The pioneering research by the Game & Wildlife Conservation Trust (GWCT) in the 1970s, mentioned by David Gibbons of the RSPB, showed the link between weeds, insects and grey partridge chick survival (Potts, 1986). These detailed studies have continued ever since.
Over the past 50 years, total insect abundance has declined by 35%, but in recent years it has shown an increase. In contrast to the article (Where have all our insects gone, June 17), we have found that wheat crops can contain many insects and a surprising diversity of them.
Work published in 2015 (Ewald et al., 2015) assessed 26 insect groups found in cereal crops. Of these, 12 had declined in abundance, two increased and the remainder show variability over time. In other studies, we found up to one-and-a-half million beetles per hectare emerging in cropped fields (Holland et al., 2007). Extreme weather, insecticides and herbicides were all shown to affect insect abundance.
The widespread uptake of agri-environment schemes and greater awareness of the impact of insecticides by farmers is helping to support insects. Remedial measures should focus on encouraging greater plant diversity, upon which so many insects depend, in our crops, pastures and urban areas.
Professor John Holland (head of farmland ecology)
Dr Julie Ewald (head of geographical information systems)
Game & Wildlife Conservation Trust
References
Ewald, J. A., Wheatley, C. J., Aebischer, N. J., Moreby, S. J., Duffield, S. J., Crick, H. Q. P. and Morecroft, M. B. 2015, Influences of extreme weather, climate and pesticide use on invertebrates in cereal fields over 42 years. Global Change Biology, 21: 3931-3950.
Holland, J. M., Thomas, C. F. G., Birkett, T., Southway, S. 2007. Spatio-temporal distribution and emergence of beetles in arable fields in relation to soil moisture. Bulletin of Entomological Research 97, 89-100.
Potts, G.R. 1986. The Partridge: Pesticides, Predation and Conservation. Collins, London.
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