A review of introductions of pathogens and nematodes for classical biological control of insects and mites

Abstract

Compared with parasitoids and predators, classical biological control programs targeting arthropod pests have used pathogens and nematodes very little. However, some pathogens and nematodes that have been introduced have become established and provided excellent control and have been introduced in increasing numbers of areas over decades, often after distributions of pests have increased. We summarize 131 introductions, the majority of which have occurred since 1950. The most commonly introduced microorganisms have been fungi, viruses and nematodes, although microsporidia, bacteria and oomycetes have also been introduced; among these groups, viruses were the most successful in establishing followed by nematodes, fungi and microsporidia. All major orders of insects and prostigmatid mites have been targeted and in 63.6% of the programs the pests being targeted were invasive species and not native. Pathogens and nematodes yielded excellent success in establishment against sawflies and wood wasps (100% of programs) and 40–48% establishment among other host orders. Classical biological control has been used for long-term control of arthropod pests on islands almost as much as in mainland areas. It has been used most frequently in perennial systems and highest rates of establishment of arthropod pathogens and insect parasitic nematodes were documented from forests (63.0%) and tree crops (66.7%). One explanation for the low number of releases of arthropod pathogens and insect parasitic nematodes has been confusing and difficult regulations but recent changes and institution of the FAO’s Code of Conduct is expected to improve scientists’ ability to introduce microbial natural enemies for classical biological control.