Shady business: understanding the spatial ecology of exophilic Anopheles mosquitoes

Abstract

Background: Understanding the ecology of exophilic anophelines is a key step toward developing outdoor control strategies to complement existing indoor control tools against malaria vectors. This study was conducted to assess the movement pattern of exophilic Anopheles mosquitoes between blood meal sources and resting habitats, and the landscape factors dictating their resting habitat choice.

Results: Resting clay pots were placed at 5 m, 25 m, 50 m, 75 m and 100 m away from isolated focal houses, radiating from them in four directions. The locations of the clay pots represent heterogeneous land cover types at a relatively fine spatial scale in the landscape. The effect of the landscape characters on the number of both female and male anophelines caught was modelled using zero-inflated negative binomial regression with a log link function. A total of 420 Anopheles mosquitoes (353 females and 67 males) belonging to three species; Anopheles arabiensis, Anopheles pharoensis, and Anopheles tenebrosus were caught in the resting clay pots, with An. arabiensis being the dominant species. Canopy cover, distance from the house, and land cover type were the significant landscape characters influencing the aggregation of resting mosquitoes. Both the count and binary models showed that canopy cover was the strongest predictor variable on the counts and the presence of Anopheles mosquitoes in the clay pots. Female Anopheles were most frequently found resting in the pots placed in banana plantations, and at sampling points that were at the greater distances (75 m and 100 m) from the focal house.

Conclusions: This study showed that exophilic Anopheles mosquitoes tend to rest in shaded areas some distance away from human habitation. These findings are important when targeting mosquitoes outdoors, complementing the existing effort being made to control malaria vectors indoors.

Keywords: Anopheles; Canopy; Exophilic; Land cover; Landscape.

Fig. 1

Maps showing a district map of Ethiopia indicating the Gamo-Gofa zone; b the Gamo-Gofa zone indicating Arba Minch Zuria district; and c the study area with the sampling points

Fig. 2

Schematic representation of the clay pot arrangement for collecting outdoor resting Anopheles mosquitoes (a) and a resting clay pot (b)

Fig. 3

Proportion of different physiological states of Anopheles mosquitoes caught in clay pots distributed amongst different land cover types

Fig. 4

Mean number of Anopheles mosquitoes caught in the resting clay pots in different land cover types

Fig. 5

Estimated probability of catching at least one single Anopheles mosquito in relation to percent canopy coverage