Sex traps lure wasps
THE use of sex pheromone lures to get naturally-occurring parasitic wasps to move into the cereal crop in time to have an effect on aphid populations has been tested successfully at IACR-Rothamsted.
Field margins were established in the autumn, with pheromones initially being used to attract and establish parasitoid populations. In the spring, the beneficial insects were persuaded to move into the crop with lures containing the sex hormones.
The results showed that it is possible to increase parasitoid numbers. If they can be raised by 20%, there is an effect on aphid populations.
"Each season is different, so the results have varied in different years," says Rothamsteds Rob Glinwood. "In some years, there are only low numbers of parasitoids around."
The pheromone used in the Rothamsted work is produced naturally by the catmint plant. Mr Glintwood believes that the next stage of the work should focus on the over-wintering behaviour of the parasitoids in field margins.
• Fears that aphids which escape natural predators could speed BYDV transmission in the autumn have proved unfounded.
The worry was that aphid alarm pheromone would push other aphids on to neighbouring plants, explains IACR Rothamsted researcher Adam Burgess. A trial used cages containing BYDV-infected aphids with and without predators. There was no significant increase in the spread of BYDV.