Nectar-Collecting Behavior of Diadegma insulare (Hymenoptera: Ichneumonidae), a Parasitoid of Diamondback Moth (Lepidoptera: Plutellidae)

Abstract

We observed 5 nectar-collecting behaviors of Diadegma insulare (Cresson), a major parasitoid of diamondback moth, Plutella xylostella (L.). The most striking behavior of D. insulare was chewing at the base of Barbarea vulgaris R. Br. and Brassica napus L. flowers and creating holes that probably released the floral nectar. D. insulare visited more frequently and spent longer times on Rower species that supported longer life and high fecundity ( B. vulgaris, Brassica kaber (D.C.) Wheeler, B. napus and Daucus carota L.). Time spent per visit was positively correlated with the number of previous visits for B. vulgaris and B. kaber , flowers that support long life and high fecundity. Time spent per visit was negatively correlated with the number of previous visits for Berteroa incana L. (D.C.) and Erysimum cheiranthoides L. (flowers that cause shorter lives and low fecundity of D. insulare ). This suggests that D. insulare , after experience, was able to positively correlate nectar rewards with the Rower characters. Flower color did not affect parasitoid choice of flowers. D. insulare spent significantly longer time at the upper one-third of D. carota corolla and at the lower one-third of B. kaber and B. vulgaris corollas than oilier Rowers. Behavioral flexibility of D. insulare to flower characters and its nectar-collecting behaviors should be considered for increased impact of this parasitoid in diamondback moth management programs.