Impact of cruciferous trap crops on lepidopteran pests of cabbage in Hawaii

The objective of this study was to determine if trap crops of Indian mustard, Brassica juncea (L.) Czern., and 'Tastie' head cabbage, Brassica oleracea variety capitata L., gown alongside a main crop of 'Scorpio' head cabbage would significantly reduce lepidopteran pest numbers and improve yields on the main crop. For the 2 most economically important lepidopteran pests in the trials, diamondback moth, Plutella xylostella (L.), and imported cabbageworm, Pieris rapae (L.), significantly higher numbers were found on trap-cropped Scorpio than on monoculture Scorpio for certain key sampling dates. Numbers of Plutella xylostella were higher on the trap crops than on trap-cropped Scorpio for certain key dates. It appears that Indian mustard and Tastie cabbage acted effectively as attractants, but through an undetermined mechanism contamination of the adjacent Scorpio crop occurred. There were no significant differences in yield or marketability between monoculture Scorpio and trap-cropped Scorpio. Various changes in agroecosystem management might allow the attractiveness of the trap crops to be used in a beneficial manner. Indian mustard and Tastie cabbage show potential for use as trap crops for Hellula undalis (F.), cabbage looper, Trichoplusia ni (Hubner), and green garden looper, Chrysodeixis eriosoma (Doubleday). An understanding of the mechanisms that explain the movement of Lepidoptera within vegetationally diverse agroecosystems would be useful for on-farm implementation of this technique. Problems inherent in field experiments that compare the effects of different cropping systems on mobile insect populations are also discussed.