Effects of nonhost plant neighbors on population densities and parasitism rates of the Diamondback Moth (Lepidoptera: Plutellidae)

This study examined effects of nonhost plant neighbors on population densities and parasitism rates of the diamondback moth, Plutella xylostella (L.), in Hawaii. Monospecific cabbage plots had greater larval densities, lower numbers of larvae parasitized by Cotesia plutellae (Kurdjumov), and lower percentage of parasitism compared with plots of cabbage interplanted with tomato. Larval densities were affected directly by tomato neighbors rather than by indirect changes in host plant size or quality. However, tomato neighbors did not significantly influence densities of pupae, emerging adults, or total leaf herbivory. Laboratory experiments showed that ovipositing females did not discriminate between cabbage grown alone versus cabbage grown with tomato. These results suggest that tomato neighbors affect long-range host finding or early egg-larval survival, or both, in the field as well as parasitism rates.