Who mourns the wasps? Me.

This is the sad story of some little wasps killed by poisoned potatoes.

Not those big yellow and black nuisances which wasp their waspish ways around the garden (and house) in the warmer months, but some fragile little wasps by the name of Metaphycus helvolus. They are about 2 mm long, and they parasitise the soft scale insects which otherwise plague my citrus trees. The female wasp lays her eggs in the young stages of the soft scales, and the wasp larva develops inside the scale and kills it. The parasite pupates inside the scale body and emerges as an adult wasp, cutting a circular hole in the dead scale.

Metaphycus used to be available to buy as a biological control for scale on houseplants, but no longer. I had this response from Wye Bugs to an enquiry I sent:

“Hello Hilary

After selling the soft scale control for 30 years we had a batch of potatoes for rearing the scales that turned out to have come from a field in which the previous crop had been oilseed rape with a neonicotinoid seed dressing.  As you know these pesticides are causing problems with bees.  We found that our little wasps are also susceptible and it now is suggested that the rape seed dressing will be active in the soil for the next 10 years.  Potato tubers accumulate the pesticide from the soil and take in enough of the material to kill the beneficial wasps.

 …

…unfortunately, for the past 2 years all of our European contacts have also had production problems so cannot provide us with a start-up culture of Metaphycus or Encyrtus infelix…

We hope we might get a culture going again at some point, but at the moment don’t know when.”

So sad. And it hit home just how astonishingly toxic those neonicotinoids are. The potatoes weren’t even treated with the pesticide, but carried lethal doses of it just from growing in soil where pesticide-treated seed had been sown before.