Modifying Soil Nutrient Level Affects Soybean Insect Predators

Abstract

AbstractSoil nutrients can influence the population dynamics of arthropod pests and their natural enemies. Previous research has revealed that overfertilization increases the likelihood of pest outbreak in a subsequent soybean [Glycine max (L.) Merr.] crop following winter wheat (Triticum aestivum L.). Improving biological control from natural enemies is an important aspect of integrated pest management. Our objectives in this field study were to (i) determine the effect of soil nutrition on population densities of the predators Geocoris spp. (bigeyed bugs), Nabis and Hoplistoscelis spp. (damsel bugs), and spiders (Araneae) in a soybean canopy and (ii) relate densities of each predator to pest densities and determine if previously reported effects of overfertilization on pest densities were the indirect result of influences of soil nutrients on predator populations. Soil nutrient levels were four levels of P and three levels of K and Mg. The study was conducted in 1986 and 1987. High P favored population density of damsel bug nymphs in 1986 only, but populations were not significantly affected by K or Mg. High P significantly affected population densities of bigeyed bug nymphs each year. Density estimates of spiders were significantly increased by P only in 1986. Densities of spiders were not affected by K and Mg either year. Increased pest outbreaks from overfertilization of soybean were not the result of fertility effects on population densities of these major predators.