Studying the interaction between plant nutrition and pests for the reduction of pesticide use and optimization of fertilizer application
Abstract: Our general hypothesis is that high levels of Nitrogen (N) will positively affect pests while high levels of potassium (K) will negatively affect pests. Our research objectives are to: 1) investigate the effect of plant nutrition with varying combinations of N + K on pests feeding on different plant tissues (parenchyma, phloem and cell content) on the same crop, and 2) on crops of different botanical families. In order to test our hypothesis we have built a system with 8 different fertilization treatments: 4 different level of N with a standard level of K and 4 different levels of K with a standard level of N. All other minerals were kept constant in all treatments. Tomato and bean plants were grown in flowerpots filed with perlite and the fecundity, survival and development rate of 3 pests Bemisia tabaci, Helicoverpa armigera and Tetranychus urticae were measured. Females of B. tabaci, a sap feeding insect, are sensitive to the amount of N in tomato plants and avoid oviposition on plants with lower levels of N. Similarly, lower levels of N or higher levels of K negatively affect B. tabaci's development rate. Helicoverpa armigera, a leaf chewing insect, was also positively affected by N levels in tomatoes, having larger larvae developing on plants fertilized with high levels of N, while higher levels of K lead to smaller larvae. Survival rate and longevity were also affected in the same way. When growing on beans, the results were not significant although the trend was similar. Tetranychus urticae, a cell content feeding mite, was also positively affected by high levels of N, having higher population on plants with higher levels of N, but K had no effect on this pest. In beans both mineral treatments had no effect on the mite population. After the first year of research, our results partially support our hypothesis that both K and N can affect pests depending on the feeding tissue and the plant family.