A Comparison of the Relative Resistance of some Tomato Cultivars to the Cotton-Melon Aphid, Aphis gossypii (Hom.: Aphidiae), under Greenhouse Conditions

The cotton-melon aphid, Aphis gossypii Glover (Hom.: Aphidiae), is an injuriously important pest of tomatoes in farms and greenhouses. In the greenhouse environment its damage ranks second to whiteflies (Trialeurodes vaporariorum Westw.). In this research the resistance of nine different tomato cultivars namely: Strian, Caligen, Super Bita, Super Strian, Super Af1, HAS2274, GS-12-f1, Sun-6200 f1 and Calj was investigated in greenhouse environment. Antixenosis studies showed the lowest number of aphids on Super Strian and the highest on Calj. Antibiosis experiments revealed the longest and shortest mean developmental times of the aphid nymphs on HAS2274 (6.9 day) and Calj (5.4 day) respectively. The highest and lowest rm values were obtained for Calj (0.306 day -1) and HAS2274 (0.185 day -1), respectively. The highest and lowest oviposition periods were observed on Calj (12.6 day) and HAS2274 (5.9 day), respectively. Tolerance level on Calj was the lowest while those of the cultivars Super Strian, Super Bita and HAS2274 were higher in comparison with the others. Based on the three mechanisms of resistance it was concluded that HAS2274 and Calj were the most resistant and susceptible tomato cultivars respectively to the cotton-melon aphid among the cultivars studied.