Itoe, M. A. | bioRxiv Science

bioRxiv2021

Cuticular hydrocarbons are associated with mating success and insecticide resistance in malaria vectors

Anopheles coluzzii females, important malaria vectors in Africa, mate only once in their lifetime. Mating occurs in aerial swarms with a high male-to-female ratio, where the traits underlying male mating success are largely unknown. Here, we investigated whether cuticular hydrocarbons (CHCs) influence mating success in natural mating swarms in Burkina Faso. As insecticides are widely used in this area for malaria control, we also determined whether CHCs affect insecticide resistance levels. We find that mated males have higher CHC abundance than unmated controls, suggesting CHCs could be a determinant of mating success. Additionally, mated males have higher insecticide resistance under pyrethroid challenge, and we show a link between resistance intensity and CHC abundance. Taken together, our results reveal overlapping roles played by CHCs in mate choice and insecticide resistance, and point to sexual selection for insecticide resistance traits that limit the efficacy of our best malaria control tools.

ecology↗

bioRxiv2021

Wolbachia cifB induces cytoplasmic incompatibility in the malaria mosquito

Wolbachia infections are a fascinating example of reproductive parasitism with strong potential to combat vector-borne diseases, due to their combined ability to spread in insect populations and block pathogen replication. Though the Wolbachia factors mediating the notable reproductive manipulation cytoplasmic incompatibility (CI) have now been identified as prophage WO genes cifA and cifB, the relative role of these genes is still intensely debated, with different models claiming that CI requires either both factors or cifB alone. Here we investigated whether cifA and cifB are sufficient to induce conditional sterility in the major malaria vector Anopheles gambiae, a species that appears to have limited susceptibility to invasion by Wolbachia. We report that CI can be fully recapitulated in these mosquitoes, and that cifB is sufficient to cause this reproductive manipulation. cifB-induced sterility is fully rescued by high levels of cifA expression in females. Surprisingly, however, when cifA is highly expressed in males alongside cifB, the CI phenotype is attenuated. cifB strongly impairs fertility also when expressed in the female germline, again mitigated by cifA. These data support a system whereby cifB and cifA must be fine-tuned to exercise CI and rescue, respectively, possibly explaining the limited success of Wolbachia at invading Anopheles. Our findings pave the way towards facilitating Wolbachia infections in anopheline vectors, for use in malaria control strategies.

microbiology↗

bioRxiv2020

Current estimates of malaria basic reproduction number underestimate parasite transmission efficiency due to multiple blood feeding

Many mosquito species, including the major malaria vector Anopheles gambiae, naturally undergo multiple reproductive cycles of blood feeding, egg development and egg laying in their lifespan. Such complex mosquito behavior is regularly overlooked when mosquitoes are experimentally infected with malaria parasites, limiting our ability to accurately describe potential effects on transmission. Here, we examine how Plasmodium falciparum development and transmission potential is impacted when infected mosquitoes feed an additional time. We measured P. falciparum oocyst size and performed sporozoite time course analyses to determine the parasite’s extrinsic incubation period (EIP), i.e. the time required by parasites to reach infectious sporozoite stages, in An. gambiae females blood fed either once or twice. An additional blood feed at 3 days post infection drastically accelerates oocyst growth rates, causing earlier sporozoite accumulation in the salivary glands, thereby shortening the EIP (reduction of 2.25 ± 0.39 days). Moreover, parasite growth is further accelerated in transgenic mosquitoes with reduced reproductive capacity, which mimic genetic modifications currently proposed in population suppression gene drives. We incorporate our shortened EIP values into a measure of transmission potential, the basic reproduction number R0, and find the average R0 is remarkably higher (range: 10.1%–12.1% increase) across sub-Saharan Africa than when using traditional EIP measurements. These data suggest that malaria elimination may be substantially more challenging and that younger mosquitoes or those with reduced reproductive ability may provide a larger contribution to infection than currently believed. Our findings have profound implications for current and future mosquito control interventions.Significance Statement In natural settings the female Anopheles gambiae mosquito, the major malaria vector, blood feeds multiple times in her lifespan. Here we demonstrate that an additional blood feed accelerates the growth of Plasmodium falciparum malaria parasites in this mosquito. Incorporating these data into a mathematical model across sub-Saharan Africa reveals that malaria transmission potential is likely to be substantially higher than previously thought, making disease elimination more difficult. Additionally, we show that control strategies that manipulate mosquito reproduction with the aim of suppressing Anopheles populations may inadvertently favor malaria transmission. Our data also suggest that parasites can be transmitted by younger mosquitoes, which are less susceptible to insecticide killing, with negative implications for the success of insecticide-based strategies.Competing Interest StatementThe authors have declared no competing interest.View Full Text

microbiology↗