Is Biological Control of Weeds Conservation’s Blind Spot?

Invasive alien species are among the most important threats to biodiversity, with invasive plants ranking among the highest. Classical weed biological control-or biocontrol-reunites exotic plants with host-specific natural enemies from their native range with the aim of controlling the invasive plant. We reviewed the attention classical weed biocontrol has received from scientific publications for the last 30 years, classified according to the area of academia and applied sciences, as well as the region of the world. Biological control journals were excluded from the analyses to avoid bias. This process allowed us to evaluate the support classical weed biocontrol has among the scientific community. We also recorded the number of weed biocontrol agents released from 1900 to date, where they were collected, and where they were released as a way to analyze the evolution of classical weed biocontrol policies in different parts of the world. Classical weed biocontrol releases peaked between 1990 and 1999, but have declined since, probably due to funding issues, increases in regulations, and bad publicity. Researchers in theoretical ecology appear to be more skeptical toward weed biocontrol than scientists in applied and experimental biology. Our synthesis also suggests that despite resistance to classical weed biocontrol in some quarters of the scientific community, the general scientific perception of the discipline has been consistently favorable. This means that the general scientific perception of classical weed biocontrol contradicts its level of current application. The five main objections against classical weed biocontrol-direct nontarget effects, indirect and hidden nontarget effects, evolution of host shifts in biocontrol agents, dispersion to unwanted areas, and disagreements on its level of success in the field-are summarized and analyzed in terms of their relevance and probability of occurrence. We also describe the way classical weed biocontrol practitioners deal with them at present to ensure safety and sustainability. Our analysis suggests the potential of classical weed biocontrol is undervalued in some areas of science and management due to objections that are plausible in theory, although their likelihood is very low and on-ground evidence scant.