Vector development and reproduction are imperative to combating vector-borne illness. Dr. Kevin Vogel and his research team at the University of Georgia are employing an integrative approach to further understanding of these factors in mosquitoes and a triatomine kissing bug.
Dr. Vogel devoted the first half of the seminar to his work identifying the receptor of ovary ecdysteroidogenic hormone in the mosquito Aedes aegypti. In A. aegypti, like all mosquitoes, females require a blood meal prior to oocyte (egg) maturation and subsequent egg laying. Once a female mosquito has obtained a blood meal, peptide hormones produced in the brain are transported to the ovaries where they initiate a signaling cascade that results in the secretion of yolk proteins from the fat body to the oocytes (a process known as vitellogenesis, after the yolk protein vitellogenin). There are two peptide hormones in A. aegypti known to transmit this signal from the brain to the ovaries: ovary ecdysteroidogenic hormone (OEH) and insulin-like peptide 3 (ILP3). While the receptor of ILP3 is known to be the mosquito insulin receptor (MIR), the OEH receptor had been a mystery.
In their juvenile life stages, mosquitoes are restricted to aquatic environments, where they gain the energetic reserves available to them when they emerge as adults. This portion of the life cycle, though imperative for mosquito development, does not garner as much research as does the adult stage. Dr. Vogel and his colleagues found that axenic larvae- those that are not exposed to microbes- will not molt from the first larval instar stage to the second larval instar stage (Figure 4). Yet, this process of development can be rescued with the addition of non-sterile media containing bacteria. Even the larvae of Toxorhynchites spp., mosquitoes that are predatory in their larval stage, and therefore have access to non-microbial nutrition, require bacteria to develop. Therefore, there must be some aspect of the microorganisms associated with mosquitoes in their larval stage that is required for development. Many species of bacteria can facilitate this process, and the bacteria found in larvae are identical, although in different relative abundance, to those in the aquatic environment.
These axenic larvae still consumed food at the same rate as non-sterile larvae and were able to survive in this state, but never reached the size required to molt into the subsequent instar (Figure 5). Through an RNASeq experiment, Dr. Vogel saw a significant reduction in digestive peptides in axenic larvae, as well as a reduced ability to absorb nutrients. The results demonstrated an increase in the use of metabolic pathways consistent with starvation.
The research of Dr. Vogel and his laboratory members offer insights into the physiology and host-microbe interactions of insect vectors that are of particular importance to the Americas. You can find more about his lab at the University of Georgia here.
Bhatt, Samir, D. J. Weiss, E. Cameron, D. Bisanzio, B. Mappin, U. Dalrymple, K. E. Battle et al. (2015) The effect of malaria control on Plasmodium falciparum in Africa between 2000 and 2015. Nature, 526 (7572).
Coon, K.L., Vogel, K.J., Brown, M.R. and Strand, M.R., (2014). Mosquitoes rely on their gut microbiota for development. Molecular ecology, 23(11), 2727-2739.
Veenstra, J. (2010) What the loss of the hormone neuroparsin in the melanogaster subgroup of Drosophila can tell us about its function. Insect Biochemistry and Molecular Biology, 40(4).
Vogel, K., Brown, M., & Strand, M. (2013) Phylogenetic investigation of peptide hormone and growth factor receptors in five dipteran genomes. Endocrinol., 4(193).
Vogel, K., Brown, M., & Strand, M. (2015) Ovary ecdysteroidogenic hormone requires a receptor tyrosine kinase to activate egg formation in the mosquito Aedes aegypti. PNAS, 112(16).
Vogel, K.J., Valzania, L., Coon, K.L., Brown, M.R. and Strand, M.R., (2017) Transcriptome sequencing reveals large-scale changes in axenic Aedes aegypti larvae. PLoS Neglected Tropical Diseases, 11(1).
About the authors
Arielle Arsenault-Benoit is a first-year PhD student in the Fritz lab who studies ecology and landscape genomics of Culex pipiens mosquitoes on an urban to rural gradient.
Katie Reding is a first-year PhD student in the Pick lab who studies the formation of segments in the embryo of a hemipteran.