Using data to advance a point of view:

Sánchez‐Bayo and Wyckhuys (2019) recently compiled and reviewed long‐term insect surveys from the peer‐reviewed literature. They report high average rates of decline in entomofauna and suggest 40% of the world's insect species could go extinct within decades.

We welcome this detailed focus on insect declines: their consistent underrepresentation is a shortcoming of the ecological literature, and it is essential that we improve and synthesize our knowledge, particularly given widespread anthropogenic threats. Many insect populations are undergoing rapid and worrying declines (Hallmann et al., 2017), which could have serious impacts on ecosystem function. 

However, we suggest the approach used in the review has four important limitations that could affect the conclusions: (a) biased search terms, (b) geographic biases, (c) incorrect estimation of extinction risks and rates, and (d) qualitative assignment of drivers to trends that was sometimes inaccurate, ignoring detail in the original work.

As an example, a study of Auchenorrhyncha declines is included in the review, while a similar piece of research published in the same year, by the same authors, in the same country finds increases in Heteroptera, but is not included. Similarly, the review of honey bees (Apis mellifera) mentions declines in the USA, Australia, and Europe, but not the global increase in the number of Western honey bee hives.

Second, the acknowledged geographic bias toward North America and Europe means it is not appropriate to title the paper “Worldwide declines.” 

As conservation scientists, we strive to communicate honest and accurate messages about our knowledge of the natural world. While we believe the authors’ study is a useful review of insect population declines in North America and Europe, it should not be used as evidence of global insect population trends and threats. 

Simmons, Benno I., et al. "Worldwide insect declines: An important message, but interpret with caution." Ecology and Evolution (2019).

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