Flying insects plummet

Where have all the flower-pollinating insects have gone?

I recognise that this headline is likely to be attention-grabbing*: How can it be that flying animals, masters of that atmospheric fluid medium, fall from the sky very quickly and suddenly – ‘plummet’ – to the ground?

Sheep
Photo: Carlos Antonio Writte / Flickr

Laughter and some bemusement aside, there is a much more serious side to the news that numbers of flying insects have markedly reduced – ‘plummeted’ (definition 1 here) – over recent years. What’s behind the heading is work by Caspar Hallmann et al. that demonstrates a “more than 75 percent decline over 27 years in total flying insect biomass”. Working in 63 nature protection areas in Germany, the team recorded estimated seasonal decline of 76%, and mid-summer decline of 82%, in flying insect biomass. Understandably, that’s not good news for the insects themselves and the animals that use them as a food source, but, as plantspeople, should we be concerned by this?

Yes! [And I can’t believe you had to ask that question!]

Anybody who knows anything about plants will know how important their relationship with insects is: Many flowering plants are pollinated by flying insects. For those species, insects are crucial to the very existence of a next generation of plants. And, from a selfish human perspective, we must be concerned by any potential reduction – or maybe even loss – of pollination services of these insects for our crop plants**.

Now, one could argue that, since the greater part of humankind’s food calories come from cereal members of the Poaceae (the grass family) such as wheat, maize, and rice – crops that are almost exclusively wind- or self-pollinated – this loss of insects is of no great concern from the point of view of basic future food security. However, that would be rather naïve since it overlooks all the other services that such insects provide, and the fact that proper ecological functioning of the planet is probably best achieved with as much biodiversity as possible. And ignores the fact that those staples are not enough for a well-balanced, nutritious diet. And the list of those crops that are pollinated just by bees amongst the tens of thousands of insect species is extensive.

Although the study sites are considered to be representative of “Western European low-altitude nature protection areas embedded in a human-dominated landscape”, how worldwide may these reductions be is not known. But in view of the dramatic decline that has been recognised, and given the global importance of insects to ecology in the widest sense, a repeat, and extension, of such work more globally is highly desirable. Though one wouldn’t want so many repeat investigations carried out that their sampling efforts would contribute unduly to an even greater decline in insect numbers! But, and arguably of more pressing concern, is trying to understand what has caused these reductions in the first place.

Somewhat worryingly, Hallman et al. concluded that the decline they demonstrate is apparent regardless of habitat type, and couldn’t be explained by changes in weather, land use, and habitat characteristics over that time period. However, in their discussion they do suggest that “agricultural intensification (e.g. pesticide usage, year-round tillage, increased use of fertilizers and frequency of agronomic measures) that we could not incorporate in our analyses, may form a plausible cause”***. Which brings to mind current concerns over use of ‘neonics’ – shorthand for neonicotinoid insecticides – in regard to decline in bee populations. More worrying still is that the study sites were supposedly “protected nature areas”.

With such a drop in insect numbers, one wonders how well ‘protected’ other biota were – and are? – in those locations…

 

* For those of us of a certain generation – for whom the madcap antics of the ensemble known as Monty Python’s Flying Circus loomed large during our youth – this headline may call to mind that troupe’s ‘flying sheep’ sketch. This contains the memorable fact that sheep are not creatures of the air: They do not so much fly as … plummet.

** Some idea of the economic importance of these organisms to humankind can be gleaned from work by Losey and Vaughan which estimates that the annual value of all the ecological services provided by insects in the United States alone is at least US$57 billion(!)

*** One thing they don’t consider is whether the ‘missing’ insects may have been eaten by humans. A suggestion to ease future food security issues is for mankind to eat – more! – insects. Could it be that the commendably compliant citizens of the German countryside have taken that culinary advice to heart and have been doing their bit for future food security by catching ’em, cooking ’em and consuming ’em?

[Ed. – from a science writing point of view, one of the most interesting aspects of the Hallman et al. article is the recognition of 14 separate categories of activity that contributed to the overall paper. Caspar Hallman features in at least 9 of those, demonstrating how much of a multi-tasker scientists are!]

Further reading

Hallmann, C. A., Sorg, M., Jongejans, E., Siepel, H., Hofland, N., Schwan, H., … de Kroon, H. (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

LOSEY, J. E., & VAUGHAN, M. (2006). The Economic Value of Ecological Services Provided by Insects. BioScience, 56(4), 311. https://doi.org/10.1641/0006-3568(2006)56[311:TEVOES]2.0.CO;2

Schowalter, T. D., Noriega, J. A., & Tscharntke, T. (2018). Insect effects on ecosystem services—Introduction. Basic and Applied Ecology, 26, 1–7. https://doi.org/10.1016/j.baae.2017.09.011

Oehri, J., Schmid, B., Schaepman-Strub, G., & Niklaus, P. A. (2017). Biodiversity promotes primary productivity and growing season lengthening at the landscape scale. Proceedings of the National Academy of Sciences, 114(38), 10160–10165. https://doi.org/10.1073/pnas.1703928114

Tsvetkov, N., Samson-Robert, O., Sood, K., Patel, H. S., Malena, D. A., Gajiwala, P. H., … Zayed, A. (2017). Chronic exposure to neonicotinoids reduces honey bee health near corn crops. Science, 356(6345), 1395–1397. https://doi.org/10.1126/science.aam7470

Woodcock, B. A., Bullock, J. M., Shore, R. F., Heard, M. S., Pereira, M. G., Redhead, J., … Pywell, R. F. (2017). Country-specific effects of neonicotinoid pesticides on honey bees and wild bees. Science, 356(6345), 1393–1395. https://doi.org/10.1126/science.aaa1190