Impact of the naturalized weed Virginia pepperweed (Lepidium virginicum) on the behavior of the diamondback moth (Plutella xylostella) and its parasitoid (Cotesia plutellae) in Hawaii

Plant diversity in agricultural fields, including weeds and flowering plants in the field edges, can perform important roles in supporting the health and reproduction of pest natural enemies. They can provide predators and parasitoids with food (nectar and pollen), prey/hosts, shelter and refuge from pesticides. Virginia pepperweed, Lepidium virginicum, is a naturalized weed in Hawaii and can often be found growing in the edge of cruciferous vegetable fields. Since L. virginicum is in the family Brassicaceae and is a known host plant of diamondback moths, Plutella xylostella, we conducted lab and field experiments to determine the preference of P. xylostella adults for laying eggs on L. virginicum and the preference of a parasitoid (Cotesia plutellae) to parasitize P. xylostella larvae on L. virginicum compared to larvae on cabbage. We found that P. xylostella preferred to lay eggs on L. virginicum in the presence of cabbage, indicating that it may act as a trap crop. Moreover, we found that in the lab and field, C. plutellae parasitized more P. xylostella larvae when the larvae were feeding on L. virginicum than when they were feeding on cabbage. Additionally, in a field experiment, we found more spiders on L. virginicum plants than on cabbage and the presence of more spiders was associated fewer P. xylostella larvae. Our findings suggest that L. virginicum could serve as a beneficial weed to enhance conservation biological control efforts for the management of P. xylostella.