The cabbage webworm (Hellula undalis) on tickweed (Cleome viscosa) in Samoa

Abstract

Cabbages (Brassica spp.) are important components of the diet of many South Pacific island people, but their production is often constrained by pests and diseases. Leaf-eating caterpillars, particularly Crocidolomia pavonana, Plutella xylostella and Hellula undalis, are the most important insect pest constraints in Samoa. In 2006, it was observed that H. undalis infests a wild plant, Cleome viscosa, in Samoa. Field surveys, laboratory and cage experiments were then conducted from 2007 to 2009 to investigate aspects of the ecology of H. undalis in Samoa. The study showed that H. undalis is present on C. viscosa throughout the year. Findings also suggest that parasitism of H. undalis in Samoa is either negligible or non-existent. Only Brassica rapa chinensis, Brassica oleracea capitata and C. viscosa were confirmed as hosts of H. undalis. Laboratory and cage experiments suggested that C. viscosa was more attractive for H. undalis larval feeding than the Brassica spp. However, overall indication from this study is that the main role of C. viscosa, under field conditions, is as source of recruitment of H. undalis onto cultivated hosts. We recommended that C. viscosa should be controlled in cabbage growing areas.