Using adult mosquitoes to transfer insecticides to Aedes aegypti larval habitats

Abstract

Vector control is a key means of combating mosquito-borne diseases and the only tool available for tackling the transmission of dengue, a disease for which no vaccine, prophylaxis, or therapeutant currently exists. The most effective mosquito control methods include a variety of insecticidal tools that target adults or juveniles. Their successful implementation depends on impacting the largest proportion of the vector population possible. We demonstrate a control strategy that dramatically improves the efficiency with which high coverage of aquatic mosquito habitats can be achieved. The method exploits adult mosquitoes as vehicles of insecticide transfer by harnessing their fundamental behaviors to disseminate a juvenile hormone analogue (JHA) between resting and oviposition sites. A series of field trials undertaken in an Amazon city (Iquitos, Peru) showed that the placement of JHA dissemination stations in just 3-5% of the available resting area resulted in almost complete coverage of sentinel aquatic habitats. More than control mortality occurred in 95-100% of the larval cohorts of Aedes aegypti developing at those sites. Overall reductions in adult emergence of 42-98% were achieved during the trials. A deterministic simulation model predicts amplifications in coverage consistent with our observations and highlights the importance of the residual activity of the insecticide for this technique.

Fig. 1.

Schematic of experimental design in the Iquitos public cemetery. (A) Schematic of avenues and tombs in cemetery (not to scale). (B) Detail of tomb wall. (C) JHA dissemination station in a tomb. (D) Positioning of dissemination stations and sentinel sites (not to scale). Gray circles indicate sentinel sites with larval cohorts (n = 40). Black circles indicate dissemination stations treated with JHA (n = 10).

Fig. 2.

Effect of the presence of JHA-treated dissemination stations on the mortality of juvenile cohorts developing in sentinel sites (mean ± 95% confidence limits). Schematic shows how adults transfer JHA to the sentinel sites.

Fig. 3.

Postdeployment mortality in individual sentinel sites during the field trials. Points marked with * denote the only 3 sentinel sites that showed ≤ control mortality (i.e., ≤ the higher 95% CI displayed in Fig. 2). Simple regressions of sentinel site mortality against average distances from JHA dissemination stations are shown for trials 1 (black circles and line), 2 (gray circles and line), and 3 (white circles and dashed lines).

Fig. 4.

Deterministic simulation model outcomes. (A) Resting site coverage (C_r) can be amplified by insecticide persistence (U) and the number of ovipositions per habitat (O/H) to achieve high habitat coverage (C_h). (B) Under stable conditions of contamination (O/H Ω = 1) the persistence of the insecticide (U) is the key to achieving high habitat coverage.

Fig. 5.

SEM image of JHA particles adhering to the tarsi of an A. aegypti female. The large and complex surface area of a mosquito leg is ideal for such adhesion and transfer.