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Insect decline: a global database under scrutiny shows the urgent need to review scientific journal assessments

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In response to the ecological crisis, databases are multiplying to measure biodiversity trends, but they are not systematically evaluated. Laurence Gaume from the Amap laboratory (UM, CNRS) and Marion Desquilbet (TSE, INRAE) examined InsectChange, published in Ecology, which compiles time series of insect abundance and biomass on a global scale. Their comprehensive analysis highlights more than 500 errors that call into question the results obtained from this database, particularly those of the meta-analysis published in Science in 2020. It also provides essential information for improving InsectChange. Their study, recommended by Peer Community in Ecology and published in Peer Community Journal on October 8, 2024, highlights the problem of quality in large databases. While opening up new methodological avenues, it calls on scientific journals to put in place protective measures against these deleterious effects on science and knowledge.

Lycaenidae butterfly on a Nepenthes flower bud in northern Borneo. © Michaël Guéroult/INRAE.

The decline of insects is creating major environmental, economic, and societal challenges. A new scientific publication just released in Peer Community Journal identifies more than 500 problems in the global temporal database on insects, InsectChange, published in Ecology in 2021.

This database was based on a meta-analysis published in Science in 2020, which claimed that insect decline was not as significant as previously thought and that agriculture was not one of the causes of this decline. Despite international criticism from 65 scientists, only a minimalist erratum was published, leaving the results of this meta-analysis unchanged and widely publicized, conveying a reassuring message to the general public.

This publication by Laurence Gaume and Marion Desquilbet highlights a multitude of new problems and deciphers their origin and nature (erroneous counts transmitted from one database to another, sampling bias, non-standardized units of measurement, data from experiments, geographical coordinates of samples that are inadequate for measuring the impact of agriculture or urbanization using satellite land cover data, etc.). It concludes that these 553 problems, categorized as errors, inconsistencies, methodological issues, and information gaps, call into question any insect trends estimated from InsectChange and do not allow for testing, based on this database, whether land use is likely to explain the observed trends.

For example, many datasets concerning freshwater environments actually include all aquatic invertebrates, and increases in "insects" turn out to be proliferations of invasive mussels. By correcting these data, the two scientists find that the trends for freshwater insects published in Science have been greatly overestimated. Another problem is that half of the InsectChange datasets are not representative of insect dynamics under natural conditions. This is the case with dragonflies colonizing experimental ponds created by a British scientist to study them. These data are incorporated without mention of the experimental context, artificially leading to an increase in these insects. Furthermore, the transformation of these non-standardized data as performed in the meta-analysis compromises the comparison of time series slopes and the estimation of overall insect trends. Finally, the coverage of agricultural land around sampling areas is greatly overestimated, partly due to inaccurate geographic coordinates in two-thirds of the datasets, which leads to the exclusion of crop areas as a possible cause of insect decline.

Need for systematic evaluation of ecological baseline data

This observation raises various issues:

  • It is essential to ensure the quality of global databases in ecology, which are multiplying in the context of biodiversity decline. In particular, this publication provides detailed and crucial information to improve InsectChange and enable its informed use.
  • This publication develops a reproducible analysis method that can inspire the development of systemic evaluation grids for database quality.
  • She calls on scientific journals to improve peer review prior to publication and to take comments into account after publication, particularly for publications based on large datasets, and especially for renowned journals, which are the preferred intermediaries for journalists.
  • Finally, it highlights the important role played by the non-profit organization Peer Community In, particularly its open science approach and independent, transparent evaluation process, which helps to preserve scientific integrity and the quality of science.

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