Riboflavin instability is a key factor underlying the requirement of a gut microbiota for mosquito development.

We previously determined that several diets used to rear Aedes aegypti and other mosquito species support the development of larvae with a gut microbiota but do not support the development of axenic larvae. In contrast, axenic larvae have been shown to develop when fed other diets. To understand the mechanisms underlying this dichotomy, we developed a defined diet that could be manipulated in concert with microbiota composition and environmental conditions. Initial studies showed that axenic larvae could not grow under standard rearing conditions (27 °C, 16-h light: 8-h dark photoperiod) when fed a defined diet but could develop when maintained in darkness. Downstream assays identified riboflavin decay to lumichrome as the key factor that prevented axenic larvae from growing under standard conditions, while gut community members like Escherichia coli rescued development by being able to synthesize riboflavin. Earlier results showed that conventional and gnotobiotic but not axenic larvae exhibit midgut hypoxia under standard rearing conditions, which correlated with activation of several pathways with essential growth functions. In this study, axenic larvae in darkness also exhibited midgut hypoxia and activation of growth signaling but rapidly shifted to midgut normoxia and arrested growth in light, which indicated that gut hypoxia was not due to aerobic respiration by the gut microbiota but did depend on riboflavin that only resident microbes could provide under standard conditions. Overall, our results identify riboflavin provisioning as an essential function for the gut microbiota under most conditions A. aegypti larvae experience in the laboratory and field.

The UGA-CiE1 cell line from Chrysodeixis includens exhibits characteristics of granulocytes and is permissive to infection by two viruses.

The soybean looper, Chrysodeixis (Pseudoplusia) includens (Lepidoptera: Noctuidae) is an economically important insect pest and a highly permissive host for the parasitoid Microplitis demolitor and its associated polydnavirus M. demolitor bracovirus (MdBV). Here we established a cell line from C. includens embryos designated UGA-CiE1 cells. CiE1 cells morphologically resemble granulocytes, which are a subpopulation of C. includens hemocytes. Antibody and RT-PCR analyses indicated that CiE1 cells express several molecular and functional markers that identify granulocytes. We further determined that CiE1 cells are permissive to infection by MdBV, exhibiting alterations very similar to MdBV-infected granulocytes, and Autographa californica multiple nucleopolyhedrosis virus (AcMNPV). Combined with the ability to transfect CiE1 cells with high efficiency and knock down expression of viral genes by RNA interference, we conclude this cell line has several attributes of value for studying immune interactions with polydnaviruses and potentially other pathogens.