Behavioural response of Coccinella transversalis to the volatiles from Aphis craccivora and Cowpea

Abstract

The behaviour and orientation modifying cues from host plant and prey insect play key role in the process of host selection and acceptance by predators. So, we conducted an experiment to understand the orientation behaviour of Coccinella transversalis on cowpea aphid, Aphis crhHexane and DCM extracts from healthy cowpea leaves, cowpea leaves infested with aphid, only aphid injured leaves and body extracts of aphids. Response in terms of number of adult beetles reaching to the source was significantly more for 10% concentration of extracts from infested cowpea leaves along with aphids followed by response to aphid injured leaves extract, aphid body extracts and healthy leaves extracts of both hexane and DCM solvent. Response in terms of time taken to reach the source was also significantly more at 10% concentration followed by 15, 5 and 20% in both hexane and DCM by male and female C. transversalis. Further the GC-MS analysis of hexane extract of infested cowpea leaves along with aphid shown the presence of compounds viz., octane, 5-ethyl-2-methyl-nonane, 5-butyltetracosyl acetate etc., similarly, in DCM octacosanal, nonadecanol, 2, 6, 11-trimethyl-dodecane etc., were found prominent and these compounds could be responsible for eliciting attraction in predator towards extracts from aphid infested leaves. Our study suggested that synomones (volatiles from cowpea plant) and kairomones (volatiles from aphid body) are playing a vital role in orientation behaviour of C. transversalis to locate the cowpea aphid.