Novel Mechanism for Resistance to Colorado Potato Beetle (Coleoptera: Chrysomelidae) in Wild Solanum Species

Abstract

The Colorado potato beetle, Leptinotarsa decemlineata (Say), is the most destructive insect pest of the potato, Solanum tuberosum L., worldwide and has shown remarkable adaptability to insecticides. In wild Solanum species, the best known host-plant resistance mechanisms are a high level of foliar glycoalkaloids and the presence of specialized, glandular trichomes. Through a preliminary field-test screen, 3 Solanum species, Solanum trifidum, S. raphanifolium, and S. circaeifolium, were identified with low foliar glycoalkaloid levels and no glandular trichomes, but still exhibiting substantial resistance to L. decemlineata. These 3 species along with 2 species, S. berthaultii and S. chacoense, representing the 2 known mechanisms of resistance, were examined in bioassays for larval leaf consumption, effect on larval growth, and percentage of larval mortality. The best S. trifidum accessions had 10-fold less foliar consumption per larva than controls and induced 54 % reduction in larval weight compared with controls during a 24-h feeding period. Forty-eight hour mortality rates were 100 % for 2nd and 3rd instars feeding on S. trifidum compared with 22 % for the S. tuberosum controls. Despite low foliar glycoalkaloid levels and the absence of glandular trichomes, S. trifidum accessions exhibited both an effective antinutritive and deterrent mechanism for resistance to L. decemlineata.