RESPONSES OF NAIVE FEMALE DBM (PLUTELLA XYLOSTELLA) TO VOLATILE ORGANIC CHEMICALS OF SELECTED BRASSICACEAE PLANTS

Plants respond to insect feeding damage by releasing a variety of volatiles from the damaged site. The profile of the volatiles emitted from undamaged and mechanically damaged plants is markedly different. The diamondback moth (DBM), Plutella xylostella L, which feed on the plants of the family Brassicaceae is a major pest of Brassica crops in Malaysia and other part of the world where these crops are grown. It is also the most serious insect pest of crucifers worldwide. This study has been conducted to evaluate the effect of volatile organic compounds emitted by three different crucifer plants damaged in four different ways on the naive DBM female by using a Y-olfactometer-based analysis. The DBM females were provided with a dual choice of damaged or undamaged cabbage (Brassica oleracea), Chinese mustard (Brassica nigra) or Indian mustard (Brassica juncea) plants. The results suggest that DBM females attracted to the volatiles organic compounds of the cabbage plant damaged by the DBM’s own larvae and to plants damaged by aphids. The female DBM adult is attracted more to Chinese mustard plants damaged mechanically or by the cabbage head caterpillar (Crocidolomia binotalis Zeller) than to the plants damaged by DBM larvae. Also, the number of female DBMs that responded to undamaged Chinese mustard plants was significantly higher than the number that responded to the plants attacked by DBM larvae or by aphids. The naive DBM female adult also showed a significant preference for undamaged Indian mustard plants compared to Indian mustard plants colonised by aphids. From our results it can be concluded that the naive female DBM adult chooses not to land on host plants either damaged by its own larvae of other insect species to oviposit in order to secure a better food supply for her offspring. Probably also, on undamaged plants, they will face less exposure to their natural enemies - the parasitoid and predators- but this needs further investigation.