Tomato cultivar susceptibility to Egyptian cotton leafworm (Lepidoptera: Noctuidae) and Colorado potato beetle (Coleoptera: Chrysomelidae)

The development and deployment of crop varieties that resist or tolerate insect infestation is one tactic for pest management that can eliminate one or more spray applications per season, a significant savings to the grower. Seven commercial tomato, Lycopersicon esculentum Mill, cultivars 'Marmand', 'Edkawy', VF-145, GS-27, 'Pakmor-B', 'Floradade', and UCX281 grown under greenhouse conditions were evaluated for differences in mortality and feeding (leaf area ingested) of fourth-instar larvae of cotton leafworm, Spodoptera littoralis (Boisduvar), and Colorado potato beetle, Leptinotarsa decemlineata (Say). Plants of the cultivars Floradade, GS-27, and Packmor-B sustained the most damage (more leaf area ingested) by cotton leafworm, while GS-27 and VF-145 sustained the most damage by Colorado potato beetle. Mortality of Colorado potato beetle was lowest on the F1 hybrid GS-27, indicating that GS-27 was the most susceptible cultivar to Colorado potato beetle. Variation in chemical and nutrient composition (reducing sugars, total sugars, ascorbic acid, total phenols and total protein content) of leaves explained some of the observed differences in mortality and feeding among the tomato cultivars and insect species. The correlation coefficient of reducing sugars with leaf consumption was positive (0.758) for S. littoralis and negative (-0.485) for L. decemlineata. The correlation coefficients of ascorbic acid with insect mortality were negative (-0.389 for S. littoralis and -0.459 for L. decemlineata) indicating that they may require ascorbic acid for growth. Total phenols in tomato leaflets were positively correlated with mortality of S. littoralis. Edkawy, VF145, and UCX-281 were the most resistant cultivars.