Host location and host discrimination behavior of Telenomus isis, an egg parasitoid of the African cereal stem borer Sesamia calamistis

In the Republic of Benin, the scelionid egg parasitoid Telenomus isis (Pola szek) is one of the most important control factors of the noctuid maize ste m borer Sesamia calamistis. In the present study, the role of various sourc es of contact kairomones (male or virgin or mated female moths) and of the moth's oviposition substrate (leaf sheath versus filter paper; host plant s pecies) in host location and oviposition behavior of T. isis was investigat ed in Munger cells, open arenas, and/or Petri dish assays. Furthermore, its ability to distinguish between unparasitized eggs and eggs parasitized by a conspecific female or by the trichogrammatid Lathromeris ovicida was stud ied. In the Munger cell experiment, T. isis spent more time in moths' odor fields than in the control. There was no difference between virgin and mate d females. In the open arena assay, traces left by both the male and female moths acted as contact cues, which elicited an arrestment response in the parasitoid. The residence and patch retention time in the arena with virgin or mated females of S. calamistis was about 4.8 times as long as that with males. The presence of maize leaf sheaths stimulated the oviposition behav ior of T. isis when compared to eggs offered on filter paper. During the fi rst 6 hr, more eggs were parasitized on maize leaves, although there was no difference in the final number of offspring between the two substrates. In addition, if eggs of S. calamistis were offered together with different ho st plant species or alone, maize and sorghum were both more attractive than miller or the egg alone and equally attractive between themselves, indicat ing that the plant tissue influences host finding of T. isis. Both T. isis and L. ovicida recognized markings of conspecific females. and intraspecifi c superparasitism was therefore low. Interspecific superparasitism was more than three times higher for L. ovicida than for T. isis, indicating that o nly T. isis was able to recognize the marking of the other species and trie d to avoid superparasitism. Emergence of parasitoids from multiparasitized eggs generally was in favor of L. ovicida regardless of species order.