Extended Abstract 
1.    Introduction: The melon aphid, Aphis gossypii Glover (Hemi.: Aphididae), is a polyphagous aphid species that causes severe damage to many crops worldwide. It feeds on the host plants by sucking the sap from leaves, flower buds, and stems. A. gossypii can also transmit several plant viruses. The population of A. gossypii is usually controlled by chemical insecticides. However, the excessive use of insecticides has resulted in developing resistance to the insecticides. For sustainable management of A. gossypii on host plants, alternative methods such as the use of resistant plant cultivars and plant hormones seem to be effective strategies. Host plant resistance is a fundamental factor for a successful integrated pest management (IPM) system. Gibberellic acid is one the most important plant hormones that regulates many aspects of plant growth and promotes plant resistance to some insect pests. In this study, we investigated the involvement of gibberellic acid in the defense responses of two caltivers (Capsicum annuum L.) against A. gossypii.
2.    Materials and Methods: The effects of gibberellic acid and two cultivars [poblano (as susceptible cultivar) and paprika (as resistant cultivar)] on A. gossypii were determined by analyzing the life history and life table parameters of the pest at 25 ± 2 ˚C, 65 ± 5 % RH, and a photoperiod of 16L: 8D h. The initial colony of A. gossypii was obtained from the laboratory of Department of Plant Protection, University of Mohaghegh Ardabili (Ardabil, Iran). The plants were grown individually in 16 cm-diameter plastic pots filled with a mixture of soil and sand (1:1). When they had reached the four- or six-leaf stage, they were used either for rearing the aphids or for the experiments. The experiments were initiated by spraying the entire leaves of each pepper cultivar with a solution of gibberellic acid at a concentration of 0.005 g. The control plants were treated with distilled water. After 24h, apterous adults were randomly selected from the colony and transffered to the clipcages (6 cm diameter) set on the tested cultivars leaves. They were permitted to produce nymphs for 24h. Then, the adults and all nymphs except one were removed from the clipcages. Each cage were monitored daily for the aphid’s survival and developmental time. After maturity, daily observations were continued until the death of last individual. The numbers of nymphs produced per female aphid were counted daily, and then all nymphs were eliminated from the clipcages. The obtained data were analyzed via the TWOSEX-MSChart program based on the age-stage, two-sex life table theory.
3.    Results and Discussions: The results show that, A. gossypii exhibited a longer nymphal period and lower adult longevity on the tested cultivars sprayed with gibberellic acid than on the control. The oviposition period and fecundity of the aphid were lower in the plants treated with gibberellic acid than in control. Finally, the lowest and highest lifespan were 6.97 days (gibberellic acid treatment in Paprika) and 10.25 days (control treatment in Poblano), respectively. In addition, spraying the pepper cultivars with gibberellic acid significantly decreased the gross reproductive rate (GRR), net reproductive rate (R0), intrinsic rate of increase (r), and finite rate of increase (λ) of A. gossypii compared to the control. The minimum and maximum values of r were 0.2839 (gibberellic acid treatment in Paprika) and 0.4046 day (control treatment in Poblano). The results exhibited that the gibberellic acid was more effective in decreasing the life -history and -table parameters of A. gossypii on cultivar paprika. These parameters are appropriate indexes to compare insect pests’ performance on different host plants as well as the host plant’s induce resistance versus the insects. Comparing the results of the life history and life table parameters of A. gossypii on the tested treatments indicated that pepper plants especially the cultivar paprika treated with gibberellic acid was more effective in controlling A. gossypii due to slow development, poor fecundity, and low r value of the aphid. The lower performance of A. gossypii on this treatment would result in a lower population growth that in turn would lead to lower subsequent infestations. 
4.    Conclusions: The results of the current study showed that, gibberllic acid had a suitable potential for controlling the population of A. gossypii and can be used in the integrated pest management (IPM) programs.