Consequences of larval competition and exposure to permethrin for the development of the rodent malaria Plasmodium berghei in the mosquito Anopheles gambiae

Abstract

Background: Mosquitoes and other vectors are often exposed to sublethal doses of insecticides. Larvae can be exposed to the runoff of agricultural use, and adults can be irritated by insecticides used against them and move away before they have picked up a lethal dose. This sublethal exposure may affect the success of control of insectborne diseases, for it may affect the competence of insects to transmit parasites, in particular if the insects are undernourished. Methods: We assessed how exposure of larvae and adults to a sublethal dose of permethrin (a pyrethroid) and how larval competition for food affect several aspects of the vector competence of the mosquito Anopheles gambiae for the malaria parasite Plasmodium berghei. We infected mosquitoes with P. berghei and measured the longevity and the prevalence and intensity of infection to test for an effect of our treatments. Results: Our general result was that the exposure to the insecticide helped mosquitoes deal with infection by malaria. Exposure of either larvae or adults decreased the likelihood that mosquitoes were infected by about 20%, but did not effect the parasite load. Exposure also increased the lifespan of infected mosquitoes, but only if they had been reared in competition. Larval competition had no effect on the prevalence of infection, but increased parasite load. These effects may be a consequence of the machinery governing oxidative stress, which underlies the responses of mosquitoes to insecticides, to food stress and to parasites. Conclusions: We conclude that insecticide residues are likely to affect the ability of mosquitoes to carry and transmit pathogens such as malaria, irrespective of the stage at which they are exposed to the insecticide. Our results stress the need for further studies to consider sublethal doses in the context of vector ecology and vector-borne disease epidemiology.

Human practices promote presence and abundance of disease-transmitting mosquito species

“…While most insects are declining 2 , many mosquito species are thriving 3 , 4 . Recent laboratory and mesocosm studies provided important clues suggesting that anthropogenic disturbances can promote population growth of several pathogen-transmitting mosquito species, or disease vectors 5 - 8 , and potentially mediate interactions between mosquito species 9 , their hosts 10 , their pathogens 11 , 12 , and their predators 13 . This hints that, if these patterns hold true for natural systems, the way humans influence their local environment presents a critical driver of disease risk 14 .…”

Root exudate chemical cues of an invasive plant modulate oviposition behavior and survivorship of a malaria mosquito vector

“…Additionally, it has been shown that the adaptation of anopheline vectors to polluted water can influence adult emergence times 28 – 30 . Similarly, exposure to sub-lethal doses of insecticides has been reported to increase the life span of infected mosquitoes 31 . In the current study, we found that presence of the sesquiterpene lactone parthenin released from the root exudate of P. hysterophorus to the oviposition site environment influenced mosquito bionomics.…”

Implications of Sublethal Insecticide Exposure and the Development of Resistance on Mosquito Physiology, Behavior, and Pathogen Transmission

“…The sublethal exposure to permethrin at larvae or adults of An. gambiae reduced the infection prevalence by Plasmodium berghei [94]. These studies with laboratory-consolidated models pointed that the level of interference of the exposure of the larvae to insecticides in the process of infection of mosquitoes depends on the species of both vector and pathogen and the mode of action of the compounds.…”

“…Studies have been carried out considering the interaction between adult mosquitoes derived from exposed larvae and malaria-causing parasites [86,87,94]. For instance, the exposure of Culex pipiens to the neonicotinoid imidacloprid did not affect the life history traits of individuals nor the susceptibility of adults to infection by avian malaria parasite (Plasmodium gallinaceum) [86].…”