REVIEW Exotic generalist arthropod biological control agents: need to improve environmental risk assessment to ensure safe use David A. Andow . Barbara I. P. Barratt . Robert S. Pfannenstiel . De ´bora Pires Paula Received: 26 September 2020 / Accepted: 12 November 2020 Ó International Organization for Biological Control (IOBC) 2020 Abstract Exotic generalist arthropod biological control agents (GABCAs) have been historically marginalized in classical and augmentative biological control due to their broad diet breadth, but an increasing demand for a more sustainable pest control is encouraging their reconsideration. This special issue compiles a collection of papers revealing that risks of several exotic GABCAs were overestimated, not all generalists are riskier than specialists and their envi- ronmental risk assessment (ERA) solely based on exposure analysis is inadequate. Three papers demon- strated that generalists were not involved in predicted non-target interactions: generalist idiobiont para- sitoids probably do not exhibit interference competi- tion with each other, an oligophagous exotic egg- larval koinobiont parasitoid does not compete with a native larval koinobiont, and an invasive generalist predator does not escape from its enemies. Two innovative methods for selecting non-target species are proposed, one based on existing food web data to predict indirect non-target effects, and the other on functional traits to predict competition with native natural enemies. Also a comprehensive GABCA-ERA method is proposed that integrates adverse effect analysis to the ‘conventional’ exposure analysis. The method was scrutinized by two studies: one suggesting that it could have resulted in faster and less costly decisions on two exotic generalists in New Zealand, and the other suggesting that eight exotic GABCAs released in Argentina might potentially reduce native natural enemies. We hope this special issue will stimulate the continued advance in the biosafety research of GABCAs so their safe use does not stagnate. Keywords Classical biological control Á Augmentative biological control Á Biosafety Á Non- target risks Á Host range tests Introduction The first thing that crosses the mind of most biological control experts and practitioners when they hear about using generalist arthropods as biological control Handling Editor: Eric Wajnberg D. A. Andow (&) Department of Entomology, University of Minnesota, St. Paul, MN, USA e-mail: dandow@umn.edu B. I. P. Barratt Invermay Research Centre, AgResearch Ltd., Mosgiel, New Zealand R. S. Pfannenstiel Plant Health Programs, USDA APHIS PPQ, Riverdale, MD, USA D. P. Paula Embrapa Recursos Gene ´ticos E Biotecnologia, Brası ´lia, DF, Brazil 123 BioControl https://doi.org/10.1007/s10526-020-10067-2