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The hemlock woolly adelgid (HWA), Adelges tsugae, has threatened the sustainable management of Tsuga canadensis in the eastern United States. Biological control efforts have led to the establishment of Laricobius nigrinus, a specialist predator of HWA. Although L. nigrinus has a significant impact on HWA populations, its effect on the health of HWA’s host is unknown. In 2020, 14 eastern hemlocks at one site in Virginia were selected to determine whether predation of L. nigrinus at different densities on HWA populations had an effect on tree health. Laricobius nigrinus predation significantly impacted the HWA sistens generation, resulting in significantly more new shoots produced on treatment branches with the greatest density of L. nigrinus adults. Final HWA density was lowest on treatment branches with L. nigrinus, followed by the negative control, and the treatment without L. nigrinus. In June, the photosynthetic rate was significantly greater for the negative control, followed by L. nigrinus treatments. There were no statistical differences among measured tree physiological parameters in July and October, indicating a temporary effect from L. nigrinus predation on hemlock tree physiology.

Classical biological control (CBC) is the introduction of a natural enemy of exotic origin to control a pest, usually also exotic, aiming at permanent control of the pest. CBC has been carried out widely over a variety of target organisms, but most commonly against insects, using parasitoids and predators and, occasionally, pathogens. Until 2010, 6158 introductions of parasitoids and predators were made against 588 insect pests, leading to the control of 172 pests. About 55% of these introductions were made against pests of woody plants. Establishment rates of natural enemies and success rates were higher in CBC projects targeting pests of woody plants than other pests. This review aims to answer the questions most commonly asked regarding CBC against insect pests, with particular emphasis on tree pests. The topics covered include, among others: variations in rates of successes among different systems, different target insect groups and different agents; temporal trends in CBC practices and successes; economic and environmental benefits; risks and ways to mitigate the risks; CBC against native pests; accidental successes through the adoption of the invasive pests by native natural enemies or accidentally introduced agents; and prospects and constraints for the practice of CBC in the future. Questions are answered based on the analysis of two databases, the BIOCAT2010 database of introductions of insect biological control agents for the CBC of insect pests, and a database of introductions of entomopathogens against insect pests.

The role of dipteran predators in biological pest control programs is reviewed and discussed. Diptera encompasses a large number of potentially efficient predators for biological pest control, yet only a few species are routinary used. The families Syrphidae and Cecidomyiidae provide some of the most successful examples of biological control, but other families (e.g., Muscidae, Sarcophagidae, Sciomyzidae) also include species with that potential. Most applications of Diptera as predators involve the conservation biological control approach, while the augmentative approach has involved only a few species, almost exclusively of Syrphidae and Cecidomyiidae. In a few cases, classical biological control has been employed. Commercialization of species mainly to be used in the augmentative approach is discussed, also focusing on the critical issues linked to rearing methods. The dual services performed by Diptera (pollination as adults and biological control as larvae) have been studied in detail for Syrphidae only, but would deserve further study in other families, e.g., Sarcophagidae. This is the first review in which the use of predatory Diptera in biological control programs is investigated for all families and in all types of applications. This review recommends a multi-taxon approach in the use of Diptera in biological control since a large number of taxa have considerable potential, although this has not yet been tested in practical applications.

Biological control is a valuable and effective strategy for controlling arthropod pests and has been used extensively against invasive arthropods. As one approach for control of invasives, exotic natural enemies from the native range of the pest are introduced to areas where control is needed. Classical biological control began to be used in the late 1800s and its use increased until, beginning in 1983, scientists began raising significant concerns and questions about nontarget and indirect effects that can be caused by these introductions. In recent years, similar issues have been raised about augmentative use of exotic natural enemies. Subsequently, international guidelines, national regulations and scientific methods being used for exotic natural enemies in biological control have changed to require appropriate specificity testing, risk assessment and regulatory oversight before exotic natural enemies can be released. National and international standards aimed at minimizing risk have increased awareness and promoted more careful consideration of the costs and benefits associated with biological control. The barriers to the implementation of classical and augmentative biological control with exotic natural enemies now are sometimes difficult and, as a consequence, the numbers of classical biological control programs and releases have decreased significantly. Based in part on this new, more careful approach, classical biological control programs more recently undertaken are increasingly aimed at controlling especially damaging invasive arthropod pests that otherwise cannot be controlled. We examine evidence for these revised procedures and regulations aimed at increasing success and minimizing risk. We also discuss limitations linked to the apparent paucity of postintroduction monitoring and inherent unpredictability of indirect effects.

Classical biological control using insects has led to the partial or complete control of at least 226 invasive insect and 57 invasive weed species worldwide since 1888. However, at least ten introductions of biological control agents have led to unintended negative consequences and these cases have led to a focus on risk that came to dominate the science and practice of classical biological control by the 1990s. Based upon historical developments in the field we consider that the era of focus on benefits began in 1888 and that it was supplanted by an era in which the focus was on risks during the 1990s. This paradigm shift greatly improved the safety of biological control releases but also led to a decline in the number of introductions, probably resulting in opportunity costs. We note here the development of a third paradigm: one in which the benefits and risks of biological control are clearly and explicitly balanced so that decisions can be made that maximize benefits while minimizing risks.

Spathius galinae is a larval parasitoid native to the Russian Far East that was approved for release in the United States in 2015 for biological control of the emerald ash borer (EAB), Agrilus planipennis, an invasive beetle from Asia responsible for widespread mortality of ash trees (Fraxinus spp.) in North America. From 2015 to 2017, 1,340–1,445 females of S. galinae along with males were released into each release plot, paired with a nonrelease control plot (1–12.5 km apart), at 6 postinvasion forested sites containing abundant pole-sized ash trees in Michigan. By 2018, S. galinae had spread to all but one control plot. Based on the first year that S. galinae was found in trees in each control plot and the distances of those trees to the parasitoid release point within each site, we estimated that S. galinae spread at 3.7 (±1.9) km per year after its initial releases in 2015. The proportion of sampled trees with S. galinae broods, brood densities within sampled trees, and parasitism of EAB larvae increased sharply in both control and release plots after the last field releases in 2017, with the highest parasitism rates (42.8–60.3%) in 2020. Life table analysis showed that S. galinae alone reduced EAB's net population growth rate by 35–55% across sites from 2018 to 2020. These results demonstrate that S. galinae has established an increasing population in Michigan and now plays a significant role in reducing EAB populations in the area.

Invasive insect pests are a significant and accelerating threat to agricultural productivity, they degrade wilderness areas, and reduce quality of life in urban zones. Introduction biological control, the introduction, release, and establishment of host-specific efficacious natural enemies, is an effective management tool for permanently suppressing invasive pest populations over vast areas, often to levels that may no longer cause economic or environmental damage. However, introduction biological control programs are reactive: they are only initiated after an invasive pest has established, spread, and is causing damage that requires mitigation. Host specificity and host range testing of natural enemies for use in an introduction biological control program against an invasive pest can take years to complete. During this time, the target pest population continues to increase, invades new areas, and inflicts damage. Proactive biological control research programs identify prior to their establishment pest species that have high invasion potential and are likely to cause economic or environmental damage once established. Natural enemies are selected, screened, and if sufficiently host-specific, approved for release in advance of the anticipated establishment of the target pest. Following detection of the target pest and determination that incipient populations cannot be eradicated, natural enemies already approved for release are liberated into infested areas. This proactive approach to introduction biological control could significantly reduce project development time post-invasion, thereby lessening opportunities for pest populations to build, spread, and cause damage.

We investigated trends in biological control to both capture its evolution and explore future opportunities. We examined recent changes in public interest, international networking and peer-reviewed research. A Google Trends analysis revealed that the popularity of biological control is decreasing in terms of search hits on the internet. This trend is potentially worrying for the biological control community, given that public interest tends to drive political decisions regarding regulatory processes and governmental funding of research. To examine patterns of international collaboration, we established the list of authors who published their work in the three main biological control journals from the early 1990s to 2016. International co-authorship has intensified and the biological control sector is increasingly characterized by multilateral collaboration. We surveyed papers published in BioControl and Biological Control over the last 25 years to identify research trends with respect to target pests, commodities, biological control agents and biological control approaches. Finally, we report that articles on biological control are published in the broad-based scientific journals Science and Nature on a regular basis. This reflects contributions that biological control research makes to scientific discussions in general. Our analyses revealed a thriving scientific discipline with several major research trends in arthropod, plant pathogen and weed biological control.

A wide variety of organisms use the regular seasonal changes in photoperiod as a cue to align their life cycles with favorable conditions. Yet the phenological consequences of photoperiodism for organisms exposed to new climates are often overlooked. We present a conceptual approach and phenology model that maps voltinism (generations per year) and the degree of phenological mismatch that can arise when organisms with a short-day diapause response are introduced to new regions or are otherwise exposed to new climates. Our degree-day-based model combines continent-wide spatialized daily climate data, calculated date-specific and latitude-specific day lengths, and experimentally determined developmental responses to both photoperiod and temperature. Using the case of the knotweed psyllid Aphalara itadori, a new biological control agent being introduced from Japan to North America and Europe to control an invasive weed, we show how incorporating a short-day diapause response will result in geographic patterns of attempted voltinism that are strikingly different from the potential number of generations based on degreedays alone. The difference between the attempted and potential generations represents a quantitative measure of phenological mismatch between diapause timing and the end of the growing season. We conclude that insects moved from lower to higher latitudes (or to cooler climates) will tend to diapause too late, potentially resulting in high mortality from inclement weather, and those moved from higher to lower latitude (to warmer climates) may be prone to diapausing too early, therefore not fully exploiting the growing season and/or suffering from insufficient reserves for the longer duration in diapause. Mapped output reveals a central region with good phenology match that shifts north or south depending on the geographic source of the insect and its corresponding critical photoperiod for diapause. These results have direct relevance for efforts to establish populations of classical biocontrol agents. More generally, our approach and model could be applied to a wide variety of photoperiod- and temperature-sensitive organisms that are exposed to changes in climate, including resident and invasive agricultural pests and species of conservation concern.

Ganaspis Foerster includes several cryptic species that are important larval parasitoids of the invasive pest Drosophila suzukii (Matsumura), spotted-wing drosophila (SWD). Drosophila suzukii, native to Asia, was first discovered in 2008 in North America and Europe, becoming a devastating pest of soft-skinned fruit crops. Biological control could be among the safest, most environmentally benign, and cost-effective methods for long-term and landscape-level management of this invasive pest. Foreign exploration in East Asia discovered several major larval D. suzukii parasitoids. One of them was initially described as Ganaspis brasiliensis (Ihering) and consisted of 2 major genetic groups (G1 and G3). The groups are now recognized as 2 different species, Ganaspis kimorum Buffington and Ganaspis lupini Buffington. The more host-specific species G. kimorum was selected and approved for field release in the United States in 2021 and has been widely released since 2022. Here, we provide a comprehensive overview of the parasitoid’s taxonomy, current known distribution, biology, ecology, mass-rearing methods, and biological control potential.