THE ROLE OF DIFFERENT MICROORGANISMS IN THE LIFE CYCLE OF Culex pipiens, A WIDE SPREAD VECTOR OF PARASITES AND PATHOGENS

DÍAZ-NIETO, LM; PEROTTI, MA; D'ALESSIO, C; BERÓN, CM

Cordoba

Congreso; XI CONGRESO ARGENTINO DE MICROBIOLOGÍA GENERAL SAMIGE; 2015

The Pipiens Assemblage is a widespread group of mosquito vectors that transmit several vertebrate pathogens and parasites. One member of this group, Culex pipiens, was detected as a competent vector of West Nile and Saint Louis encephalitis virus in Argentina. Like many other insects, mosquitoes interact with microorganisms throughout their life cycle. Recently, mosquito symbiont bacteria have been used in the development of new strategies for the control of human and animal parasites and pathogens carried by these insects. Some bacteria and yeasts have been identified in the gut of many insects and found to be transmitted vertically to their progeny by residing in special organs or by covering the egg shell that could be consumed by the hatching larva. In mosquitoes, some yeast species were detected during their life cycle but transmission to progeny was not proven. The aim of this work was to study the role of several microorganisms in different developmental stages of the mosquito-vector Cx. pipiens. Groups of neonates? larvae were fed with cyanobacteria, microalgae, yeasts and mosquito native bacteria to analyze the nutritional quality of these microorganisms. Cx. pipiens larvae can use yeast as an efficient food source allowing the complete mosquito development, showing the shortest developmental time and the highest survival rate. The insects reached the adult stage after 25 days when they were fed with yeasts showing similar survival rate as fish food as control diet. However, when fed with microalgae, they could only reach up to larval stage III after 25 days of treatment, showing also a decreasing survival rate after 10 days. When fed with cyanobacteria and native bacteria, the larvae survival rate decreased drastically, dying on day 15th at larval stage II. To analyze if the yeast Saccharomyces cerevisiae is transmitted along oviposition and the developmental stages of the insect, larvae were fed with GFP-labelled cells. The growth of GFP-labelled yeast in specific culture medium and the presence of the GFP gene by PCR were evaluated during the entire mosquito developmental stages including the offspring eggs. We determined that S. cerevisiae could not be transmitted to the eggs. However, we identified two bacteria species present in the eggs that could be inoculated by females during the oviposition providing the first food for the neonate larvae. Finally, we carried on oviposition tests offering females different substrates inoculated with specific microorganisms. The two native bacteria present in the eggs, Klebsiella sp. and Aeromonas sp. were chosen by mosquito females for oviposition but yeast substrates were not chosen. The native bacteria identified in this work could provide the first progeny intake but it might not be sufficient to complete the entire mosquito developmental stages. The function of these bacteria in the Cx. pipiens life cycle is being further investigated.