Influence of trichome exudates from species of Lycopersicon on oviposition behavior of Heliothis zea (Boddie)

Cage experiments revealed that accessions of the wild tomato species Lycopersicon hirsutum were preferred sites for oviposition by Heliothis zea. Hexane extracts from the leaves of L. hirsutum were also preferred sites of oviposition in choice experiments among extracts from several Lycopersicon species. Extracts of L. hirsutum were still biologically active several days after application, indicating that the phytochemical(s) involved are relatively stable and of low volatility. Gas Chromatographic analysis of leaf hexane extracts from 12 different accessions of the L. hirsutum complex and three tomato cultivars revealed substantial qualitative and quantitative variation in the chemical composition of these extracts. Comparison of these results with extract oviposition studies implicate a group of structurally related compounds as the active agents. Mass spectroscopy has tentatively identified these compounds as sesquiterpenes with the chemical formula C₁₅H₂₂O₂. These compounds are apparently synthesized and secreted from glandular trichomes on the leaf surface. These phytochemicals did not stimulate ovipositional behavior in females of the cabbage looper, Trichoplusia ni. The existence of genetic variation for the presence and amount of kairomones that serve as cues for insect orientation and oviposition could be utilized in a breeding program to develop tomato cultivars with genetically modified allelochemic profiles that would disrupt the sequential behavioral processes of insect host-plant selection.