The role of grass infusions as oviposition attractants and oviposition stimulants for Aedes aegypti

Á. E. Eiras

Dept. of Parasitology, Universidade Federal de Minas Gerais, Brazil

The mosquito A. aegypti is the main urban vector of dengue and yellow fever, arboviral diseases that can spread rapidly in explosive epidemics in South America. Oviposition traps (ovitrap) provide a very sensitive and economical method for detecting Aedes mosquitoes”) when the population density is low, whereas general larval surveys and adult collections produce unsatisfactory results. The addition of grass infusion in the ovitrap enhances significantly the number of eggs collected, thus increasing the trap efficacy. We evaluated grass infusions aiming to identify the volatiles that attract gravid Ae. aegypti female mosquitoes to ovitraps. We screened infusions of four grasses (Pennisetum purpureum; Panicum maximum; Cynadon plectosa chyus and Cynadon dactylon) and the results showed that P. maximum associated traps collected a significantly higher number of eggs than the control. Infusions of fresh and dried leaves of P. maximum were also evaluated and showed that the egg detection of ovitraps baited with fresh leaves infusions was significantly higher than other treatments. The volatiles from grass infusions are likely to be produced by microorganisms, as ovitraps baited with aerobic fermentation collected significantly more eggs than those with anaerobic and sterilized infusions. The fermentation period and concentration of infusions are also important to produce a blend of active compounds. The identification of the volatiles released from grass infusions that attract gravid Ae. aegypti female mosquitoes to ovitraps has being carried out in order to use specific synthetic chemicals to eliminate the need to create infusions. We also evaluated in laboratory and field, larval holding water as oviposition attractant and in combination with grass infusions. The highest? concentration of larval holding water increased significantly the number of eggs collected and a synergistic effect was observed when both stimuli were presented in combination. Video recordings of the oviposition behavior of gravid A. aegypti females showed that there is a pattern of behavioral sequences during the pre-oviposition and oviposition period. Discrimination between oviposition attractants and stimulants, and how gravid female mosquitoes exploit baited ovitraps will be discussed. Supported by CNPq, FAPEMIG, FUNASA, IFS (Sweden)

Index terms: Aedes aegypti, infusions, oviposition stimulants.

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