Induced resistance in cucumber, Cucumissativus, to cotton aphid, Aphis gossypii (Hem.:Aphididae) under greenhouse conditions

Melon aphid, Aphis gossypii, is an important pest of cucumber in greenhouses. In this research the possibility of using induced resistance for reducing population growth rate of the pest has been investigated. The life history parameters of aphid were determined in a growth chamber at 25±2° C, 60 ± 5% R.H and 14:10 L D conditionsin a completely random design in a split plot experiment. The main factor was two cucumber cultivars of Royal and Storm and the subplot consisted of five different pre-infestation periods (0, 2, 4, 6 and 8 days pre-infestation with five melon aphid/plant). At the end of each pre-infestation period, the aphids were removed and the plants kept aphid-free for 48 h. The life history and population growth parameters of aphid were determined through 40 replications. The results indicated that there were significant differences among the treatments in aspect of the nymph growth duration, duration of reproduction of adult aphids and the longevity of the adult aphids. Furthermore, among the treatments R0, r, λ and DT had significant differences in both cultivars, but there was no significant difference among the treatments in terms of generation time (T). The lowest and highest R0 in Royal (19.27 and 49.65 nymph/female/generation)and the lowest and highest r(0.311and 0.480 /day) were observed on 6 and 0 days pre-infestation period treatments, respectively. The lowest and the highest R0 in Storm (13/25 and 44/63 nymph/female/generation)and the lowest and highest r(0.273and 0.463 /day) were observed on 6 and 0 days pre-infestation period treatments, respectively. WE conclude that the pre-infestation of the cucumber plants with A. gossypii can induce resistance in cucumber within 6-8 days leading to population growth rate reduction in the melon aphid.