Assessement of Kairomones as a Monitoring Tool for Cotesia Flavipes Cameron (Hymenoptera: Braconidae)

Abstract

Chilo partellus (Swinhoe) is a major pest of maize in East Africa. Its indigenous natural enemies are unable to regulate its densities to a level acceptable to farmers. Cotesia flavipes Cameron (Hymenoptera: Braconidae), a larval parasitoid of C. partellus now established in Kenya, was released in 1993 from Pakistan for the control of this pest. A major constraint in evaluating the establishment of C. flavipes, is the great amount of time spent for its field collection and identification. Use of traps may facilitate the assessment of the establishment and spread of this parasitoid. A number of chemical compounds released by C. partellus infested maize plants influence the searching behaviour of C. flavipes. This work investigated the potential of these kairomones and other green leaf volatiles for use as bait in traps for the purpose of monitoring the establishment of C.flavipes in released areas. The attraction of these kairomones, which include (Z)-3-Hexenylacetate, (E)-PFamesene, 4,8-Dimethyl-1,3,7-nonatriene, Thomac oil (natural oil containing 85% (E)- p-Famesene), heptanal, and a blend of (Z)-3-Hexenylacetate and Thomac oil (1:1), to C. flavipes female parasitoids was studied in the Y-tube olfactometer. Results showed that parasitoids were attracted to all the kairomones; however, this attraction varied with the dose of the kairomone. Odours from host plant complex (HPC), obtained from maize stalk in which C. partellus had been feeding for 24 hours and parasitoid diet (20% honey/water solution) were also very attractive to C.flavipes. A preliminary field test evaluating the delta trap baited with HPC for its potential in trapping C.flavipes under field conditions showed that C.flavipes was caught in 2 out of the 12 fields used for the study, suggesting that with some improvement an effective trap could be developed for use as a monitoring tool for C. flavipes. To improve on the trap catches, diff~rent other traps including water traps, delta traps, plastic plates, plastic cups and modified delta traps, and different baits including parasitoid diet and HPC were evaluated. The vertical sticky trap was the most effective both in the laboratory and under semi-field conditions; however, no difference was observed between the two baits tested. The effect of the number of traps placed in a cage on the number of insects caught was assessed. A positive correlation between the density of traps and the number of C. flavipes trapped in a cage was noted. The vertical sticky trap baited with different kairomones was also evaluated under semi-field conditions for 8 hours. Results indicated that all the kairomones tested were able to attract C. flavipes to the trap. A blend of (Z)-3-Hexenylacetate and Thomac oil (1:1) (150llg per disc) attracted more parasitoids. In conclusionvtraps baited with herbivore-induced kairomones can effectively be used in trapping C. flavipes under semi-field conditions; however their effectiveness under large field areas needs to be investigated before they are used as bait in traps for monitoring purposes. Evaluation of the trap and monitoring of Cotesia flavipes could also be done using HPC or parasitoid diet as baits since they are inexpensive and are attractive to the parasitoid.