Abstract
BackgroundA good understanding of mosquito ecology is imperative for integrated vector control of malaria. In breeding sites, Anopheles larvae are concurrently exposed to predators and parasites. However, to our knowledge, there is no study on combined effects of predators and parasites on development and survival of larvae and their carry-over effects on adult survivorship and susceptibility to further parasite infection.MethodsThis study focused on effects of the nymphs of the dragonfly Pantala flavescens and the parasitic fungus Beauveria bassiana on Anopheles gambiae, to determine: predation efficacy of nymphs against An. gambiae larvae; development rate of An. gambiae larvae in the presence of one, two or four constrained nymphs; efficacy of B. bassiana against An. gambiae larvae at doses of 3, 6 and 12 mg; and survival of adult mosquitoes exposed to B. bassiana, following pre-exposure to a constrained predator and/or parasite at the larval stage. The experiments consisted of survival bioassays quantified as pupation day, or dead larvae and/or adults.ResultsNymphs had an average predation efficacy of 88.3% (95% CI: 87.5–89.1) at 24 hours, against An. gambiae larvae. The presence of one or two nymphs reduced development time of larvae by 0.65 and 0.35 days, respectively. However, development time of larvae exposed to four nymphs was similar to the control larvae. Larvae exposed to 3, 6 and 12 mg of B. bassiana were 2.0, 2.5 and 3.5 times more likely to die, respectively, compared to control larvae. Adults not pre-exposed, those pre-exposed to predator, parasite, or both were 45.8, 67.4, 50.9 and 112.0 times more likely to die, respectively, compared to control that were unexposed to predator or parasite, at larval and adult stage.ConclusionsThis study shows that both predator and parasite can reduce larval population of An. gambiae, and presence of predator cues decreases development time in breeding sites, as well as, increases the susceptibility of emerging adult to fungus. Predator and parasite both have an additive effect on survival of adults exposed to B. bassiana. Field studies are required for an in-depth understanding of predator and parasite influence on mosquito development time, survival and susceptibility in nature.
Highlights
A good understanding of mosquito ecology is imperative for integrated vector control of malaria
An. stephensi females exposed to the fungus Beauveria bassiana at the larval stage and re-exposed to the same fungus during the adult stage had equal survival as females exposed only during the adult stage showing no influence of larval exposure on adult susceptibility [18]
Development rate of An. gambiae larvae reared in the presence of varying densities of constrained P. flavescens nymph Varying the density of the constrained predator had a variable effect on the development rates of An. gambiae larvae over time
Summary
A good understanding of mosquito ecology is imperative for integrated vector control of malaria. It is known that a high proportion of the An. gambiae female population is resistant to infection with Plasmodium parasites and does not contribute to malaria transmission This resistance is genetic and linked to the immune response of the mosquitoes [9]. Predation (presence of predation reduces phenoloxidase activity) and climatic conditions (appropriate environmental temperature can favor the immune response) indirectly influence the immune system while parasites can directly or indirectly influence the immune system [11, 12] These indirect non-lethal effects of both parasites and predators can influence the fecundity, survival and immune response of the surviving individuals and malaria transmission [13,14,15,16,17]. The presence of predator cues reduced oviposition and resulted in the emergence of more female mosquitoes compared to male [19]
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