Yield Loss of Soyabean in Nepal due to Leaf Feeding White Spotted Beetles, Monolepta signata O1. (Coleoptera : Galerucidae)

  • B. K. Gyawali Entomology Division, Nepal Agricultural Research Council, Khumaltal, Lalitpur

Abstract

Yield loss in soyabean due to leaf feeding beetle, Monolepta signata O1. was studied at Khumaltar during 1985 and 1986 wet-seasons. Field experiments were conducted during vegetative as well as reproductive stages of soyabean. Adult beetles were introduced in nylon cages measuring 32 cm in diameter and 1 m high installed at the central rows of each plot just after germination. Beetles were kept at population density of 25, 50 and 100/m2. At maximum population density, the potential grain yield losses on cultivar Ransom in  vegetative and reproductive stages were 61.3 and 37.8 mg per day from each adult of M. signata. Percentages of yield losses were 12. 1, 24.9 and 58.5 in vegetative and 19.5, 34.7 and 55.5 in reproductive stages from the population of 25, 50 and 100, respectively. The yield loss was not in accordance with the level of increased population density. 2 Yield reduction was greater at 53.1 mg / m2 per day from each adult of M. signata in the lower 25-population density in the reproductive stage whereas in the vegetative stage, yield loss was not different at the 25 and 50 population densities