Anecdotal evidence points to severe decline in insect abundance - without going into details I mention here windscreens, typically full of smashed insects after a cross-country drive, and clean in recent years. Personally I observed overall decline in abundance at light traps.However, I did not find reliable data, with few exceptions, e.g. Rothamstead light trap http://www.rothamsted.ac.uk/. There must be more data out there! In a recent article about disappearance of Canadian arial insectivores (e.g. swallows) I found this remark "Though insect populations are now a recognized area of study, Grooms says that like aerial insectivores, they have largely been ignored in the past. The absence of historic data and the difficulty in assessing insect populations across the birds’ vast range present significant challenges in establishing a solid link between the two groups." http://rabble.ca/blogs/bloggers/jenhalsall/2016/03/hard-to-swallow-mysterious-disappearance-canadas-aerial-insect-eat
Which means that this question is highly significant for ornithologists!
In subsaharan Africa, I am not aware of any comprehensive data on insect decline.
Working on floral visitors in East Africa, the only reliable answer would be extrapolation due to reduced plant species as a result of anthropogenic factors. The environmental degradation due to agriculture: (pesticides, slash-and-burn, clean farming/removing all vegetation before planting, even on previously cultivated land); Overgrazing, deforestation, Invasive species e.g parthenium and prosopis. Urbanization and landscaping with exotic plants as well as street lighting which has now increase in Kenya with new administrative centre created in the recent past. This has occurred in places where the local biodiversity is poorly studied.
Do let me know if you come across any such data in subsaharan Africa.
Yes, citizen scientists in Germany have been using Malaise Traps for 30 years and can show a loss of 80% of biomass:
https://www.nabu.de/news/2016/01/20033.html
Klaus
Your impression I am is correct bit your question underlines the need to establish now baselines of biodiversity especially of they can be linked to previously recorded data as indicated for Germany. Note I have published several papers (to be found on RG) on setting biodiversity quality baselines.
Alan
The trouble is that the study from Germany is very local (from the area near Krefeld). There are butterfly monitoring programs in the UK and other parts of Europe. In the UK there are also monitoring programs for other species and we currently plan to develop a cross-European Orthoptera monitoring scheme. Anyway, this would be something that definitely needs some long-term funding by governmental organizations (such as the monitoring of chemicals pollutants in the environmental specimen bank).
I am working on honeybee pests, earlier authors have indicated a general decline in insect pollinators.But as to date there is no comprehensive study on the global insect abundance, if there is then it has not been published. The existing evidence highlights regional decrease in pollinator density, and as such, it is still a debate.
I do believe there is a decline but without scientific proof it is meaningless.
I concur with Axel Hochkirch, there is need for inter-governmental organizations to fund a research work aimed at determining the global insect density.
Just found this:
http://www.gbif.org/newsroom/news/18-years-of-moth-data
And here is the paper belonging to it:
http://onlinelibrary.wiley.com/doi/10.1111/1365-2656.12452/abstract;jsessionid=91FE7C469F41DBF3B3DFC5398C4C4731.f01t03
Here in New Jersey we have been operating black light traps for eighteen or more years for the purposes of tracking crop pests. We have seen a decline in two moth species, Heliothis zea and Ostrinia nubilalis in that time period, however we generally think that this is due to the use of GMO field and sweet corn and other GMO crops like cotton. Unfortunately we have not tracked non-pest groups. The total catch of insects in out traps, though is highly dependent upon the weather and can vary dramatically week to week. As for an overall decline in the number of insects collected in our traps, I doubt that we have seen this. But, what sort of decline are you asking about - the number of species, or decline in the populations?
I used 17 years data from the De Vlinderstichting butterfly monitoring programme to show that decline of some butterflies was due to nitrogen deposition in the same way as some others were increasing for the same reason (plus three non climate based reasons for this to happen!). Paper is in RG.
The most important biodiversity quality index from the point of view of Ecosystem Services (as in the IPBES) seems to be biomass and decline in biomass would be an important biodiversity quality to monitor
Dear contributors, thanks for all your interesting answers - it seems we do have severe datagaps, but I also have the impression that a careful scanning of literature might reveal much more of what would be needed to get something like a baseline. In fact, LivingPlanetIndex does contain some insect longterm data (database was with NERC, now with ZSL?), and eventually regional RedList data could be used as a proxy - I suppose that biomass from every extirpated species is not compensated for by an abundant one (which would be another question...). May be some more bibliographic hints occur,just found this one by MacGregor et alon "Pollination by nocturnal Lepidoptera, and the effects of light pollution: a review" (see link) stating: Long-term declines in populations and distributions of many moth species have been found in Great Britain (Conrad et al., 2004, 2006; Fox et al., 2011, 2013), the Netherlands
Thanks again, yours Klaus Riede
http://www.sciencemag.org/news/2017/05/where-have-all-insects-gone
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