Leg loss in Lutzomyia longipalpis (Diptera: Psychodidae) due to pyrethroid exposure: Toxic effect or defense by autotomy?

BACKGROUND & OBJECTIVES: Phlebotomine sandflies lose their legs after exposure to pyrethroids. In some insects leg loss helps to defend them from intoxication and predation, a phenomenon known as autotomy. A field observation has shown that sandflies that have lost some legs are still able to blood-feed. The aims of the study were to determine whether leg loss in sandflies, after exposure to deltamethrin, is due to autotomy and to establish the effect of the leg loss on blood-feeding. METHODS: Two experiments were carried out with Lutzomyia longipalpis: (i) Females were individually exposed to a sublethal time of deltamethrin and mortality and the number of leg loss were recorded; and (ii) Groups of females with complete legs or with 1-3 legs lost due to pyrethroid exposure were offered a blood meal and percentages of blood-fed and fully-fed females were recorded. RESULTS: Most females lost a median of 1 leg within 1-48 h post-exposure to deltamethrin. Mortality (after 24 h) was significantly higher for exposed females with lost legs (31.1%), compared to exposed females with complete legs (7.3%), and there were no differences in mortality between females with complete legs and the control (unexposed females). There were no differences between the three treatments in the percentages of blood-fed and fully-fed females. INTERPRETATION & CONCLUSION: Leg loss in sandflies is a toxic effect of pyrethroids and there was no evidence of autotomy. The loss of up to three legs after exposure to pyrethroids does not affect blood-feeding behaviour in laboratory and probably also in wild conditions.

Effect of fluorescent powder on Lutzomyia longipalpis (Diptera: Psychodidae) and a simple device for marking sand flies.

A simple device for marking phlebotomine sand flies with fluorescent powders is described and tested; the design of the new device is characterized by separate compartments for sand flies and powder. The effect of fluorescent powder on survival and mobility of the sand fly Lutzomyia longipalpis was compared using our device (method A) and a single-container method (method B). Mortality within 1 h of powder application was negligible for method A (0.9%), but was 19.8% for method B; in addition, method B also reduced sand fly mobility. Adherence of excess powder to the sand flies observed with method B was responsible for the negative effects observed during the marking process. In field releases, however, recapture rates were the same for each method. Neither sand fly mobility or survival were adversely affected if appropriate quantities (method A) of fluorescent powder were applied to the exoskeleton of these insects.