Parasites and Vectors (2020) 13 (259) - Effects of larval exposure to

Steven Gowelo, James Chirombo, Jeroen Spitzen, Constantianus J.M. Koenraadt, Themba Mzilahowa, Henk van den Berg, Willem Takken and Robert McCann (2020)
Effects of larval exposure to sublethal doses of Bacillus thuringiensis var. israelensis on body size, oviposition and survival of adult Anopheles coluzzii mosquitoes
Parasites and Vectors 13 (259)
Abstract:
Background
Application of the larvicide Bacillus thuringiensis var. israelensis (Bti) is a viable complementary strategy for malaria control. Efficacy of Bti is dose-dependent. There is a knowledge gap on the effects of larval exposure to sublethal Bti doses on emerging adult mosquitoes. The present study examined the effect of larval exposure to sublethal doses of Bti on the survival, body size and oviposition rate in adult Anopheles coluzzii.
Methods
Third-instar An. coluzzii larvae were exposed to control and sublethal Bti concentrations at LC₂₀, LC₅₀ and LC₇₀ for 48 h. Surviving larvae were reared to adults under standard colony conditions. Thirty randomly selected females from each treatment were placed in separate cages and allowed to blood feed. Twenty-five gravid females from the blood-feeding cages were randomly selected and transferred into new cages where they were provided with oviposition cups. Numbers of eggs laid in each cage and mortality of all adult mosquitoes were recorded daily. Wing lengths were measured of 570 mosquitoes as a proxy for body size.
Results
Exposure to LC₇₀Bti doses for 48 h as third-instar larvae reduced longevity of adult An. coluzzii mosquitoes. Time to death was 2.58 times shorter in females exposed to LC₇₀Bti when compared to the control females. Estimated mortality hazard rates were also higher in females exposed to the LC₅₀ and LC₂₀ treatments, but these differences were not statistically significant. The females exposed to LC₇₀ concentrations had 12% longer wings than the control group (P < 0.01). No differences in oviposition rate of the gravid females were observed between the treatments.
Conclusions
Exposure of An. coluzzii larvae to sublethal Bti doses reduces longevity of resultant adults and is associated with larger adult size and unclear effect on oviposition. These findings suggest that anopheline larval exposure to sublethal Bti doses, though not recommended, could reduce vectorial capacity for malaria vector populations by increasing mortality of resultant adults.
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Full text of article
Database assignments for author(s): Constantianus J.M. Koenraadt, Henk van den Berg, Willem Takken

Research topic(s) for pests/diseases/weeds:
biocontrol - natural enemies
Research topic(s) for beneficials or antagonists:
general biology - morphology - evolution
application technology

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Anopheles coluzzii
Bacillus thuringiensis var. israelensis (entomopathogen)	Anopheles coluzzii