BEHAVIORAL-RESPONSE OF TRICHOGRAMMA-PRETIOSUM RILEY AND TELENOMUS-SPHINGIS (ASHMEAD) TO TRICHOME/METHYL KETONE MEDIATED RESISTANCE IN TOMATO

Effects of methyl ketone (2-tridecanone and 2-undecanone)/glandular trichome-based resistance to insects of Lycopersicon hirsutum f. glabratum C.H. Mull, PI 134417, on the behavioral responses of Trichogramma pretiosum Riley and Telenomus sphingis (Ashmead) were observed in the laboratory. For T. pretiosum, these effects included (1) longer time required by the wasps to cross a leaf disk (diam. 16.3 mm), (2) higher percentage of wasps initiating flight from disks before reaching the edge, and (3) entrapment of wasps in trichome exudates. In tomato genotypes with varying densities of type VI glandular trichomes (3.1-9.2/mm2) but with no methyl ketones in the trichome tips, no such adverse effects were observed. The time taken to cross a disk or initiate flight by T. sphingis, a larger wasp than T. pretiosum, was not significantly affected on 16.3-mm leaf disks, although the percentage of T. sphingis initiating flight was directly correlated with trichome density among lines with no ketones. When placed on whole leaflets of plant lines with or without methyl ketones, T. sphingis was entangled by trichome exudates. However, unlike T. pretiosum, T. sphingis was eventually able to free itself from entanglement. Landing rates by T. sphingis on PI 134417 foliage contained in dialysis tubes were also reduced. Data indicate that suppression of egg parasitism by T. sphingis on resistant foliage is due to both repellent action of its foliar volatiles and reduced searching rates by the parasitoids. Results indicate that a significant portion of the reduction of egg parasitism by T. pretiosum and T. sphingis is attributable to the effects of 2-tridecanone and/or 2-undecanone present in the tips of type VI glandular trichomes on PI 134417 foliage, although the trichomes also adversely affect the wasps even in plant lines without ketones.