Entrapment of Helicoverpa armigera (Hubner) (Lepidoptera : Noctuidae) on glandular trichomes of Lycopersicon species

Cotton bollworm, Helicoverpa armigera (Hubner), is a major pest of tomato (Lycopersicon esculentum) in Australia. Host-plant resistance may prove an alternative to current control methods. The role of entrapment in glandular-trichome-induced mortality of H. armigera on Lycopersicon spp. has not previously been confirmed. Levels of entrapment and mortality on accessions of L. hirsutum and L. pennellii were compared with those on a L. esculentum control 24, 48 and 72 h after placement on leaflets with trichomes intact or with exudates removed. Accessions PI 127827 (L. hirsutum) and PI 473422 (L. pennellii) had a significantly greater number of neonates trapped after 24 and 48 h and dead after 72 h than did L. esculentum. Removal of trichome exudates significantly reduced effects on insects. A relationship between the density of type IV trichomes and the number of trapped neonates was established. Entrapment led to mortality of H. armigera, but levels were low, suggesting that entrapment alone offers scope to contribute only partially to resistance to H. armigera. The implications of these results in the selection of an accession for use in a breeding program for resistance to a range of arthropod pests are discussed.