Testing a pyriproxyfen auto-dissemination station attractive to gravid Anopheles gambiae sensu stricto for the development of a novel attract-release -and-kill strategy for malaria vector control

Abstract

Background Larviciding is an effective supplementary tool for malaria vector control, but the identification and accessibility of aquatic habitats impedes application. Dissemination of the insect growth regulator, pyriproxyfen (PPF), by gravid Anopheles might constitute a novel application strategy. This study aimed to explore the feasibility of using an attractive bait-station to contaminate gravid Anopheles gambiae sensu stricto with PPF and subsequently transfer PPF to larval habitats. Methods A bait-station was developed comprising of an artificial pond containing water treated with 20 ppm cedrol, an oviposition attractant, and a netting-cover treated with PPF. Three identical semi-field cages were used to assess the potential of gravid Anopheles to transfer PPF from the bait-station to ponds. Gravid females were released in two semi-field cages, one with PPF on its bait-station (test) and one without PPF (control). No mosquitoes were released in the third cage with a PPF-treated station (control). Transfer of PPF to open ponds was assessed by monitoring emergence of late instar insectary-reared larvae introduced into the ponds. The amount of PPF carried by a mosquito and transferred to water was quantified using liquid chromatography-mass spectrometry. Results In the controls, 86% (95% CI 81–89%) of larvae introduced into open ponds developed into adults, indicating that wind did not distribute PPF in absence of mosquitoes. Emergence inhibition was observed in the test cage but was dependent on the distance between pond and bait-station. Only 25% (95% CI 22–29%) of larvae emerged as adults from ponds 4 m from the bait-station, but 92% (95% CI 89–94%) emerged from ponds 10 m away. Each mosquito was contaminated on average with 112 μg (95% CI 93–123 μg) PPF resulting in the transfer of 230 ng/L (95% CI 180–290 ng/L) PPF to 100 ml volumes of water. Conclusions The bait-stations successfully attracted gravid females which were subsequently dusted with effective levels of PPF. However, in this study design, attraction and dissemination was limited to short distances. To make this approach feasible for malaria vector control, stronger attractants that lure gravid females from longer distances, in landscapes with many water bodies, and better PPF delivery systems are needed.

Using UPLC–MS/MS to Evaluate the Dissemination of Pyriproxyfen by Aedes Mosquitoes to Combat Cryptic Larval Habitats after Source Reduction in Kaohsiung in Southern Taiwan

“…Spatial-temporal heterogeneity could affect the EI effect in autodissemination studies [16,31]. Suman et al evaluated the spatial-temporal efficacy of PPF autodissemination via dual-treatment autodissemination stations (container type) in the field, and the results showed that efficacy could be observed for 8-12 weeks (2-3 months), and PPF could be detected in sentinel cups up to 200 m from stations [32].…”

Olfactory mediation of oviposition in Anopheles mosquitoes : A new strategy for malaria vector control

“…In a study conducted in north-east Tanzania (Schorkopf et al 2016), a mixture of attractants (acetoxy hexadecanolide) and biological larvicides (Bacillus thuringiensis israelensis and Bacillus sphaericus) was shown to synergize the control of mosquito disease vectors. A similar study was conducted recently in Kenya, where mosquitoes were lured by the oviposition attractant cedrol to bait stations and contaminated by an insect growth regulator pyriproxyfen, after which they transferred it to breeding sites and thereby contaminated larvae (Mbare et al 2019). All these findings demonstrate the potential of infochemicals to be used in surveillance and control of mosquito vectors.…”

Development of a chimeric odour blend for attracting gravid malaria vectors

“…From this study and others [ 7 , 41 , 42 ], it is obvious that trap type and placement with respect to ground level is critical for ensuring the optimal efficacy of odour-based lures for malaria vectors. Previous evaluations of gravid traps targeting gravid Anopheles mosquitoes have identified the presence of water in, the direction of airflow into (up- or down-draft) and the placement of the trap with respect to ground level to be important factors when capturing these females [ 7 , 9 , 41 , 42 ].…”

“…From this study and others [ 7 , 41 , 42 ], it is obvious that trap type and placement with respect to ground level is critical for ensuring the optimal efficacy of odour-based lures for malaria vectors. Previous evaluations of gravid traps targeting gravid Anopheles mosquitoes have identified the presence of water in, the direction of airflow into (up- or down-draft) and the placement of the trap with respect to ground level to be important factors when capturing these females [ 7 , 9 , 41 , 42 ]. In addition, trap type has been identified as a critical factor when capturing host-seeking Anopheles mosquitoes, with various versions of the BG-Sentinel traps, including the BG-Malaria trap and the Suna trap, often demonstrated to be superior compared to other trap types, e.g., the CDC light trap [ 33 , 43 , 44 ].…”