SPECIAL ISSUE: MULTILEVEL FEEDING ECOLOGY Selective effects of floral food sources and honey on life-history traits of a pest–parasitoid system Sadia Munir 1 * , Lloyd M. Dosdall 1 & Andrew Keddie 2 1 Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB, Canada, and 2 Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada Accepted: 18 April 2018 Key words: longevity, body weight, nectar, Plutella xylostella, Lepidoptera, Plutellidae, Diadegma insulare, Hymenoptera, Ichneumonidae, IPM, integrated pest management, diamondback moth Abstract 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 sur- vived the longest on Thlaspi arvense L. (Brassicaceae) and P. xylostella on Sinapis arvensis L. (Brassi- caceae). 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. Dia- degma 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. xy- lostella management. Introduction The successful growth and development of an insect depend on the fulfillment of its qualitative and quantita- tive nutritional requirements (Barbehenn et al., 1999). Studies have shown that carbohydrate-rich food is a vital source of energy for many parasitoids and their hosts dur- ing the adult stage (W€ ackers, 2004; Winkler et al., 2005). Planting and maintaining carbohydrate resources as nec- tar-producing flowering plants near the cropping areas is often recommended for the fitness of parasitoids (Gour- dine et al., 2003). The provision of floral food sources can be a crucial part in biological control. Feeding on floral resources substantially affects life-history traits of parasitoids, such as survival, longevity, development, fecundity, and parasitism (Lee et al., 2004; Lee & Heimpel, 2008; Tunc ßbilek et al., 2012). Nectar feeding has been reported to increase the longevity of several hymenopteran parasitoids up to 20-fold under laboratory conditions (Jervis et al., 1996; Fadamiro & Heimpel, 2001; W€ ackers, 2001). Diadegma insulare (Cresson) (Hymenoptera: Ichneu- monidae) is a dominant, solitary, synovigenic, larval para- sitoid of diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), a destructive cosmopolitan pest of brassicaceous crops (Harcourt, 1986; Sarfraz et al., 2005; Lee & Heimpel, 2008). Diadegma insulare is one of the primary P. xylostella biocontrol agents in Canada and the USA (Harcourt, 1986; Sarfraz et al., 2005; Wold-Burk- ness et al., 2005; Young, 2013). In North America, para- sitism by this wasp varies from 50 to 98% in the field depending on host instars (Legaspi et al., 2000; Hutchison et al., 2004). Earlier studies had reported higher parasitism rates and longevity of D. insulare when the crop was *Correspondence: Sadia Munir, Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada T6G 2P5. E-mail: smunir@ualberta.ca 500 © 2018 The Netherlands Entomological Society Entomologia Experimentalis et Applicata 166: 500–507, 2018 DOI: 10.1111/eea.12695