Selective effects of floral food sources and honey on life-history traits of a pest-parasitoid system

Many parasitoids and their herbivorous hosts forage on the same floral resources in agroecosystems. Floral resources that benefit natural enemies without supporting pests can improve the efficacy of biological control agents. Here, we report the results of a study on selective effects of floral and non-floral food sources on the life-history traits of the parasitoid Diadegma insulare (Cresson) (Hymenoptera: Ichneumonidae) and its host Plutella xylostella (L.) (Lepidoptera: Plutellidae). Under standard laboratory conditions, insects were exposed to four flowering plant species, 10% honey solution, and water. All food sources increased the longevity of the herbivore and its parasitoid by as much as four- to nine-fold, respectively, compared to the water control diet. Diadegma insulare survived the longest on Thlaspi arvense L. (Brassicaceae) and P.xylostella on Sinapis arvensis L. (Brassicaceae). However, none of the food sources tested was beneficial to the parasitoid alone, though Lobularia maritima L. (Brassicaceae) was found to selectively favor the longevity of D. insulare. Diadegma insulare adults were heavier when fed on S.arvensis, whereas feeding on the honey solution led to higher body weights of P.xylostella. In conclusion, we demonstrated that floral and non-floral food sources varied in their suitability and acted differently on life-history traits of a host-parasitoid system. The selective characteristics of nectar-producing plants and their influence on the herbivore-natural enemy combination can, therefore, be employed to increase their impact in integrated P.xylostella management.