Occurrence of mortality due to bacterial infection by a gram negative bacterium and the hymenopteran entomophagous parasite Apanteles glomeratus (L.) was observed in a natural population of Catopsilia crocale Cramer, a defoliator of the ornamental and medicinal plant Cassia alata. On regular field observation during the seasons 1980–1981 and 1981–1982, it was found that mortality due to these factors was mostly confined to the Final larval instar and the pupa of C. crocale. A direct correlation was obtained between population density of C. crocale and the number of larvae'pupae killed due to these factors. As the incidence of the hymenopteran parasite and bacteria fluctuate along with the C. crocale population, consideration of the foregoing factors as potential biological control agents for the pest population of C. crocale, is suggested.

The body weight of the host was considerably reduced on attack by the parasitoid, Apanteles glomeratus Linnaeus. It varied from 466.65 ± 87.78 mg to 177.94 ± 52.01 mg. Average weight of the parasitoids per host was 268.54 ± 80.86 mg and individual parasitoid weighed 3.12mg. There was a reduction in the total body lipid: from 8.85 ± 1.27% (wet wt) in the normal caterpillar to 1.93 ± 0.42% in one batch and to 5.16 ± 0.80 in another batch of infected caterpillars. The haemolymph protein content of the host also showed a reduction from 9.89 ± 1.29 to 3.59 ± 0.76%.

Parasitization of P. brassicae L. by A. glomeratus L. was found to be between 63.79 and 76.52% in Farm 1 and 92.68 and 93.43% in Farm 2. Population density of the parasitoids ranged between 35.16 ± 6.05 and 57.76 ± 13.20. The developmental period of the parasitoids within the host was 21 days and the pupal period 9 to 10 days. The population of the parasitoid showed a steady increase during November–December. The rate of pupation of P. brassicae showed a decline from 36.21% in mid-November to 23.48% in later November in Farm 1 with an early crop. In Farm 2 with a late crop the pupation rate dwindled from an already low 7.32 to 6.57% by late December.