STUDIES ON THE OCCURRENCE OF BIPUPATE AND TRIPUPATE COCOONS IN A BIVOLTINE HYBRID, SK6 x SK7 OF THE MULBERRY SILKWORM, BOMBYX MORI L.

In mulberry silkworm, occurrence of bipupate cocoon is a common phenomenon but tripupate cocoon formation is rare. It is formed by the joint labour of two or three larvae. The formation of bipupate and tripupate cocoons is a phenomenon determined by ontogenetic circumstances depending upon the amount of space available to the spinning worms. Studies conducted during autumn crop rearing revealed that the occurrence of bipupate and tripupate cocoon was 3.94% and 1.0% out of the total cocoon observed. In bipupate cocoons, the highest frequency of association was observed in M: F (66.85%) and lowest was in F: F (13.92%). In tripupate cocoons, the highest frequency of association was in 2M: 1F (43.13%) and lowest was in 3F (23.28%). The information on the occurrence of tripupate cocoons in other silkworm is scanty.