Science - February 23, 2010

Ichneumon wasp back in favour

The Aphidius matricariae wasp of the Ichneumon family was widely used to get rid of plant lice in greenhouse agriculture up to fifteen years ago. Since then, it has given way to its American cousin, Aphidius colemani. A comparative study by the Wageningen UR Greenhouse Horticulture group has led to its re-introduction by Koppert, the market leader in organic pest control.

A. matricariae had always been effective against red aphids and green peach aphids in greenhouses with tomatoes, aubergines and bell peppers. But it is ineffective against the cotton aphid in gourd plants. In the 1990's, when breeders had to deal with serious resistance problems concerning plant lice, A. colemani was introduced. This is a parasitoid for both types of plant lice. A. matricariae was then left aside.
'The tables have now been turned', says Pierre Ramakers of the Wageningen UR Greenhouse Horticulture group. 'The use of organic pest control alone appears to be ineffective in controlling the cotton aphid in cucumber plants. Cucumber growers prefer to use new, selective insecticides.'
A comparative study done by his colleague Gerben Messelink has shown that A. matricariae is still the best aphid control agent in Solanaceae vegetation such as bell peppers and tomatoes. Messelink has compared the effectiveness of six species of Ichneumon wasps used in countering plant lice in horticulture in different parts of the world. A. matricariae is clearly the best for bell peppers and tomatoes.
Market leader Koppert is re-introducing the old trusted Ichneumon wasp (and possibly other species as well) into the market in an attempt to make up for the loss when natural pest control measures were used.

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