Entomopathogenic nematodes as biopesticides

Abstract

Entomopathogenic nematodes (EPNs) are microbial control agents which have become important in biological control or integrated pest management of insect pests as biopesticides. EPNs are widespread all over the world and are found in almost all places where there is agricultural land and forests, and in the desert where there are desert plants. Where insects are present in the environment, they may help the spread of EPNs of a number of species of the genera Steinernema (more than 61 species) and Heterorhabditis (more than 14 species). The factors responsible for aggregated distribution of EPNs may include behavior and the spatial and temporal variability of the nematodes' natural enemies, such as nematode trapping fungus. Nematodes also have limited dispersal ability. Many infective juveniles are produced from a single host, which can also produce aggregates. Patchy EPN distributions may also reflect the uneven distribution of the host and nutrients in the soil. The metapopulation as a whole can persist as long as the rate of colonization is greater than or equal to the rate of population extinction. EPNs infect only insects and live inside the body of their insect host, so they are designated endoparasitic. EPNs infect many different types of soil insects, including the larval and pupal forms of butterflies, moths, beetles, and flies, as well as adult crickets and grasshoppers. EPNs have been found in all inhabited continents and a range of ecologically diverse habitats, from cultivated fields to deserts, yet are safe for plants and animals. Most biopesticides require days or weeks to kill their host, yet nematodes, working with their symbiotic bacteria (Xenorhabdus for the family Stienernematidae and Photorhabdus for the family Heterorhabditidae), can kill their insect hosts within 24-48 h. Dozens of different insect pests are susceptible to infection, yet no adverse effects have been shown against beneficial insects or other nontarget organisms in field study experiments. Nematodes are amenable to mass production and do not require specialized application equipment as they are compatible with standard agrochemical equipment, including various sprayers and irrigation systems. Although the biological control industry has acknowledged EPNs since the 1980s, today thousands of researchers representing more than 50 countries are working to develop nematodes as biological insecticides. Nematodes have been marketed on every continent except Antarctica for control of insect pests in high-value horticulture, agriculture, home gardens and garden niche markets. In this chapter, we focus on EPNs as biopesticides in insect control. Isolation and distribution, application techniques, and field application models of EPNs as biopesticides throughout the world are discussed. The chapter closes with a discussion of mass production of EPNs, the safety of EPNs, and quality control of EPN production.