Survey on distribution of Milkweed, Calotropis gigantea L. (Apocynaceae) in Sri Lanka and the associated insect diversity

Abstract

Calotropis gigantea is a drought-resistant and salt-tolerant small shrub native to Sri Lanka. It is a poisonous plant often used in herbal medicine for asthma, leprosy, nausea, vomiting and fever. The present study was carried out to find out the distribution of Calotropis gigantea and to identify the insect fauna associated with the plant. Surveys were conducted from December 2014 to June 2015 in 120 sites covering all provinces of Sri Lanka, and the incidence of C. gigantea and the insect fauna on them were recorded. Calotropis gigantea was recorded in all provinces of Sri Lanka except the Central Province. The plant widely spreads along coastal regions of the island, but its incidence was low in the Western as well as Sabaragamuwa provinces. A total of 28 morphospecies of phytophagous insects and three species of pollinators across nine families were documented in the present study. Occasional insect visitors to the plant were recorded with a high diversity and they belonged to five orders. Among the phytophagous insects, Dacus persicus and Paramecops farinosus are highly damaging to Calotropis fruits while Sphaeroderma sp. was more common in the area. Carpenter bees were the most abundant insect pollinator of the plant. Findings of the present study provide basic information on distribution of Calotropis gigantea and its associated insect fauna in Sri Lanka.