Last year I noted a change in local ant and wasp populations in my garden and nearby allotment.
For the last seven or eight years the plum trees in both areas have been heavily infested by aphids. These were well attended by the usual black ants. As the season developed wasps also clearly had a great interest in the trees. So much so that I had to be wary when doing any light pruning.
In spring last year 2017, the aphids began to appear as normal but I noted a number of what I discovered were Harlequin ladybirds. They were first noticeable in the allotment the previous year. There was then a very noticeable flush of ladybird larvae and then subsequent pupae. Much more than I have observed in the past. When these hatched the greenfly were clearly under attack. By late July there was hardly an aphid left.
In my allotment I have a mature plot of asparagus. Each year these are attacked by Asparagus beetles. A wonderful insect to look at but the caterpillars reduce the fronds to nothing. And nothing seemed to predate them. Not a wasp to be seen. However this year while the infestation was developing it seemed to stall and then I saw a Harlequin ladybird actually eatiing a beetle grub. Within a fortnight the whole infestation had gone. The same situation developed on the broadbeans which are highly susceptable to black greenfly being 'farmed' by black ants. You could see where the aphids had damaged the plants but they had all gone. At the time I thought this was great but I now worry about the wider implications.
Normally in mid summer the ants swarm. The actual date changes but the swarms have been large and consistant with many coming up into our kitchen through the brickwork over two or three days. Last year the swams barely happened. Small, fitful and late. I thought it might have been the weather but at the same time the wasps which usually make it difficult to pick the plums were much depleted. They normally don't seem too bothered and bite holes in any plum that's about ripe. Last year the lack of wasps was remarkable. And now I think worrying.
It looks on the face of it that the ants and wasps are being squeezes out from their normal sources of food/prey by the Harlequins. If this is so then this year if vast numbers of Harlequins survive the winter then the aphids will never develop in any numbers and this can't be good for the ants or wasps. And if this is right then what on earth is going to happen to other insects with vulnerable larval stages? Will butterflies disappear next year as well as ants and wasps?
I know this isn't scientifically recorded but I feel I need to flag up to someone. Will record dates etc. this year.