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 acompetent vector of West Nile and Saint Louis encephalitis virus in Argentina. Likemany other insects, mosquitoes interact with microorganisms throughout theirlife cycle. Recently, mosquito symbiont bacteria have been used in thedevelopment of new strategies for the control of human and animal parasites andpathogens carried by these insects. Some bacteria and yeasts have been identified in the gutof many insects and found to be transmitted vertically to their progeny byresiding in special organs or by covering the egg shell that could be consumedby the hatching larva. In mosquitoes, some yeast species were detected during theirlife cycle but transmission to progeny was not proven. The aim of this work was to study the role of several microorganisms indifferent developmental stages of the mosquito-vector Cx. pipiens. Groups of neonates? larvae were fedwith cyanobacteria, microalgae, yeasts and mosquito native bacteria to analyzethe nutritional quality of these microorganisms. Cx. pipiens larvae can use yeast as an efficient food sourceallowing the complete mosquito development, showing the shortest developmentaltime and the highest survival rate. The insects reached the adult stage after25 days when they were fed with yeasts showing similar survival rate as fishfood as control diet. However, when fed with microalgae, they could only reachup to larval stage III after 25 days of treatment, showing also a decreasingsurvival rate after 10 days. When fed with cyanobacteria and native bacteria, thelarvae survival rate decreased drastically, dying on day 15th atlarval stage II. To analyze if the yeast Saccharomycescerevisiae is transmitted along oviposition and the developmental stages ofthe insect, larvae were fed with GFP-labelled cells. The growth of GFP-labelledyeast in specific culture medium and the presence of the GFP gene by PCR wereevaluated during the entire mosquito developmental stages including theoffspring eggs. We determined that S.cerevisiae could not be transmitted to the eggs. However, we identified twobacteria species present in the eggs that could be inoculated by females duringthe oviposition providing the first food for the neonate larvae. Finally, wecarried on oviposition tests offering females different substrates inoculatedwith specific microorganisms. The two native bacteria present in the eggs, Klebsiella sp. and Aeromonas sp. were chosen by mosquito females for oviposition butyeast substrates were not chosen. The native bacteria identified in this workcould provide the first progeny intake but it might not be sufficient tocomplete the entire mosquito developmental stages. The function of thesebacteria in the Cx. pipiens life cycleis being further investigated