Does Cattle Milieu Provide a Potential Point to Target Wild Exophilic Anopheles arabiensis (Diptera: Culicidae) with Entomopathogenic Fungus? A Bioinsecticide Zooprophylaxis Strategy for Vector Control

Abstract

Background. Anopheles arabiensis is increasingly dominating malaria transmission in Africa. The exophagy in mosquitoes threatens the effectiveness of indoor vector control strategies. This study aimed to evaluate the effectiveness of fungus against An. arabiensis when applied on cattle and their environments. Methods. Experiments were conducted under semi-field and small-scale field conditions within Kilombero valley. The semi-field reared females of 5-7 days old An. arabiensis were exposed to fungus-treated and untreated calf. Further, wild An. arabiensis were exposed to fungus-treated calves, mud-huts, and their controls. Mosquitoes were recaptured the next morning and proportion fed, infected, and survived were evaluated. Experiments were replicated three times using different individuals of calves. Results. A high proportion of An. arabiensis was fed on calves (>0.90) and become infected (0.94) while resting on fungus-treated mud walls than on other surfaces. However, fungus treatments reduced fecundity and survival of mosquitoes. Conclusion. This study demonstrates for the first time the potential of cattle and their milieu for controlling An. arabiensis. Most of An. arabiensis were fed and infected while resting on fungus-treated mud walls than on other surfaces. Fungus treatments reduced fecundity and survival of mosquitoes. These results suggest deployment of bioinsecticide zooprophylaxis against exophilic An. arabiensis.

Figure 1

Picture of a rectangular net hut and its schematic representation. The sections of net hut are (A) left-hand side releasing chamber, (B) host or middle chamber, (C) right-hand side releasing chamber, and (D) open eaves with baffles to allow host-seeking mosquitoes to enter host chamber.

Figure 2

Mud hut at Lupiro village with fixed (A) cotton-cloth roof treated with fungal conidia, (B) baffles to reduce exit of mosquitoes, (C) mud walls either treated with fungal conidia or untreated for resting mosquitoes, and (D) open eave to allow host seeking mosquitoes to enter inside the hut.

Figure 3

Effects of B. bassiana against semifield reared exophilic An. arabiensis populations: (a) Estimated proportion (±  1s.e) of fed after exposure to fungus-treated and untreated calf, BB calf indicates a calf sprayed with conidia suspension of Beauvaria bassiana. (b) Estimated proportion (±  1s.e) of infected mosquitoes after exposure to fungus treated calf on 0 d and 3 d. (c) Estimates (±  1s.e) of the mean number of eggs laid by mosquitoes after exposure to fungus-treated and untreated calf. (d) Survival of mosquitoes after exposure to fungus-treated and untreated calf, the lines represent the survival function as estimated from fitting Cox proportional hazard model (controlling for random variation between individual calves).

Figure 4

Effects of M. anisopliae IP 46 against wild exophilic An. arabiensis. (a) Estimated proportion (±  1s.e ) of fed mosquitoes after exposure to fungus-treated and untreated calf inside experimental hut. (b) Estimated proportion (±  1s.e) of infected mosquitoes after exposure to fungus-treated and untreated surfaces. (c) Estimates (±  1s.e) of the mean number of eggs laid by mosquitoes after exposure to fungus-treated and untreated surfaces. (d) Survival of mosquitoes after exposure to fungus-treated and untreated surfaces. The lines represent the survival function as estimated from the fitting Cox proportional hazard model (controlling for random variation between individual calves).