Biology and impact of Hypsipyla robusta (Moore) on Toona ciliata M. Roem. in Himachal Pradesh.
Toona ciliata is a versatile timber tree that grows in forest and agroforestry situations under sub-tropical and tropical conditions of India, Southeast Asia and the Pacific. It is attacked by an insect, Hypsipyla robusta which voraciously feeds on its fruits and shoots. The infested trees become stag-headed with crooked boles. Studies on the biology of H. robusta revealed that oval, white eggs with an average size of 0.9 × 0.5 mm were laid on young fruits and shoots. Incubation period was 3-4 days. There were five brownish instars. Full-fed larvae were violet blue and pupated in a cocoon. Pupae were obtect, 14.2 × 4.07 mm in size and lasted for 10-11 days. Male moths were smaller (26 mm in wing span) than females (28 mm). Insects completed four generations in a year and over-wintered as prepupae from October to mid-March. Larvae fed voraciously, particularly after the third instar. A single larva was found to feed on 6-10 fruits, or to form a tunnel with an average length of 65 cm in shoots. Tress between 2 and 3 m in height had the highest incidence of damage (93.3%) and the maximum shoot infestation per tree (66.5%). In addition to the effects on form and growth of the affected saplings, insect infestation also adversely affected seed germination. There was 20% seed germination in heavily infested fruits compared with 98% in seeds obtained from healthy fruits. The impact of insect damage on natural regeneration of T. ciliata saplings growing in pure stands and in solitary situations was studied.