Sarita Kumar/Research publications/Abstract 12

Abstract

Larvicidal bioassay was carried out in the laboratory to assess the potential of ethanolic extracts of dried fruits of three species of peppercorns; Long pepper, Piper longum L., Black pepper, P. nigrum, and White pepper, P. nigrum; against the different instars of field collected Indian strain of dengue fever mosquito (Aedes aegypti L.). The investigations established the larvicidal potential of all the varieties of pepper fruits against Ae. aegypti. Against early fourth instar the ethanolic extracts of Black and White P. nigrum proved to be 30-40% less toxic than the extracts of P. longum, whereas against third instars white pepper extracts exhibited 7% more efficacy than that of black pepper and 47% more toxicity than that of long pepper. The results also revealed that the extracts of all the three pepper species were 11-25 times more toxic against the third instar larvae as compared to the early fourth instars. The LC₅₀ values obtained with ethanolic extracts of P. longum, White P. nigrum and Black P. nigrum against early fourth instar larvae were 0.248, 0.356, and 0.405 ppm, respectively and the LC₉₀ values were 0.605, 0.758 and 0.801 ppm, respectively. Whereas against third instar larvae, the LC₅₀ values recorded with three extracts were 0.022, 0.015 and 0.016 ppm and LC₉₀ values recorded were 0.054, 0.034 and 0.046 ppm, respectively. The larvae treated with all the pepper species showed initial abnormal behaviour in their motion followed by excitation, convulsions and paralysis leading to 100% kill indicating delayed larval toxicity and effects of the extracts on the neuromuscular system. Observations of morphological alterations on treated larvae under light microscopy revealed that most organs, except anal papillae, had a normal structural appearance as that of controls. The structural deformation in the form of shrinkage in the internal membrane exhibited by anal papillae suggests the anal papillae as the probable action sites of the pepper extracts. The potential of peppercorns as new types of larvicides for the control of mosquitoes are explored.