Biology, feeding and oviposition preference of Helopeltis theivora, with notes on the differential distribution of species of the tea mosquito bug species complex across elevations

摘要

Cocoa (Theobroma cacao L.) is an important beverage crop and commercially grown as a plantation crop. With the changing climate, the tea mosquito bug species complex, viz., Helopeltis theivora, H. bradyi and H. antonii, is emerging as a major threat to cocoa cultivation in India. Among the species of this complex H. theivora is responsible for causing considerable damage. The present investigations were carried out to find a weak link in the life cycle of H. theivora so it can be managed effectively. Specimens of the tea mosquito bug were found to first appear during the first week of September in South India. Helopeltis theivora requires on average 29.28 days to complete its life cycle on cocoa. The highest level of natural mortality was recorded in the first-instar nymph. The total developmental period of the fifth-instar nymph was significantly longer than that for the other nymphal instars. The sex ratio reflects that the population is highly female-biased, which may contribute to the dominant nature of this species in the cocoa ecosystem. Observation of the feeding and oviposition behavior of H. theivora revealed that the insect prefers to feed and oviposit on developing pods rather than on leaves and shoots. Analysis of the species distribution of tea mosquito bug at different elevations revealed that cocoa gardens situated less than 300 meter above mean sea level are dominated by H. theivora, whereas gardens situated more than 300 meter above mean sea level are dominated by H. bradyi. This separation of species across elevation may be driven either by abiotic or biotic factors.