Fifty years of monitoring changes in the abundance of invertebrates in the cereal ecosystem of the Sussex Downs, England

Abstract

Changes in insect abundance are receiving much attention, with agricultural intensification considered to be one of the main drivers of decline. We report on changes in invertebrates collected in cereal fields in Sussex, Southern England, UK, from 1970 to 2019. Samples were taken using D-vac suction sampling in the third week of June from an average of 95 cereal fields per year (4757 samples in total, comprising 2,983,124 individual invertebrates identified mainly to family level). The study area comprises 12 farms, whose land use, crop rotations and intensity of pesticide use were also recorded, showing marked changes over time. Overall invertebrate abundance declined by 37% across all taxa, and by 48% when excluding the most numerous taxa (Collembola, Aphididae and Thysanoptera). Declines in abundance were identified for 47% of 51 non-overlapping taxa at the order or family level, increases for 16% and no change for 37%. Most declines occurred in the first decade of the study, most increases in the 1990s. Latterly there have been further declines from 2010. As functional groups, mycetophages, phytophages, predators (both aphid-specific and polyphagous), parasitoids and cophrophages declined significantly, while there was no detectable change in pollinators. Four of five measures of avian chick-food invertebrate abundance declined significantly, while one (corn bunting chick-food index) showed no detectable change. A multivariate constrained redundancy analysis revealed that cropping, field size, pesticide use and weather all significantly explained the variation in the abundance of the 51 non-overlapping taxa. For functional groups, significant explanatory variables were weather and pesticide use. Changes in farming practices and adoption of measures such as integrated pest management, regenerative farming, agri-environmental scheme options and intercropping could help to mitigate the factors associated with decline.