. With public concern about traditional insecticides, cockroach control agents should be environmentally friendly, highly efficient, and economical. In this article, 12 essential oils were screened to test their repellent effect against Blattella germanica. To develop essential oils as repellent agents, the oils were further examined in binary synergistic combinations. Ilex chinensis Sims (Sapindales: Aquifoliaceae) oil, Lavandula spp (Tubiflorae: Labiatae) oil, and Elsholtzia ciliata (Thunb.) Hyland (Tubiflorae: Labiatae) oil showed excellent repellent activities with lower RD50 (repellency dose for 50% of treated adults) values of 218.634, 154.590, and 223.989 µg/cm2, respectively, compared to those of other oils and the positive control. The I. chinensis oil and E. ciliata oil (weight ratio of 1:1.41) combination also displayed a remarkable synergistic effect against B. germanica. Their cotoxicity coefficient was 214.4. The major chemical constituents in E. ciliata and I. chinensis oils were respectively 3,7-dimethyl-1, 6-octadien-3-ol and methyl salicylate. The binary oil mixtures were formulated as a sustained release agent with γ-CD. The optimal preparation should be an 8:1 ratio of γ-CD to oils, with a 1 h stirring time, 50°C stirring temperature, and 1:12 ratio of γ-CD to ddH2O. The results of this study suggest that sustained release of binary oil-γ-CD exhibited a prolonged repellent activity (10 h) against B. germanica. This sustained-release agent could be further investigated and developed as a novel repellent preparation.

Essential Oil Components in Superabsorbent Polymer Gel Modify Reproduction of Blattella germanica (Blattodea: Ectobiidae)

The use of essential oil components (EOCs) against the German cockroach, Blattella germanica (L.), has increasingly received attention from researchers. However, the determination of lethal doses/concentrations alone does not provide enough information on the range of biological effects of these EOCs. To improve our understanding of the potential effects of EOCs, we examined biological parameters of B. germanica exposed to sublethal EOCs formulated in gels. This study employed superabsorbent polymer (SAP) gel to prolong bioavailability of limonene, carvacrol, and β-thujaplicin, and evaluated how these EOCs shape biological parameters of B. germanica. Overall, median survival days ranged from 57 to 69.5 d for males and 73 to 99 d for females. The survival day ranking for the EOCs was limonene > β-thujaplicin > carvacrol. Carvacrol and β-thujaplicin gels reduced male longevity by at least 34 and 39%, respectively, while limonene had no effect. The longevity of females was reduced by limonene, but not by carvacrol and β-thujaplicin gels. EOCs significantly suppressed overall adult females' reproductive period, oothecal hatchability, reduced fecundity, and interoothecal period, but not the number of oothecae formed and egg incubation period. The preoviposition period (mean: 2-25 d) ranking was limonene < carvacrol < β-thujaplicin. Based on these results, limonene, carvacrol, and β-thujaplicin in SAP gels show promising potential to reduce adult male survival/longevity, suppress egg hatchability and female fecundity, and delay the interoothecal period. These findings may represent the basis for the practical use of EOCs as a tactic in integrated pest management systems for B. germanica.

Insecticide Resistance, and Its Effects on Bait Performance in Field-Collected German Cockroaches (Blattodea: Ectobiidae) From Taiwan

Insecticide resistance in the German cockroach, Blattella germanica (L.), is a significant challenge to the pest management professionals worldwide. We collected 24 field populations of B. germanica from different localities in Taiwan island, reared them for one to two generations, and evaluated them for their resistance to deltamethrin, propoxur, and fipronil using the surface-contact method. Results showed that deltamethrin resistance ratio ranged from 1.5 to 817.5×. Among the strains, TC Supermarket, TC Sanshang Logistics, TC THSR, and TC 1Taichungsteak strains showed very high resistance to deltamethrin, which mortality ranged between 0 and 33% at 7-d post-treatment. On the other hand, resistance to propoxur and fipronil RR were 0.70-7.13× and 1.67-3.72×, respectively. Synergism studies using piperonyl butoxide (PBO) and S,S,S-tributylphosphorotrithioate (DEF) suggested the major involvement of cytochrome P450 monooxygenase and minor involvement of esterases. However, deltamethrin resistance in two strains (i.e., TC Supermarket and TC THSR) was not affected by both PBO and DEF, indicating that other mechanisms are involved in the resistance, including kdr resistance. Evaluation of the field strains using commercial gel baits containing fipronil, imidacloprid, hydramethylnon, and indoxacarb for up to 7 d resulted in 24.4-100%, 11.3-78.5%, 15.8-75.5%, and 63.3-100% mortality, respectively. We found that high deltamethrin resistance in some strains could affect the performance of fipronil, imidacloprid, and indoxacarb baits, indicating the potential involvement of cytochrome P450 monooxygenase in reducing the effectiveness of the bait toxicants.

The Behavioral Response of Blattella germanica (Blattodea: Ectobiidae) Exposed to DEET Varies Throughout Its Life Cycle

The German cockroach, Blattella germanica L., is a hemimetabolous insect pest of economical and medical importance. N,N-diethyl-3-methylbenzamide (DEET) is an insect repellent whose effect on this species has received very little attention. The objective of this work was to determine whether the behavioral response of B. germanica to DEET varies along its life cycle. DEET repellence was assessed in small, medium, and large nymphs, and in adults of both sexes, all originated from the same laboratory colony (CIPEIN). The experimental arena consisted in a piece of filter paper treated with repellent on one half (195 µg/cm2) and solvent alone on the other half. A cockroach was placed on the filter paper, and its behavior was filmed. An image analyzer was used to quantify how long the insect spent on each side of the paper. As a control, a cockroach was exposed to a piece of filter paper treated with solvent (acetone) alone. Each assay was repeated independently six times. Distribution coefficient (DC) values were calculated, a parameter that ranges between 0 (attraction) and 1 (repellence). Small nymphs were more sensitive to DEET (mean DC = 0.93). The mean DC values of the other groups varied between 0.62 (medium nymphs) and 0.71 (male adults). The group of medium nymphs was the only one whose behavior was not significantly altered by exposure to DEET. The results show the importance of assessing insect repellents at different stages of the insect's life cycle in order to obtain a complete panorama of its effect.

Quantifying the Efficacy of an Assessment-Based Pest Management (APM) Program for German Cockroach (L.) (Blattodea: Blattellidae) Control in Low-Income Public Housing Units

Over the last several decades, low-income public housing facilities have been known to be infested with particularly large German cockroach populations. These populations persist even though the housing pest control contracts often require, and pay for, IPM practices to be used in their facilities. When Virginia Tech researchers began reviewing public housing contracts in Virginia and North Carolina, it was easy to see why these 'IPM programs' were not successful. Many of these 'low-bidder' contracts do not allow the technician enough time in each apartment to assess the size of the pest population. In addition, these pest management contracts did not require German cockroach population monitoring, even though all IPM programs are based on assessments of the pest population. There was a clear need for an effective, easy to apply cockroach management program in U.S. public housing authorities. This study determined the long-term efficacy of an Assessment-based Pest Management (APM) program for German cockroach control in U.S. public housing facilities. Specifically, we evaluated an APM program where the residents were not asked to clean or prepare for treatment, and where overnight cockroach trap counts were used to determine the volume of gel bait that would be applied. The APM baiting program was conducted for 15 mo in three housing authorities. In all three housing authorities, cockroach populations in test units were typically reduced by >90%. German cockroach infestations were even eliminated from 49 of the 65 (75%) test units during this study.

Potency of Papaya Leaf (<i>Carica papaya</i> L.) as Toxicant and Repellent against German Cockroach (<i>Blattella germanica</i> L.)

BACKGROUND AND OBJECTIVE

Papaya leaves have the potency to be developed as alternative insecticide to control the German cockroaches that have been resistant to synthetic insecticides. This study aimed to determine the potency of ethanolic extract of papaya leaf as toxicant and repellent against 2 populations of German cockroaches which are known resistant to synthetic insecticide.

MATERIALS AND METHODS

The methods that used was contact toxicity test and repellency test. The ethanolic extract of papaya leaf residues were used in contact toxicity test of 4 residues and a sub-lethal residue in repellency test. Three populations of German cockroach were collected in field and kept in laboratory.

RESULTS

Lethal residue 50% (LR50) of ethanolic extract of papaya leaf between 2.97-4.72 mg cm-2 while lethal residue 90% (LR90) between 6.05-8.92 mg cm-2 and very effective killed all population of German cockroach. Repellency value of ethanolic extract of papaya leaf with a sub-lethal residue of 0.39 mg cm-2 between 88.89 -94.74% and level of repellency was very repellent.

CONCLUSION

Ethanolic extract of papaya leaf could be formulated as a potent natural insecticide to control populations of German cockroach that have been resistant to synthetic insecticides.

Involvement of integument-rich CYP4G19 in hydrocarbon biosynthesis and cuticular penetration resistance in Blattella germanica (L.)

BACKGROUND

Cuticle penetration plays an important role as a mechanism of insecticide resistance, but the underlying molecular mechanism remains poorly understood. In Blattella germanica, the cytochrome P450 gene, CYP4G19, is overexpressed in a pyrethroid-resistant strain. Here, we investigated whether CYP4G19 is involved in the biosynthesis of hydrocarbons and further contributes to cuticular penetration resistance in B. germanica.

RESULTS

Compared with the susceptible strain, pyrethroid-resistant cockroaches showed lower cuticular permeability with Eosin Y staining. Removal of epicuticular lipids, mainly nonpolar hydrocarbons, with a hexane wash intensified the cuticular permeability and decreased the resistance index of the resistant strain. CYP4G19 was predominately expressed in the abdominal integument and could be upregulated by desiccation stress or short exposure to beta-cypermethrin. Overexpression of CYP4G19 in the resistant strain was positively correlated with a higher level of cuticular hydrocarbons (CHCs). RNAi-mediated knockdown of CYP4G19 significantly decreased its expression and caused a reduction in CHCs. Meanwhile, CYP4G19 suppression resulted in a non-uniform array of the lipid layer, enhanced cuticle permeability, and compromised insecticide tolerance.

CONCLUSION

Our findings confirm that CYP4G19 is involved in hydrocarbon production and appears to contribute to hydrocarbon-based penetration resistance in B. germanica. This study highlights the lipid-based penetration resistance, advancing our understanding of the molecular mechanism underlying P450-mediated cuticular penetration resistance in insects. © 2019 Society of Chemical Industry.

Pervasive Resistance to Pyrethroids in German Cockroaches (Blattodea: Ectobiidae) Related to Lack of Efficacy of Total Release Foggers

Despite limited efficacy data, do-it-yourself (DIY) insecticide products often promise low-cost alternatives to professional pest control. Total release foggers (TRFs, 'bug bombs'), which are prominent DIY products, were recently shown to be ineffective at reducing German cockroach (Blattella germanica L.) infestations, in contrast to highly effective baits. However, the reason(s) for TRF failure remain unknown. Therefore, we investigated insecticide resistance of apartment-collected cockroaches from homes where TRFs failed. In topical (direct) application assays, resistance to cypermethrin (a common active ingredient in TRFs) was 202 ± 33 times that of a laboratory insecticide-susceptible population (based on LD50 ratios), while resistance to fipronil, a common bait active ingredient, was considerably lower at 14 ± 2 times that of the laboratory insecticide-susceptible population. The addition of PBO, a P450 inhibitor that synergizes pyrethroids, enhanced the efficacy of cypermethrin, but only at high doses of cypermethrin. Additionally, >96% of screened cockroaches possessed at least one copy of the L993F mutation in the voltage-gated sodium channel, known to confer resistance to pyrethroids (knockdown resistance, kdr). Because TRF treatments killed insecticide-susceptible sentinel cockroaches but failed to kill apartment-collected cockroaches, these results suggest that pyrethroid resistance is a major factor contributing to the failure of TRFs. Multiple mechanisms of resistance, including metabolic detoxification of the pyrethroids and kdr mutations that confer target-site insensitivity, suggest that TRFs would lack efficacy against German cockroaches in residential settings, where high levels of pyrethroid resistance have been documented globally.

Spatial Distribution of German Cockroaches in a High-Rise Apartment Building During Building-Wide Integrated Pest Management

The German cockroach Blattella germanica (L.) (Blattodea, Ectobiidae) is one of the most common indoor pests in multifamily housing communities. Our objectives were to investigate the spatial distribution patterns of German cockroach infestations in a multiunit dwelling before and after building-wide integrated pest management (IPM) implementation. The study was conducted in a high-rise apartment building with 188 residential units in Paterson, New Jersey. All the identified infestations were treated by researchers using IPM implementation, and monitoring was repeated at 6 and 12 mo after the initial survey. We examined cockroach spatial distribution patterns within and between apartments. Traps placed by the stove and refrigerator caught significantly more cockroaches than traps placed in the kitchen cabinet under the sink or in the bathroom. At month 0, cockroach infestations within the building were spatially correlated. At 12 mo after implementation of IPM, only infestations cross the floors remained to be correlated. Therefore, IPM not only eliminates cockroach infestations in individual units, but also reduces cockroach dispersal between units.

Role of Cuticular Hydrocarbons in German Cockroach (Blattodea: Ectobiidae) Aggregation Behavior

Aggregation can be adaptive by providing protection from predators, facilitating thermoregulation, and expediting the location of food, shelter, and mates. German cockroaches Blattella germanica L. (Blattodea: Ectobiidae), are obligatory commensals in human-built structures, where they aggregate in crevices during the day. The source of the aggregation pheromone that drives this behavior and its chemical identity remain unclear. Cuticular hydrocarbons (CHCs) in feces have been proposed to serve as aggregation pheromone, but this function has not been investigated in relation to visual and tactile cues that mediate aggregation. Our objective was to delineate how CHCs in the feces and on the cockroach body operate in conditions that reflect the German cockroach's ecology-either applied to shelters, representing fecal deposition, or to previously extracted cockroaches, representing shelter co-habitation with other cockroaches. Cockroaches and feces-conditioned filter papers were extracted, CHCs were purified by flash chromatography, and two-choice behavior assays were performed with first instar nymphs. Our results confirmed that nymphs preferred to rest within feces-conditioned shelters. However, purified CHCs did not elicit more aggregation than solvent-treated control shelters. Nymphs significantly preferred to rest in shelters that contained a CHC-free dead female, but the addition of CHCs to the female did not enhance aggregation. Nymphs preferred to aggregate with the CHC-free female over CHC-treated shelters. Finally, a methanol extract of feces was highly effective at eliciting aggregation, contesting previous reports that fecal CHCs serve as aggregation pheromone. We assert that CHCs play a minor, if any, role in the aggregation behavior of German cockroaches.

Comparative Proteomics Analysis Between the Short-Term Stress and Long-Term Adaptation of the Blattella germanica (Blattodea: Blattellidae) in Response to Beta-Cypermethrin

A proteomic method combining two-dimensional polyacrylamide gel electrophoresis and tandem mass spectrometry was used to compare the hemolymph expression profiles of a beta-cypermethrin-resistant Blattella germanica L. strain (R) and a susceptible strain (S) after 24 h of beta-cypermethrin induction. The results showed that there were 42 differentially expressed proteins after induction of the R strain: 4 proteins were upregulated and 38 proteins were downregulated. One hundred one hemolymph proteins were differentially expressed after induction of the S strain: 53 proteins were upregulated and 48 proteins were downregulated. The identified proteins were mainly classified into the following categories: energy metabolism proteins such as arginine kinase and triose phosphate isomerase, detoxification-related proteins such as glutathione S-transferases (GSTs), signal molecule-regulated proteins such as nitric oxide synthase (NOS), and other proteins such as kinetic-related proteins and gene expression-related proteins. Several proteins show significant differences in response to short-term stress and long-term adaptation, and differential expression of these proteins reflects an overall change in cellular structure and metabolism associated with resistance to pyrethroid insecticides. In summary, our research has improved the understanding of the molecular mechanisms of beta-cypermethrin resistance in German cockroaches, which will facilitate the development of rational methods to improve the management of this pest.

Residents Attitudes and Home Sanitation Predict Presence of German Cockroaches (Blattodea: Ectobiidae) in Apartments for Low-Income Senior Residents

The German cockroach, Blattella germanica (L.), is a common pest found in apartment buildings. Prevalence of cockroach infestations is affected by both environmental conditions and building occupant behavior, but their relationships are not well studied. The objective of this study was to analyze the presence of German cockroaches in relation to environmental conditions, resident demographics, and residents' tolerance of cockroaches. We conducted resident interviews, placed sticky traps to detect the presence of German cockroaches, and assessed apartment conditions. A total of 388 apartments from seven low-income apartment buildings, occupied by senior citizens in New Jersey, United States, were included. Among the 344 apartments where trap count data were obtained, 30% had German cockroaches. Among interviewed residents whose apartments had existing cockroach infestations, 36% were unaware of the presence of cockroaches. The odds of having cockroaches in apartments with a 'poor' sanitation rating in kitchens and bathrooms was 2.7 times greater than that in apartments with better sanitation conditions. Residents' tolerance to cockroaches is significantly associated with presence of cockroaches and cockroach population size. The median cockroach count when residents were bothered by cockroaches was ≥3, based on deployment of 4 sticky traps per apartment, over a 2-wk period. Assessing and reducing cockroach tolerance thresholds and improving housekeeping through resident education and assistance from community and housing management should be incorporated in future cockroach management programs in order to reduce high cockroach infestation rates found in similar communities.

A Review on the Insecticide Resistance of Three Species of Cockroaches (Blattodea: Blattidae) in Iran

In Iran, there are four pest domestic species of cockroaches: Periplaneta americana (Linnaeus, Blattodea: Blattidae), Blatta orientalis (Linnaeus, Blattodea: Blattidae), Blattella germanica (Linnaeus, Blattodea: Blattidae), and Supella longipalpa (Fabricius, Blattodea: Blattellidae). The aim of this study was to compile and review studies conducted on insecticide resistance of domestic cockroaches in Iran to assess the current knowledge and gaps. Twenty insecticides were used in susceptibility testing of cockroaches. The bioassay methods varied, and included surface contact (exposure tests), topical applications and feeding studies on baits. Resistance ratio (RR) stated in the reviewed studies showed that B. germanica was resistant (RR > 10) to DDT, permethrin, and cypermethrin, while P. americana and S. longipalpa were categorized as low levels of resistance (RR = 1-2). S. longipalpa is newly reported from houses in some areas of Iran, including Tehran, and there are very few studies on its' biology, ecology and insecticidal resistance. Most studies used adult cockroaches, while the susceptibility status of nymphs was evaluated only in few studies. Use of different test methods and lack of a World Health Organization (WHO) updated procedure, including revised/updated insecticide diagnostic dosages and test kits. The lack of susceptible strains of cockroaches was a major challenge in the assessment of data. A comprehensive national program for monitoring susceptibility of household pests to insecticides in Iran is of great concern and is highly recommended.

Repellency and Laboratory Performance of Selected Insecticides to Field-Collected Insecticide Resistant German Cockroaches (Blattodea: Ectobiidae)

German cockroaches, Blattella germanica (L.) (Blattodea: Ectobiidae), are important indoor insect pests and remain difficult to control because of their ability to develop resistance to insecticides. The toxicity, resistance levels, repellency, and performance index (PI) value of five formulated insecticides (permethrin, chlorpyrifos, propoxur, imidacloprid, and fipronil) were determined for adult males of seven strains of the German cockroach: a laboratory-reared susceptible strain (S) and six field-collected strains (B, D, E, G, H, and I). Propoxur was generally the most toxic insecticide to all strains using continuous exposure methods; however, using Ebeling choice box methods, chlorpyrifos, and fipronil were most toxic. In both continuous exposure and Ebeling choice box tests, the field-collected strains were generally most resistant to permethrin among the five insecticides. The greatest increase in resistance ratios between the two exposure methods was for permethrin and propoxur. Permethrin was the most repellent insecticide against all but two strains (D and H). PI values reached 100 (no repellency and complete mortality) for the susceptible strain against only chlorpyrifos and fipronil. Only fipronil resulted in a PI value of 100 for any of the field-collected strains. Continuous exposure and Ebeling choice box resistance ratios were correlated, and both were correlated with previously reported resistance ratios (based on LD50 values). Choice box repellency, however, was only correlated with LD50 resistance ratios. PIMax was negatively correlated with all measures of resistance ratios.

Effectiveness of Boric Acid by Ingestion, But Not by Contact, Against the Common Bed Bug (Hemiptera: Cimicidae)

Boric acid has been used as an insecticide in the successful control of agricultural, public health and urban pests long before the advent of synthetic organic pesticides. Boric acid products, formulated as dusts, sprays, granular baits, pastes, gels, and liquids, are widely available to consumers and pest management professionals, especially to control pest infestations within homes. Boric acid dust is commonly used against bed bugs (Cimex lectularius L. [Hemiptera: Cimicidae]), but its efficacy has not been demonstrated. We evaluated the efficacy of boric acid as an ingestible and residual contact insecticide on bed bugs, and compared its efficacy on the German cockroach (Blattella germanica L. [Blattodea: Ectobiidae]) which is known to be susceptible to boric acid by both routes. Dose-response studies of 0-5% boric acid in blood demonstrated that ingested boric acid caused rapid mortality at concentrations of ≥2%, and even 0.5% and 1% boric acid caused 100% mortality, albeit at a slower time course. In contrast, bed bugs survived contact with high concentrations of boric acid dust. Smaller boric acid particles did not increase mortality of either unfed or recently fed bed bugs. The same boric acid products were effective at causing mortality of German cockroaches by both contact and ingestion. We thus conclude that although boric acid is an excellent candidate active ingredient for an ingestible bait formulation, residual applications of dust or spray would be ineffective in bed bug interventions.

Isolation, Identification, and Virulence of a New Metarhizium anisopliae Strain on the German Cockroach

The efficacy of a new and highly virulent Metarhizium anisopliae (Hypocreales: Clavicipitaceae) strain was evaluated against Blattella germanica (L.) (Blattaria: Blattellidae) in the laboratory; this strain was obtained and purified from field-collected Eupolyphaga sinensis cadavers. The status of this fungus as a new and genetically distinct species was supported by ITS sequence comparisons. The new strain was compared with other M. anisopliae isolates and was found to be highly infectious and virulent against B. germanica. The virulence of this new strain against different instars of male and female cockroaches at five conidia concentrations (1 × 105, 1 × 106, 1 × 107, 1 × 108, and 1 × 109 conidia/ml) was evaluated in vitro, and the mortality (measured as lethal concentrations, LC50) was determined. According to the pathogenicity test, M. anisopliae isolate EB0732 produced 100% mortality of one- to three-instar nymph (LC50 = 0.37 × 105conidia/ml) and 78.33% mortality of adult female (LC50 = 1.39 × 107 conidia/ml) at 15 d post-inoculation at a concentration of 1 × 109 conidia/ml. There was an overall significant effect on mortality between the age and sex of B. germanica. A M. anisopliae susceptibility test showed that the survival rate of cockroaches after treatment with topical applications and mixed infection was lower than per os. These studies shed light on a valuable integrated pest management against the German cockroach.

Pest Cockroaches May Overcome Environmental Restriction Due to Anthropization

Our species have altered their surroundings since its early dispersion on Earth. Unfortunately, thanks to human-modified habitats, several pest organisms such as domiciliary insects have expanded their distributions. Moreover, pest-related microorganisms may also be aided by anthropization. Pest cockroaches are globally distributed and capable of carrying several diseases. We explored if urbanization may buffer environmental conditions allowing pest insects to expand their distribution. Specifically, we suggest that human settlements may generate suitable microhabitats for synanthropic cockroaches, helping them to survive and establish with disregard to overall climatic restrictions. To test this idea we studied the distribution of pest cockroaches spanning the length of Chilean territory. Chile, along its 4270 km length north to south extent, is a country offering a formidable sampling of Earth's climatic diversity accompanied by dense urbanizations. We studied entomological collections and spatially analyzed pest cockroach distribution found in Chile and discovered that synanthropic cockroach populations are consistently concentrated near most urban developed zones of the country and not limited by overall temperature. Furthermore, health-concern pest cockroach species were widely distributed in Chilean territory, found even in its most southern urban centers as well as Easter Island. Therefore, these disease vectors could exist even in isolated and extreme climatic zones as long as urbanization provides the adequate microhabitat. We discuss the need for further research in order to assess if these distributions can be extrapolated to the pathogenic strains these pest insects may be carrying as reported in other regions of the planet.

Insecticidal Activity of Lamiaceae Plant Essential Oils and Their Constituents Against Blattella germanica L. Adult

The insecticidal activities of 13 Lamiaceae plant oils and their components against adult German cockroaches, Blattella germanica L. (Blattodea: Blattellidae), were evaluated using fumigant and contact bioassay. Among the tested oils, basil, pennyroyal, and spearmint showed the strongest insecticidal activities against adult B. germanica. Insecticidal activity of pennyroyal was 100% against male B. germanica at 1.25 mg concentration in fumigant bioassay. Basil and spearmint revealed 100% and 100% insecticidal activity against male B. germanica at 5 mg concentration, but their activities reduced to 80% and 25% at 2.5 mg concentration, respectively. In contact, toxicity bioassay, basil, pennyroyal, and spearmint oils exhibited 100%, 100%, and 98% mortality against female B. germanica at 1 mg/♀, respectively. Among the constituents identified in basil, pennyroyal, and spearmint oils, insecticidal activity of pulegone was the strongest against male and female B. germanica.

Pest Prevalence and Evaluation of Community-Wide Integrated Pest Management for Reducing Cockroach Infestations and Indoor Insecticide Residues

Pest infestations in residential buildings are common, but community-wide pest survey data are lacking. Frequent insecticide applications for controlling indoor pests leave insecticide residues and pose potential health risks to residents. In this study, a community-wide pest survey was carried out in a housing complex consisting of 258 units in 40 buildings in New Brunswick, New Jersey. It was immediately followed by implementation of an integrated pest management (IPM) program in all the cockroach-infested apartments and two bed bug apartments with the goal of eliminating pest infestations, reducing pyrethroid residues, and increasing resident satisfaction with pest control services. The IPM-treated apartments were revisited and treated biweekly or monthly for 7 mo. Initial inspection found the top three pests and their infestation rates to be as follows: German cockroaches (Blattella germanica L. [Blattodea: Blattellidae]), 28%; rodents, 11%; and bed bugs (Cimex lectularius L. [Hemiptera: Cimicidae]), 8%. Floor wipe samples were collected in the kitchens and bedrooms of 20 apartments for pyrethroid residue analysis before the IPM implementation; 17 of the 20 apartments were resampled again at 7 mo. The IPM program reduced cockroach counts per apartment by 88% at 7 wk after initial treatment. At 7 mo, 85% of the cockroach infestations found in the initial survey were eliminated. The average number of pyrethroids detected decreased significantly from 6 ± 1 (mean ± SEM) and 5 ± 1 to 2 ± 1 and 3 ± 1 in the kitchens and bedrooms, respectively. The average concentrations of targeted pyrethroids residue also decreased significantly in the kitchens and bedrooms.