Effect of different nitrogen fertilizer levels on the functional response of the predatory gall midge Aphidoletes aphidimyza in feeding on the melon aphid Aphis gossypii

 The functional response is one of the important components of predator-prey interactions. It can be affected by different factors such as host plant quality. In this research, the functional response of the predatory gall midge Aphidoletes aphidimyza larvae to the nymphs of the melon aphid, Aphis gossypii reared on cucumber plants amended with different levels of nitrogen fertilizer (0, 100, 150 and 200 kg/ha) was investigated. The experiments were carried out at 25±1 °C, 60±5 % RH and a photoperiod of 16: 8(L: D). Different densities (2, 4, 6, 8, 12, 16 and 24) of mixed 2- and 3-d old nymphs of the aphid were separately offered to 4-d-old predator larvae. The numbers of killed preys were recorded after 18 h. Logistic and nonlinear regression analyses were used to determine the type of functional response and estimate of attack rate (a) and handling time (Th) parameters, respectively. At all treatments, the predator exhibited a type II functional response to change in A. gossypii density. The attack rate and handling time of the predator were ranged from 0.0623 to 0.1512 h-1 and 1.4646 to 1.8716 h, respectively. The highest value of attack rate and the lowest value of the handling time of A. aphidimyza were obtained at treatment of 200 kg/ha nitrogen. This study revealed that adding nitrogen to the soil in cucumber cultivation can improve the predatory ability of A. aphidimyza on A. gossypii. However, for understanding further details of the effects of different levels of nitrogen fertilizer on cucumber- A. gossypii- A. aphidimyza interactions, further studies need to be carried out.