The aphid population won't be affected by cold weather, contrary to popular myth. Photograph: srboisvert/Flickr/Some rights reserved
At moments like this, desperately searching for a silver lining to the recent cold snap in the UK, it would not be unusual for a gardener to mutter something along the lines of, "Ah well, my pelargoniums are mush and my gingers are goners, but at least this cold will be knocking back the pests". I expect I've done it myself, probably while scratching my chin and squinting wisely at the horizon.
The idea that warm winters allow aphids and slugs to procreate luxuriantly while cold ones knock them back to a struggling skeleton population is ingrained. I was certain lily beetles in particular, with their flamboyant colouring and the fact that they have spread roughly from south to north, in line with the general warming of the oceans, would be utter softies and would have taken a proper whipping over the last couple of months.
I was emailing Dr Andrew Salisbury from the RHS and so I asked him if it was true, and, I'm sorry to report, he put me straight: "In fact the effect of cold winters on insects in the UK is a myth," he begins. "Those insects that are native can cope, those that are alien from central Europe etc can cope with colder winters. Lily beetle is native to mainland Europe and Asia and is found from Siberia to N. Africa. Parts of that range have winters that are far colder than winters here."
Cold weather at a time of the year when we are meant to have cold weather is no use at all, it seems. "Greater effects may happen if a cold spell happens in late winter or early spring such as in March. In December, January and February insects are well prepared for cold spells. Warm winters may have a greater effect. The distribution of the Tiger moth, once common in S. England (now rare) has moved northwards, due to winters being warmer and wetter!"
Finally, he goes on to give one possible reason for cheer. "There may be an effect on species which have recently established from the Mediterranean (eg Rosemary beetle), but this is an unknown."
That will be a no then.
