Enhancing the performance of the egg parasitoid, Trichogramma.chilonis Ishii (Trichogrammatidae : Hymenoptera)

Abstract

A study entitled ‘Enhancing the effectiveness of the egg parasitoid Trichogrmma chilonis Ishii (Trichogrammatidae: Hymenoptera)’ was carried out at the College of Horticulture, Vellanikkara with the objectives of increasing the effectiveness of T. chilonis and to standardize the optimum storage period of the trichocards. A prototype of an olfactometer suitable to monitor the movements of T. chilonis was at first made using polyester film for standardizing the design. The prototype was validated by keeping the kairomones in each of the four arms. As this was found to be a success, it was further fabricated in transparent acrylic sheet incorporating slight modifications. Various error factors were identified during the continued studies and they were eliminated and an improved design was standardized as uniform air inflow olfactometer. The responses of T. chilonis to different semiochemicals were studied in the uniform air inflow olfactometer. A higher response of adult parasitoids was noticed towards moth extracts of C. medinalis and Corcyra cephalonica and also moth scale extract of C. cephalonica in hexane solvent. This may be because hexane could extract more concentration or wider range of the kairomones which attract the parasitoids. The results corresponding to the response to plant volatiles emanating from the weeds in the paddy ecosystem are a clear pointer to the ecological adaptation of T. chilonis for survival. The highest attraction was towards the leaf folder damaged leaves followed by plant parts of Oryza rufipogon. Among the different semiochemicals, significant attraction was towards 10 per cent honey solution. The results thus established that a band or grid application of honey solution will increase the longevity of adults as well as the per cent parasitism. The adult moth which is the primary producer of eggs is the most preferred from among the different life stages of C. medinalis tried. A wind tunnel set up was fabricated to evaluate the olfactory responses of T. chilonis to the best semiochemicals. The distance travelled by the parasitoids was observed for every 30 minutes, for a total duration of three hours. Maximum distance travelled by the adult parasitoids was towards honey solution. The results validate the findings observed using the four arm olfactometer (free choice test) with a single source wind tunnel (no choice test). The effect of refrigerated storage on the emergence and parasitization efficiency of T. chilonis was studied. More than 50 per cent emergence was noticed up to 36 days in four day old cards which is of interest to nucleus stock of Trichogramma being maintained at the laboratories. The results of the study have shown that the Trichogramma emergence can be delayed even up to 50 days under ordinary refrigerated storage. Such cards even with around 10 per cent efficiency would be more economical than continuous rearing of Corcyra culture and production of trichogrammatids. Even for farmer situations, it may be more advisable to manage initial leaf folder populations at its first level of emergence itself. At this time the population is very low and even a 10 per cent parasitoid emergence can easily take care of first generation of leaf folder.