21 January 2000

Ladybird killer could herald aphid plague

APHID control costs could rocket if the ravages of a parasitic wasp already causing concern in Scotland are repeated throughout the UK.

Irene Geoghegan of the Scottish Crops Research Institute is concerned that Scottish ladybirds, key aphid predators, are being hit unusually hard by a small flying ant-like insect, Dinocampus coccinellae. It 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, says Mrs Geoghegan. That was almost twice the level a year earlier. 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." 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 5,500 aphids through the summer and each of its 1000 larvae can eat the same amount."

The UK aphicide bill is about £100m/yr. "If we lose biological control from ladybirds, farms could have to spray twice as much pesticide and would face a vast increase in costs," she suggests.

Little can be done to arrest the wasp, but ladybird populations can tolerate up to 20% parasitism, Mrs Geoghegan estimates.

LADYBIRD PARASITE

&#8226 Egg-laying wasp.

&#8226 Larvae paralyse host.

&#8226 Scots numbers doubled.

&#8226 Global warming to blame?

LADYBIRD PARASITE

&#8226 Egg-laying wasp.

&#8226 Larvae paralyse host.

&#8226 Scots numbers doubled.

&#8226 Global warming to blame?

Watch out…this parasitic wasp could devastate ladybird populations, sending aphid numbers soaring.