|Romeis, J - ICRISAT|
|Zebitz, C - UNIV OF HOHENHEIM|
Submitted to: Entomologia Experimentalis et Applicata
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 19, 2001
Publication Date: N/A
Interpretive Summary: Several plant characters are known to affect the searching behavior and efficiency of Trichogramma egg parasites. In this study, the physical and chemical plant characters that contribute to the low parasitism levels of Helicoverpa armigera eggs on pigeonpea were studied. Host eggs laid on leaves were most frequently parasitized, while eggs found on pods had the lowest parasitism levels. Chemicals from pigeonpea pods repelled the egg parasites in laboratory studies, though in the field wind and rain may reduce the impact of these chemicals. In addition to chemicals, the long sticky hairs on pigeonpea pods and leaves also inhibited the activity of th parasites.
Technical Abstract: Several plant characters are known to affect the searching behaviour and parasitization efficiency of Trichogramma spp. (Hymenoptera: Trichogrammatidae). In this study, plant characters contributing to the lo Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) egg parasitism level on pigeonpea (Cajanus cajan(L.) Millspaugh) were investigated. The efficiency of T. chilonis on pigeonpea was dependent on the plant structur on which the host eggs were found. In a cage experiment, more than 55% of eggs placed on leaves were parasitized, while 1% of eggs on calyxes and no eggs on pods were parasitized. In a filter paper bioassay, parasitoids wer deterred by acetone and hexane surface extracts from pigeonpea pods but showed no response to water extract. The searching behaviour of the parasitoids was not affected by different solvent extracts from the surface of pigeonpea leaves. In a four-armed airflow olfactometer, T. chilonis was srepelled by volatiles from pigeonpea pods but showed no response to volatiles derived from hexane extract of pod surfaces. Volatile infochemicals and hexane surface extracts from pods of two wild Cajanus species, C. scarabaeoides (L.) Thours and C. platycarpus (Bentham) van der Maesen, were similarly deterrent to T. chilonis. The movement of the parasitoids on pigeonpea pods and calyxes was inhibited by long trichomes and wasps were trapped by sticky trichome exudates. Parasitoids walked significantly faster on leaves than on pods. The walking speed on both pod and leaves increased significantly after washing with hexane. The results presented in this paper show that hte plant growth stage and the plant structures preferred by H armigera for oviposition are the least suitable for T. chilonis, contributing to the low parasitoid efficiency on pigeonpea