Ecological Understanding of Insects in Organic Farming Systems

Why an Ecological Understanding of Insects?

The National Organic Program (NOP) final rule (United States Department of Agriculture, 2000) requires that organic producers annually develop a comprehensive farm plan that includes a description, in advance, of how management practices—including crop rotations, soil and nutrient management, sanitation, and cultural practices—will be used to prevent pest damage, and how physical and mechanical means will be used to manage pest problems that do occur. In contrast to most nonorganic farming systems, organic farming systems can employ insecticides to manage pest populations only as a last resort, and only using approved nonsynthetic or synthetic materials.  Organic producers are also required to adopt practices that "maintain or improve the natural resources of the operation, including soil and water quality" (USDA, 2000). An ecological understanding of insects—especially their biology and their interactions with plants, other organisms and their environment—is essential to the design of a successful organic farm plan.  An ecological understanding of insects can provide information on how they live and obtain resources, what life stages are especially vulnerable, what conditions affect the growth and decline of their populations, what roles they play in agricultural production systems, and how they respond to changes in the environment and to management practices. With an ecological understanding of insects, an organic producer can develop a farm plan that  takes advantage of the beneficial roles that insects play to reduce the likelihood of insect pests reaching economically damaging levels, and to identify the most appropriate ways of managing pest populations when they do approach damaging levels. Successful organic farm managers use their ecological understanding of insects to recruit insects as allies in maintaining and improving their natural resource base, and to reduce the opportunities for pests to become damaging.

Maintaining and Improving the Natural Resource Base: Insects as Allies

Insects and other arthropods, such as spiders and mites, are among the most common and diverse organisms in the environment. Over a million different species of insects have been described worldwide, and another 10,000 or so new species are described each year. The vast majority of insects and other arthropods are beneficial or neutral with respect to crop production—fewer than 1% of known insect species are considered to be pests. Insects and other arthropods serve in a number of beneficial ecological roles (sometimes called ecosystem services) in agricultural and natural systems:

• As decomposers, helping to mediate the breakdown of plant and other organic residues, and the mineralization and recycling of plant nutrients from those residues.
• As pollinators, ensuring the fertilization and reproduction of many plants, including many crops.
• As natural enemies (predators and parasitoids), helping to prevent the outbreak of pest insects and weeds.
• As prey, providing food for other organisms, including wildlife and natural enemies of pests.

Some plant-feeding arthropod species only reach damaging levels under particular conditions, while others are well-adapted to tolerate or exploit particular crops or crop production systems, and can regularly cause economic losses. These losses can arise through the direct consumption of plant material such as leaves, fruits, seeds, roots, and sap, or through the transmission of plant disease—for example, the transmission of tomato spotted wilt virus by thrips, and the transmission of bacterial wilt of cucurbits by cucumber beetles. Understanding the ecological principles that underlie the dynamics of insect populations and interactions of populations within communities can help organic producers manage arthropods on their farm, both pest and beneficial species, to prevent or reduce economic crop losses.