The silkworm is the larva of the domesticated silk moth, Bombyx mori. It is an economically important insect, being a primary producer of silk in sericulture industry. Among the silkworm diseases, white muscardine and green muscardine caused by Beauveria bassiana and Metarhizium anisopliae respectively possess a major threat to silk cocoon production. White muscardine is more common during rainy and winter seasons whereas green muscardine has its profound effect during hot and humid spells. Both these fungi Beauveria bassiana and Metarhizium anisopliae can be used as biopesticides to control a number of pests such as termites, whiteflies, and many other insects from larvae to adult stages. In this paper in vitro biological control of B. bassiana and M. anisopliae and cellular abnormalities induced by the application of two strains

(T12 and T13) of Trichoderma viride, Trichoderma harzianum and Trichoderma spp. were studied, where T. viride T 12 (80.52%) provides maximum in vitro control of B. bassiana followed by T. harzianum (71.88%), Trichoderma spp. (68.16%) and T. viride

T13 (62.89%). Against M. anisopliae, T. harzianum provides maximum in vitro control (68.02%), followed by T. viride T13 (64.68%), T. viride T12 (59.47%) and Trichoderma sp. (57.98%). During the interaction of pathogens and biocontrol agents hyphal coiling, granulation, distortion, vacuolation and bulging were recorded.