Interpreting insect declines: seven challenges and a way forward

Abstract

Many insect species are under threat from the anthropogenic drivers of global change. There have been numerous well‐documented examples of insect population declines and extinctions in the scientific literature, but recent weaker studies making extreme claims of a global crisis have drawn widespread media coverage and brought unprecedented public attention. This spotlight might be a double‐edged sword if the veracity of alarmist insect decline statements do not stand up to close scrutiny. We identify seven key challenges in drawing robust inference about insect population declines: establishment of the historical baseline, representativeness of site selection, robustness of time series trend estimation, mitigation of detection bias effects, and ability to account for potential artefacts of density dependence, phenological shifts and scale‐dependence in extrapolation from sample abundance to population‐level inference. Insect population fluctuations are complex. Greater care is needed when evaluating evidence for population trends and in identifying drivers of those trends. We present guidelines for best‐practise approaches that avoid methodological errors, mitigate potential biases and produce more robust analyses of time series trends. Despite many existing challenges and pitfalls, we present a forward‐looking prospectus for the future of insect population monitoring, highlighting opportunities for more creative exploitation of existing baseline data, technological advances in sampling and novel computational approaches. Entomologists cannot tackle these challenges alone, and it is only through collaboration with citizen scientists, other research scientists in many disciplines, and data analysts that the next generation of researchers will bridge the gap between little bugs and big data.

Decline of six native mason bee species following the arrival of an exotic congener

“…Dialogue concerning insect declines in the Anthropocene often fails to tease apart the insect “winners” and “losers” 32 . We report a significant surge in the abundance of the exotic solitary bee species Osmia taurus with concurrent losses of all six native Osmia species in our analysis.…”

Taxonomic, temporal, and spatial variation in the dynamics of High-Arctic arthropod populations

“…Recent commentaries of insect declines have called for standardised methodology, well-designed syntheses of insect demography (31), balanced analysis (14), and realistic interpretation of results given the limitations of available data (32). In this study, we attempt to meet these challenges by presenting all relevant data from a long-term, standardised monitoring programme in the Arctic whereby arthropods were sampled weekly across the entire growing season.…”

“…New monitoring initiatives should align with established programs to ensure inter-site comparability with respect to sampling methodology, spatio-temporal coverage, curation of samples and specimens, and digitization of collections (15, 31, 64). More efforts should also be made to address the common problems with monitoring and analysing arthropod trends described at length by Didham, et al (32). Complementary to this, large-scale programs utilizing standardized sampling protocols and covering vast gradients in environmental conditions should be implemented (15).…”

Changes in phenology and abundance of suction‐trapped Diptera from a farmland site in the UK over four decades

“…It is possible to determine the effects of individual stressors at the species level under experimental conditions. In the field, however, these drivers work together, and the overall effects are difficult to predict, especially for whole insect communities (Robinet & Roques, 2010;Damien & Tougeron, 2019;Montgomery et al, 2020;Didham et al, 2020).…”