Novel methods for the control of phlebotomine sand flies (Diptera: Psychodidae)

In arid and semi-arid parts of the Old World, Phlebotomus paptasi is a significant biting pest of man and is the primary vector of Leishmania major, the causative agent of zoonotic cutaneous leishmaniasis (ZCL). Phlebotomus papatasi exhibits a close association with the burrowing rodents that serve as the reservoirs of L. major. Rodent burrows are considered to be the primary habitat of immature P. papatasi in ZCL foci, and sand fly larvae have been observed feeding on rodent feces. In laboratory studies, five insecticides (diflubenzuron, novaluron, methoprene, pyriproxyfen, or ivermectin) were incorporated into the diet of Syrian hamsters and evaluated as feed-throughs to control immature sand flies. Feces of hamsters fed a diet containing approximately 10 mg/kg diflubenzuron, novaluron, or pyriproxyfen, or 20 mg/kg ivermectin killed 100% of sand fly larvae that consumed these feces. Feces of hamsters fed a diet containing up to 978.8 mg/kg methoprene caused significant, but not complete, mortality of sand fly larvae. Feces of novaluron-treated hamsters also were held under simulated field conditions for up to 30 d, and all larvae that consumed these feces died before pupation; a significant reduction in treated larval survival relative to control was observed when the feces were aged for up to 150 d. Novaluron also was shown to be effective as a feed-though larvicide when novaluron-treated food made up only a portion of the diet of hamsters. Ivermectin also was evaluated as a systemic insecticide; ivermectin treatment of hamsters was 100% effective against bloodfeeding sand flies for up to 7 d after hamsters were withdrawn from ivermectin-treated diets. In the final study, proof of concept was established for a novel biomarker system using a feed-through fluorescent dye. The value of this method is that it can mark rodents and their feces to establish the consumption of treated-baits, mark adult female sand flies that feed rodents for the duration of persistence of the dye in rodents, and mark adult male and female sand flies that had fed on feces of bait-fed rodents as larvae

Laboratory evaluation of oral treatment of rodents with systemic insecticides for control of bloodfeeding sand flies (Diptera: Psychodidae)

The purpose of this study was to evaluate the efficacy of oral treatment of rodents with diets containing the systemic insecticides ivermectin, abamectin, imidacloprid, or spinosad, to control bloodfeeding sand flies. We found that diets containing concentrations higher than 10 mg/kg abamectin were not palatable to rodents, and that a diet containing 10 mg/kg abamectin (a palatable concentration) did not cause 100% mortality of bloodfeeding sand flies. Treatment of rodents with imidacloprid was effective for less than 3 days post-treatment. Treatment of rodents with diets containing 20 mg/kg ivermectin or 5000 mg/kg spinosad caused 100% mortality of bloodfeeding sand flies for at least 1 week. The efficacy of ivermectin and spinosad also were not reduced when combined with the fluorescent tracer dye rhodamine B in a single diet. We also did not observe significant benefits by increasing the feeding period of the rodents from 3 to 6 or 9 days. We conclude that ivermectin and spinosad are effective as rodent systemic insecticides against bloodfeeding sand flies, and suggest that weekly treatment of wild rodent reservoirs of Leishmania major with bait containing one of these systemic insecticides could be a useful tool as part of a sand fly control program. © Copyright 2012, Mary Ann Liebert, Inc. 2012

Efficacy of the spatial repellent product Mosquito Shield™ against wild pyrethroid-resistant Anopheles arabiensis in south-eastern Tanzania

Abstract Background Spatial repellents that create airborne concentrations of an active ingredient (AI) within a space offer a scalable solution to further reduce transmission of malaria, by disrupting mosquito behaviours in ways that ultimately lead to reduced human-vector contact. Passive emanator spatial repellents can protect multiple people within the treated space and can last for multiple weeks without the need for daily user touchpoints, making them less intrusive interventions. They may be particularly advantageous in certain use cases where implementation of core tools may be constrained, such as in humanitarian emergencies and among mobile at-risk populations. The purpose of this study was to assess the efficacy of Mosquito Shield™ deployed in experimental huts against wild, free-flying, pyrethroid-resistant Anopheles arabiensis mosquitoes in Tanzania over 1 month. Methods The efficacy of Mosquito Shield™ transfluthrin spatial repellent in reducing mosquito lands and blood-feeding was evaluated using 24 huts: sixteen huts were allocated to Human Landing Catch (HLC) collections and eight huts to estimating blood-feeding. In both experiments, half of the huts received no intervention (control) while the remaining received the intervention randomly allocated to huts and remained fixed for the study duration. Outcomes measured were mosquito landings, blood-fed, resting and dead mosquitoes. Data were analysed by multilevel mixed effects regression with appropriate dispersion and link function accounting for volunteer, hut and day. Results Landing inhibition was estimated to be 70% (57–78%) [IRR 0.30 (95% CI 0.22–0.43); p < 0.0001] and blood-feeding inhibition was estimated to be 69% (56–79%) [IRR 0.31 (95% CI 0.21–0.44; p < 0.0001] There was no difference in the protective efficacy estimates of landing and blood-feeding inhibition [IRR 0.98 (95% CI 0.53–1.82; p = 0.958]. Conclusions This study demonstrated that Mosquito Shield™ was efficacious against a wild pyrethroid-resistant strain of An. arabiensis mosquitoes in Tanzania for up to 1 month and could be used as a complementary or stand-alone tool where gaps in protection offered by core malaria vector control tools exist. HLC is a suitable technique for estimating bite reductions conferred by spatial repellents especially where direct blood-feeding measurements are not practical or are ethically limited