Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2003
Publication Date: 5/1/2004
Citation: Campbell, C.L., Mummey, D.L., Schmidtmann, E.T., Wilson, W.C. 2004. Culture-independent analysis of midgut microbiota in the arbovirus vector Culicoides sonorensis (diptera: ceratopogonidae). Journal of Medical Entomology. 41:340-348 Interpretive Summary: Culicoides sonorensis is a biting midge that transmits virus (bluetongue and epizootic hemorrhagic disease virus) diseases to animals, such as cows and deer. The only time that these viruses are transmitted to animals is through an insect bite. Thus the insects are referred to as disease vectors. The insects pick up the virus by biting an infected host animal. Before the virus can be transferred to a new host animal, the virus must first successfully infect the vector insect and move from the initial infection site, the gut, to the salivary glands for a subsequent bite. For this reason, we are especially interested in learning how the virus infects the insect gut. Increased knowledge about the insect gut and how the virus invades and grows in it will make it possible to devise ways to prevent virus spread to the salivary glands. If successful, this would interrupt the virus disease cycle and prevent further spread of the disease to uninfected animals. Knowledge of the specific kinds of bacteria that inhabit the gut of the biting midge may also enable us to design novel insect control measures. For these reasons, we designed the following experiment. It is well known that microbes inhabit the guts of all living organisms, including insects. We suggest that the presence or absence of certain groups of bacteria might change the ability of the biting midge to spread virus diseases. We tested this hypothesis by looking at two groups of midges, one that can efficiently spread the virus and a second group of midges from a different location that was expected to be an inefficient vector of viruses. We used DNA sequence information to provisionally identify 36 groups of bacteria in guts of two groups of wild adult female midges from two independent geographical locations. Identification of the bacteria was made by analysis of bacterial DNA sequences present in the adult guts. Of 36 bacterial groups identified, 13 had been previously identified in other in other studies of biting insects, such as mosquitoes and sand flies. Significant differences in bacterial community composition were found between all three groups of wild adult females analyzed: live-trapped C. sonorensis, lab-emerged C. sonorensis, and lab-emerged C. variipennis.
Technical Abstract: Differences in midgut microbial communities inhabiting Culicoides spp, insect vectors of virus pathogens, may affect the variation observed in the ability of these biting midges to propagate arthropod-borne viruses. As a first step toward addressing this hypothesis, midgut bacterial communities were compared between Culicoides species expected to be efficient and inefficient vectors of virus pathogens. We used 16S rDNA sequence and restriction fragment information to provisionally identify 36 bacterial genera from guts of wild adult female biting midges, C. sonorensis and C. variipennis, from two geographical locations. Bacterial identification was made by sequence analysis of 16S rDNA fragments and by terminal restriction fragment length polymorphism (T-RFLP) analysis of PCR amplified 16S rDNA fragments from adult guts. Of 36 bacterial genera identified, 12 had been previously identified in other insects: Comomonas, Enterobacter, Klebsiella, Acinetobacter, Pseudomonas, Stenotrophomonas, Staphylococcus, Chryseobacterium, Moraxella, Acholeplasma, Flavobacterium and Rickettsia. Significant differences in bacterial community composition were found between all three groups of wild adult females analyzed: live-trapped C. sonorensis, lab-emerged C. sonorensis, and lab-emerged C. variipennis.