Response to An Outbreak of Locally Transmitted Dengue in Key Largo, FL, by The Florida Keys Mosquito Control District

Dengue virus (DENV) is an ever-increasing threat to the residents of South Florida. Seventy-two cases of locally acquired dengue were contracted by residents and visitors of Key Largo, FL, in 2020. The primary vector, Aedes aegypti, has been a large focus of the Florida Keys Mosquito Control District's (FKMCD) control measures for over a decade. This paper recounts the 2020 outbreak of DENV in Key Largo, FL, and the FKMCD's Ae. aegypti operational response. The overall House Index (13.43%) during the outbreak was considered high (>5%) risk for local transmission. Larval habitat characterized from property inspections was similar to previous larval (τ = 0.78, P < 0.005) and pupal (τ = 0.745, P < 0.005) habitat studies. Adult surveillance of the active dengue transmission area provided 3 positive pools out of 1,518 mosquitoes tested resulting in a minimum infection rate of 1.976. Increased personnel response with long-term larvicide formulations and increased aerial, truck, and handheld ultra-low-volume adulticide control measures quickly reduced the Ae. aegypti surveillance numbers below the action threshold. No active cases of dengue have been reported since October 2020.

Field Evaluation of Fyfanon Ew Against Aedes Aegypti: A Low Odor Ultra-Low Volume Formulation of Malathion

A low odor formulation of ultra-low volume (ULV) malathion (Fyfanon EW®) mosquito adulticide was evaluated in the field for its efficacy using caged female Aedes aegypti. Cages were placed in three rows, 30 m apart at 30, 60, and 90 m from the spray line. The product was applied at the manufacturer's suggested operational rate of 0.28 liter/min (9.5 fl oz/min) and at the maximum label rate of 0.37 liter/min (12.6 fl oz/min) with a Guardian 190ES truck mounted ULV sprayer. At 1 h post-treatment for the manufacturer's suggested operational rate, adult mortality ranged from 85% at 30 m to 46% at 90 m (overall average 65.5%). At 24 h post-treatment, mortality was significantly greater at each distance with complete control of caged mosquitoes at 30 m and >95% at 90 m. Overall, 24-h average mortality at this rate was 96.8%. At the maximum label rate, mosquito mortality at 1 h was considerably greater at all distances and ranged from about 89% to 75% with an overall average of 84.3%. At 24 h post-treatment, complete mortality was recorded at all transect distances at this higher rate. In conclusion, our results showed that at 24 h, Fyfanon EW® was considered very effective when applied by ULV truck mounted ground equipment for area-wide control of mosquitoes.

Evaluation of An Aerial Application of Duet Hd® Against Aedes Dorsalis and Culex Tarsalis in Rural Habitats of the Great Salt Lake, Utah

The Salt Lake City Mosquito Abatement District (SLCMAD) has been conducting aerial applications using an organophosphate insecticide against adult mosquitoes for several decades. In order to evaluate a potential rotation product, aerial applications of Duet HD™, a pyrethroid, were conducted under operational conditions against wild populations of Aedes dorsalis and Culex tarsalis and against colony strains of Cx. pipiens and Cx. quinquefasciatus. The erratic wind patterns of the greater Salt Lake area did not prevent sufficient droplet deposition flux at 9 monitoring locations spread across a 5,120-acre (2,072 ha) spray block within rural habitats. Three separate aerial application trials showed great efficacy against Ae. dorsalis. In contrast, Cx. tarsalis exhibited inconsistent treatment-associated mortalities, suggesting the presence of less susceptible or resistant field populations as a result of spillover from agricultural or residential pyrethroid usage. Bottle bioassays to diagnose pyrethroid resistance using field-collected Cx. tarsalis indicated that some populations of this species, especially those closest to urban edges, failed to show adequate mortality in resistance assays. Despite challenging weather conditions, Duet HD worked reasonably well against susceptible mosquito species, and it may provide a crucial role as an alternative for organophosphate applications within specific and sensitive areas. However, its area-wide adoption into control applications by the SLCMAD could be problematic due to reduced impacts on the most important arboviral vector species, Cx. tarsalis, in this area. This study demonstrates the importance of testing mosquito control products under different operational environments and against potentially resistant mosquito populations by municipal mosquito control districts.

Effects of doxycycline dose rate and pre-adulticide wait period on heartworm-associated pathology and adult worm mass

BACKGROUND

The American Heartworm Society canine guidelines recommend treatment with doxycycline prior to adulticide administration to reduce levels of Wolbachia and its associated metabolites, which are known to be a leading cause of pulmonary pathology. Studies have determined that doxycycline administered at 10 mg/kg BID for 28 days is an effective dose for eliminating Wolbachia, but what has not been determined is the clinical relevance of this elimination. The current guidelines also recommend a 30-day wait period following administration of doxycycline to allow for clearance of metabolites, such as Wolbachia surface protein, and for further reduction in heartworm biomass before administration of adulticide. Reducing the doxycycline dose and eliminating the wait period may carry practical benefits for the animal, client, and practitioner.

METHODS

To investigate these treatment practices, Dirofilaria immitis adults were surgically transplanted into each of 45 dogs, which were divided into nine study groups of five dogs each. Seventy-five days after transplantation, two groups each were administered 5, 7.5, or 10 mg/kg BID doxycycline orally for 28 days and 6 µg/kg ivermectin monthly, with three untreated groups serving as controls. Study animals were necropsied and examined prior to treatment as well as 30 and 60 days post-treatment.

RESULTS

Mean worm weight was unaffected by dosage but exhibited a significant increase at 30 days and significant decrease at 60 days post-treatment, including in control groups. Histopathology lesion scores did not significantly differ among groups, with the exception of the lung composite score for one untreated group. Liver enzymes, the levels of which are a concern in doxycycline treatment, were also examined, with no abnormalities in alanine aminotransferase or alkaline phosphatase observed.

CONCLUSIONS

No consistent worsening of tissue lesions was observed with or without the AHS-recommended 30-day wait period, nor did reduced dosages of doxycycline lead to worsening of pathology or any change in efficacy in depleting worm weight. Mean worm weight did significantly increase prior to, and decrease following, the wait period. Future work that also includes adulticide treatment (i.e. melarsomine) will study treatment recommendations that may improve both animal health and owner compliance.

Further variation of the adulticide protocol for the treatment of canine heartworm infection: can it be even shorter and cost less?

BACKGROUND

This retrospective study evaluated modified three-dose melarsomine treatment protocols in a shelter setting and compared them to the American Heartworm Society (AHS)-recommended protocol.

METHODS

As compared with the AHS protocol, the shelter protocols utilized doxycycline 10 mg/kg once daily (SID) or twice daily (BID), and varied the time from initiation of doxycycline (day 1) to the first melarsomine injection (M1). Dogs were retrospectively grouped based on the shelter's current protocol (M1 on day 14; Group A) and the AHS protocol (M1 on day 60; Group C), allowing a week on either side of the target M1 day. Treatments that fell outside these ranges formed two additional treatment groups (Groups B and D). Respiratory complications were defined as respiratory signs requiring additional treatment, and were statistically compared for Groups A and C. New respiratory signs and gastrointestinal (GI) signs were compared between dogs receiving SID or BID doxycycline.

RESULTS

One hundred fifty-seven dogs with asymptomatic or mild heartworm disease at presentation were included. All dogs survived to discharge. There was no statistically significant difference between Groups A (n = 79) and C (n = 27) for new respiratory signs post-melarsomine (P = 0.73). The time to M1 for 14 dogs that developed new respiratory signs was a median of 19 days, compared with 22 days for 143 dogs without new respiratory signs (P = 0.2). Respiratory complications post-melarsomine were uncommon. New respiratory signs post-melarsomine occurred in 10/109 (9.2%) dogs receiving SID doxycycline and 4/48 (8.3%) dogs receiving BID doxycycline (P > 0.999). GI signs prior to M1 were recorded for 40/109 (36.7%) dogs receiving SID doxycycline and 25/48 (52.1%) receiving BID doxycycline (P = 0.08). Forty-four follow-up antigen test results were available; all tests performed > 3 months after the third melarsomine injection were negative.

CONCLUSIONS

This study provided support for initiating melarsomine after 14 days of doxycycline and for a lower doxycycline dose. Shorter and less expensive treatment protocols can increase lifesaving capacity and improve quality of life for shelter dogs by reducing the duration of exercise restriction and length of stay.

Insecticidal effects of some selected plant extracts against Anopheles stephensi (Culicidae: Diptera)

BACKGROUND

The use of synthetic insecticides against mosquitoes may lead to resistance development and potential health hazards in humans and the environment. Consequently, a paradigm needs to shift towards the alternative use of botanical insecticides that could strengthen an insecticide resistance management programme. This study aimed to assess the insecticidal effects aqueous, hexane, and methanol crude leaf extracts of Calpurnia aurea, Momordica foetida, and Zehneria scabra on an insectary colony of Anopheles stephensi larvae and adults.

METHODS

Fresh leaves of C. aurea, M. foetida and Z. scabra were collected and dried, then separately ground to powder. Powdered leaves of test plants were extracted using sonication with aqueous, hexane, and methanol solvents. The extracts were concentrated, and a stock solution was prepared. For comparison, Temephos (Abate®) and control solutions (a mixture of water and emulsifier) were used as the positive and negative controls, respectively. Different test concentrations for the larvae and the adults were prepared and tested according to WHO (2005) and CDC (2010) guidelines to determine lethal concentration (LC) values. Mortality was observed after 24 h exposure. The statistical analyses were performed using Statistical Package for the Social Sciences (SPSS) software (Kruskal-Wallis test) and R software (a generalized linear model was used to determine LC₅₀ and LC₉₀ values of the extracts).

RESULTS

The lowest LC₅₀ values were observed in aqueous extracts of M. foetida followed by Z. scabra extract and C. aurea leaves at 34.61, 35.85, and 38.69 ppm, respectively, against the larvae. Larval mortality was not observed from the hexane extracts and negative control, while the standard larvicide (temephos) achieved 100% mortality. Further, the adulticidal efficacy was greatest for aqueous extract of Z. scabra with LC₅₀ = 176.20 ppm followed by aqueous extract of C. aurea (LC₅₀ = 297.75 ppm).

CONCLUSION

The results suggest that the leaf extracts of the three test plants have the potential of being used for the control of vector An. stephensi larvae and adult instead of synthetic mosquitocides. Further studies need to be conducted to identify the active ingredients and their mode of action.

Implicit versus explicit vector management strategies in models for vector-borne disease epidemiology

Throughout the vector-borne disease modeling literature, there exist two general frameworks for incorporating vector management strategies (e.g. area-wide adulticide spraying and larval source reduction campaigns) into vector population models, namely, the "implicit" and "explicit" control frameworks. The more simplistic "implicit" framework facilitates derivation of mathematically rigorous results on disease suppression and optimal control, but the biological connection of these results to real-world "explicit" control actions that could guide specific management actions is vague at best. Here, we formally define a biological and mathematical relationship between implicit and explicit control, and we provide mathematical expressions relating the strength of implicit control to management-relevant properties of explicit control for four common intervention strategies. These expressions allow the optimal control and basic reproduction number analyses typically utilized in implicit control modeling to be interpreted directly in terms of real-world actions and real-world monetary costs. Our methods reveal that only certain sub-classes of explicit control protocols are able to be represented as implicit controls, and that implicit control is a meaningful approximation of explicit control only when resonance-like synergistic effects between multiple explicit controls have negligible effects on population reduction. When non-negligible synergy exists, implicit control results, despite their mathematical tidiness, fail to provide accurate predictions regarding vector control and disease spread. Collectively, these elements build an effective bridge between analytically interesting and mathematically tractable implicit control and the challenging, action-oriented explicit control.

Reduced Potential for Consecutive Truck-Mounted Ultra-Low Volume Mosquito Adulticide Applications in Chicago Metropolitan Area Due to Weather Conditions

To increase the effectiveness of adult mosquito control, more frequent ultra-low volume (ULV) applications have been suggested. In the Chicago area, weather may be a limiting factor to more frequent applications. To investigate this, ULV adulticidal application dates from the Northwest Mosquito Abatement District during June 2011 to September 2020 were compared to historical weather data-wind and rain patterns to determine optimum conditions for conducting ULV treatments. During the 85 applications performed during 2011-20, there would have been an opportunity, based on weather conditions, for an additional consecutive night for about half (48.2%) of the time. These opportunities diminished with each additional application. The most intensive response possible would have been a spray of 5 consecutive nights, which occurred once in 3 of the 10 years investigated.

Comparing the efficacy of nutmeg essential oil and a chemical pesticide against Musca domestica and Chrysomya albiceps for selecting a new insecticide agent against synantropic vectors

The insecticidal activity of Myristica fragrans (Houtt) essential seed oil, (Nutmeg) was evaluated against Musca domestica (Linnaeus) and Chrysomya albiceps (Wiedemann); both important infectious pathogenic disease vectors. The oil was extracted by distillation, and 21 components were identified during chemical analysis; principally β-pinene (26%), α-pinene (10.5%), Sabinene (9.1%) and γ-terpinen (8.5%). Insecticidal properties were identified through larvicide and adulticide tests. Using the immersion method, the oil at 5% was found to be very effective (90 ± 1%) against M. domestica larvae. The results for adulticide activity varied by fly species, dosage, time, and method of exposure. Topical application (on the insect thorax) was more toxic to C. albiceps, where the lethal concentration at 50% (LC₅₀) was 2.02 ± 0.56, and 8.57 ± 2.41 for the common flies. When the insects were exposed to oil impregnated paper, the results were similar for M. domestica and C. albiceps adults with respective LC₅₀ values of 2.74 ± 0.24, and 3.65 ± 0.48. Thus, the results demonstrated that M. fragrans oil presents insecticidal activity and can be used for control of Musca domestica and Chrysomya albiceps.

Spatio-temporal impacts of aerial adulticide applications on populations of West Nile virus vector mosquitoes

BACKGROUND

Aerial applications of insecticides that target adult mosquitoes are widely used to reduce transmission of West Nile virus to humans during periods of epidemic risk. However, estimates of the reduction in abundance following these treatments typically focus on single events, rely on pre-defined, untreated control sites and can vary widely due to stochastic variation in population dynamics and trapping success unrelated to the treatment.

METHODS

To overcome these limitations, we developed generalized additive models fitted to mosquito surveillance data collected from CO2-baited traps in Sacramento and Yolo counties, California from 2006 to 2017. The models accounted for the expected spatial and temporal trends in the abundance of adult female Culex (Cx.) tarsalis and Cx. pipiens in the absence of aerial spraying. Estimates for the magnitude of deviation from baseline abundance following aerial spray events were obtained from the models.

RESULTS

At 1-week post-treatment with full spatial coverage of the trapping area by pyrethroid or pyrethrin products, Cx. pipiens abundance was reduced by a mean of 52.4% (95% confidence intrval [CI] - 65.6, - 36.5%) while the use of at least one organophosphate pesticide resulted in a mean reduction of 76.2% (95% CI - 82.8, - 67.9%). For Cx. tarsalis, at 1-week post-treatment with full coverage there was a reduction in abundance of 30.7% (95% CI - 54.5, 2.5%). Pesticide class was not a significant factor contributing to the reduction. In comparison, repetition of spraying over three to four consecutive weeks resulted in similar estimates for Cx. pipiens and estimates of somewhat smaller magnitude for Cx. tarsalis.

CONCLUSIONS

Aerial adulticides are effective for achieving a rapid short-term reduction of the abundance of the primary West Nile virus vectors, Cx. tarsalis and Cx. pipiens. A larger magnitude of reduction was estimated in Cx. pipiens, possibly due to the species' focal distribution. Effects of aerial sprays on Cx. tarsalis populations are likely modulated by the species' large dispersal ability, population sizes and vast productive larval habitat present in the study area. Our modeling approach provides a new way to estimate effects of public health pesticides on vector populations using routinely collected observational data and accounting for spatio-temporal trends and contextual factors like weather and habitat. This approach does not require pre-selected control sites and expands upon past studies that have focused on the effects of individual aerial treatment events.

Heartworm control in Grenada, West Indies: Results of a field study using imidacloprid 10% + moxidectin 2.5% and doxycycline for naturally-acquired Dirofilaria immitis infections

Canine heartworm disease (CHD) results from infection with Dirofilaria immitis and while it is of global concern, it is most prevalent in tropical climates where conditions support the parasite and vector life cycles. Melarsomine dihydrochloride is the sole treatment for CHD recommended by the American Heartworm Society. However, in cases where cost or access to melarsomine precludes treatment of an infected dog, therapeutic alternatives are warranted. This randomized, controlled field study evaluated the adulticidal efficacy of a combination therapeutic protocol using 10 % imidacloprid + 2.5 % moxidectin spot-on and a single 28-day course of doxycycline and compared with that of a 2-dose melarsomine dihydrochloride protocol. Of 37 naturally-infected domestic dogs with class 1, 2 or early class 3 CHD enrolled in the study, 30 were evaluated for a minimum of 12 months. Seven dogs were withdrawn due to canine ehrlichiosis, non-compliance, or wrongful inclusion. Dogs were randomly assigned to a control (CP, n = 15) or investigational (IVP, n = 15) treatment group. CP dogs received two injections of melarsomine dihydrochloride (2.5 mg/kg) 24 -hs apart and maintained on monthly ivermectin/pyrantel. IVP dogs were treated with oral doxycycline (10 mg/kg twice daily for 28 days) and topical 10 % imidacloprid + 2.5 % moxidectin once monthly for 9 months. Dogs were evaluated up to 18 months - monthly for the first 9 months, then every 3 months. Parasiticidal efficacy was based on antigen status using the IDEXX PetChek® 34 Heartworm-PF Antigen test. By month 18, antigen was not detected in any study dog except one from the IVP group. One other IVP dog was persistently antigenemic and treated with melarsomine at month 12 according to the initial study protocol. Mean antigen concentration (based on optical density) decreased more rapidly in the CP group and by month 15 was 0.11 for the IVP and 0.07 for CP groups, with equivalent median concentrations (0.04) in both groups. Conversion following heat-treatment of antigen-negative samples occurred frequently and at similar rates in both treatment groups. Based on the bias of diagnostic tests towards detection of female worms, we conclude that monthly application of 10 % imidacloprid + 2.5 % moxidectin for 9 months combined with a course of doxycycline twice daily for 28 days resulted in effective therapy against female adults in CHD. This therapeutic option may be particularly useful in cases where financial constraint or access to melarsomine precludes treatment of an infected individual. This study was supported by Bayer Animal Health.

Evaluation of different dosages of doxycycline during the adulticide treatment of heartworm (Dirofilaria immitis) in dogs

The endosymbiont bacteria Wolbachia plays an important role in the pathogenesis and inflammatory immune response to heartworm (Dirofilaria immitis) infection in dogs. Doxycycline is used to reduce Wolbachia from all life stages of heartworm to avoid large releases of the bacteria during the death of the worms. However, the dose and duration currently recommended have been extrapolated from the treatment of other rickettsial infections. Therefore, the aim was to study the dynamics of Wolbachia IgG antibodies in heartworm-infected dogs under adulticide treatment using different dosages of doxycycline. Forty-nine heartworm-infected dogs were recruited. On day 0 (diagnosis), monthly ivermectin (6 μg/kg) was prescribed, as well as daily doxycycline for 30 days, at 10 mg/kg/12 h (n = 13), 5 mg/kg/12 h (n = 19), and 10 mg/kg/24 h (n = 17). Dogs underwent adulticide treatment and blood samples were collected on days 0, 30, 90, and 120. All dogs had antibodies against recombinant Wolbachia surface protein (rWSP), confirming the important role of the bacteria in heartworm. No significant differences were found in anti-rWSP response by presence/absence of microfilariae, or by parasite burden on day 0. In all treated groups, the anti-rWSP antibody response was not significantly different between days 0 and 30 but was significantly lower between days 0 and 120 (p < 0.05). The results of the present study suggest that the administration of a lower dose than currently recommended is sufficient to achieve a significant reduction of Wolbachia in dogs infected by D. immitis.

Population Outbreaks of Mosquitoes After Hurricanes Matthew and Irma and the Control Efforts in St. Johns County, Northeastern Florida

Major flooding occurred throughout St. John's County, FL, from Hurricane Matthew on October 8, 2016, and Hurricane Irma on September 11, 2017. The flooding caused mosquito population outbreaks in the middle of October in 2016 and September in 2017. Due to the mosquito population outbreaks, Anastasia Mosquito Control District (AMCD) received >3,500 service requests countywide in October 2016 and ≥1,400 service requests in September 2017. During the response to the mosquito population outbreaks caused by the hurricanes, AMCD collaborated with the Emergency Operations Center, Department of Health of St. Johns County, and local media, including television stations, newspapers, and radio stations for public outreach. The AMCD also employed contractors for aerial adulticiding and used every possible resource to successfully control the outbreaks of mosquitoes using both ground and aerial applications.

Promising insecticidal efficacy of the essential oils from the halophyte Echinophora spinosa (Apiaceae) growing in Corsica Island, France

Echinophora spinosa (Apiaceae) is a psammophilous species growing along Mediterranean coastal sand dunes. This species secretes essential oils made up of monoterpenoids, phenylpropanoids, and polyacetylenes, which may represent effective, eco-friendly and safe active ingredients for the preparation of green insecticides. Based on this, in the present study, we selected a French accession of E. spinosa growing on the coastal dunes of Corsica, extracting the essential oils from aerial parts and roots by hydrodistillation. The essential oils were analyzed by GC-MS for chemical composition and screened for their insecticidal activity on three target insects, Culex quinquefasciatus, Spodoptera littoralis, and Musca domestica. The essential oil from roots was dominated by the phenylpropanoid myristicin and the monoterpene hydrocarbon terpinolene, with a minor contribution of (Z)-falcarinol. The oil from the aerial parts was characterized by monoterpenes, mainly p-cymene, a-phellandrene, and α-pinene. The root essential oil exhibited promising toxicity on the target insects, with special reference to C. quinquefasciatus larvae (LC₅₀ = 15.7 mg L^-1), while on M. domestica and S. littoralis, it showed LD₅₀ of 38.3 μg adult^-1 and 55.6 μg larva^-1, respectively. Based on our findings, E. spinosa can be viewed as a new potential crop to produce insecticidal essential oils in arid salty areas. However, synergistic and antagonistic effects of the major constituents of both oils tested here deserve future research. Further studies on the efficacy of stable formulations of the E. spinosa root essential oil, with special reference to micro- and nanoformulations, are ongoing.

Ascaridole-rich essential oil from marsh rosemary (Ledum palustre) growing in Poland exerts insecticidal activity on mosquitoes, moths and flies without serious effects on non-target organisms and human cells

Marsh rosemary (Ledum palustre, Ericaceae) has been widely used in the traditional medicine of various regions worldwide, and as insect repellent. Little is known on its essential oil insecticidal potential. This study explored the insecticidal effects of the essential oil obtained from L. palustre growing in Poland on selected insect pests and vectors. GC-MS analysis evidenced an uncommon chemotype characterized by ascaridole (35.3% as sum of cis-ascaridole and isoascaridole) and p-cymene (25.5%). The essential oil was effective against Culex quinquefasciatus, Spodoptera littoralis and Musca domestica, showing LC₅₀/LD₅₀ of 66.6 mg L^-1, 117.2 μg larva^-1 and 61.4 μg adult^-1, respectively. It was not toxic to non-target Eisenia fetida earthworms and moderately toxic to Daphnia magna microcrustaceans, over the positive control α-cypermethrin. The essential oil cytotoxicity on human keratinocytes and fibroblasts showed high IC₅₀ values (71.3 and 84.4 μg mL^-1, respectively). Comet assay data highlighted no DNA damages. Based on our findings, this essential oil, characterized by the ascaridole/p-cymene chemotype, could be a candidate for the formulation of botanical insecticides; large-scale production of green insecticides by this rare species may be assured by ex situ cultivation and biotechnological techniques.

Gravid Culex pipiens Exhibit A Reduced Susceptibility to Ultra-Low Volume Adult Control Treatments Under Field Conditions

In July and August of 2018, a field trial was conducted to examine the effectiveness of the North Shore Mosquito Abatement District's operational ultra-low volume (ULV) adulticide program. Two study sites were selected in Skokie, IL, and treated by truck-based ULV with d-phenothrin and prallethrin synergized with piperonyl butoxide over the course of a month. Natural mosquito populations were sampled via Biogents (BG)-counter baited with CO₂ or Alfalfa infusion. The results from this study demonstrate that host-seeking mosquitoes were reduced by 65.3% after ULV treatment while gravid mosquitoes were reduced by only 29.2%. In addition, host-seeking mosquitoes rebounded dramatically (303.1%) 3 days posttreatment while gravid mosquitoes did not (5.7%). Based on the differential effect between gravid and host-seeking mosquitoes, we concluded that the gonotrophic cycle and timing of ULV adulticide operations are important factors affecting the resistance of West Nile virus vectors to pyrethroid exposures.

In vitro Safety and Efficacy of Lavender Essential Oil (Lamiales: Lamiaceae) as an Insecticide Against Houseflies (Diptera: Muscidae) and Blowflies (Diptera: Calliphoridae)

Essential oils are considered an alternative for replacement of conventional insecticides that have provoked an increasing number of resistant species and damages to health. The objective of this work was to investigate the insecticidal activity of Lavandula dentata L. (Lamiales: Lamiaceae) oil against the species Musca domestica L. (Diptera: Muscidae) and Chrysomya albiceps Wiedemann (Diptera: Calliphoridae). Extraction of the essential oil from the aerial parts of the plant was carried out using hydro-distillation. Its principal compounds (1,8-cineol, camphor, and linalool oxide) were identified. Insecticidal activity was determined by evaluating adulticidal effect using topical application methods and exposure to impregnated paper; larvicidal effect was determined using immersion method. The essential oil presented toxicity in M. domestica and C. albiceps adults; the lethal concentration values (LC50) in the superficial application method were respectively 3.13 ± 0.64 and 1.39 ± 0.19% live weight (l/v). Toxicity was also found in the oil impregnated paper exposure test; the LC50 results for M. domestica and C. albiceps were respectively 4.15 ± 0.64 and 5.14 ± 0.81%. Larvicidal effect was observed on third stage M. domestica larvae when exposed to an oil concentration of 2.5% (m/v). In addition, the oil was evaluated for cytotoxicity, mutagenicity, and genotoxicity in human cells, and the in vitro safety of this oil in human cells was verified. Thus, L. dentata oil presented insecticidal activity in M. domestica and C. albiceps and can be used as an alternative for control of these dipterans.

Evaluation of larvicidal, adulticidal, and anticholinesterase activities of essential oils of Illicium verum Hook. f., Pimenta dioica (L.) Merr., and Myristica fragrans Houtt. against Zika virus vectors

Aedes aegypti is the vector responsible for transmitting pathogens that cause various infectious diseases, such as dengue, Zika, yellow fever, and chikungunya, worrying health authorities in the tropics. Due to resistance of mosquitoes to synthetic insecticides, the search for more effective insecticidal agents becomes crucial. The aim of this study was to verify the larvicidal, adulticidal, and anticholinesterase activities of the essential oils of the Illicium verum (EOIV), Pimenta dioica (EOPD), and Myristica fragrans (EOMF) against Ae. aegypti. The essential oils (EOs) were obtained by hydrodistillation and analyzed by gas chromatography-mass spectrometry (GC-MS). The larvicidal and adulticidal activities of EOs were evaluated against third instar larvae and Ae. aegypti adult females, respectively, using the procedures of the World Health Organization (WHO) and the anticholinesterase activity of the EOs by the modified Ellman method. The following major components were identified: (E)-anethole (90.1%) for EOIV, methyl eugenol (55.0%) for EOPD, and sabinene (52.1%) for EOMF. All EOs exhibited larvicidal and adulticidal activity against Ae. aegypti. The highest larval mortality was observed in EOMF with LC₅₀ = 28.2 μg mL^-1. Adult mortality was observed after 1 (knockdown) and 24 h exposure, with the highest potential established by the EOIV, KC₅₀ = 7.3 μg mg female^-1 and LC₅₀ = 10.3 μg mg female^-1. EOIV (IC₅₀ = 4800 μg mL^-1), EOMF (IC₅₀ = 4510 μg mL^-1), and EOPD (IC₅₀ = 1320 μg mL^-1) inhibited AChE. EOMF (4130 μg mL^-1) and EOPD (IC₅₀ = 3340 μg mL^-1) inhibited BChE whereas EOIV showed no inhibition. The EOs were toxic to larvae and adults of Ae. aegypti, as well as being less toxic to humans than the currently used insecticides, opening the possibility of elaboration of a natural, safe, and ecological bioinsecticide for vector control.

Efficacy of Deltagard®, Fyfanon®, and Evoluer™ 31-66 Against Culex quinquefasciatus In Harris County, Texas

The comparative efficacy of ultra-low volume applications of deltamethrin, permethrin, and malathion against specific adult populations of Culex quinquefasciatus , a primary regional vector of Saint Louis encephalitis and West Nile virus, using field cage tests is described. At labeled application rates, the estimated mass median diameters for Fyfanon^®, Evoluer™, and DeltaGard^® were 18.32, 19.24, and 17.44 μm, respectively. No significant differences (P ≥ 0.01) in mean percent control were observed across all 3 wild populations and a susceptible Sebring strain tested with Fyfanon, DeltaGard, and Evoluer, providing 98.25%, 98.20%, and 97.24% mean percent control. Mean percent control for Sebring and 3 wild populations was 99.38%, 97.79%, 97.26%, and 97.15%, respectively, which were not significantly different from one another (P ≥ 0.01). Across all tests, highly significant differences (P ≤ 0.01) in mean percent control were obtained at 30.48, 60.96, and 91.44 m distances downwind, with mean percent control at 91.44 m being significantly less than that observed at 30.48 m, but not at 60.96 m. Individually, tests for DeltaGard, Fyfanon, and Evoluer resulted in no significant differences (P ≥ 0.01) in mean percent control between all mosquito populations tested, ranging from 96.47 to 100. However, Evoluer obtained significantly less (P ≤ 0.01) mean percent control at 91.44 m compared to DeltaGard and Fyfanon. Data suggest that the wild Cx. quinquefasciatus specimens collected were as susceptible as the laboratory Sebring strain. The use of Sebring as positive controls downwind strongly supported determination of the efficacy of all adulticides and susceptibility of wild populations tested.

Evaluation of a New Thermal Fog Machine for Control of Adult Aedes albopictus in a Large Enclosed Space

Testing of the PSO BASDKA-AC1200 multifunction ultrafine particle atomization machine, a thermal fog machine, with Aqualuer 20-20(®) (permethrin 20.6%, piperonyl butoxide 20.6%) was conducted against Aedes albopictus. The machine was set at a 40 sec maximum burst interval dispersing 36 ml of chemical with an average droplet volume of 50%. Female adult Ae. albopictus were placed into cylindrical paper cages and adhered to poles at 5, 8, 10, 15, and 25 m from the center point of the machine. Control cages consisted of 1 cage placed at 5, 10, and 25 m. Control and treatment groups were left in the experiment area for 15 min. Initial knockdown after 15 min and 24 h mortality were documented. At 15 min post-treatment, Ae. albopictus displayed less than 50% knockdown. After 24 h, all treatment cages displayed greater than 90% mortality. Further bottle bioassays were conducted to determine the lowest chemical dose possible to achieve a lethal dose of 90%. A 1% dilution (10 ml Aqualuer 20-20 to 1,000 ml of polyether) of Aqualuer showed high mortality in the laboratory. However, after running 3 repetitions of a 1% dilution, there was no significant difference between the mortality of the mosquitoes at any of the distances 24 h post-treatment. This study indicates that the test machine would be an applicable and suitable machine for control of Ae. albopictus in enclosed spaces.

Bioefficacy of Mentha piperita essential oil against dengue fever mosquito Aedes aegypti L

OBJECTIVE

To assess the larvicidal and repellent potential of the essential oil extracted from the leaves of peppermint plant, Mentha piperita (M. piperita) against the larval and adult stages of Aedes aegypti (Ae. Aegypti).

METHODS

The larvicidal potential of peppermint oil was evaluated against early fourth instar larvae of Ae. aegypti using WHO protocol. The mortality counts were made after 24 and 48 h, and LC50 and LC90 values were calculated. The efficacy of peppermint oil as mosquito repellent was assessed using the human-bait technique. The measured area of one arm of a human volunteer was applied with the oil and the other arm was applied with ethanol. The mosquito bites on both the arms were recorded for 3 min after every 15 min. The experiment continued for 3 h and the percent protection was calculated.

RESULTS

The essential oil extracted from M. piperita possessed excellent larvicidal efficiency against dengue vector. The bioassays showed an LC50 and LC90 value of 111.9 and 295.18 ppm, respectively after 24 h of exposure. The toxicity of the oil increased 11.8% when the larvae were exposed to the oil for 48 h. The remarkable repellent properties of M. piperita essential oil were established against adults Ae. aegypti. The application of oil resulted in 100% protection till 150 min. After next 30 min, only 1-2 bites were recorded as compared with 8-9 bites on the control arm.

CONCLUSIONS

The peppermint essential oil is proved to be efficient larvicide and repellent against dengue vector. Further studies are needed to identify the possible role of oil as adulticide, oviposition deterrent and ovicidal agent. The isolation of active ingredient from the oil could help in formulating strategies for mosquito control.

Adulticidal Activity of Olea vera, Linum usitatissimum and Piper nigera against Anopheles stephensi and Aedes aegypti under Laboratory Conditions

BACKGROUND

There are several plant extractions which are being used for mosquito control. The aim of this study was to evaluate the efficacy of Olea vera, Linum usitatissimum and Piper nigera against Anopheles stephensi and Aedes aegypti under laboratory conditions.

METHODS

These tests were carried out using WHO recommended bioassay method for adult mosquitoes.

RESULTS

The extracts from black pepper was more effective as adulticide with lowest LC(50) values (2.26% and 8.4%) against Aedes aegypti and Anopheles stephensi after 24 h of exposure while after 48h (1.56% and 5.11%) respectively. In terms of LC(90) value black pepper was best with (8.66% and 30.1%) against Ae. aegypti and An. stephensi after 24 h of exposure while after 48h (4.59% and 17.3%) respectively. In terms of LT(50) black pepper took 15 h to kill 50% tested population of Ae. aegypti while against An. stephensi it took more than 2 days. In terms of percentage mortality black pepper kill 84% of the population of Ae. aegypti and 44.75% of the An. stephensi population.

CONCLUSION

Black pepper showed best results in term of LC(50), LC(90), LT(50) and percentage mortality against Ae. aegypti and An. stephensi. Our study suggested that the plant extracts have potential to kill adult mosquitoes, are environment friendly and can be used for the control of mosquitoes.