Host-searching by Goniozus natalensis females elicited by a short- range kairomone in the frass of its natural host Eldana Saccharina.

Abstract

Petri dish and olfactometer tests demonstrated that Goniozus natalensis (Gordh) females exhibit a host-searching response upon contact and at a short distance by olfaction, to a kairomone in the frass of its natural host Eldana saccharina (Walker). The host-searching response was found to be elicited by E. saccharina frass from a range of substrates, namely: two host plants of E. saccharina, papyrus and sugarcane, and four media: sugarcane, papyrus, and cellulose based media and a synthetic medium containing no plant material. The host-searching response was not elicited by Sesamia calamistis (Hamps) sugarcane medium frass. The sexual state and age of G. natalensis females were found to influence the host-searching behaviour. Mated females showed the behaviour in the petri dish bioassays only after completing their preoviposition time of two to three days, whilst virgin females took longer, even though their preoviposition time was found to be the same. The response to male or female produced E. saccharina sugarcane frass was not statistically different, nor was there a statistically significant preference for either frass type, given the choice. Four way olfactometer tests showed that an E. saccharina sugarcane frass odour elicited a host-searching behaviour in mated two to three day old G. natalensis females. Various solvents were tested for their ability to isolate the kairomone from E. saccharina sugarcane frass. Chloroform proved to be the best solvent when tested in petri dish and olfactometer bioassays. The preliminary results of the GC/MS analysis of the chloroform extract of E. saccharina sugarcane frass are presented. The chemicals identified are compared with chemicals identified as host location kairomones for other insect parasitoid-host studies.