Studies on the fruit feeding weevil, Paramecops farinosa (Coleoptera Curculionidae) in Sri Lanka as a prospective weed biological control agent of the invasive weed, Calotropis spp.

Abstract

Calotropis gigantea is a large shrub or a small tree native to Sri Lanka with an Ayurvedic medicinal value. The plant is considered as an invasive weed in countries where it has been introduced. Paramecops farinosa Schoenherr (Aak weevil) is a monophagous pest that feeds on C. gigantea. Present study was conducted to elucidate the life history and damage potential of P. farinosa, in order to assess its potential as a biological control agent against C. procera and C. gigantea in countries where the plants are invasive. The field sampling was done throughout Sri Lanka covering 120 sampling sites from December 2014 to October 2015, and C. gigantea fruits were examined for the incidence and intensity of damage by P. farinosa. It lays 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. Paramecops farinosa larvae voraciously feed on all Calotropis seeds (100%) and fifth larval instar pupated by forming silky cocoons within the seed chamber. The adults feed on leaves, buds and flowers and its damage is highly correlated with the amount of P. farinosa inhabit on trees. P. farinosa is a seed predator and highly damage reproductive structures of C. gigantea thus directly influences the reproductive ability of the plant. These results provide baseline information needed in adopting P. farinosa as potential biological control agent against C. procera and C. gigantea.