Metarhizium anisopliae blastospores are highly virulent to adult Aedes aegypti, an important arbovirus vector

Abstract

Background: The use of entomopathogenic fungi (EPF) for the control of adult mosquitoes is a promising alternative to synthetic insecticides. Previous studies have only evaluated conidiospores against adult mosquitoes. However, blastospores, which are highly virulent against mosquito larvae and pupae, could also be effective against adults.

Methods: Metarhizium anisopliae (ESALQ 818 and LEF 2000) blastospores and conidia were first tested against adult Aedes aegypti by spraying insects with spore suspensions. Blastospores were then tested using an indirect contact bioassay, exposing mosquitoes to fungus-impregnated cloths. Virulence when using blastospores suspended in 20% sunflower oil was also investigated.

Results: Female mosquitoes sprayed with blastospores or conidia at a concentration of 10⁸ propagules ml^-1 were highly susceptible to both types of spores, resulting in 100% mortality within 7 days. However, significant differences in virulence of the isolates and propagules became apparent at 10⁷ spores ml^-1, with ESALQ 818 blastospores being more virulent than LEF 2000 blastospores. ESALQ 818 blastospores were highly virulent when mosquitoes were exposed to black cotton cloths impregnated with blastospores shortly after preparing the suspensions, but virulence declined rapidly 12 h post-application. The addition of vegetable oil to blastospores helped maintain virulence for up to 48 h.

Conclusion: The results showed that blastospores were more virulent to adult female Ae. aegypti than conidia when sprayed onto the insects or applied to black cloths. Vegetable oil helped maintain blastospore virulence. The results show that blastospores have potential for use in integrated vector management, although new formulations and drying techniques need to be investigated.

Keywords: Arbovirus; Biological control; Blastospores; Conidia; Dengue; Fungus; Pathogen.

Fig. 1

a Survival curves of Aedes aegypti females sprayed with conidia or blastospore suspensions of two Metarhizium anisopliae isolates (ESALQ 818 and LEF 2000) at a concentration of 1 × 10⁸ propagules ml⁻¹. b Survival curves of Ae. aegypti females sprayed with conidia or blastospore suspensions of two Metarhizium anisopliae isolates (ESALQ 818 and LEF 2000) at a concentration of 1 × 10 propagules ml⁻¹. Control data for all treatment groups were combined and are represented as a single survival curve. Error bars are ± SD (standard deviation of the mean)

Fig. 2

Survival curves of Aedes aegypti females following exposure to ESALQ 818 blastospore (1 × 10⁷ ml⁻¹)-impregnated black cotton cloths immediately after applying the blastospore suspensions to the cloths (0 h), 12 h after preparing the cloths, and 24 h after preparing the cloths. Control data for all treatment groups were combined and represented as a single survival curve. Error bars are ± SD (standard deviation of the mean)

Fig. 3

Survival curves of Aedes aegypti females following exposure to ESALQ 818 blastospore (1 × 10⁷ ml⁻¹)-impregnated black cotton cloths with and without the addition of 20% sunflower oil to the suspensions. Mosquitoes were exposed to the cloths immediately after application of fungi to the cloths (0 h), or 12 h later, 24 h later, or 48 h later. Control data for all treatment groups were combined and represented as a single survival curve. Error bars are ± SD (standard deviation of the mean)