Insecticide resistance and nutrition interactively shape life-history parameters in German cockroaches

Cypermethrin induced physiological and metabolic changes in susceptible and resistant populations of Spodoptera litura (Fabricius)

Spodoptera litura (Lepidoptera: Noctuidae) is one of the most destructive insect pests. Insecticides remain the principal management tool to control this pest. However, indiscriminate use of insecticides has resulted in the development of resistance to a variety of insecticides in S. litura. Cypermethrin, a synthetic pyrethroid, is commonly used in pest management. In addition to the mortality produced by cypermethrin, S. litura may suffer a range of sublethal consequences when exposed to low or sublethal levels. This study investigates the effect of cypermethrin exposure on nutritional physiology, digestive, detoxifying, and antioxidant enzymes of lab-selected susceptible (Unsel-Lab) and resistant (CYP-Sel) populations of S. litura. Our findings demonstrated that cypermethrin exposure has a considerable impact on the nutritional physiology of S. litura, as revealed by altered nutrient assimilation and utilization, alongside varying responses in digestive enzymes. In the CYP-Sel population, activity levels of key digestive enzymes- α-amylase, α-glucosidase, ß-glucosidase, α-galactosidase, ß-galactosidase, lipases, and proteases- decreased by 69.30, 81.40, 49.18, 86.36, 73.94, 70.50, and 72.34%, respectively, compared to the control of Unsel-Lab population. Furthermore, detoxification enzymes including mixed-function oxidase (by 1.87 times), glutathione-S-transferase (by 1.71 times), and esterases (by 2.86 times) showed considerably increased activity in CYP-Sel population as compared to Unsel-Lab population, indicating an adaptive response to detoxification processes. Antioxidant enzyme activity, including SOD (increased by 19.66%) and CAT (decreased by 26.19%), changed significantly, indicating oxidative stress caused by cypermethrin. The study gives useful information for developing pest management strategies that reduce the unexpected impacts of chemical exposure.

Fitness costs of resistance to insecticides in insects

The chemical application is considered one of the most crucial methods for controlling insect pests, especially in intensive farming practices. Owing to the chemical application, insect pests are exposed to toxic chemical insecticides along with other stress factors in the environment. Insects require energy and resources for survival and adaptation to cope with these conditions. Also, insects use behavioral, physiological, and genetic mechanisms to combat stressors, like new environments, which may include chemicals insecticides. Sometimes, the continuous selection pressure of insecticides is metabolically costly, which leads to resistance development through constitutive upregulation of detoxification genes and/or target-site mutations. These actions are costly and can potentially affect the biological traits, including development and reproduction parameters and other key variables that ultimately affect the overall fitness of insects. This review synthesizes published in-depth information on fitness costs induced by insecticide resistance in insect pests in the past decade. It thereby highlights the insecticides resistant to insect populations that might help design integrated pest management (IPM) programs for controlling the spread of resistant populations.

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.

Integration of whole genome sequencing and transcriptomics reveals a complex picture of the reestablishment of insecticide resistance in the major malaria vector Anopheles coluzzii

Insecticide resistance is a major threat to gains in malaria control, which have been stalling and potentially reversing since 2015. Studies into the causal mechanisms of insecticide resistance are painting an increasingly complicated picture, underlining the need to design and implement targeted studies on this phenotype. In this study, we compare three populations of the major malaria vector An. coluzzii: a susceptible and two resistant colonies with the same genetic background. The original colonised resistant population rapidly lost resistance over a 6-month period, a subset of this population was reselected with pyrethroids, and a third population of this colony that did not lose resistance was also available. The original resistant, susceptible and re-selected colonies were subject to RNAseq and whole genome sequencing, which identified a number of changes across the transcriptome and genome linked with resistance. Firstly, an increase in the expression of genes within the oxidative phosphorylation pathway were seen in both resistant populations compared to the susceptible control; this translated phenotypically through an increased respiratory rate, indicating that elevated metabolism is linked directly with resistance. Genome sequencing highlighted several blocks clearly associated with resistance, including the 2Rb inversion. Finally, changes in the microbiome profile were seen, indicating that the microbial composition may play a role in the resistance phenotype. Taken together, this study reveals a highly complicated phenotype in which multiple transcriptomic, genomic and microbiome changes combine to result in insecticide resistance.

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.

Fitness studies of insecticide resistant strains: lessons learned and future directions

The evolution of insecticide resistance is generally thought to be associated with a fitness cost in the absence of insecticide exposure. However, it is not clear how these fitness costs manifest or how universal this phenomenon is. To investigate this, we conducted a literature review of publications that studied fitness costs of insecticide resistance, selected papers that met our criteria for scientific rigor, and analyzed each class of insecticides separately as well as in aggregate. The more than 170 publications on fitness costs of insecticide resistance show that in 60% of the experiments there is a cost to having resistance, particularly for measurements of reversion of resistance and reproduction. There were differences between classes of insecticides, with fitness costs seen less commonly for organochlorines. There was considerable variation in the experiments performed. We suggest that future papers will have maximum value to the community if they quantitatively determine resistance levels, identify the resistance mechanisms present (and the associated mutations), have replicated experiments, use related strains (optimally congenic with the resistance mutation introgressed into different genetic backgrounds) and measure fitness by multiple metrics. Studies on the fitness costs of insecticide resistance will continue to enlighten our understanding of the evolutionary process and provide valuable information for resistance management. © 2021 Society of Chemical Industry.

Gut bacteria of the silkworm Bombyx mori facilitate host resistance against the toxic effects of organophosphate insecticides

Organophosphate insecticides that are heavily used in agriculture for pest control have caused growing environmental problems and public health concerns worldwide. Ironically, insecticide resistance develops quickly in major lepidopteran pests, partially via their microbial symbionts. To investigate the possible mechanisms by which the microbiota confers insecticide resistance to Lepidoptera, the model organism silkworm Bombyx mori (Lepidoptera: Bombycidae) was fed different antibiotics to induce gut dysbiosis (microbiota imbalance). Larvae treated with polymyxin showed a significantly lower survival rate when exposed to chlorpyrifos. Through high-throughput sequencing, we found that the abundances of Stenotrophomonas and Enterococcus spp. changed substantially after treatment. To assess the roles played by these two groups of bacteria in chlorpyrifos resistance, a germ-free (GF) silkworm rearing protocol was established to avoid the influence of natural microbiota and antibiotics. Monoassociation of GF silkworms with Stenotrophomonas enhanced host resistance to chlorpyrifos, but not in Enterococcus-fed larvae, consistent with larval detoxification activity. GC-μECD detection of chlorpyrifos residues in feces indicated that neither Stenotrophomonas nor Enterococcus degraded chlorpyrifos directly in the gut. However, gut metabolomics analysis revealed a highly species-specific pattern, with higher levels of essential amino acid produced in the gut of silkworm larvae monoassociated with Stenotrophomonas. This critical nutrient provisioning significantly increased host fitness and thereby allowed larvae to circumvent the deleterious effects of these toxic chemicals more efficiently. Altogether, our study not only suggests a new mechanism for insecticide resistance in notorious lepidopteran pests but also provides a useful template for investigating the interplay between host and gut bacteria in complex environmental systems.

Life history and functional capacity of the microbiome are altered in beta-cypermethrin-resistant cockroaches

Cockroaches are widely perceived to evolve resistance to insecticides. Over-expression of a resistance-conferring gene can be costly and may require energy and resource reallocation for metabolic and developmental processes. To evaluate whether changes in the composition of gut microbiota in Blattella germanica affected its resistance evolution to beta-cypermethrin and to determine the role of gut microbiota in host growth and development, we studied the relationship between insecticide resistance and the diversity and genetic content of gut microbiota in cockroaches. Results suggest beta-cypermethrin-resistant cockroaches (R strain) exhibited a delayed development period and reduced adult longevity compared with susceptible cockroaches (S strain). Based on 16S rRNA gene sequencing and community metagenomics, we found that the relative abundance of Lactobacillus and Acetobacteraceae were significantly lower in the R strain compared with the S strain in the foregut and midgut of both strains. Functional annotation of Kyoto Encyclopedia of Genes and Genomes (KEGG) modules of midgut genes in the two strains revealed that 10.6% were involved in metabolism, while the relative abundance in the R strain was 7.4%. Unigenes were also translated into amino acid sequences and assigned to protein families based on hits to the Carbohydrate-Active enzymes (CAZy) database. This process identified the glycoside hydrolases, glycosyl transferases and carbohydrate-binding modules of the S strain as all being significantly higher in diversity than those in the R strain. Overall, we conclude that fitness-related costs increased in the resistant strain of cockroaches compared with the susceptible strain, and the variation in insect gut microbiota, especially those related to growth and development, was an important influencing factor.

Effect of imidacloprid exposure on life history traits in the agricultural generalist predator Paederus beetle: Lack of fitness cost but strong hormetic effect and skewed sex ratio

A trade-off between life history traits in the evolution of insecticide resistance is common in insects because energy acquisition is mainly channeled for detoxification enzyme production. In addition, sublethal exposure to insecticides may have an effect on the physiology and behaviors of surviving insects. Similar to other agricultural pests, pesticide use may have led to insecticide resistance in populations of Paederus fuscipes Curtis. In this study, we determined the median lethal time of 10 field-collected strains in Taiwan for three insecticides that are commonly employed to manage agricultural pests. We determined that the susceptibility of these strains to cyhalothrin and fenitrothion were similar, with resistance ratios (RRs) ranging from 1 to 4; however, significantly different to imidacloprid (RRs: 1-16). The effect of imidacloprid resistance on the life history traits studied of Paederus beetles was limited; only a prolonged egg incubation period, and adult longevity decreased as imidacloprid resistance increased. Regarding sublethal exposure to imidacloprid, adult sex ratios were female biased in most combinations, though nonsignificant. The quality of offspring, particularly the length of eggs significantly decreased. In addition, a hormetic effect was apparent when the individual was exposed to LT₂₅ and LT₅₀; mean fecundity per female increased from 12.80 ± 8.95 (± standard error [SE]) to 42.70 ± 13.77 eggs compared with that of the control (7.10 ± 1.32). However, the hormetic effect was inconsistent among the tested strains, possibly because of the difference in insecticide resistance levels given that reproductive compensation was absent among the resistant population.

Effects of bistrifluron resistance on the biological traits of Spodoptera litura (Fab.) (Noctuidae: Lepidoptera)

Spodoptera litura is one of the major insect pests of vegetables in Sichuan, China, and it has developed serious resistance to many traditional chemical insecticides. In this present study, S. litura individuals collected from five regions in Sichuan in 2017, which were detected the resistance to bistrifluron. We found that the resistance ratios (RRs) bistrifluron were in the ranges of 15.9- to 77.7-fold, respectively, compared with a laboratory susceptible (Lab-HN) strain. To elucidate the effect of bistrifluron on the life history parameters of S. litura, we established the bistrifluron-susceptible (Bis-UNSEL) and bistrifluron-resistant (Bis-SEL) strains based on the DY field population with the highest RR of 77.7-fold among the all field populations to bistrifluron compared with a laboratory Lab-HN strain. The results show that the Bis-SEL strain developed a 113.8-fold RR while that of the Bis-UNSEL strain was almost equal to that of the Lab-HN strain (with overlapping confidence intervals (CI) of their LC₅₀ values, P < 0.05). Meanwhile, the life span of the egg and pupa stage of the Bis-UNSEL strain was prolonged, and the strain also showed shorter adult duration and lower fecundity. Demographic characteristics, such as the intrinsic rate of increase (r), finite rate of increase (λ) and net reproductive rate (R₀) in the Bis-SEL strain were significantly higher than the Bis-UNSEL strain, whereas the mean generation time (T) and gross reproduction rate (GRR) were lower. The results clearly showed that the developing resistance of bistriflueon on S. litura promoted its population growth. Therefore, the present study could provide useful informations for determining potential management methods to prevent the development of bistrifluron resistance in S. litura.

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.

Disruption of the microbiota affects physiological and evolutionary aspects of insecticide resistance in the German cockroach, an important urban pest

The German cockroach, Blatella germanica, is a common pest in urban environments and is among the most resilient insects in the world. The remarkable ability of the German cockroach to develop resistance when exposed to toxic insecticides is a prime example of adaptive evolution and makes control of this insect an ongoing struggle. Like many other organisms, the German cockroach is host to a diverse community of symbiotic microbes that play important roles in its physiology. In some insect species, there is a strong correlation between the commensal microbial community and insecticide resistance. In particular, several bacteria have been implicated in the detoxification of xenobiotics, including synthetic insecticides. While multiple mechanisms that mediate insecticide resistance in cockroaches have been discovered, significant knowledge gaps still exist in this area of research. Here, we examine the effects of altering the microbiota on resistance to a common insecticide using antibiotic treatments. We describe an indoxacarb-resistant laboratory strain in which treatment with antibiotic increases susceptibility to orally administered insecticide. We further reveal that this strains harbors a gut microbial community that differs significantly from that of susceptible cockroaches in which insecticide resistance is unaffected by antibiotic. More importantly, we demonstrate that transfer of gut microbes from the resistant to the susceptible strain via fecal transplant increases its resistance. Lastly, our data show that antibiotic treatment adversely affects several reproductive life-history traits that may contribute to the dynamics of resistance at the population level. Together these results suggest that the microbiota contributes to both physiological and evolutionary aspects of insecticide resistance and that targeting this community may be an effective strategy to control the German cockroach.

Patterns of Tarnished Plant Bug (Hemiptera: Miridae) Resistance to Pyrethroid Insecticides in the Lower Mississippi Delta for 2008-2015: Linkage to Pyrethroid Use and Cotton Insect Management

Populations of tarnished plant bug, Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae), from the Lower Mississippi Delta regions of Arkansas, Louisiana, and Mississippi were evaluated from 2008 through 2015 for susceptibility to pyrethroid insecticides using a diagnostic-dose assay with permethrin. Resulting data add to the compilation of pyrethroid susceptibility data carefully tracked in this pest since 1994 and provide continuing evidence of high frequencies of pyrethroid resistance in field populations of the tarnished plant bug. Resistance levels are variable, and some populations remain susceptible suggesting practical value in the continued use of the diagnostic-dose assays prior to pyrethroid treatments. Recent studies with dose-response models suggest that levels of pyrethroid resistance in some populations may still be evolving, with some populations requiring higher doses to reach levels of control comparable to those observed 10 yr ago. Concerns for frequent use of multiple classes of insecticides and possible selection for tarnished plant bugs with metabolic resistance mechanisms capable of detoxifying available insecticide chemistries warrant continued efforts to manage resistance in this important crop pest. Associations among measured pyrethroid resistance levels, published data on annual use of pyrethroid insecticides, and annual estimates of cotton insect losses and control costs were explored and summarized for the 8 yr of this investigation. Mortality of tarnished plant bugs at the diagnostic-dose of permethrin was negatively correlated with kilograms of pyrethroids applied per acre of harvested cropland.

Longitudinal Measurements of Tarnished Plant Bug (Hemiptera: Miridae) Susceptibility to Insecticides in Arkansas, Louisiana, and Mississippi: Associations with Insecticide Use and Insect Control Recommendations

Concentration-response assays were conducted from 2008 through 2015 to measure the susceptibility of field populations of Lygus lineolaris (Palisot de Beauvois) from the Delta regions of Arkansas, Louisiana, and Mississippi to acephate, imidacloprid, thiamethoxam, permethrin, and sulfoxaflor. A total of 229 field populations were examined for susceptibility to acephate, 145 for susceptibility to imidacloprid, and 208 for susceptibility to thiamethoxam. Permethrin assays were conducted in 2014 and 2015 to measure levels of pyrethroid resistance in 44 field populations, and sulfoxaflor assays were conducted against 24 field populations in 2015. Resistance to acephate and permethrin is as high or higher than that previously reported, although some populations, especially those exposed to permethrin, appear to be susceptible. Variable assay responses were measured for populations exposed to imidacloprid and thiamethoxam. Average response metrics suggest that populations are generally susceptible to the neonicotinoids, but a few populations from cotton fields experiencing control problems exhibited elevated LC50s. Efforts to associate variability in LC50s with recorded use of insecticides and estimated cotton insect losses and control costs suggest that intensive use of insecticides over several decades may have elevated general detoxifying enzymes in L. lineolaris and some field populations may be exhibiting resistance to multiple classes of insecticide. These results suggest that efforts should be made to manage these pests more efficiently with a reduced use of insecticides and alternative controls.

Detecting pyrethroid resistance in predatory mites inhabiting soil and litter: an in vitro test

BACKGROUND

While resistance against insecticides is widely known in pest arthropods, it remains poorly known in non-target arthropods of the same agrosystems. This may be of crucial importance in the context of organic pest management or integrated pest management. First, stopping of pesticide pressure during farm conversion may lead to important rearrangements of non-target communities due to fitness cost of resistance in populations of some species. Second, resistant biological agents may be useful to farms with low synthetic pesticide use. Communities of mesostigmatid mites, encompassing numerous predatory species, are supposed to be involved in important ecological processes in both crop soils and animal litter/manure.

RESULTS

Here we provide a tarsal contact method for assessing resistance in different populations from various species of mesostigmatid mites. Analyses of data from repeated tests on three populations from different mesostigmatid families proved the method to be robust and able to generate consistent and reliable mortality percentages according to insecticide concentration.

CONCLUSION

Our bioassay system allows for both one-shot estimate of pyrethroid sensitivity in mite populations and estimation of how it changes over time, making possible survival analyses and assessment of recovery from knockdown. The rating system retained makes it possible to score response to insecticides in a consistent and standard way in species from different mesostigmatid families. © 2016 Society of Chemical Industry.

Persistence of a sugar-rejecting cockroach genotype under various dietary regimes

Glucose-aversion is a heritable trait that evolved in a number of German cockroach (Blattella germanica L.) populations in response to strong selection with glucose-containing insecticide baits. However, in the absence of glucose-containing bait, glucose-averse (GA) cockroaches have lower performance than wild-type (WT) cockroaches in several fitness-determining traits. We allocated 48 caged populations initiated with homozygous GA and WT adults to four dietary treatments consisting of either pure rodent chow, rodent chow mixed to yield a content of either 20% glucose or 20% fructose, or a treatment consisting of choice between the 20% glucose- and the 20% fructose-containing food. After 6 months we found significantly higher frequency of WT individuals in populations restricted to the 20% glucose food, and after 12 months all dietary treatments contained significantly more WT individuals than expected. In accompanying experiments, we found lower survival and longer development time of GA nymphs restricted to glucose-containing food. We furthermore found evidence for assortative mating of females with males from their own genotype, with significant differences within WT cockroaches. Our study shows experimental evidence that within heterogeneous populations, WT German cockroaches will over time prevail in abundance over GA individuals, even when glucose is not a dietary component.