Performance and population growth rate of the cotton aphid, and associated yield losses in cucumber, under different nitrogen fertilization regimes

Performance and population growth rate of the cotton aphid Aphis gossypii Glover, and the yield losses inflicted by that pest, were studied in relation to varying nitrogen fertilization levels (90, 110, 150 and 190 ppm) on cucumber, Cucumis sativus L., under greenhouse conditions. The results showed that some plant variables, including leaf biomass, water and nitrogen content, increased at higher levels of nitrogen fertilization. Aphids developing on cucumber plants receiving the highest nitrogen fertilization had a significantly shorter development time and produced more offspring per capita than aphids subjected to the other regimes. However, no significant differences were observed in juvenile survivorship under different nitrogen treatments. Aphid adult body weight and mean relative growth rate (MRGR), as well as the intrinsic rate of natural increase (r(m)), were positively correlated with nitrogen fertilization levels in the treated plants. Additionally, aphid abundance and population growth rate (r) were significantly influenced by interaction between nitrogen fertilization level and sampling date. Plant yield was significantly affected by the interaction between nitrogen fertilization rate and aphid presence. In the absence of aphids, plant yield increased linearly with higher nitrogen fertilization; however, in the presence of aphids yield decreased linearly with nitrogen fertilization, the lowest yield being produced by plants fertilized with 190 ppm nitrogen. We discuss the results in relation to aphid population dynamics and management.