Impact of light and dark conditions on the mating and life cycle of a generalist parasitoid, Bracon brevicornis

Das, Bipasha (2025) Impact of light and dark conditions on the mating and life cycle of a generalist parasitoid, Bracon brevicornis. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS Dissertation of Bipasha Das (20MS222)) 20MS222_Thesis_file.pdf - Submitted Version Restricted to Repository staff only Download (1MB)

Abstract

The generalist ectoparasitoid wasp, Bracon brevicornis (Family: Braconidae), preys on various lepidopteran larvae and serves as a natural biocontrol agent valuable in agroecosystems. This study aimed to determine the impact of light and dark conditions on the reproductive behaviour (mating and parasitization) of B. brevicornis. In 12 hrs Light (L):Dark (D) conditions, mating was low in the dark period and a higher number of male offspring was recorded from these matings, while in the light period, a lower number of male offspring were recorded. There was no significant difference in the number of females observed. There was no significant difference in the developmental period of the adults that emerged. In shorter 6 hour intervals of L:D, we found that mating was significantly lower in the dark conditions as earlier. More number of males resulted from matings at night from 12 am to 6 am, and the least number of males were observed from matings set up in the afternoon from 12 pm to 6 pm. When presented with a host in 12h L:D conditions, host paralysis was recorded and it was observed that it was more in light conditions than in the dark conditions on Days 1, 2 and 3. The total number of adults emerged was also higher in the ones where parasitization occurred in light than in dark conditions for Day 1 and Day 2. However, no significant difference was observed on Day 3, as there were very adults emerged in Day 3. Similarly, for shorter intervals of 6 hours L:D, it was observed that host paralysis and the number of adults emerged were highly lower in the dark conditions. The highest number of host larvae were paralysed in the early morning from 6 am to 12 pm, while the lowest paralysis was recorded from 12 am to 6 am across all three days. The highest number of adults emerged occurred in the ones where parasitization occurred from 6 am to 12 pm while the lowest was recorded from 12 am to 6 am for Day 1. There was no significant difference observed on Day 2 while no adults were emerged on Day 3. As there was only 6 hours available for oviposition and also continuous oviposition occurred in Day 1, no. of adults emerged is very less in Day 2 and there were no adults emerged in Day 3.

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