Fitness of the parasitoid Diadegma insulare is affected by its host's food plants

The diamondback moth, Plutella xylostella (L.) is considered a specialist on Brassicaceae, but it is capable of expanding its food range by incorporation of non-brassicaceous plants into its diet. The use of a new food plant may change food availability and vulnerability of P. xylostella to its natural enemies, especially specialist parasitoids. In this laboratory study, we evaluated the bottom-up effects of two Brassicaceae viz. Brassica napus L. and Descurainia sophia (L.) Webb ex Prantl and two non-Brassicaceae viz. Tropaeolum majus L. and Cleome hassleriana Chodat on several fitness correlates of the specialist parasitoid, Diadegma insulare (Cresson) reared on P. xylostella larvae. Percentage of parasitism of host larvae by D. insulare varied among the plant species and was highest on T. majus and lowest on D. sophia. Values of several fitness correlates for D. insulare differed when the host was feeding on various plant species. Egg to adult development was fastest on B. napus followed by C. hassleriana, D. sophia and T. majus. Female wasps reared on C. hasseleriana lived the longest in absence of food. The response of D. insulare to potential food-plant expansion by its host P. xylostella is discussed.