Bionomics and Damage Estimation of Dolichothrips indicus (Hood, 1919) (Thysanoptera: Phlaeothripidae) in a New Host in Tamil Nadu, India

Abstract

Bionomics and damage of a polyphagous and an enigmatic phlaeothripid insect, Dolichothrips indicus (Hood, 1919) has been described on a profitable and popular agro-forestry crop Melia dubia (Malabar Neem) in Tamil Nadu, a southern state of India. This little-known target thrips species, previously known to feed flowers and shoots of different plant families has come out as a pest of M. dubia which is persistent in nurseries and regular in plantations. Molecular aided taxonomic identification of D. indicus performed during the study revealed their highest compatibility with the type specimens of D. rambhutanae (Ananthakrishnan) and D. pumilus (Priesner). Population assessment and mapping of D. indicus for over a year showed nil to very high population. Population density with individuals <50 had occurred in 3 out of total 23 study locations comprised of 13 districts of Tamil Nadu triggered by positively correlated (r=0.384) relative humidity. Whereas other weather parameters did not impact the population significantly. Alteration in food plant selection from Ailanthus excelsa shoots feeder to ravenous shoot and leaf feeder of host M. dubia was documented. Infected leaves of M. dubia encountered the development of boundless branched stellate trichomes on the abaxial surface. The feeding and egg laying damage of D. indicus on M. dubia resulted the loss of average 52% of chlorophyll content and 80% of total leaf lamina compared to the healthy one after heavy infestation. Other secondary infection symptoms seen in the adaxial surface of leaves during infestation are yet to be investigated.