Classical insect biocontrol in North America, 1985 to 2018: a pest control strategy that is dying out?

Abstract

Abstract This review is a summary of a new catalog on the use of classical biological control of arthropods in North America since 1985. In this new catalog, we reviewed releases since 1985 of exotic parasitoids and predaceous insects for classical biocontrol of invasive insects in Canada, Mexico, the continental USA, and U.S. overseas areas. Here, we summarize the catalog and extract trends in usage and success. Trends measured included numbers of agents released, numbers established, numbers having a positive impact on the target pests, and numbers of projects initiated, which allow readers to determine if use of this method of insect control has increased, declined, or held steady over the studied period. These trends provide understanding of the social relationship between countries and this form of pest control and how it has changed over time. During this period, there were 208 parasitoid releases (=species × country or overseas U.S. area) compared to 29 for predators. Of these parasitoid releases, 112 (53.8%) resulted in establishment, and 57 (27.4%) controlled the target pest partially or completely. Most releases occurred in the USA, and we calculated trends for parasitoids per 5-year period. From 1985 to 2018, numbers of parasitoids released (counting the continental USA, Hawaii, Puerto Rico, Guam, Marianna Islands, and the U.S. Virgin Islands separately) declined per 5-year interval from 52 to 7, an 86.5% reduction. The percentage of newly released parasitoids that established increased from 42 to 71%, a 1.7-fold increase, but the number of newly established parasitoid species that reduced their target pests declined from 73 to 40%. Also, the number of new projects initiated per 5-year period decreased from 31 to 5, an 84% decrease. The percentage of projects reducing their target pests showed no strong trend: 1985–1989, 42% vs. 2010–2014, 60%. Chalcidoids were most effective; of 119 chalcidoid releases, 76 (63.9%) established, and 45 (37.8%) reduced their target pests. Chalcidoids, based on available literature host records, were not more specific than less effective groups, despite the view that higher efficacy would be associated with greater host-specificity. The predominance of chalcidoids is likely due to their frequent use against scales, whiteflies, mealybugs, aphids, and psyllids, which are tightly associated with live plants, tend to be moved frequently internationally, and often become agricultural pests in areas where they are introduced.