I'm pretty convinced that this is due to drainage. Over the last 30 years ditches have been cluveted and ponds drained on all farms, irrigation is now an art - very tightly managed - and farmers round here have dug deep reservoirs to run it. Hedgerows and roads used to have long swampy bits that were ideal for insect breeding, but that's all gone. Farmers here now farm arable or intensive pig/chicken. The mixed economy farms are gone - and with them the small ponds and wallows that were common.

I've got two ponds in my garden, they are a source of head shaking from keen urban gardeners because they are shallow, muddy and a bit smelly - but they team with life and now, in the summer, the air is thick with insects.