Analyses of two parasitoids with convergent foraging strategies

We compared the foraging strategies of two key braconid endoparasitoids of the tobacco budworm. (Heliothis virescens Fab.), Cardiochiles nigriceps Vier. and Microplitis croceipes Cresson, that differ in host and habitat range but otherwise share comparable, overlapping niches. The most important host-location cues by far for both species were materials associated with damaged plants. Both species demonstrated a significant preference for volatiles released from plants damaged by H. virescens larvae over those released from undamaged tobacco and cotton plants. In choice experiments with damaged tobacco versus cotton, M. croceipes showed a significant preference for cotton plants. In contrast, C. nigriceps preferred damaged tobacco plants. Plant compounds provoked a strong response even when released from systemically induced plants (from which damaged leaves, host, and host by-products were removed). C. nigriceps appears to have a much keener ability to locate hosts over long distances than M. croceipes. This observation may be related to the highly specialized nature of this parasitoid. The possible adaptive significance of the foraging behaviors of these two parasitoids is discussed.