Almost 40 years ago, Terry L. Erwin published a seemingly audacious proposition: There may be as many as 30 million species of insects in the world. Here, we translate Erwin's verbal argument into a diversity‐ratio model—the Erwin Equation of Biodiversity—and discuss how it has inspired other biodiversity estimates. We categorize, describe the assumptions for, and summarize the most commonly used methods for calculating estimates of global biodiversity. Subsequent diversity‐ratio extrapolations have incorporated parameters representing empirical insect specialization ratios, and how insect specialization changes at different spatial scales. Other approaches include macroecological diversity models and diversity curves. For many insect groups with poorly known taxonomies, diversity estimates are based on the opinions of taxonomic experts. We illustrate our current understanding of insect diversity by focusing on the six most speciose insect orders worldwide. For each order, we compiled estimates of the (a) maximum estimated number of species, (b) minimum estimated number of species, and (c) number of currently described species. By integrating these approaches and considering new information, we believe an estimate of 5.5 million species of insects in the world is much too low. New molecular methodologies (e.g., metabarcoding and NGS studies) are revealing daunting numbers of cryptic and previously undescribed species, at the same time increasing our precision but also uncertainty about present estimates. Not until technologies advance and sampling become more comprehensive, especially of tropical biotas, will we be able to make robust estimates of the total number of insect species on Earth.

中文翻译：

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生物多样性的欧文方程式：从发现热带昆虫多样性的小步骤到量子飞跃

大约40年前，特里·欧文（Terry L. Erwin）发表了一个看似大胆的主张：世界上可能有多达3000万种昆虫。在这里，我们将欧文的口头论据转化为多样性比率模型（即欧文生物多样性方程式），并讨论了它如何启发了其他生物多样性估计。我们对用于计算全球生物多样性估计数的最常见方法进行分类，描述和总结。随后的多样性比率外推法结合了代表经验昆虫专业化比率以及昆虫专业化如何在不同空间尺度上变化的参数。其他方法包括宏观生态多样性模型和多样性曲线。对于许多生物分类学知之甚少的昆虫，其多样性估计是基于生物分类学专家的意见。我们通过关注全球六种最特殊的昆虫订单来说明我们对昆虫多样性的当前理解。对于每个订单，我们汇总了（a）最大估计物种数量，（b）最小估计物种数量和（c）当前描述的物种数量的估计值。通过整合这些方法并考虑新的信息，我们认为世界上有550万种昆虫的估计值太低了。新的分子方法学（例如元条形码和NGS研究）揭示了令人生畏的隐性物种和先前未描述的物种，同时提高了我们的精度，但也不确定目前的估计。直到技术进步和采样变得更加全面，尤其是热带生物区系之后，