Impact of fertilization on cotton aphid population in Bt-cotton production system

Understanding the relationship between fertilization and the incidence of insect pests is essential for the management of chemical fertilization and insect pests in modern agroecosystem. In this paper, effects of potassium supply alone and combination of nitrogen and potassium fertilizers on population dynamics and density of cotton aphid Aphis gossypii (Hemiptera: Aphididae) were investigated during seedling stage in Bacillus thuringiensis (Bt)-cotton production system. The results showed that high concentration of potassium fertilizer significantly reduced cotton aphid population density when nitrogen fertilizer was not used. Aphid population dynamics and density at peak time were obviously affected by the combination of nitrogen and potassium fertilizers in different rate, whereas different population dynamics of aphid were showed among different treatments. Compared with potassium fertilizer used alone, the same or significantly reduced aphid densities were observed in combination treatments of 120 kg/ha potassium with 108 kg/ha and 144 kg/ha nitrogen levels in both years. In addition, cotton aphid population density was significantly affected by interaction of nitrogen and potassium fertilizers in field experiments of two years, these results indicated that cotton aphid population density at seedling stage was suppressed by potassium fertilizer and the combination of potassium and nitrogen fertilizers in proper rate (K:N = 1:0.9 or 1:1.2 kg/ha). Suggesting that proper application of potassium and nitrogen fertilizers should be beneficial to controlling insect herbivores such as cotton aphid and plant growth at seedling stage of Bt-cotton field in Central China.