Preliminary studies on the biology of Orasema assectator Kerrich (Hym., Eucharitidae), parasitic on Pheidole and causing damage to leaves of tea in Assam

Abstract

The so-called ‘sewing blight ’ of tea in Assam is an effect of oviposition in the young leaves by two species of Eucharitid, Orasema initiator Kerrich and O. assectator Kerrich. The affected leaves develop brown spots round the oviposition punctures, wither prematurely and adversely affect the quality of the made tea. Normally only a small proportion of bushes is affected and these are associated with the presence of nests of an undetermined species of Pheidole.An account is given of the life-history of O. assectator, and the developmental stages are briefly described. The eggs are laid singly in incisions made by the ovipositor on the underside of the leaf in parallel rows arranged lengthwise. The newly hatched larvae exist as free-living planidia on the leaf surface, whence they are carried by unknown means into the ants' nests in the soil beneath the tea bushes. Here the planidium transfers to the last-instar larva of the ant and penetrates its body. There it remains inactive until its host reaches the prepupal stage, whereupon endoparasitic feeding and development start. After the host pupa has formed, the parasite larva emerges, establishes itself below the thorax of its host, and remains there, feeding ectoparasitically, through two further instars, completely consuming the contents of its host. The mature larvae remain scattered in the ant's nest and pupate a few days later; both larvae and pupae are cared for by the worker ants.