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The compilation of papers in this Special Issue (SI) derives from a Symposium at the 25th International Congress of Entomology, in 2016, entitled ‘‘Rise or demise? A global outlook on the future of classical biological weed control’’. In the SIopening-paper, a summary of the 5th edition of the world catalogue of weed biocontrol agents and their target weeds provides a comprehensive international perspective. Weed biocontrol implementation is beleaguered by perceptions of risk and restrictive regulatory procedures, notably in the USA, and less so in Canada. Thus, most of the papers in this SI comprise accounts of innovative responses to these challenges from scientists in the USA. Political and funding issues have inhibited weed biocontrol in Australia over the past decade, but there appears to be a gradual reversal of this trend in recent years. In contrast, in New Zealand and in South Africa, the practice is flourishing, and there are significant recent initiatives in Europe. Overall, the contributions in the SI suggest an optimistic prognosis for weed biological control.
It is clear that the considerable constraints in the USA and Hawaii (and to a lesser extent, in Canada and Australia) over the last two decades have shed a pessimistic light on the entire practice of weed biocontrol worldwide. Our impression, however, is that a nadir has been reached and that the precedents of the highly successful programs in New Zealand and South Africa, and early signs of rejuvenation of the discipline in Australia, lead to optimism. This confi- dence is given considerable added weight by the recent, intentional implementation of weed biocontrol in England and Portugal (Shaw et al. 2018)—an involvement which took a decade to gain approval from the European Union authorities, but it is undoubtedly a major step forward. It is also most encouraging that Argentina and Brazil, that have long been crucially-important source nations for weed biocontrol agents, have now become the first countries in South America to commit to the implementation of weed biological control in their homelands (e.g. McKay et al. 2018).
In spite of the multifaceted challenges and constraints facing biological control, generally and globally (Barratt et al. 2018; Messing and Brodeur 2018), absolute necessity and pragmatism in the face of increasing threats from alien invasive plants will ensure the eventual renaissance of weed biocontrol as a practice. If the proceedings at the ICE2016 Symposium, and the publications in this Special Issue of BioControl serve to offer a balanced and optimistic prognosis and provide an added impetus for weed biocontrol, then all these initiatives will have been worthwhile.