The recent paper on pollinating insects in Britain (Widespread losses of pollinating insects revealed across Britain, March 26) highlights the long-term loss of insect pollinators from parts of the UK countryside. The authors are to be congratulated on taking a scientific approach in their consideration of the causes behind these changes. Some good news is to be welcomed and the authors have included this in their discussion.
The GWCT has monitored insects on arable land through two annual surveys – the Sussex Study and at our demonstration farm in Loddington. They’re particularly valuable because densities of insects are measured in the same locations and on an annual basis allowing trends over time to be investigated.
The total number of invertebrates collected has declined by 35% over the monitoring period, although the majority of these declines occurred between 1970 and 1980 which we attribute primarily to use of insecticides (Ewald et al., 2015 Global Change Biology). There is much variation between the different species of insects. One group that has declined the most is aphids that can become a crop pest but which are an important food for some hoverfly larvae.
Over the course of the Sussex Study (i.e. from 1970) the decline of average annual aphid abundance correlated with long-term trends in weather, but on a field basis this was attributed to insecticides. There is a good possibility that the decline in hoverflies is related to that of the aphids.
Powney et al. also highlight the importance of agri-environmental schemes in supporting common species for crop pollination. Agri-environment options, such as conservation headlands and wild bird covers, can support high densities. Just as important as identifying the declines in insects is acknowledging the work that farmers currently do to counteract these declines.
Dr Julie Ewald (head of geographical information systems)
Professor John Holland (head of farmland ecology)
Game & Wildlife Conservation Trust