Influence of the parasitoid Cotesia vestalis on the distribution of diamondback moth larvae on cabbage plants

Abstract

Fear associated with perceived predation risk can elicit behavioral and physiological changes in animals, including insects. Diamondback moth (DBM), Plutella xylostella, larvae are known to wriggle violently backwards and even fall off plants when attacked by predators and parasitoids. In the laboratory, the DBM larvae exposed to the specialist parasitoid Diadegma insulare were found to move to lower quality, older foliage, which negatively affected their development. In Hawaii, by far the dominant parasitoid species of DBM is the generalist Cotesia vestalis, with many sampling efforts often only yielding this species. Thus, in this study, we investigated the influence of C. vestalis on the behavior of DBM larvae. We focused on the distribution of DBM on cabbage plants, from the youngest to oldest leaves (leaf position 1–12, respectively), in the presence of C. vestalis in the lab and field. We found that in the lab, DBM larvae showed a clear preference for younger leaves (leaf positions 3–5). However, when C. vestalis was present, regardless of whether the parasitoids could touch the DBM, larvae were less likely to be on those preferred leaf positions. This change in larval distribution was also replicated when potted cabbage plants containing DBM larvae were placed in cabbage fields. Changes in herbivore feeding sites, whether mediated by natural enemies or other environmental factors, could have significant implications, not only for herbivore fitness, but also for economic damage to crops based on the value of plant parts affected.