Antagonist Potential of Vorticella microstoma on the larval development of Culex gelidus and Aedes aegypti

Abstract

Selection of effective biological agents which can suppress the growth of immature stages of mosquito vectors has drawn a wide attention in disease control programmes. Vorticella microstoma is a parasitic ciliate which has an ability to parsitize on larval stages of mosquitoes and inhibit their growth. However, the potential antagonist activity has not been evaluated in detail in Sri Lanka. Fifteen each of first, second, and third instar larvae of Cx. gelidus and Ae. aegypti were placed in separate V. microstoma culture bottles at room temperature (27± 2 ºC) and mortality rate of mosquito larvae was observed after 48 h. Bioassay was done in completely randomized design with controls. The first, second, and third instar larvae of Cx. gelidus were allowed to be infested with the trophont stage of V. microstoma. Heavily infested larvae with V. microstoma were identified by the presence of parasites attached all over the body surface. V. microstoma trophonts did not usually attach to siphon region of mosquito larvae when they are alive. None of the instar levels of Ae. aegypti showed susceptible to infection with V. microstoma. In the first instar larvae of Cx. gelidus, thorax and the abdominal segments had the attachment of 30–35 trophonts of V. microstoma, whereas 2–4 trophonts had attached to the anal papillae. Higher densities of V. microstoma were found in abdominal segments of second instar larvae of Cx. gelidus, whereas total of 45–50 trophonts had attached to thoracic region and abdominal segments. Fifty to fifty-five trophonts of V. microstoma had attached to third instar larvae of Cx. gelidus, with higher densities in the anal papillae followed by abdominal segments; in the anal papillae, 20–25 trophonts were found to be attached. V. microstoma infection was positively correlated with the body size of mosquito larvae. The percentage mortality of the first, second, and third instar larvae of Cx. gelidus did not significantly differ from each other (One-Way ANOVA: IBM SPSS Statistic Software, P<0.05). Therefore, the study results would be a new avenue to work on environmentally agreeable manner in reducing the Cx. gelidus vector mosquito populations.