Biology morphology nature of attack and dispersal of cytobagous salviniae calder and sands (Curculionidae coleoptera)

Abstract

In studies on the biology and morphology of cyrtobagous salviniae calder & sands (curcullionidae: Coloeptera) a very successful agent for the bio control of the menacing weed salyinia molesta Mitchell, the females were found to insert their eggs on leaf base and rhizome scars. The egg period was 7.9 days. There are three instars, the average larva period was 23.5 days. The pupal period extended for 11.3 days. Adults showed a mean life span of 211.9 days. A pre ovipositional period of five to ten days was recorded. The three larval instars differed in respect of the relative size of head capsule and width of mandible. Adult females are slightly larger than the males. The spine like processes towards the distal end of the hind tibia are arranged in a linear manner, while in fore and midlegs these spines are arranged in a circular manner. The hind leg spur does not have a hump. Observations on the nature of damage showed that the adults were capable of arresting the growth of the weed by feeding on the buds and leaves. Occassionally they feed on rhizomes and roots. Larval scraping followed by tunneling resulted in the decay of plant parts. Weed mass showed discolouration about 15 days after initiation of feeding by the weevil and the whole weed became a black mass in about 90 days. The rate of dispersal of adult weevils was found to be very slow.