|January 2005. A grower who manages vegetable gardens for a hotel group in the Maldives has one site that is attacked regularly by a range of different caterpillars that do a lot of damage, particularly to rocket and lettuce. There are some caterpillars that are smooth skinned, beige with darker brown stripes and a black spot at one end, roughly 0.5 cm long; and others that are covered in yellowish hairs, that are dark grey with two antennae are about 1 cm long. The garden is situated on Kunfunadhoo Island in the Baa atoll and surrounded by jungle (screwpine, cork tree, hibiscus, Indian almond, taro). Certain caterpillars eat the stems of plants and others the leaves. The grower had considered several options – Bt, neem oil, exclusion nets, Trichogramma wasps – but would like to hear other ideas.
Photos of reared adult moths would be usefu; but Bt for small caterpillars would probably be the best foliar insecticide. However, Bt is not so good on large caterpillars. There is an organic formulation of spinosad that is now available or soon to be available. It would be the best foliar insecticide for larger caterpillars. Bt is harmless to natural enemies, but spinosad when first applied can knock out small hymenopterans parasitic wasps (natural enemies), although fairly harmless to predators. Exclusion nets would help if there are sufficient resources.
Some of the caterpillars were thought to be Spodoptera spp. Two or three species of Spodoptera can occur at the same time within vegetable growing areas. Eggs are laid in batches of 200-400, easily visible on the upper leaves (and upper surface). The egg mass are 5 to 10 mm in diameter. In intensive cultivation of green peppers, it has been worthwhile to pick infested leaves and destroy them. The economics of this method of control on salad crops would obviously warrant greater consideration.
A photo with a scale is needed. The caterpillars might be Pyralidae – so not Spodoptera. A good picture of the back of the head and thorax would help. Also, some information on the level of infestation and damage caused would be useful. Is it a new pest in Maldives?