Cabbage Webworm on Crucifers in Malaysia

The cabbage webworm, Hellula undalis (F.) is a major pest of cruciferous vegetables in the lowlands of Malaysia. The common host plants include cabbage, radish, cauliflower, Chinese kale, Chinese mustard and the Cleome weed spp. Damage by cabbage webworm is particularly serious on cabbage because damage on the shoot by a single larva can cause either death of the plant or production of unmarketable multiple heads. The critical period of damage is usually from transplantation to the heading stage of cabbage. Generally, higher populations of CWW on cabbage coincided with the drier periods of the year, and low populations during the wetter ones. Within a single season, peak population generally occurred around 40 days after transplanting. Under laboratory conditions, the total developmental period from egg eclosion to adult emergence was about 26 days. Incubation period was about 3 days and the larval period about 14 days. There were usually five instars. The pupal period lasted 8.5 days. Adult longevity was about 7 days for both sexes and the shape of the survivorship curve was a Slobodkin's Type 1. The mean number of eggs laid per female was 175 and the mean egg per day per female was 27. Cabbage webworm was effectively controlled by shoot-tip treatment using Bacillus thuringiensis applied once a week until head formation. So far, two species of parasitoids have been recorded but their incidence was low.