Volume 17, Issue 2
February 1943, pages 27-58
pp 27-36 February 1943
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.
pp 37-40 February 1943
It is shown that the pink-flowered type has arisen by a recessive mutation of the scarlet type. The inheritance of scarlet and pink flower colours inS. coccinea Juss ex Murr. follows a monogenic inheritance.
The suitability of this species for demonstrating simple mendelian inheritance is explained.
pp 41-58 February 1943
The seasonal changes for a year in the physico-chemical variables of a garden pond containing abundant zoo-plankton are traced. The important features of the pond water are its low oxygen content, slight alkalinity, high organic content, scarcity of phyto-plankton and abundance of zoo-plankton and mussels.
The dominant zoo-plankton consisted of Copepods.
Interrelationship existing between the environmental conditions in the pond on the one hand and the animals on the other is discussed.