Optimization of native biocontrol agents, with parasitoids of the invasive pest Drosophila suzukii as an example

Abstract

The development of biological control methods for exotic invasive pest species has become more challenging during the last decade. Compared to indigenous natural enemies, species from the pest area of origin are often more efficient due to their long coevolutionary history with the pest. The import of these well‐adapted exotic species, however, has become restricted under the Nagoya Protocol on Access and Benefit Sharing, reducing the number of available biocontrol candidates. Finding new agents and ways to improve important traits for control agents (“biocontrol traits”) is therefore of crucial importance. Here, we demonstrate the potential of a surprisingly under‐rated method for improvement of biocontrol: the exploitation of intraspecific variation in biocontrol traits, for example, by selective breeding. We propose a four‐step approach to investigate the potential of this method: investigation of the amount of (a) inter‐ and (b) intraspecific variation for biocontrol traits, (c) determination of the environmental and genetic factors shaping this variation, and (d) exploitation of this variation in breeding programs. We illustrate this approach with a case study on parasitoids of Drosophila suzukii, a highly invasive pest species in Europe and North America. We review all known parasitoids of D. suzukii and find large variation among and within species in their ability to kill this fly. We then consider which genetic and environmental factors shape the interaction between D. suzukii and its parasitoids to explain this variation. Insight into the causes of variation informs us on how and to what extent candidate agents can be improved. Moreover, it aids in predicting the effectiveness of the agent upon release and provides insight into the selective forces that are limiting the adaptation of indigenous species to the new pest. We use this knowledge to give future research directions for the development of selective breeding methods for biocontrol agents.

Does experimental evolution produce better biological control agents? A critical review of the evidence

“…This is particularly relevant today, in the modern era of genomics, as this method could further be enhanced by genomic approaches, for example, genomic selection (Routray et al, 2016;Lommen et al, 2017;Kruitwagen et al, 2018). We suggest that the interest of the community in this method should not fade away, but rather get stronger.…”

“…Still, whereas the improvement in crops has been largely dependent upon selective breeding, this is not the case for the production of natural enemies. Nevertheless, recent years have witnessed a renewed interest in improving biocontrol agents via experimental evolution or artificial selection, judging from recent reviews (Arora & Shera, 2014;Venkatesan & Jalali, 2015;Routray et al, 2016;Lommen et al, 2017;Kruitwagen et al, 2018). One reason may be that selective breeding in agriculture has been done for thousands of years and thus is currently a fine-tuned methodology, whereas improvement of natural enemies for biological control is a recent strategy, still under development.…”

“…We do not focus on the genetics and genomics of biocontrol traits, as this has been the object of recent reviews (Routray et al, 2016;Lommen et al, 2017;Kruitwagen et al, 2018). First, we refer to the methodological underpinnings of experimental evolution and how they are (not) met in studies on biocontrol agents.…”

“…Improvement in natural enemies through experimental evolution is not a new idea (Mally, 1916;DeBach, 1958;Sailer, 1961) and has frequently been reviewed (Table S1). Indeed, it seems more feasible to apply this methodology to biocontrol agents, which are generally short-lived and small-bodied arthropods, than to livestock and crops (Kruitwagen et al, 2018). Still, whereas the improvement in crops has been largely dependent upon selective breeding, this is not the case for the production of natural enemies.…”

“…Another reason could be that this method is time-and space-consuming, requiring a substantial amount of biological and ecological knowledge, compared to classical importation (Hoy, 1986(Hoy, , 1988a. Nevertheless, recent years have witnessed a renewed interest in improving biocontrol agents via experimental evolution or artificial selection, judging from recent reviews (Arora & Shera, 2014;Venkatesan & Jalali, 2015;Routray et al, 2016;Lommen et al, 2017;Kruitwagen et al, 2018). However, none of these reviews focuses specifically on experimental evolution and/or artificial selection.…”