Insects 2015, 6, 13-37; doi:10.3390/insects6010013 OPEN ACCESS insects ISSN 2075-4450 www.mdpi.com/journal/insects/ Review Classical Biological Control of Invasive Legacy Crop Pests: New Technologies Offer Opportunities to Revisit Old Pest Problems in Perennial Tree Crops Mark S. Hoddle 1,†,*, Keith Warner 2,†, John Steggall 3,† and Karen M. Jetter 4,† 1 Department of Entomology, University of California, Riverside, CA 92521, USA 2 Center for Science, Technology, and Society, Santa Clara University, CA 95053, USA; E-Mail:
[email protected] 3 California Department of Food and Agriculture, Sacramento, CA 95814, USA; E-Mail:
[email protected] 4 UC Agricultural Issues Center, University of California, Davis, CA 95616, USA; E-Mail:
[email protected] † These authors contributed equally to this work. * Author to whom correspondence should be addressed; E-Mail:
[email protected]; Tel.: +1-951-827-4714; Fax: +1-951-827-3086. Academic Editor: Michael J. Stout Received: 11 November 2014 / Accepted: 13 December 2014 / Published: 23 December 2014 Abstract: Advances in scientific disciplines that support classical biological control have provided “new tools” that could have important applications for biocontrol programs for some long-established invasive arthropod pests. We suggest that these previously unavailable tools should be used in biological control programs targeting “legacy pests”, even if they have been targets of previously unsuccessful biocontrol projects. Examples of “new tools” include molecular analyses to verify species identities and likely geographic area of origin, climate matching and ecological niche modeling, preservation of natural enemy genetic diversity in quarantine, the use of theory from invasion biology to maximize establishment likelihoods for natural enemies, and improved understanding of the interactions between natural enemy and target pest microbiomes.