|Romeis, J - INT'L CROP RES INSTITUTE|
|Zebitz, C - UNIV OF HOHENHEIM|
Submitted to: Entomological Research Bulletin of
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 22, 1998
Publication Date: N/A
Interpretive Summary: Why Trichogramma (Hymenoptera: Trichogrammatidae) egg parasitoids of Helicoverpa armigera (Lepidoptera: Noctuidae) fail on chickpea Interpretive summary: Egg parasitoids belonging to the genus Trichogramma rarely attack Helicoverpa armigera eggs on chickpea. The reasons for this were investigated in a series of experiments. Female parasitoids are deterred from searching for host eggs by trichomes and trichome exudates on the plant surface. High concentrations of malic and oxalic acids, the major components of the acid exudates, deterred female parasitoids. There was no response by females to volatiles emitted from chickpea plants. Field releases of high concentrations did not increase parasitism rates in the field, and sticky trap catches indicated that the parasitoids quickly left the field.
Technical Abstract: Trichogramma spp. egg parasitoids are generally absent in eggs of Helicoverpa armigera (Hubner) collected from chickpea, Cicer arietinum. In this study, the plant characters responsible for the absence of egg parasitoids and the feasibility of increasing parasitism levels on chickpea by mass-releasing Trichogramma chilonis Ishii were investigated. The residence time of female T. chilonis on chickpea leaves was affected by trichomes and the acidic trichome exudates secreted on all green parts of the plant. The parasitoids spent a longer time on chickpea leaves where th acidic trichome exudates had been washed off than on unwashed leaves, and longer on leaves of a glabrous chickpea mutant than on washed leaves. When placed on unwashed chickpea leaves, 6.8% of the parasitoids were trapped an killed by the exudates. In a filter paper bioassay, female T. chilonis wer deterred by high concentrations of malic and oxalic acids, the major components of the trichome exudates. Acetone and hexane extracts from the surface of chickpea leaves did not elicit a response from the parasitoid in the bioassay. Similarly, the parasitoids did not respond to volatiles emitted by chickpea plants in a four-armed airflow olfactometer. No parasitized eggs were collected from a chickpea filed in which T. chilonis were released five times at a weekly interval of a rate of > 137,00 females ha-1. Sticky trap catches showed that no parasitoid population was sustained in the release field.