The infectivity of the entomopathogenic fungus Beauveria bassiana to insecticide-resistant and susceptible Anopheles arabiensis mosquitoes at two different temperatures

Abstract

BackgroundControl of the major African malaria vector species continues to rely extensively on the application of residual insecticides through indoor house spraying or bed net impregnation. Insecticide resistance is undermining the sustainability of these control strategies. Alternatives to the currently available conventional chemical insecticides are, therefore, urgently needed. Use of fungal pathogens as biopesticides is one such possibility. However, one of the challenges to the approach is the potential influence of varied environmental conditions and target species that could affect the efficacy of a biological 'active ingredient'. An initial investigation into this was carried out to assess the susceptibility of insecticide-susceptible and resistant laboratory strains and wild-collected Anopheles arabiensis mosquitoes to infection with the fungus Beauveria bassiana under two different laboratory temperature regimes.MethodsInsecticide susceptibility to all four classes of insecticides recommended by WHO for vector control was tested on laboratory and wild-caught An. arabiensis, using standard WHO bioassay protocols. Mosquito susceptibility to fungus infection was tested using dry spores of B. bassiana under two temperature regimes (21 ± 1°C or 25 ± 2°C) representative of indoor conditions observed in western Kenya. Cox regression analysis was used to assess the effect of fungal infection on mosquito survival and the effect of insecticide resistance status and temperature on mortality rates following fungus infection.ResultsSurvival data showed no relationship between insecticide susceptibility and susceptibility to B. bassiana. All tested colonies showed complete susceptibility to fungal infection despite some showing high resistance levels to chemical insecticides. There was, however, a difference in fungus-induced mortality rates between temperature treatments with virulence significantly higher at 25°C than 21°C. Even so, because malaria parasite development is also known to slow as temperatures fall, expected reductions in malaria transmission potential due to fungal infection under the cooler conditions would still be high.ConclusionsThese results provide evidence that the entomopathogenic fungus B. bassiana has potential for use as an alternative vector control tool against insecticide-resistant mosquitoes under conditions typical of indoor resting environments. Nonetheless, the observed variation in effective virulence reveals the need for further study to optimize selection of isolates, dose and use strategy in different eco-epidemiological settings.

Lethal and Pre-Lethal Effects of a Fungal Biopesticide Contribute to Substantial and Rapid Control of Malaria Vectors

“…The rapid mortality of mosquitoes following short-term residual contact with fungal spores on a realistic substrate is much faster than reported in many earlier studies [7], [8], [10], [13], [16], [18]. We are not sure why this should be; the fungal isolate has been tested before, and at the doses we used here.…”

Effects of Beauveria bassiana on Survival, Blood-Feeding Success, and Fecundity of Aedes aegypti in Laboratory and Semi-Field Conditions

“…[1][2][3][4] In recent years, entomopathogenic fungi have shown considerable promise as alternative methods of control. Various fungus strains have been shown to be virulent against malaria vectors [5][6][7] and Ae. aegypti.…”

Hemozoin as an immune stimulant of the mosquitoAnopheles gambiaeresponse against the malaria parasite

“…Tools for larval control have found some success and include the use of larvivorous fish (that feed on larvae) (Mohamed, 2003;Ghosh et al, 2005), as well as microbial larvicides, formulated to deliver toxins from bacteria such as Bacillus thuringiensis israelensis and Bacillus sphaericus, that disrupt the cells from the larva gut (Majambere et al, 2007). For the control of adult Anopheles vectors, entomopathogenic fungi (which infect insects), such as Beauvaria bassiana, have been used with good achievement (Kikankie et al, 2010).…”