Plant quality effects on intraguild predation between Orius laevigatus and Aphidoletes aphidimyza

To understand the influence of plant quality on intraguild predation and consequently on the suppression of a shared prey population as well as on plant yield, the interactions between . Aphis gossypii Glover (Hemiptera: Aphididae) (shared prey), . Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae) (intermediate predator), and . Orius laevigatus Fieber (Hemiptera: Anthocoridae) (top predator) were investigated in 25-day experiments on cucumber, . Cucumis sativus L. (Cucurbitaceae) at various N fertilization levels (90, 150, and 190 p.p.m.) in microcosm set-ups under greenhouse conditions. The final aphid population size was significantly affected by an interactive effect of N fertilization and predator application. Regardless of the N fertilization levels, . O. laevigatus alone was more effective in aphid suppression than . A. aphidimyza alone. In addition, the risk for aphids of being predated upon by both predators together was significantly reduced in the low and medium-N fertilization levels, whereas it was additive in the high-N fertilization treatment. The . A. aphidimyza population was suppressed by . O. laevigatus in both the 90 and 150 p.p.m. N treatments. However, there was no intraguild predation of . O. laevigatus on . A. aphidimyza at the 190 p.p.m. N level. Total plant yield depended on predator treatments and N fertilization levels, with the highest yield produced at the 150 p.p.m. N fertilization level in treatments with either . O. laevigatus alone or with both predators together. Our results demonstrate that the weak asymmetric intraguild predation among . A. aphidimyza and . O. laevigatus does not influence the ability of both predators together to diminish bottom-up effects on aphid populations and the yield losses associated with aphid infestations.