Indoor use of attractive toxic sugar bait (ATSB) to effectively control malaria vectors in Mali, West Africa

Abstract

BackgroundAttractive toxic sugar bait (ATSB) solutions containing any gut toxins can be either sprayed on plants or used in simple bait stations to attract and kill sugar-feeding female and male mosquitoes. This field study in Mali demonstrates the effect of ATSB bait stations inside houses as a vector control method that targets and kills endophilic African malaria vectors.MethodsThe studies were conducted in five villages located near the River Niger, Mali. Baseline village-wide assessments of densities for female and male Anopheles gambiae sensu lato were performed by pyrethrum spray collections (PSC) in ten houses in each of five villages. To determine the rate of mosquito feeding on bait stations, one bait station per house containing attractive sugar bait (ASB) (without toxin) plus a food dye marker, was set up in ten houses in each of the five villages. PSC collections were conducted on the following day and the percentage of female and male mosquitoes that had fed was determined by visual inspection for the dye marker. Then, a 50-day field trial was done. In an experimental village, one bait station containing ATSB (1% boric acid active ingredient) was placed per bedroom (58 bedrooms), and indoor densities of female and male An. gambiae s.l. were subsequently determined by PSC, and female mosquitoes were age graded.ResultsIn the five villages, the percentages of An. gambiae s.l. feeding inside houses on the non-toxic bait stations ranged from 28.3 to 53.1% for females and 36.9 to 78.3% for males. Following ATSB indoor bait station presentation, there was a significant reduction, 90% in female and 93% in male populations, of An. gambiae s.l. at the experimental village. A 3.8-fold decrease in the proportion of females that had undergone four or more gonotrophic cycles was recorded at the experimental village, compared to a 1.2-fold increase at the control village.ConclusionThe field trial demonstrates that An. gambiae s.l. feed readily from ATSB bait stations situated indoors, leading to a substantial reduction in the proportion of older female mosquitoes. This study demonstrates that ATSB inside houses can achieve impressive malaria vector control in Africa.

Priorities for Broadening the Malaria Vector Control Tool Kit

“…ATSBs can be used in outdoor bait stations, indoor bait stations, or can be sprayed directly onto non flowering vegetation [35–37]. The products appear inexpensive and require minimal change in user behavior [38]. Moreover, the wide choice of candidate stomach toxins creates options for control of mosquitoes resistant to the currently used contact insecticides [39].…”

“…A similar study in the Rift Valley showed a 95% reduction in female Anopheles sergentii populations, while completely eradicating males [41]. Even with indoor bait stations, both males and female mosquitoes were attracted to and fed from this source, with more than 90% reduction in populations [38]. Moreover, these studies report changes in population age structure towards younger mosquitoes; an important result as it is the old mosquitoes that are responsible for transmission.…”

RNA Interference for Mosquito and Mosquito-Borne Disease Control

“…RNAi knockdown in larvae by per os exposure is efficacious using scalable bacterial and yeast expression systems, demonstrating potential for RNAi in larval control applications [13,27]. Novel interventions have also been explored to provide oral applications to adults in the form of Attractive Toxic Sugar Baits (ATSB) [28,29,30,31,32,33,34,35,36,37]. Formulations for ATSBs include simple sucrose solutions and complex mixtures of fruit sugars with minimal effects on non-target organisms [30,36,38].…”

“…Surprisingly high ATSB efficacy has been found in spray formulations on flowering and non-flowering plants in arid and wet climates [30,31,35,36,39]. Additionally, strategically placed ATSB stations near breeding sites (dubbed Attractive Baited Oviposition Trap, ABOT) or indoors can attract and kill vector species in proximity to people [32,33,40,41]. Although ATSB have not been studied in conjunction with RNAi, successful gene silencing by oral exposure routes has been documented using sucrose meals and artificial blood meals demonstrating the potential in combining these control approaches [11,42].…”

Prospects for malaria control through manipulation of mosquito larval habitats and olfactory-mediated behavioural responses using plant-derived compounds

“…Most formulations of ATSB involve the use of fruit juices from guavas and mangoes as phytochemical lures, sugar solution as feeding stimulant, and an oral toxin of 1% boric acid that kills mosquitoes upon ingestion [106, 160]. The technique has been successfully deployed for mass trapping of mosquitoes during vector surveillance operations, and for studies aimed at reducing the proportion of endophagic female mosquitoes [163]. Although this new technique is still in the early stages of development, upscaling of its potential to cover large field applications would prove it a powerful malaria vector management tool that complements the existing vector control strategies.…”