Studies on the bionomics of the jute stem girdler, Nupserha bicolor postbrunnea Dutt (COL., LAMIIDAE)

Nupserha bicolor postbrunnea Dutt has become established on olitorius jute (Corchorus olitorius), possibly from its wild food-plant, Sesbania aegyptiaca, and from jute it has spread to other agricultural crops. Incidence on the green-manure crop, Sesbania bispinosa, has increased so much in recent years that it has surpassed that on olitorius jute. The stem diameter most favourable for girdling and oviposition in S. bispinosa ranges from 3·1 to 5 mm., whilst in C. olitorius it is from 2·6 to 3 mm. In spite of this wide difference in preferred stem diameter, the ratio of mandibular length to depth of extra-medullary tissue of such stems in the two plants agrees well.All the varieties of capsularis jute (C.capsularis) are unacceptable to the adults though they are acceptable to the larvae. Adults obtained from larvae reared on varieties of capsularis jute also show aversion to capsularis types. The pest selects the susceptible olitorius from amongst capsularis jute when these are grown as a mixed crop. Amongst the olitorius varieties, C.G. is the most susceptible. Plants coming within the height range of 100 to 200 cm. are attacked more than others. Girdling causes suspension of unidirectional vertical growth, and this is followed by the appearance of a number of side branches, which are of little value from the point of view of fibre.