I posted recently regarding blackfly on our broad beans. There I mentioned my expectation that our healthy population of ladybirds would soon assist in addressing this pest. However, we have not seen a single ladybird this year; not that we have been looking out for them, specifically, but we are usually inundated with them. I fear, then, that the population has much declined this last year, and we may, then, have to resort to a spray of a mild solution of soft soap to control the blackfly.
What the cause of this decline might be I cannot tell. I have read that the overly wet summer last year resulted in fewer aphids, which are the ladybirds’ primary prey, and that the cold winter may have further harmed the population. Additionally, there is the threat posed by the Harlequin ladybird, which is said not only to outcompete native species but also predate them. These were introduced to Europe much as they were to North America for commercial pest control. There appears to be strong evidence of decline in native species since its arrival in this country. How many times has a short sighted intervention in the natural order of things had unforeseen and unfortunate consequences?