STUDIES ON PSYLLIDS (HOMOPTERA) FORMING GALLS ON PALAQUIUM OBOVATUM KING

Abstract

The two psyllids attacking Palaquium obovatum studied differ strikingly in structure of the galls, the time taken for larval development, the structure and placement of the eggs and the mechanisms for disposal of waste products and defence. Both galls are initiated by the larva and not by the oviposition of the female psyllid.

Although both galls develop on young leaves, M. stylata attacks much earlier, its eggs being laid on the unopened bud. Zetrioza sp. oviposits on the expanded leaf and galls are initiated slightly later. The extent of differentiation in the gall tissue is related to the duration of time spent by the larval stages within the gall. M. stylata develops in 14 days, forming histologically simple marginal leaf rolls which are the cumulative effect of several larvae. Zetrioza sp. makes complex individual galls with thick sclerenchyma and takes at least 72 days to complete development. The larvae differ in structure and habits, especially in relation to defence and hygiene within the gall. M. stylata produce copious honeydew and wax, while Zetrioza, which has to occupy a restricted space for a longer time, produces very little.