Fruit tree pests

The apple blossom weevil is one of the best known members of its family. It is widespread in England and Wales and often very common where apples are grown. It is much rarer in Scotland and Ireland. The apple blossom weevil is a dark ashy red colour, with two broad oblique greyish stripes towards the end of each wing case – the two stripes together forming a somewhat flattened V shape.

Apple blossom weevils come out in spring from behind loose bark, leaf debris and other sheltered spots where they have hibernated. They live almost exclusively by feeding on young apple leaves, in which they make small holes. Occasionally they attack the leaves of pear trees.

The female bores a hole into an unopened blossom bud with her long rostrum, then turns round and deposits an egg into the hole. Each female lays about 50 eggs. Soon a pale grub with a dark brown head hatches and eats its way into the bud, gradually destroying it so that it turns brown and never opens. The grub then eats away the base of the flower and after about two weeks is fully grown and ready to turn into a white pupa. As with many weevils, the pupal stage is short; it takes only seven to ten days before the adult bites its way out and starts to feed on the leaves. At this stage in its life the young adult does not make holes in the leaves but rasps at their tissues, skeletonizing them with its tiny jaws. This takes place mostly during the hours of darkness.

After about a month the weevil disappears to hibernate, emerging again the following spring to feed on the leaves, this time making the familiar round holes.

Birds, especially the tits, are important predators on apple blossom weevils. The ichneumon wasp Pimpkipomorum parasitises both the larvae and the pupae, but the proportion of parasites is never enough to make a really big difference in a concentrated population of weevils in an orchard. After all, it is not in the parasite’s interests to destroy its host. Modern control of the apple blossom weevil is effected by careful spraying with one of the organophosphorus compounds.

14. November 2011 by Dave Pinkney
Categories: Featured Articles, Woodlands | Tags: , , , , , , , , , , | Comments Off on Fruit tree pests

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