Agricultural insect pests reveal overlooked environmental damage mechanisms

A systematic review of three globally important agricultural insect pests has found that their effects on native biodiversity are broader and potentially more severe than previous invasion-biology assessments recognized. The species examined were the brown marmorated stink bug, Halyomorpha halys; the cotton bollworm, Helicoverpa armigera; and the fall armyworm, Spodoptera frugiperda. Their documented impacts included competition with native insects, apparent competition through shared natural enemies, hybridization, and non-target effects arising from pest control. Yet many studies reported these consequences in the language of crop damage or agricultural economics rather than environmental impact, helping conceal the ecological significance of the evidence. The analysis also identified an important additional risk: the pesticides used against invasive pests can themselves harm non-target organisms and alter ecosystems.

The review used the Environmental Impact Classification for Alien Taxa, or EICAT, framework to organize searches around specific mechanisms through which alien organisms can affect native species. For the insect pests, these included herbivory, competition, hybridization, interactions with other species and management interventions. The researchers also examined two forest pathogens—pinewood nematode, Bursaphelenchus xylophilus, and the water mould Phytophthora ramorum—as comparisons with organisms already well known for environmental damage. The literature searches were deliberately designed to find studies that mentioned the relevant mechanism even when their authors did not describe the findings as environmental impacts. This approach allowed the team to detect potentially overlooked evidence scattered across research on crop loss, pest biology, biological control and crop protection.

Across the five organisms, the searches identified 327 studies whose findings suggested environmental impacts, including 203 under EICAT mechanisms and the remainder under the separately assessed category of management. The pattern differed sharply between agricultural insects and forest pathogens. Publications about the three insect pests usually contained only implicit evidence: their authors measured competitive displacement, altered host quality, hybridization or effects on natural enemies without evaluating the consequences for native biodiversity. By contrast, most studies concerning P. ramorum directly discussed environmental damage. Forest pathogens also produced a broader range of clearly classified impact severities, as expected given their established reputation for changing tree mortality, forest composition and disturbance regimes. Even so, the comparison exposed less conspicuous mechanisms around competition, hybridization and species interactions that had also received limited attention.

Brown marmorated stink bug provided the clearest evidence for indirect impacts through interactions with other species. It can act as an evolutionary trap for native parasitoid wasps: females recognize the invasive stink bug as a suitable host and lay eggs, but their offspring fail to develop or emerge. Such encounters may weaken parasitoid communities and native stink bug populations by generating apparent competition, in which species sharing natural enemies suffer from the presence of a new host. The review classified the highest severity recorded for this mechanism as moderate. Most studies involving native parasitoids focused on their performance or biological-control effectiveness, however, rather than measuring population-level changes among native species. A separate study that compared relative stink bug population sizes provided stronger evidence that the interaction can extend beyond impaired individual fitness.

The cotton bollworm generated particularly striking evidence concerning hybridization. In Brazil, introduced H. armigera interbreeds with the native Helicoverpa zea, a close relative and agricultural pest. Studies meeting the EICAT criteria classified this widespread hybridization as massive in severity, the highest category in the framework, which normally denotes irreversible local extinction of native species. Other mechanisms affecting the cotton bollworm included competition involving native parasitoids and consequences associated with trapping, insecticide use and genetically modified Bt crops. The species also showed moderate-severity impacts through management. The severity ranking does not mean the hybridization itself necessarily eliminated H. zea throughout Brazil; rather, it follows the framework’s prescribed treatment of common, widespread hybridization and its associated risks. The authors stress that such cases may be interpreted differently by conservationists, farmers and other stakeholders because the native species involved is itself not threatened.

For the fall armyworm, the best-supported mechanism was direct competition with native herbivores that use the same host plants. Research documented population declines or competitive displacement among native moth species, producing evidence classified as moderate under EICAT. Because those studies did not determine whether local extinctions had occurred, the review could not assign a more severe category. This is a central example of how study design determines what can be detected: evidence of population reduction may reveal an important impact while remaining unable to establish its ultimate ecological scale. Fall armyworm management also generated substantial evidence concerning the effects of insecticides, Bt-expressing crops and biological control, with the highest management classification reaching major severity. As with the cotton bollworm, researchers often evaluated those consequences through the effectiveness of crop protection rather than through the lens of environmental damage.

Herbivory by agricultural insects was an important knowledge gap. Every relevant study concerning feeding on native plants was rated data deficient because researchers documented herbivory without measuring its consequences for native individual performance or population size. The authors distinguish this from well-studied invasive herbivores that cause severe and widespread damage to native vegetation. In practice, the same polyphagous pests may move from crops into adjoining natural habitats, where their feeding can be difficult to distinguish from ordinary herbivory. The lack of severity measurements means that the available literature cannot establish whether recorded feeding represents a minor disturbance, a population-level threat or something more severe. Targeted studies that link pest abundance to native plant recruitment, survival and reproduction are therefore needed before agricultural relevance can be translated into a reliable assessment of environmental risk.

Management emerged as a major, though frequently overlooked, pathway of environmental harm. The review examined 46 pesticide active substances registered in European countries against brown marmorated stink bug, cotton bollworm or P. ramorum, or considered potentially usable against fall armyworm if it became widespread. Only one substance was rated as having low ecotoxicity, 14 were rated moderate and 31 high. The ecotoxicity ratings drew on data for groups including birds, earthworms, bees, freshwater fish and freshwater invertebrates. The analysis was not intended to prove that every registered product causes unacceptable harm in every landscape; exposure, application method and local ecological conditions can vary considerably. Nevertheless, the pattern shows that chemical control cannot be treated as a neutral response to invasion. A widely used intervention may generate environmental consequences alongside the benefits of suppressing an invasive pest.

Management can also involve biological control, genetically modified crops, traps and forest removal, each with a different ecological profile. Research on brown marmorated stink bug focused largely on the non-target risks of the parasitoid wasps Trissolcus japonicus and T. mitsukurii, whereas work on both moth pests examined pesticides, Bt crops and biological control. For pinewood nematode, management studies concentrated on clear-cutting affected forests and on trapping its Monochamus vector. The severity of these management effects ranged from minimal concern to major, with most records for the insect pests falling in the lower categories. The review emphasizes that broad-spectrum insecticides, host-specific biological control agents and localized trunk injection do not pose equivalent risks. Management therefore belongs in a holistic evaluation of invasive species, but assessing it requires local information about the tool, receiving environment and non-target organisms rather than a single generalization.

The findings point to a broader change in how invasions are monitored. Agricultural pests are usually studied because they threaten yields, food security or trade, not because their effects on native species are central to the research question. As a result, ecological signals can be embedded inside studies of crop damage, pest suppression or insecticide performance without being recognized as environmental-impact evidence. The review shows that careful reading of this literature can reveal impacts that broad reviews of invasive insects have largely overlooked. At the same time, data deficiencies and study designs that measure individual performance but not population responses mean that current evidence cannot provide a complete map of severity. Future research should connect pest abundance, native-species responses, management practices and ecosystem change, giving agricultural pests the same ecological scrutiny long applied to conspicuous forest pathogens.

Subject of Research: Environmental impacts of invasive agricultural insect pests and their management

Article Title: Environmental impacts of agricultural pest insects: five case studies reveal overlooked impact mechanisms and specify knowledge gaps

Article References: Horrocks, K. J., Romeis, J., & Collatz, J. (2025). Environmental impacts of agricultural pest insects: five case studies reveal overlooked impact mechanisms and specify knowledge gaps. NeoBiota, 104, 251-279. https://doi.org/10.3897/neobiota.104.158217

Image Credits: AI Generated

DOI: 10.3897/neobiota.104.158217

Keywords: agricultural pests, biodiversity, brown marmorated stink bug, cotton bollworm, fall armyworm, invasive species, environmental impact, pesticide ecotoxicity, native species, forest pathogens, Environmental, impacts