Biology of a new ichneumonid parasite of the amaranthus stem weevil of South India

Summary

In exploring the possibilities of biological control of the cotton stem weevil of South India, some attention was directed towards the study of the biology and natural ememies of allied curculionids of similar habits. Among such forms, the common Amaranthus weevil of South India,Hypolixus truncatulus B. proved to be the most useful laboratory host for many species of parasites. An account of this weevil and its parasites was presented before the Science Congress session (Calcutta, 1938).

Since then, the studies have been continued, though intermittently, and a few new and interesting species of parasites have been encountered. One such species forms the subject of this short paper.

The parasite in question is a new species of Ichneumonid belonging to the genusXoridescopus. An account of this parasite together with its life-history and habits is furnished.

It is a primary ectophagous larval parasite ofHypolixus truncatulus B. preferring the late third and fourth instars of the host grubs for parasitisation. It has a few other hosts which are all stem-boring weevils. The parasite stings and completely paralyses the host before oviposition with a maximum capacity of 34 eggs per fertilised female in captivity. On account of intense larval fight, never more than one larva was seen to survive beyond the first stage on a single host. The total life-cycle covered an average of 27 days made up of an egg period of about 30 hours, larval period of 8·4 days, a prepupal period of 4 days and a pupal period of 13·7 days. The length of life of adults never exceeded 67 days. Detailed descriptions of the immature stages, the nature and development of cephalic skeleton and mouth parts and the prepupal phases have been presented since these form the most characteristic and distinguishing features of the species.