Impacts of Sugar Feeding on Parasitoid Behavior in the Field

Diversifying agroecosystems with floral habitats has the potential to conserve natural enemies and enhance pest control. In the laboratory, many adult parasitoids readily utilize nectar sources that have substantially increased their longevity and parasitism rates. However, in the field, does the floral habitat retain parasitoids locally so they exert greater control on pests? We studied the post-feeding and aggregation behavior of Diadegma insulare (Cresson) (Hymenoptera: Ichneumonidae), an abundant parasitoid of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae). First, sugar-fed and hungry D. insulare were compared for retention inside cabbage plots (12 x 20 m in 2003; 9 x 15 m in 2004). Sugarfed and hungry wasps were marked, released inside the plot and recaptured outside the border over 1-3 days. Sugar feeding did not appear to affect dispersal behavior of D. insulare in the field. Second, we determined whether sugar sources attracted/retained parasitoids in the crop field by monitoring the abundance of D. insulare inside cabbage plots (12 m x 20 m) bordered by 3 m wide buckwheat strips and cabbage plots devoid of floral habitat. For three summers, D. insulare were monitored within plots using sticky traps, and the number of adults captured in plots with and without floral borders did not differ. Neither experiment showed evidence that buckwheat flowers increased retention of D. insulare.