Physiological Mechanisms of Host-plant Resistance in the Genus Lycopersicon to Heliothis zea and Spodoptera exigua, Two Insect Pests of the Cultivated Tomato1

Abstract

When larvae of Heliothis zea (Boddie) were caged on fruits of varying developmental ages from 3 accessions of Lycopersicon , the length of the larval stage and mortality were positively correlated with fruit α-tomatine content. Larval growth rates and adult weights of H. zea were found to be inversely correlated with fruit alkaloid content. Growth and survival of caged Spodoptera exigua (Hubner) were not related to the levels of tomatine in the fruit. However, a highly significant correlation exists between fruit cuticular toughness and S. exigua mortality. Compared to the processing tomato line VF145B-7879, lower H. zea and S. exigua survival rates were observed when the larvae were reared on the tougher, higher-alkaloid fruits of L. esculentum var. cerasiforme and L. pimpinellifolium accessions. These results indicate a possibility of enhancing cultivar resistance to these insect pests through the development of tough-fruited, high-α-tomatine genotypes.