Mission: pest controllers 2020

How to take part

Full instructions are below, but you can also download them for printing [pdf].

Part 1. Between 4th and 13th July

Find a horse chestnut tree attacked by the leaf miner moth. It will have pale or brown patches on the leaves. Pick a leaf that is within your reach. Don't climb the tree or use a ladder!

Select from the leaf just one leaflet (a 'finger' from the hand-like leaf), which will fit in your bag without being folded over.
Count the number of mines on the leaflet. Each mine is one whitish-brown patch with a darker brown spot.

Put the leaflet in a transparent ‘ziplock’ plastic bag (about A4 size and available as a food bag from supermarkets). Seal the bag, but don’t squeeze all the air out. (If there are insects on the leaf, brush them off. The insects we are interested in are still inside the leaf so cannot be brushed off.)

Write on the bag:

  • The tree’s location
  • The leaf miner damage
  • What was under the tree
  • The number of mines in the leaflet.

Keep the bag in a cool room and away from bright light.

You can collect as many leaves from as many trees as you want, but put each leaflet in a separate bag.

The more you collect, the better the results will be - and the more chance you have of seeing the pest controllers!


What was under the tree?

How much leaf miner damage?

Part 2: Between 18th and 24th July (two weeks after part 1)

Look very carefully at the contents of your bag. Use a magnifying glass, if available, to identify the tiny insects that have emerged from the leaf.

How many adult moths and pest controllers can you see? One adult pest controller means one moth has been killed by it!

Record your results - the link will be available on 18th July

DO count the adult moths

  • metallic orangey with white stripes    
  • about the size of a grain of rice

DO count the pest controllers

  • tiny parasitic wasps (1-3mm long)
  • shiny, usually all or mostly dark in colour
  • have unpatterned wings and narrow ‘waists’

Don't count the caterpillars or pupal cases

  • some caterpillars come out of the leaf before they turn into pupae. Don't count these.
  • pupal cases appear to have legs, but are dark brown without white stripes. Don't count these.

Don't count other insects

  • Sometimes other insects might be present. Don't count these.
  • Often brownish or greenish in colour
  • Wings are lacking or patterned