Species-specific effects of parasitism of ectoparasitoid, Bracon hebetor (Hymenoptera: Braconidae) on the larval haemocyte counts of Corcyra cephalonica and Ephestia kuehniella (Lepidoptera: Pyralidae)

Abstract

Many studies have described post-parasitism physiological changes in hosts for koinobiont insect parasitoids. However, there is a lack of knowledge regarding idiobiont ones that how these parasitoids effect their target hosts’ physiology. In the present study, it was aimed to determine the effect of parasitism by Bracon hebetor (Hymenoptera: Braconidae), an efficient idiobiont ectoparasitoid of many lepidopterous larvae, on the host cellular and immune responses, particularly on haemocyte counts, of Corcyra cephalonica and Ephestia kuehniella, two important stored product pyralid pests. Results showed that B. hebetor parasitism played a significant role in fluctuating total haemocyte counts (THCs) in parasitized E. kuehniella and C. cephalonica larvae with the passage of time. For E. kuehniella, parasitism boosted the THCs as compared to control till 12 hours except a steep decline in the very first hour. Highest THC was observed at 6th day of parasitism. In contrary, B. hebetor venom injection seems suppressing the production of THCs gradually except for a steep increase of THC in the very first hour of observation in C. cephalonica larvae. The minimum THC was recorded at day 9 for C. cephalonica. These findings indicate that parasitism by idiobiont parasitoids alters the cellular immune response and haemocyte physiology of their hosts; however, these haemocyte-mediated responses are more species specific. B. hebetor parasitism causes a quick suppression of haemocyte production in C. cephalonica larvae than in E. kuehniella which sustain a gradual increase in THCs several days post-parasitism.