PESTS: Ecology

Pest Control Advisors use ecology, the study of relationships between organisms and their environment, to predict pest outbreaks and understand the effects of pesticide application and other management practices. When agricultural ecosystems are built around a single crop, fields provide unlimited, but unvarying sustenance to herbivorous insects, birds, and other animals. Low plant diversity makes crops more attractive to pests and more vulnerable to a fast paced attack. Without a diverse range of species, the system cannot defend the crop against the invading organisms.

Abundant food and low diversity make pest and beneficial populations more susceptible to abrupt spikes and crashes. Under optimal circumstances, predatory populations remain high enough to limit the growth of pest populations. But with only one or two predatory species keeping pests at bay, any injury to the beneficial organisms will leave the pests free to propagate unchecked. In natural ecosystems, many different predators feed on the same herbivorous insects, so if one of the beneficial species dies out, the others will continue to control the pest population size. Agricultural systems have far fewer predatory organisms, so we must rely on management practices to protect the beneficials and curb the pests by other means whenever necessary. Applying pest specific insecticides is one way we can limit crop damage while maintaining beneficial species.

Strawberries and raspberries are often threatened by the two-spotted spider mite, a tiny arachnid that feeds on plant leaves. Under the right circumstances, the predatory mite, persimilis, keeps the herbivorous mite populations low. If persimilis populations drop, the two-spotted spider mites can reproduce exponentially, causing serious crop damage and yield loss.

Ecological principles also explain why pests build resistance to agricultural chemicals after prolonged use. Frequent application of the same type of pesticide, fungicide, or herbicide will eliminate most offending organisms, but leave those who are resistant to the chemical unharmed. Resistant individuals are more likely to survive long enough to reproduce, spreading their genetic advantage through the population, and rendering the pesticide less effective as the percentage of resistant individuals increases with continued chemical application. Tri-Tech Pest Control Advisors work to prevent chemical resistance by rotating pesticides with different modes of action. Constantly changing the pesticide’s mode of action prevents one particular trait from becoming a strong competitive advantage over any other. In addition to pesticide application, other crop protection practices include bug vacuuming, crop rotation, fumigation, and careful irrigation management.


Two spotted spider mite, Tetranychus urticae, adults and eggs.