Shady business: understanding the spatial ecology of exophilic Anopheles mosquitoes

Abstract

BackgroundUnderstanding 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.ResultsResting 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.ConclusionsThis 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.Electronic supplementary materialThe online version of this article (10.1186/s12936-018-2499-7) contains supplementary material, which is available to authorized users.

Indoor and outdoor biting behaviour of malaria vectors and the potential risk factors that enhance malaria in southern Malawi

“…Although the outdoor collections with clay pots yielded lower catches of resting malaria vectors, which is contrary to other findings (Odiere et al 2007, Dandalo et al 2017, Debebe et al 2018, the most abundant vector was An. arabiensis.…”

“…Therefore, this raises the need for the development of tools that can be effective in collecting outdoor resting mosquitoes such as the recently developed host decoy trap with cattle odour (Abong'o et al 2018). Additionally, tools that can target different outdoor sites are also highly recommended as recent studies have shown that mosquitoes mostly prefer to rest in shady sites (Debebe et al 2018).…”

“…Whereas Chapter 5 has shown that the Suna trap has the potential for sampling mosquitoes indoors and outdoors, tools for monitoring mosquitoes resting outdoors remain a challenge. Development of such tools is highly recommended as recent studies have shown that malaria vectors prefer to rest in shady sites mostly outdoors (Debebe et al 2018).…”

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“…Thus, much of the exposure to malaria of these daytime travellers was likely not inside the forest. In this area, as in much of Southeast Asia, many of the malaria vectors that bite during the day are known to be present outdoors near the peripheries of villages, forest fringes and fragmented forest areas [54][55][56]. In addition to protection of forest goers, it is thus important to also protect this group of daytime travellers from infection during their workrelated travel.…”

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“…Vegetated areas also provide natural resting sites, particularly for mosquitoes that preferentially feed outdoors. During resting-periods, shade provided by vegetated cover may inhibit excess water loss, reducing mosquito’s risk of dehydration and desiccation [ 57 ].…”