17 January 2000
100m wasp threat to farmers
By Andrew Blake
APHID control costs could double if the ravages of a parasitic wasp causing concern in Scotland are repeated south of the border.
Irene Geoghegan of the Scottish Crops Research Institute is concerned that Scottish ladybirds – key aphid predators – are being hit unusually hard by a small wasp which resembles a flying ant
If their numbers continue to be decimated, the UK aphicide bill – which currently stands at around 100m a year – could double.
“If we lose biological control from ladybirds, farms could have to spray twice as much pesticide and would face a vast increase in costs,” warned Mrs Geoghegan.
The wasp, dinocampus coccinellae, lays its eggs in ladybirds, which become paralysed by the developing larvae.
Nearly three-quarters of the common seven-spot ladybirds found in the Dundee area last year were parasitised by the wasp.
That was almost twice the level a year earlier. There are suspicions that global warming could be to blame.
Normally the wasp has only two generations a year. “I have an awful feeling we are now getting three generations,” said Mrs Geoghegan.
In only two generations, a single wasp can parasitise up to 10,000 ladybirds.
“All ladybirds do a good job controlling aphids. Every one can eat up to 5500 aphids through the summer, and each of its 1000 larvae can eat the same amount.”
Little can be done to arrest the wasp, but ladybird populations can tolerate up to 20% parasitism, Mrs Geoghegan estimates.