Biology subjects

Koella, J. C.

Publications and source records attributed to Koella, J. C..

4 recordsLinked to original sources

bioRxiv2024

Sublethal insecticide exposure of larvae affects the blood-feeding behaviour of adult mosquitoes

Because of their widespread use for the control of disease vectors and agricultural pests, insecticides have become ubiquitous in the environment, including in water bodies harbouring mosquito larvae. These are therefore continuously exposed to sublethal doses. Since this has long-lasting effects on the mosquitoes physiology and life-history, we expected that it may also affect behaviours that underlie the mosquitoes population dynamics and disease epidemiology, such as egg-laying preference, blood-feeding motivation, and host-seeking behaviour. Using an insecticide-sensitive and a resistant strain of Anopheles gambiae, an important malaria vector, we evaluated the effects of sublethal exposure to permethrin throughout larval development on the resistance to the insecticide in adults, on host-seeking behaviour, on the motivation to blood-feed, and on egg-laying behaviour. Resistance, assessed by rates of knock-down and mortality, were similar between exposed and unexposed mosquitoes. However, exposure to sublethal doses of insecticide caused female mosquitoes to split their egg clutches into two parts and increased the motivation of mosquitoes to seek blood meals through permethrin-treated nets, regardless of their sensitivity to the insecticide. Furthermore, it enhanced the natural preference of resistant strains for permethrin-treated nets and increased their blood-meal size. Our results thus suggest that sublethal insecticide concentrations in larval breeding sites have important epidemiological implications.

evolutionary biology↗

bioRxiv2024

Virulence evolution: thinking outside of the host

The main theory of the evolution of virulence relies on a trade-off between virulence and transmission rate. However, it has been difficult to measure the required trade-off. A recent transmission decomposition framework explains that this might be partly due to a lack of information about the parasites survival in the environment outside its hosts, where the parasite finds itself during transmission to its next host. In this study, we used parasite lines of the microsporidian Vavraia culicis with varying levels of virulence upon infecting their host, the mosquito Anopheles gambiae, to explore the interaction between parasite-driven virulence within its host and its survival outside of the host. The parasite lines with greater virulence and growth within their hosts had a cost in their intrinsic ability to withstand the environment, irrespective of temperature. These results underscore the importance of considering the full context of transmission and other parasite fitness traits in studying and predicting the evolution and spread of infectious diseases.

evolutionary biology↗

bioRxiv2024

Complex interactions in the life cycle of a simple parasite shape the evolution of virulence

Evolutionary expectations about the virulence of parasites (i.e., the parasite-induced mortality rate of the host) often focus solely on the within-host transmission stage, overlooking the time spent between hosts and variations in transmission cycles. Moreover, the parasite growth rate within the host is closely linked to virulence. We here suggest that a simplified view of transmission and parasite evolution makes predicting how virulence will evolve difficult. We illustrate our ideas with a parasite with a simple life cycle, the microsporidian Vavraia culicis, which infects the mosquito Anopheles gambiae. We selected the parasite over six host generations for early or late host transmission, corresponding to shorter or longer time within the host. Selecting for late transmission increased their exploitation of the host, resulting in higher host mortality and a shorter life cycle with rapid infective spore production, comparatively to selection for early transmission. In response, hosts infected with late-selected spores shortened their life cycle and shifted to earlier reproduction. Using different host harm metrics, we demonstrate and discuss the pros and cons of using different it as measures of virulence. These and other findings emphasize the importance of considering the entire transmission cycle in studies of parasite evolution and raise concerns about how host density and social settings might influence virulence evolution.

evolutionary biology↗

bioRxiv2023

Exposure to Pseudomonas spp. increases Anopheles gambiae insecticide resistance in a population-dependent manner

The microbiota of mosquitoes influences many aspects of their biology, including developmental processes, mating and sexual reproduction, immune functions, and refractoriness to pathogens. Here, we considered their role in resistance against insecticides. In particular, we assessed how larval infection of a permethrin-resistant and a sensitive colony of Anopheles gambiae by four strains belonging to three different Pseudomonas species affects several life history traits and the impact of the insecticide on adult mortality. Our data showed that all four Pseudomonas strains persisted in adults until death. The bacteria increased the likelihood that mosquitoes survived 24 hours after exposure to permethrin by up to two-fold. The impact of the bacteria depended on the bacterial strains and the mosquito colony: in the resistant colony, all bacteria increased survival by about 2-fold, while in the sensitive colony, only two of the four strains increased survival. The benefit concerning insecticide resistance came with little to no impact on the other traits (i.e., larval mortality, developmental time and adult longevity). Altogether, our results highlight the importance of considering environmental microbial exposure and mosquito microbial communities in epidemiological and vector-control studies, while also suggesting a possible role for Pseudomonas spp. as a symbiont in A. gambiae.

evolutionary biology↗