Abstract
BackgroundAdult and larval mosquitoes regulate food digestion in their gut with trypsin modulating oostatic factor (TMOF), a decapeptide hormone synthesized by the ovaries and the neuroendocrine system. TMOF is currently being developed as a mosquitocide, however, delivery of the peptide to the mosquito remains a significant challenge. Entomopathogenic fungi offer a means for targeting mosquitoes with TMOF.FindingsThe efficacy of wild type and transgenic Beauveria bassiana strains expressing Aedes aegypti TMOF (Bb-Aa1) were evaluated against larvae and sugar- and blood-fed adult Anopheles gambiae mosquitoes using insect bioassays. Bb-Aa1 displayed increased virulence against larvae, and sugar and blood fed adult A. gambiae when compared to the wild type parent strain. Median lethal dose (LD50) values decreased by ~20% for larvae, and ~40% for both sugar and blood-fed mosquitoes using Bb-Aa1 relative to the wild type parent. Median lethal time (LT50) values were lower for blood-fed compared to sugar-fed mosquitoes in infections with both wild type and Bb-Aa1. However, infection using Bb-Aa1 resulted in 15% to 25% reduction in LT50 values for sugar- and blood fed mosquitoes, and ~27% for larvae, respectively, relative to the wild type parent. In addition, infection with Bb-Aa1 resulted in a dramatic reduction in fecundity of the target mosquitoes.ConclusionsB. bassiana expressing Ae. aegypti TMOF exhibited increased virulence against A. gambiae compared to the wild type strain. These data expand the range and utility of entomopathogenic fungi expressing mosquito-specific molecules to improve their biological control activities against mosquito vectors of disease.
Highlights
Adult and larval mosquitoes regulate food digestion in their gut with trypsin modulating oostatic factor (TMOF), a decapeptide hormone synthesized by the ovaries and the neuroendocrine system
B. bassiana expressing Ae. aegypti TMOF exhibited increased virulence against A. gambiae compared to the wild type strain
B. bassiana strain Bb-Aa1 expresses Aea-TMOF as a fusion protein with a 28 amino acid signal peptide derived from the B. bassiana chitinase gene to drive the extracellular secretion of the hormone [20]
Summary
Our data show that expression of (Aea)-TMOF in a mycoinsecticide can increase its effectiveness against two important mosquito vectors, Ae. aegypti and A. gambiae. Both survival times and the median lethal dose were lower in the Aea-TMOF expressing strain as compared to the wild type parent. Additional research is needed to examine issues of persistence, delivery, and even greater targeting of hosts, the principle of exploiting critical target host molecules for expression in an insect pathogen, which, during infection would compromise the host, can be expanded to a wide range of applications in the biological control of insects. Authors’ contributions MAO and NOK conceived the study. All authors were involved in data analysis and interpretation.
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