Impact of short-term temperature challenges on the larvicidal activities of the entomopathogenic watermold Leptolegnia chapmanii against Aedes aegypti, and development on infected dead larvae

CATAO ALAINE; LOPEZ LASTRA CLAUDIA; LUZ CHRISTIAN; RUEDA PÁRAMO MANUEL ENRIQUE; GARCÍA GARCÍA JUAN JOSÉ; REGOZINO MUNIZ ELEN; RODRIGUEZ JUSCELINO; FERNANDES ÉVERTON K.K.

Goiania

Simposio; International symposium on fungal stress; 2017

IPTSP-UFG, CAPES

The oomycete Leptolegnia chapmanii is a promising pathogen for biological control of Aedes aegypti. The larval stage of this mosquito can survive in small water sites that are exposed to temperature variations during the day. One of the major challenges for application of L. champanii to control mosquitoes is the susceptibility of its propagules to natural abiotic stresses. The present study evaluated the effects of short-term heat or cold stresses on the virulence against A. aegypti, production of encysted zoospores (cysts) and oogonia of L. chapmanii. Cysts of ARSEF 5499 were exposed to temperature regimes between -12 °C and 40 °C for 4, 6 or 8 h, and their infectivity was tested against third instar larvae (L3) at 25 °C. In addition, the production of cysts and oogonia was monitored on L3 killed by infection and exposed to the same temperature regimes; their larvicidal activity was also examined. Cumulative mortality of larvae dropped significantly in proportion to the increased time exposure of cysts to -12 °C, 0°C, 35 °C or 40 °C. The virulence of cysts was less negatively affected by fast thawing than by slow thawing from the frozen state. The zoosporogenesis was higher between 5°C and 30 °C in comparison to freezing or high temperatures (-12 °C, 35 °C or 40 °C), but was significantly lower than 25 °C (positive control; 1.5 × 10 4 cysts/larva). The production of oogonia on dead larvae was stimulated by exposure at freezing and cold temperatures; no oogonia was observed when infected larvae were exposed to high temperatures (≥ 25 °C). This study described the susceptibility of L. chapmanii cysts to short-term exposure at differents temperatures, and indicated which ones improved the effectiveness of L. chapmanii. The application of this patogen for A. aegypti control may be challenging in natural enviroments with extreme temperature variation.