Abstract
Aedes aegypti larvae ingest several kinds of microorganisms. In spite of studies regarding mosquito digestion, little is known about the nutritional utilization of ingested cells by larvae. We investigated the effects of using yeasts as the sole nutrient source for A. aegypti larvae. We also assessed the role of beta-1,3-glucanases in digestion of live yeast cells. Beta-1,3-glucanases are enzymes which hydrolyze the cell wall beta-1,3-glucan polyssacharide. Larvae were fed with cat food (controls), live or autoclaved Saccharomyces cerevisiae cells and larval weight, time for pupation and adult emergence, larval and pupal mortality were measured. The presence of S. cerevisiae cells inside the larval gut was demonstrated by light microscopy. Beta-1,3-glucanase was measured in dissected larval samples. Viability assays were performed with live yeast cells and larval gut homogenates, with or without addition of competing beta-1,3-glucan. A. aegypti larvae fed with yeast cells were heavier at the 4th instar and showed complete development with normal mortality rates. Yeast cells were efficiently ingested by larvae and quickly killed (10% death in 2h, 100% in 48h). Larvae showed beta-1,3-glucanase in head, gut and rest of body. Gut beta-1,3-glucanase was not derived from ingested yeast cells. Gut and rest of body activity was not affected by the yeast diet, but head homogenates showed a lower activity in animals fed with autoclaved S. cerevisiae cells. The enzymatic lysis of live S. cerevisiae cells was demonstrated using gut homogenates, and this activity was abolished when excess beta-1,3-glucan was added to assays. These results show that live yeast cells are efficiently ingested and hydrolyzed by A. aegypti larvae, which are able to fully-develop on a diet based exclusively on these organisms. Beta-1,3-glucanase seems to be essential for yeast lytic activity of A. aegypti larvae, which possess significant amounts of these enzyme in all parts investigated.
Highlights
Aedes aegypti, among other species of the genera Aedes, is the main vector of several pathogenslike Dengue, Urban Yellow Fever, Chikungunya, West Nile and Zika viruses, whose endemic areas include 40% of human populations worldwide (2.5 billion people) [1, 2]
These results show that live yeast cells are efficiently ingested and hydrolyzed by A. aegypti larvae, which are able to fully-develop on a diet based exclusively on these organisms
We discovered that A. aegypti larvae could nourish exclusively from live S. cerevisiae cells, revealing that this insect bears mechanisms for yeast cell wall breakdown and full acquisition of nutrients from this microorganism
Summary
Among other species of the genera Aedes, is the main vector of several pathogenslike Dengue, Urban Yellow Fever, Chikungunya, West Nile and Zika viruses, whose endemic areas include 40% of human populations worldwide (2.5 billion people) [1, 2]. New strategies for control of vector populations as transgenic mosquitoes, transfection of insects with Wolbachia or paratransgenesis have been proposed and are currently under evaluation [6,7,8]. Some of these strategies depend on rearing massive amounts of insects and, mosquito nutrition has become a strategic point of investigation
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