Pheromones help to suppress pests

The black vine weevil has for many years been a major problem in the cultivation of ornamental plants and nursery stock. And the apple leaf midge is another insect that causes damage in nursery stock.

This is why PPO’s scientists are searching for environmentally-friendly remedies for both pests. In both cases they are working with pheromones but the approaches are different.

Larvae black vine weevil gnaw at roots

The larvae of the black vine weevil are most damaging. These larvae live beneath the soil surface and gnaw at the roots until the roots die. And this of course results in the plant dying as well.

Nematodes, minute worms, are effective against the larvae: growers sprinkle the nematodes near the trees, the nematodes enter the soil, penetrate the larvae and kill these. The fairly high costs of this method are a drawback. Another problem is that some larvae will always be remaining; these will develop into adult weevils which will again be laying large amounts of eggs.

Weevils are attracted by pheromones

This means that a method to kill the weevils themselves is also required. There are products that kill the weevils but these are not permitted in the field. This is the reason why the researchers have – together with colleagues of Plant Research International – developed pheromones that attract the weevils. They put these pheromones - together with the insecticide – in a lure. This is how the weevils are controlled without the product getting into the environment. The researchers are testing these lures in growers’ fields. Research is also being carried out into a biological variant, a fungus that kills the black vine weevil.

Luring apple leaf midge with pheromone

The researchers have found a pheromone that lures males of the apple leaf midge. As soon as these make their first flight, they are lured into traps that are placed in the field. Growers know that they need to start spraying as soon as their numbers exceed a certain threshold value. This means that the grower only needs to spray when really needed and the population is prevented from building up.

Difficult point for growers is that they need to check regularly and that they must know when spraying needs to be carried out. The researchers are passing their knowledge about this on to advisors who are visiting growers.