Selective enhancement of parasitoids of rice Lepidoptera pests by sesame (Sesamum indicum) flowers

Rice is one of the most important global crops but, despite suffering serious insect pest damage, has been less the subject of conservation biological control research compared with crops of importance in developed countries. Earlier studies of sesame (Sesamum indicum) as a nectar plant grown on the bunds around rice crop to promote natural enemies of rice pests had focused on the natural enemies of planthopper pests. But there is little available information on the effects of this plant’s nectar on parasitoids of important rice stem borer pests, or on the extent to which sesame may be a selective food plant such that adult Lepidoptera do not feed on its nectar. The present laboratory study assessed the effect of sesame flowers on Apanteles ruficrus, Cotesia chilonis and Trichogramma chilonis and their stem borer hosts, Sesamia inferens and Chilo suppressalis. Adult survival of all parasitoid species was increased by the presence of S. indicum flowers compared with a water control. Realized fecundity of T. chilonis was significantly enhanced by sesame flowers. Egg production of both stem borer species was comparable for S. indicum and the water treatment, and significantly lower than the honey solution control. The same trend, illustrating lack of benefit from access to sesame nectar, was also apparent in adult longevity of C. suppressalis. These findings indicate that sesame is a selective food plant that is unlikely to promote key Lepidoptera pests of rice when used in the field though it does benefit parasitoids representing three genera.