We have discussed declining insect populations a number of times at meetings while I have been a member of ROC, particularly how this has affected the types and numbers of birds we now encounter locally. 

We are obviously not alone in our thinking. The Guardian article I've included below is a very interesting, albeit grim, read. Some of the numbers it quotes are alarming.

One of its studies details evidence of rapidly declining insect populations in preserved areas of rainforest (somewhere you think would be, literally, crawling with insects) and what effect this has had on bird populations. It also includes evidence from the southern US, where a relatively sudden absence of insects has had a knock-on effect not just for birds, but for lizards and snakes too.

Article: 'Half the tree of life': ecologists' horror as nature reserves are emptied of insects