Tier 1: Core GLiTRS papers that are implied by the project proposal.
Tier 2: Papers that were motivated by the core project, but where a substantial part of the work was not funded by the project. Most papers in this category will be those deriving from PhD and Master’s students on projects aligned to GLiTRS.
Tier 4: Papers where the work has been substantially funded by GLiTRS, but the work falls outside the tiers above.
Integrating multiple evidence types through threat-response models could enable measurement of insect biodiversity changes, predictions of how insects respond to environmental drivers, and identification of where conservation action will be most effective. Understanding changes in insect biodiversity is severely limited by fundamental data gaps: available time series are too short to detect reliable trends in naturally fluctuating insect populations; geographic coverage is concentrated in Europe and North America, leaving tropical and developing regions understudied; and well-studied groups (butterflies, bees) dominate evidence while taxonomically difficult groups (earwigs, icebugs) are neglected (well established). Expert knowledge, while valuable for understudied regions and taxa, is also constrained by inherent subjectivity and survey bias (well established). Despite these extensive limitations, there is sufficient existing evidence of change across multiple evidence types to warrant urgent action now - waiting decades for perfect long-term monitoring data is not an option (well established). Threat-response models that integrate these multiple evidence streams (time series, spatial comparisons, experiments, and expert knowledge) could be used not only to quantify recent changes and identify the drivers behind them, but also to predict insect biodiversity responses to future policy interventions (established but incomplete). This approach would enable policymakers to identify and prioritise conservation actions with the highest impact potential, making more efficient use of limited conservation resources to meet the 2030 and 2050 Global Biodiversity Framework targets.
To conserve insects, we need to understand what is causing their decline. GLiTRS have compiled a standardised, global database of 6,308 effect sizes from seven meta-analyses to examine how five major anthropogenic drivers, such as pollution, land use change, and invasive species, affect insect abundance, species richness, biomass and fecundity across 21 insect orders. The data populating it are drawn from meta-analyses of a vast body of literature and therefore represent the consensus of current scientific knowledge, particularly for temperate regions. This standardised structure could enable targeted questioning of, for example, which insect orders are most sensitive to invasive species, or how pollution impacts different taxa across geographic regions. However, important caveats must be considered: the database cannot quantify how threats interact with each other; geographic coverage is biased toward North America and Europe; and the current dataset reflects only five of the twelve major threat categories, leaving critical gaps in tropical and subtropical regions. As new studies are added, the database will become increasingly robust for informing conservation and regulatory priorities.
Dynameta is an interactive, updatable meta-analysis platform that enables rapid re-analysis of ecological evidence and informed decision-making as new data become available. Meta-analyses are a crucial evidence synthesis method for policymakers, but they are typically static, making them difficult to interrogate or adapt to region-specific or time-sensitive questions. Living-review platforms and dynamic meta-analyses have been recognised as important developments for improving evidence use in policy, but few generalised tools have existed in ecology until now. Dynameta is an R Shiny platform (written as an R package) that enables researchers to upload meta-analytic data in a standardised format and run analyses interactively, filtering data by threat, geographic region, taxonomic group, and biodiversity metric. As new studies are published, data can be added to the platform and analyses re-run, maintaining up-to-date evidence syntheses for policy decisions, such as pesticide regulation. However, Dynameta does not replace the need for rigorous protocol registration, proper evidence gathering, or critical interpretation; users must be aware of statistical limitations (multiple testing risks, reduced power in subsetted data), and the tool's usefulness is dependent on user expertise and careful methodology.
Climate change affects insect biodiversity through multiple mechanisms, producing complex, species-specific responses that are difficult to predict and often exacerbated by interactions with other human impacts (well established). Insects are particularly vulnerable to climate change due to their small body size and vulnerability to drying out (well established). Climate change can impact species survival by decreasing the climatic suitability of the species' habitat, often through changes in rainfall patterns or extremes of temperature (established but incomplete). In order to continue surviving in these habitats, species may change the timings of life events such as breeding and hibernation, in order to utilise the more suitable climate of a different time of year (well established). Species may also shift their ranges, expanding polewards and uphill into cooler regions, and becoming locally extinct in regions that become unsuitable (well established). Finally, species' behaviour may adapt so that they are less affected by climate change (established but incomplete). The effects of climate change on insects are often exacerbated when combined with human impacts such as habitat fragmentation, pollution, and invasive species. While much remains unknown about insect biodiversity (particularly in understudied tropical regions and lesser-known taxonomic groups) there is sufficient evidence of ongoing climate-driven changes to justify implementing conservation actions immediately, rather than delaying until all ecological mechanisms are fully understood.
Climate change is a major threat to insects, and a certain amount of future change is unavoidable, so conservation measures are needed to help insects survive in a changing climate (well established). One such measure is to improve the representativeness and connectivity of protected areas for insect communities in the UK and provide corridors for insects to move through, ideally aligned north-south or uphill-downhill, to connect current habitat with areas likely to have a more suitable climate in future (established but incomplete). To maximise the usefulness of these protected areas to insects, it may be necessary to manipulate the habitat to create small-scale heterogeneity, which provides meaningful differences in climate on the scale at which insects operate, allowing both cold-adapted and warm-adapted species to persist in different areas of the same reserve (inconclusive). Finally, for species of particular conservation concern, it may be necessary to carefully study their biology and then manage their habitat according to their needs (well established). This may include assisted colonisation, in which species with low dispersal potential are relocated to newly suitable habitat beyond their current range (established but incomplete).
Invasive alien species significantly (but unevenly) reduce insect abundance and species richness across terrestrial insect orders, enabling evidence-based prioritisation of conservation (Well established). A meta-analysis of 52 studies encompassing 318 effect sizes reveals that invasive alien species reduce the abundance of insects in four terrestrial orders by an average of 31%, and species richness by 26% (Well established). However, impacts are highly variable across insect taxa and invasive species types (Well established). Invasive alien animals (particularly ants) cause substantially stronger impacts on insect abundance (-43%) compared to invasive alien plants (-11%), while Hemiptera (true bugs) and Hymenoptera (bees, wasps, ants), show greater declines (-58% and -37% abundance) compared to Coleoptera (beetles), which show smaller, non-significant declines (Well established). The results highlight that, although insects are often viewed as drivers of invasion impacts, they are also vulnerable to them. These estimates provide quantitative evidence of where insects are most at risk, supporting targeted conservation to protect biodiversity and ecosystem services that are critical to food production and human well-being (Established but incomplete). Important data gaps remain, with most evidence originating from Europe and North America (58%), with only 16% from tropical regions and 7% from islands (Well established).
The presence of livestock around water bodies is detrimental to aquatic insects (well established). Livestock disturb soil, increasing the sediment content of water; additionally, through their faeces, cause nutrient enrichment and contamination of water bodies (well established). Data from 33 studies conducted across five continents were included in a meta-analysis to investigate how this affects aquatic insects. Ephemeroptera (mayflies), Plecoptera (stoneflies) and Trichoptera (caddisflies), which between them make up the best-studied group of freshwater invertebrates, show significantly decreased species richness in the presence of livestock. Impacts on other groups are less clear, reflecting significant context-dependence. Trends in decreased richness and stable abundance likely indicate a shift in species composition due to livestock disturbance in and around waterbodies, potentially due to losses of more sensitive species (from external literature).
Different insect groups respond very differently to the combined pressures of intensive agriculture and climate change, with some (particularly butterflies and moths) experiencing severe declines, while others show more variable responses (established but incomplete). Insect records from the PREDICTS database, taken from 26,114 sites globally, were analysed to determine how five major insect orders responded to the interactions between land use/land use intensity and climate change. Lepidoptera (butterflies and moths) showed the greatest responses, with sites under high-intensity agriculture that have also experienced climate change having 83% lower species richness and 91% lower total abundance compared to primary vegetation sites without climate change, far exceeding average insect declines. Hymenoptera (bees, wasps) showed dampened or sometimes even positive responses to the same pressures. Understanding this variation is critical for conservation planning: using average responses across all insects masks which groups are most at risk and where targeted action is most needed.
Global species-based indicators such as the Living Planet Index (LPI) often ignore insects entirely, but a similar index for insects is now within reach. The LPI is a globally influential measure of changes in species abundance, but it considers only vertebrates. As such, it misses most biodiversity change (well established). There is sufficient data from existing butterfly monitoring schemes to create an "LPI for insects". However, the data are extremely spatially biased, so the magnitude and direction of trends is not reliable in its current form (well established). Reducing spatial bias with targeted data collection should be a priority, since insects are expected to respond rapidly to changes in environmental conditions, meaning this index could be an important "leading indicator" of biodiversity change.