It is well established that invasive alien species can cause significant changes to biodiversity and the environment (Sandlund et al. 2001; Kenis et al. 2008; Pyšek et al. 2020), with adverse and complex consequences reported from all ecosystems across the world (Sheppard and Vandvik 2023). The frequency of species invasions continues to rise with the increasing globalization of human-mediated pathways such as international trade (Tobin et al. 2014; Seebens et al. 2017; Sheppard and Vandvik 2023). While it is very difficult to predict the impacts of species that have not yet been observed outside their native range, current impacts of species in already invaded areas often provide the best available indication of impacts in newly or more recently invaded regions, as impacts tend to grow over time after invasion (Blackburn et al. 2014; Cameron et al. 2016). A further challenge is to assign a common currency to environmental impacts that derive from a variety of impact mechanisms (Kenis et al. 2008; Bacher et al. 2018). These mechanisms include, for instance, competition with native species, herbivory, and chemical, physical, or structural impacts on ecosystems (Kenis et al. 2008; Hawkins et al. 2015; IUCN 2020). Mechanisms of impact can be both direct, such as the consumption of native plants, and indirect, such as apparent competition through shared natural enemies with native species (Hawkins et al. 2015; IUCN 2020; Clarke and McGeoch 2023). The indirect and non-target impacts of management approaches are also an important aspect of the environmental consequences of invasive species (McGeoch et al. 2015).

While invasive insects are well known for their agricultural impacts (Diagne et al. 2020), they are underrepresented in the invasion biology literature addressing biodiversity impacts (McGeoch et al. 2015). This is despite crop environments being a known source of spillover for agricultural pests into neighboring natural habitats (Togni et al. 2021) and the fact that environmental impacts themselves can lead to additional economic or socioeconomic consequences (Bacher et al. 2018). A large proportion of the current literature focuses on a few well-known insect taxa. Attention is largely given to eusocial Hymenoptera, such as invasive ants (Hill et al. 2003), and herbivores of trees that impact the ecosystem processes of forests, such as emerald ash borer (Agrilus planipennis Fairmaire (Coleoptera, Buprestidae)) (Klooster et al. 2018), due to the impact mechanisms and outcomes associated with such species being direct and conspicuous (Kenis et al. 2008; McGeoch et al. 2015). Consistently reported reasons for knowledge gaps surrounding the environmental impacts of invasive insects include a lack of research interest, public awareness, or perceived magnitude of their environmental threat (Novoa et al. 2017; Evans et al. 2018; Clarke and McGeoch 2023). Additionally, insect pests of socioeconomic importance, like disease-transmitting mosquitoes, are studied in preference to those of potential environmental importance (Kumschick et al. 2015). However, it remains unclear whether the biases and underrepresentation of invasive insects in environmental impact literature represent the actual extent of their impacts or a lack of research effort (Kenis et al. 2008). Existing reviews published on the environmental impacts of invasive insects have collated these conspicuously studied examples and wide-ranging knowledge gaps (Kenis et al. 2008; McGeoch et al. 2015; Cameron et al. 2016; Clarke and McGeoch 2023). However, it is unclear to what extent inconspicuous or implicit examples were considered or whether literature search strategies captured such examples, which could expose overlooked evidence of how invasive insects may exert environmental impacts despite heavy focus on their economic impacts.

Targeting literature searches toward well-known case-study invasive insects may enable scrutiny of a manageable quantity of relevant articles to assess evidence among species that are not known for conspicuous environmental impacts, such as agricultural pests. We reviewed the literature for indications of environmental impacts exerted by three invasive insect agricultural pests: brown marmorated stink bug (Halyomorpha halys Stål (Hemiptera, Pentatomidae) (BMSB)), cotton bollworm (Helicoverpa armigera Hübner (Lepidoptera, Noctuidae) (CBW)), and fall armyworm (Spodoptera frugiperda Smith (Lepidoptera, Noctuidae) (FAW)); and two invasive forest pathogens: Phytophthora ramorum Werres (Peronosporales, Peronosporaceae) and pinewood nematode (Bursaphelenchus xylophilus Nickle (Aphelenchida, Parasitaphelenchidae) (PWN)). All of these organisms are of worldwide significance with invasion histories on different continents. The agricultural pests are well known for their economic rather than environmental impacts, whereas the forest pathogens are known for both their environmental and economic impacts (ISSG 2015; Ries and Pagad 2020; Bacher et al. 2025). They are also considered major threats to Europe (Lammers and MacLeod 2007; EU 2009b; Kriticos et al. 2017; EU 2019) and, as such, are included in the European Horizon 2020 project “Plant pest prevention through technology-guided monitoring and site-specific control” (PurPest) as potential targets for the development of chemosensors for use during phytosanitary inspections and in-field detection. By focusing targeted reviews on this range of case-study species, we search for evidence of whether potential environmental impacts of economically important insect agricultural pests may be overlooked and compare the results to those of the well-known environmental impacts of forest pathogens to highlight biases in knowledge. However, any overlooked impact mechanisms uncovered for the forest pathogens will be additionally considered.

We structured our review using the Environmental Impact Classification for Alien Taxa (EICAT) scheme, as it provides a framework to target the assessment of impacts according to their mechanism and severity (Blackburn et al. 2014; Hawkins et al. 2015; IUCN 2020; Kumschick et al. 2020; Volery et al. 2020). EICAT considers environmental impacts as negative effects exerted upon native species, though it does not consider the impact of human interventions for management of invasive species, which we aim to examine as an additional impact mechanism in this review. The related frameworks EICAT+ and Socio-Economic Impact Classification of Alien Taxa (SEICAT) may be used to assess the positive environmental impacts and socioeconomic impacts of invasive species, respectively. However, our review strictly aims to investigate potentially overlooked mechanisms of environmental impact for invasive insects that are economic pests. In doing so, we hope to uncover evidence and specify knowledge gaps to stimulate future research that expands our understanding of the extent to which biological invasions impact biodiversity.

Capturing a surprisingly high number of publications for three insect pests of agriculture, particularly in comparison with previously published reviews (Kenis et al. 2008; McGeoch et al. 2015; Clarke and McGeoch 2023), provides examples of how economic insect pests may be overlooked with regard to their environmental impacts. The most recent and comprehensive review on the environmental impacts of invasive insects found evidence of impact for 125 species among 538 studies (Clarke and McGeoch 2023). However, the authors noted that a significant portion of these publications concentrated on a few well-studied species, none of which are considered agricultural pests, implying limited evidence for the majority of invasive insects captured by this study. We posit that targeting specific impact mechanism–related search terms to each pest enabled deeper scrutiny of a more manageable and relevant body of literature, beyond conspicuous examples that directly address environmental impacts. The wide geographic representation of the relevant literature (with the exception of P. ramorum) further supports case-study selection. Our approach revealed many more examples than had previously been accounted for among insect agricultural pests and provided a more refined outlook on knowledge gaps that complements broader review procedures. It was not surprising that our review recorded a large number of studies relating to environmental impacts for P. ramorum and PWN, considering that such impacts are well represented in the literature for these species and for forest pathogens in general (Grünwald et al. 2019; Kim et al. 2020). However, knowledge on the environmental impacts of forest pathogens largely focuses on conspicuous impacts on forest ecosystems, such as canopy gaps, successional and compositional changes, and changes to disturbance regimes (Tobin 2015; Lovett et al. 2016; Lapin et al. 2021). Applying this methodology to a greater diversity of taxonomies and life histories would further clarify whether environmental impacts among invasive insect agricultural pests are overlooked, as opposed to generally not exerting such impacts.

Studies addressing the environmental impact mechanisms for the three agricultural pests suggest that their impacts may result from interactions with native species in different ways. Certainly, for BMSB, interaction with other species is the most evidenced mechanism. For example, BMSB can act as an evolutionary trap for native parasitoids that recognize it as a suitable host, but their offspring fail to develop and emerge (Abram et al. 2013, 2016; Kaser et al. 2018), which could disrupt parasitoid communities and native pentatomid population dynamics due to apparent competition via shared natural enemies with BMSB (Herlihy et al. 2016; Konopka et al. 2018; Gariepy et al. 2019). For FAW, competition is the most evidenced impact mechanism, with the population decline or competitive displacement of native herbivores that share the same host plants being the prominent impact (Mutua et al. 2022; Ayra-Pardo et al. 2024; Guo et al. 2024). Interaction with other species was the best-represented impact mechanism for CBW, with competition between native parasitoids that attack it being reported (Tian et al. 2008). Hybridization resulting in introgression with the native pest and sister species H. zea in Brazil was also a prominent impact (Cordeiro et al. 2020; Valencia-Montoya et al. 2020). However, the negative impacts of FAW and CBW on native herbivores highlight the different contexts in which EICAT may be appropriately applied (Volery et al. 2020). For instance, H. zea is a native pest of maize in the Americas and is not considered threatened (Olmstead et al. 2016), though any impact on native species resulting from the invasion of CBW must be considered under EICAT (Hawkins et al. 2015; IUCN 2020). Realistically, such examples may be viewed differently by stakeholders with different values (Kumschick et al. 2020, 2024; Vimercati et al. 2022). Nevertheless, environmental impact mechanisms–and particularly indirect effects–should be explored for other globally important agricultural insect pests to assess how widespread these overlooked impacts may be.

Even for the two forest pathogens, the number of studies found for impact mechanisms other than the aforementioned ecosystem impacts is noteworthy. PWN exhibits hybridization and direct competition with a native congeneric nematode, B. mucronatus, in its invasive range in Asia (Cheng et al. 2008; Liao et al. 2014), and interacts with its associated microbiota to increase its virulence and exacerbate its impacts (Xue et al. 2020; Cai et al. 2022). However, the alien status of this nematode-associated microbiota is not entirely clear (Proença et al. 2014), which affirms the revised guidance to EICAT proposed by Volery et al. (2020) that interactions with other species–and not only with other alien species–should be considered under this impact mechanism. For P. ramorum, evidence of environmental impacts through competition includes direct competition with coexisting Phytophthora spp. (Kozanitas et al. 2017). Interaction with other species also causes apparent competition between tree species that share it as a pathogen (Cobb et al. 2010). Although effective in capturing such examples, we excluded studies demonstrating impacts on soil carbon and nutrients in forest ecosystems (Lamsal et al. 2011; Cobb et al. 2016), because EICAT explicitly limits environmental impacts to effects on native species (Blackburn et al. 2014; Hawkins et al. 2015; IUCN 2020). However, a new framework published after this review was conducted extends impact classification to the abiotic environment level and further clarifies the distinction between mechanisms and impacts (Carneiro et al. 2025).

Despite such results, most studies for the agricultural insect pests did not directly relate their findings to environmental impacts. There is a general pattern whereby many studies consider their results strictly in relation to economic relevance (e.g., Cordeiro et al. 2020; Valencia-Montoya et al. 2020; Rios et al. 2022). For BMSB and FAW, examples of competitive displacement of native herbivores and apparent competition were often only considered within the context of crop damage, pest management, and biological control efficacy (Pezzini et al. 2018; Formella et al. 2020; Cornelius et al. 2021; Nzouendja Kamtchou et al. 2022; Guo et al. 2024). However, a notable number of studies showing these impacts for BMSB and FAW did directly consider their findings in relation to environmental impacts, such as the potential for the former to impact native pentatomid–scelionid population dynamics in Canada (Konopka et al. 2018; Gariepy et al. 2019; Sokame et al. 2021; Song et al. 2023). Our findings suggest that the environmental impacts of these (and likely other) pests are overlooked not only in the primary literature but also in broad reviews on the environmental impacts of invasive insects (Kenis et al. 2008; McGeoch et al. 2015; Clarke and McGeoch 2023). Such linkages between environmental and economic or socioeconomic impacts should be further considered if sufficient data become available (Bacher et al. 2018; Dasgupta 2021). Because impacts on biodiversity can affect ecosystem services, recreation, conservation, and other human interests with socioeconomic implications (Pimentel et al. 2001; Hoffmann and Broadhurst 2016; Dasgupta 2021), this represents a potentially important avenue of inquiry in future studies of agricultural insect pest impacts.

Even for the two forest pathogens–but especially PWN–the relatively numerous publications categorized as implicit for impact mechanisms other than ecosystem impacts are intriguing. Many of the studies concerning PWN’s competitive impact on the native B. mucronatus do not directly consider environmental impacts (Liao et al. 2014; Zhou et al. 2023), but rather, for instance, the ability of the native nematode to competitively resist PWN invasion (Vincent et al. 2008). This is also true for examples demonstrating hybridization between these two species, whereby studies may be concerned with the pathogenicity of hybrid offspring from a management perspective (Tomalak and Filipiak 2021) or with using this as a model system to understand the genetic traits of hybrid populations (Taga et al. 2011), without mention of environmental impacts. This pattern was less pronounced among the studies recorded for P. ramorum but nevertheless highlights that impact mechanisms other than conspicuous and well-studied ecosystem impacts may also be overlooked among invasive species that affect forests.

Ranking each publication based on the impact severity classification may further elucidate knowledge gaps with regard to both species and impact mechanisms (Hawkins et al. 2015; IUCN 2020; Clarke and McGeoch 2023). In particular, studies that are classified as data deficient can indicate potential environmental impacts where increased research effort could be valuable. For instance, all studies selected for herbivory among the insect pests were classified as data deficient because, although they demonstrated herbivory of native plants, they did not measure impact (Zalucki et al. 1994; Hoebeke and Carter 2003; Nielsen and Hamilton 2009; Tembrock et al. 2019; Ayra-Pardo et al. 2024). Although impacts on native flora caused by polyphagous agricultural pests may be overlooked, herbivory is a direct and conspicuous impact mechanism, and some invasive insects are well studied for severe and widespread impacts on native plants, such as Aulacaspis yasumatsui Takagi (Hemiptera, Diaspididae) and Icerya purchasi Maskell (Hemiptera, Monophlebidae) (Roque-Albelo 2003; Marler and Krishnapillai 2020). In other cases, study design may not allow for the classification of potentially higher impact severities. For BMSB, most of the studies recorded for the interaction with other species impact mechanism that were not data deficient were classified as minor impact because they demonstrated reduced fitness of native individuals but did not aim to measure population-level impacts (Hawkins et al. 2015; IUCN 2020). One study that did measure relative population sizes of native stink bugs compared with BMSB was classified as moderate impact (Formella et al. 2020). For FAW, the number of studies classified as moderate impact under the competition impact mechanism is notable because it suggests the potential for this pest to exert population-level effects on native species. However, this was the maximum impact classification possible based on the data presented, since it was not measured whether local extinction of native species had occurred, which would escalate the classification to major impact (Hawkins et al. 2015; IUCN 2020; Mutua et al. 2022; Nzouendja Kamtchou et al. 2022). It is important to consider whether the study design enables the detection of higher impact severities, because this highlights the potential for underestimation (Volery et al. 2020). The highest impact severity recorded among the insect agricultural pests was for CBW, as most of the publications on hybridization that were data sufficient met the EICAT criteria for massive impact (Hawkins et al. 2015; IUCN 2020) by demonstrating common and widespread hybridization with the native H. zea in Brazil (Anderson et al. 2018; Cordeiro et al. 2020; Valencia-Montoya et al. 2020). These patterns demonstrate that the degree of environmental impact warrants more comprehensive scrutiny in order to gain a conclusive understanding within the wider context of invasive species impacts, especially since the highest impact severity recorded for these species by previous reviews was minor concern (Clarke and McGeoch 2023).

Comparatively, very few studies under the ecosystem impact mechanism for PWN and P. ramorum were deemed data deficient, and the majority were ranked moderate or major. This reflects a more robust and well-recognized understanding of the environmental impacts of species that affect forest systems compared with polyphagous insect pests of agriculture (Kenis et al. 2008; Gandhi and Herms 2009; Økland et al. 2011; Grünwald et al. 2019; Kim et al. 2020; Clarke and McGeoch 2023). However, the other impact mechanisms relevant to forest pathogens are less clear with regard to impact classification, which may relate to the aforementioned abundance of studies that do not directly address environmental impacts. For both PWN and P. ramorum, studies demonstrating interaction with other species ranged in classification from minimal to major impact, which further affirms the importance of impact mechanisms other than conspicuous ecosystem changes. Despite this, most of the articles on interaction with other species were data deficient for PWN, which highlights that even for forest pathogens, certain impact mechanisms remain underappreciated.

Although it is also important to simultaneously consider impacts in the absence of management–given that effective control may reduce the maximum impact potential of invasive species–management itself can have impacts (Blackburn et al. 2014). Management was therefore treated as an impact mechanism in this review to ensure a holistic consideration of impacts. A relatively large number of studies were recorded on the environmental impacts of pest management. In general, the environmental impacts and risks of pest control tools such as synthetic chemical pesticides, biological control, and genetically modified crops are well studied (Bigler et al. 2006; Gill and Garg 2014; Suckling et al. 2014; Meissle et al. 2022) and typically required by regulatory entities (Craig et al. 2008; EU 2009a, 2022; Mason et al. 2017; Barratt et al. 2021). Nevertheless, the focus on types of pest management varied among the case-study pest species, largely reflecting research interest. For BMSB, for example, the studies concern the risk of non-target impacts of biological control agents, such as the exotic Trissolcus japonicus Ashmead and Trissolcus mitsukurii Ashmead (Hymenoptera, Scelionidae) for classical biological control (Rondoni et al. 2022; Haye et al. 2023) or native parasitoids for augmentative biological control (Stahl et al. 2018). Studies on the environmental impacts of CBW management generally cover the non-target impacts of transgenic Bt crop plants, pesticides, and biological control (Silva and Stouthamer 1999; Men et al. 2004; Sharma et al. 2007; Sun et al. 2009), and the same control tools have also been widely studied in relation to FAW management (Méndez et al. 2002; Gontijo et al. 2018; Hussain et al. 2021; de Souza et al. 2021). However, although meeting the EICAT criteria for minor impact, negative effects on natural enemies due to reduced host/prey quality of pests targeted by Bt-expressing transgenic plants are an inevitable consequence of the intended effect and are not considered a risk (Romeis et al. 2006, 2019). For PWN, the preponderance of research effort regarding the environmental impacts of its management relates to the biodiversity impacts of clear-cutting affected forest areas and potential non-target impacts of trapping its vector, Monochamus spp. Dejean (Coleoptera, Cerambycidae) (Zhang et al. 2021; Sukovata et al. 2022). Our findings suggest that comparatively much less research has been conducted on the impacts of P. ramorum management, though all studies considered the biodiversity impacts of tree removal. We also found that, except for P. ramorum, the studies captured for the management impact mechanism were overwhelmingly represented by the less severe impact classifications of minimal and minor concern. However, few of these examples assessed the impacts of conventional chemical pesticide applications, as contemporary research on pest management tends to explore the efficacy and development of environmentally friendly and socially acceptable alternatives (Mankad et al. 2017; Suckling et al. 2017). Yet, the establishment and spread of invasive species are usually followed by a surge in pesticide use (Frisvold 2019).

We thus summarized the pesticides used against the case-study organisms (or, in the case of FAW, those likely to be used if it becomes established) based on the understanding that, despite extensive research on their environmental impacts, they remain commonly applied (Frisvold 2019). The large number of active substances, most exhibiting high ecotoxicity, registered for use against just four case-study organisms further emphasizes the importance of considering the impact of management interventions, despite their exclusion from EICAT. This is especially true considering that pesticide consumption continues to increase as the number of invasive pests requiring management escalates globally (Sharma et al. 2019). We therefore echo the advocation of McGeoch et al. (2015) regarding the importance of this impact mechanism for a holistic understanding of environmental impacts associated with invasive species. Additionally, other risk assessment protocols require consideration of management impacts, such as priority pest ranking by the European Commission’s Joint Research Centre (Sánchez et al. 2019). However, it should be noted that environmental impacts of management likely vary across recipient environments due to anthropogenic factors, such as the use of host-specific biological control agents that limit non-target impacts compared with broad-spectrum insecticides (Sharma et al. 2019; Andow et al. 2020).

Our targeted literature reviews uncovered many previously overlooked examples of the environmental impacts of three case-study insect pests of agriculture–a type of pest rarely considered for their effects on native biodiversity. However, a large portion of examples did not directly address environmental impacts or contained uncertainties, such as data deficiency and study designs that did not enable detection of potentially higher impact severities. Although studies found for the two case-study pathogens, which are well known for their environmental impacts, more commonly addressed such impacts directly, the above-described uncertainties were also observed among studies that did not fall under the ecosystem impact mechanism. Our review therefore raises awareness of the potentially underappreciated environmental impacts of invasive insect pests of agriculture and highlights impact mechanisms for which great uncertainty remains. We recommend that research on invasive insects and pathogens consider these patterns to improve our understanding of the impacts of invasive species.