Life history aspects of two monophagous insect species feeding on Calotropis gigantea in Sri Lanka

Abstract

Calotropis gigantea is a plant native to Sri Lanka with an Ayurvedic medicinal value, yet it is known to be invasive in countries where it has been introduced. Dacus persicus and Paramecops farinosus (Aak weevil) are monophagous insects that feed on C. gigantea. Present study is aimed to elucidate the life history aspects of D. persicus and P. farinosus with their damage to the plant, in order to assess the potential of them to be used as a bio-control agent against C. gigantea in countries where the plant is invasive. The field sampling was done throughout the island covering 108 sampling sites during December 2014 to October 2015, and C. gigantea fruits were examined for life stages of the two insect species, and for any signs of damage to the fruit. D. persicus eggs were found in seed chamber as only one cluster of eggs per fruit, and three larval instars were recorded feeding on Calotropis seeds. Infected fruits drop pre-maturely with fully developed larvae inside. Subsequent pupation takes place in soil, and cocoons are creamy white and cylindrical in shape. Similarly, P. farinosus lay yellowish, oval and mostly one-clustered eggs in the inner-pericarp fibrous layer of the Calotropis fruit. Newly emerged larvae were apodous, pale yellowish-white with brown head capsule whereas developing larvae were creamy-white, curved and stout. P. farinosus larvae voraciously feed on Calotropis seeds while adults feed on leaves, buds and flowers. Fifth larval instar of Aak weevil pupated by forming silky cocoons within seed chamber of Calotropis fruits. Both species being seed predators highly damage reproductive structures of C. gigantea, thus directly influences on reproductive output of the plant. These results provide baseline information needed in adopting D. persicus and P. farinosus as potential bio-control agents against C. gigantea.