Natural pest controllers

Can tiny parasitic wasps help to save our conker trees?

Examples of parasitoids found attacking the leaf miner. (Photos by Brian Valentine. Used with permission.)

Did you know that there are dozens of different kinds of tiny wasps (only distantly related to the stinging wasps that we are so familiar with) that attack the horse-chestnut leaf-miner? These wasps are so small that they lay their eggs inside the leaf-miner which is living inside the horse-chestnut leaf! The developing wasp larvae eat the leaf-miner from the inside out and then burst out of the caterpillar, in the process killing it and so acting as a natural pest controller.

Can these potential pest controllers actually help by parasitising enough of the leaf-miners to control its numbers? Answering this question was the aim of the Mission: Pest Controllers, which ran from 2010-2013. And is running again in 2020.

The simple answer to the question appears to be 'no'. The number of pest controllers that people found was low - under 10% of the leaf-mines were attacked by these parasitic wasps.

Update

We'll be running this mission again in 2020, so we're fascinated to know how the rates of attack by natural pest controllers have changed now that the leaf miner is well-established in the UK.