Relative Larvicidal Efficacy of Three Species of Peppercorns against Dengue Fever Mosquito, Aedes aegypti L.
Keywords:Aedes aegypti, Piper sp., hexane extracts, bioassay, convulsions, anal gills
The present investigations involve the laboratory study of biocontrol potential of hexane extracts of dried fruits of three species of peppercorns; Long pepper, Piper longum L., Black pepper, P. nigrum, and White pepper, P. nigrum against larval forms of Aedes aegypti (Diptera: Culicidae), the vector of dengue haemorrhagic fever. When analyzed individually, hexane extracts of Black P. nigrum were found to be most effectual against the early fourth instar larvae of Ae. aegypti, followed by P. longum, and White P. nigrum being least effective. The LC50 values obtained with hexane extracts of P. longum, White P. nigrum and Black P. nigrum against early fourth instar larvae were 0.017, 0.024, and 0.007 ppm, respectively and the LC90 values were 0.065, 0.081, and 0.027 ppm, respectively. It was observed, however, that the larvae of Ae. aegypti were most susceptible against a mixture of the three extracts when taken in 1:1:1 ratio exhibiting the LC50 and LC90 value of 0.002 and 0.011 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% kills which indicated delayed larval toxicity and effects of the extracts on the neuromuscular system. Observations of morphological alterations on treated larvae under light microscopy revealed that all organs had a normal structural appearance as that of controls except the little structural deformity in the form of shrinkage of internal membrane observed in anal gills. Potency of hexane extracts of dried peppercorns provided an excellent potential for controlling Ae. aegypti at the larval stage.
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