Effects of wild and cultivated host plants on oviposition, survival, and development of diamondback moth (Lepidoptera: Plutellidae) and its parasitoid Diadegma insulare (Hymenoptera: Ichneumonidae)

The effects of wild and cultivated Brassicaceae host plants on diamondback moth, Plutella xylostella (L.), oviposition, egg hatch, larval survival, infestation level, parasitism rate by Diadegma insulare (Cresson), and the developmental time and sex ratio of D. insulare were studied. Diamondback moth egg laying was highest on the Brassica crops, especially broccoli, and lowest on wild Brassicaceae, especially Berteroa incana L. DC. and Erysimum cheiranthoides L. Percentage of egg hatch was not significantly different among host plants. Diamondback moth larval survival was generally higher on the Brassica crops than on wild Brassicaceae and there was no survival on Barbarea vulgaris R. Br. Developmental time of diamondback moth larvae was generally longer on the wild Brassicaceae than on the Brassica crops. Percentage of parasitism by D. insulare was lowest on B. incana, Lepidium campestre R. Br. and E. cheiranthoides. Percentage of parasitism was higher when diamondback moth larvae fed on B. kaber than on the wild Brassicaceae. When fed on E. cheiranthoides, Thlaspi arvense L., and B. incana, parasitized diamondback moth larvae took significantly longer time to develop to D. insulare pupae than when they were fed on the other Brassicaceae plants. The female/male sex ratio was higher on Brassica species than on non-Brassicas. Diamondback moth infestation and percentage of parasitism in the field were higher on broccoli than on the other Brassica crops, but the proportion of D. insulare females versus males was not significantly different. The presence of wild Brassicaceae, especially B. vulgaris and B. kaber, in the field could reduce diamondback moth populations, increase the impact of D. insulare, provide a reservoir for insecticide-susceptible diamondback moth, and increase the success of diamondback moth management programs.