Cabbage Pests And Their Natural Enemies In Barbados, W.I

In Barbados, some 20 insects attack cabbage. Of these, only 5, i.e. diamond-back moth, Plutella xylostella, cabbage semi-looper, Trichoplusia ni and Pseudoplusia includens, cabbage bud-worm, Hellula phidilealis and cabbage white-butterfly, Ascia monuste monuste, were of economic importance. A large complex of indigenous natural enemies present in Barbados does not keep the pests below economic levels. As a result exotic natural enemies were introduced from India, Pakistan and the Caribbean Islands. Amongst the parasites introduced against J?. xylostella, Cotesia (=Apanteles) plutellae and Tetrastichus sokolowskii became established. The former parasite is widespread. The annual range of parasitism, from 1971-80 was 17.9 to 52.2%. This parasite introduced into the Leeward and Windward Islands by the Commonwealth Institute of Biological Control (CIBC), Trinidad, and later by the Caribbean Agricultural Research and Development Institute (CARDI) is well established. X- sokolowskii, an indigenous parasite in the East Caribbean Islands, was introduced into Barbados from India, Montserrat and St. Vincent. It is established in the island, but possibly because of the heavy applications of pesticides, has failed to achieve high populations. It has also been recorded as an incidental secondary parasite of C. plutellae. An egg-larval parasite, Litomastix sp. (truncatellum group), introduced against Trichoplusia/Pseudoplusia, from India, is very well established, attacking an average of 25.8% larvae on cabbage, 79.4% on tomato, 78.8% on sweet potato, 33.3% on okra, 58% on beans and 25% on cucumbers. Hellula phidilealis, also attacks the buds and pods of Cleome spp. and Gynandropsis gynandra in Barbados, the East Caribbean Islands and Guyana (South America). The pest population and the parasite complex on these plants was greater and more consistent than that on crucifers, suggesting that Cleome and Gynandropsis are the primary host plants. The natural enemies recorded were: Apanteles spp., Chelonus sp. nr. mexicanus, Eiphosoma annulatum, Bracon sp., hebetor and an unidentified Tachinid, which are all first records from this host. Cabbage white-butterfly, Ascia monuste monuste, a migratory pest, broods freely on Cleome spp. and G. gynandra in Barbados and the East Caribbean Islands, and also feeds on Lepidium virginicum in Barbados. A Tachinid, Phorocera sp. ?parviteres attacked 8% and 14% larvae during May and November 1973 respectively, whereas a pupal parasite, Brachymeria ovata, attacked an average of 36.4% pupae on B. oleracea in 1979, 50.3% on C. spinosa and 35.2% on £. viscosa in 1980. During outbreaks, some 93.7% larvae on B. oleracea and 94% on C. viscosa were destroyed by various predators. In the wet season, about 20% larvae and 95% pupae were killed by a polyhedrosis virus. The egg-masses of Spodoptera spp. were parasitised by Telenomus remus. The average parasitism recorded was 58.3% during 1978, 52.2% in 1979 and 41.1% in 1980.