Insects play a key role in ecosystems, but insect diversity and abundance appears to be on the decline. To gain a better understanding of the extent and underlying causes of this decline, Caspar Hallmann and colleagues measured total flying insect biomass over 27 years in nature protection areas in Germany, and recorded a dramatic decrease of over 75 percent in this period. To learn more about this research, just published in PLOS ONE, I interviewed Hallmann via email.
What prompted you to pursue science as a career?
My parents are both field biologists, which has undoubtedly contributed to me pursuing a science career. I really enjoy doing science: answering interesting research questions (or at least trying to do so!), and actively contributing to the state of knowledge in my field. A passion for nature and an eagerness to understand it has fuelled most of my efforts so far.
Why did you choose to study flying insect populations?
CH: Insects represent one of the most significant but least well investigated parts of ecosystem function. Knowledge on the state of flying insects as a group is limited to only few well-known species, and consequently so are our insights on ecosystem functioning. Luckily, a very important dataset collected, maintained and made available by the Krefeld Entomological Society enabled us to take a rare look into how flying insects as a group are performing in nature reserves.
What role do insects play in ecosystems? Why are they so important?
CH: Insects are highly significant, being responsible for plant pollination and nutrient recycling as well as acting as a food source for animals such as birds, bats and small mammals. Lack of insects is very likely to be detrimental to the entire ecosystem, in terms of its diversity as well as its stability and function.
How did you measure insect biomass during your study? What sorts of species did you include?
CH: Insect biomass was measured using tent-like structures known as Malaise traps deployed in protected areas in Germany throughout spring, summer and autumn. Malaise traps catch a relatively wide distribution of insect diversity, from small midges and mosquitos all the way to butterflies, wild bees and moths, and from leaf chewing species such as aphids to parasitic species such as wasps.
What surprised you most in your findings?
CH: We were very surprised by the extent of the decline in flying insects that we found, measuring over three-quarters of the total flying insect biomass over 27 years. Declines in several specific species, particularly vulnerable insects such as bees, butterflies and moths, have been recorded for some time. However, our results imply that the entire flying insect community has been devastated, including common species that are usually found in high numbers. Ironically, this decline was seen in protected areas, which are supposed to help preserve biodiversity and ecosystem stability.
Where do you hope your findings might lead?
CH: There is an urgent need to further investigate both causes and consequences of this alarming decline in insects. We truly hope that policy makers will respond. These results demand action at the national and international level to instigate measures that will preserve insects and the ecosystems that rely on them.
What are the next steps for your research?
CH: We would like to further consider the causes of the insect biomass decline and its extent in different insect subgroups. We also hope to elucidate how the decline depends on the quality and quantity of nature reserves. We would like to understand how this tremendous decline in insect biomass affects the ecosystem’s stability. We are presently investigating how pesticide loads may affect insect biomass in the Netherlands, and how other species in the ecosystem may also be affected.
Research Article: Hallmann CA, Sorg M, Jongejans E, Siepel H, Hofland N, Schwan H, et al. (2017) More than 75 percent decline over 27 years in total flying insect biomass in protected areas. PLoS ONE 12(10): e0185809. https://doi.org/10.1371/journal.pone.0185809
Images Credits: Hallmann et al (2017); Caspar Hallman