Relationship Between Trichome Density in Tomato and Parasitism of Heliothis spp. (Lepidoptera: Noctuidae) Eggs by Trichogramma spp. (Hymenoptera: Trichogrammatidae)

Abstract

During 1984 through 1986, eggs of Heliothis zea (Boddie) and H. virescens (F.) were collected from field-grown tomato accessions varying in levels of glandular trichome-based resistance to Manduca sexta (L.) (Lepidoptera: Sphingidae) and Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae). Eggs were subsequently held in the laboratory to determine levels of egg parasitism, mortality, and hatch. Parasitism of eggs by Trichogramma petiosum Riley and T. exiguum (Pinto and Platner) was greatest on the Lycopersicon esculentum (Mill) cultivar susceptible to M. sexta and was lowest on all backcross lines (L. esculentum × PI 134417) × PI 134417) and the highly resistant L. hirsutum f. glabratum C. H. Muller (PI 134417). Regression analyses indicated that trichome density accounted for the greatest proportion of variance in Trichogramma spp. parasitism of eggs. However, because the methyl ketones 2-tridecanone and 2-undecanone, which contribute to the insect resistance of PI 134417, occur in the glandular trichome tips, their effects on parasitism by Trichogramma could not be separated from the effects of trichome density in this study. Egg density, canopy volume, and number of stem terminals per plot were unrelated to the percentage of parasitism by the Trichogramma studied here.