Reduction of nitrogen concentration in the hydroponic solution on population growth rate of the aphids (Homoptera: Aphididae) Aphis gossypii on cucumber and Myzus persicae on pepper

Per capita population growth rates (r) of the aphids Aphis gossypii Glover on cucumber (Cucumis sativus L. 'Vetomil') and Myzus persicae (Sulzer) on pepper (Capsicum annuum L. 'Midal') were compared on plants provided varying concentrations of nitrogen (N) in nutrient solutions. For A. gossypii on cucumber, treatments included a solution first at 90 then at 175 ppm N, a constant 175, and a constant 225 ppm N solution. The rate of population growth of A. gossypii was significantly lower on the 90-175 ppm N solution than on either the 175 or 225 ppm N solution, which were nearly equal. The mean time to first offspring was significantly longer for aphids on cucumber provided the 90-175 ppm N solution than on 175 ppm N. Higher fecundity was observed for aphids on plants provided 175 and 225 ppm N. A. gossypii survivorship was shorter in the 90-175 ppm N treatment than in the higher N treatments ( chi super(2) = 6.7, P = 0.04). At the time aphids were placed on the plants, the percentage N in leaves was significantly lower in the 90-175 ppm N treatment than in the other two treatments (P < 0.01). The solutions provided to pepper plants were a 60 ppm N solution in the vegetative, 90 in the early fruit, and 120 in the late fruit stage, a constant 120 ppm N and a constant 175 ppm N. The r-values for M. persicae ranged from 0.31 to 0.36 and increased with N concentration (experiment 1, P = 0.05; experiment 2, P < 0.02).