Science Into Practice - Rhynchites attraction

The apple fruit rhynchites has increased in apple and pear orchards and if not controlled can give rise to corky scars on fruit. It can be controlled but requires treatment during or after blossom, which is undesirable. A sensitive monitoring trap is needed to direct insecticide treatments.

HDC project TF 209, being managed by Bethan Shaw at East Malling Research, aims to determine whether the weevil uses a sex or aggregation pheromone for attraction and when and by which sex it is produced. A preliminary attempt to identify candidate compounds by electrophysiology and chemical analysis will be made.

In the first year of the project, attempts to find out whether monitoring traps can be baited with live male or female weevils to attract the opposite sex were unsuccessful. But some important observations of the way the weevil causes damage to apples were made.

It was found that females sometimes lay eggs inside apple fruitlets, implying that the weevil is able to breed and increase in apple orchards, which may explain why high populations are sometimes found in orchards remote from wild hosts. It was also observed that after laying an egg in a fruitlet, the female then partially severs the fruitlet stalk (peduncle) with her rostrum, rather like the strawberry blossom weevil does to strawberry. This may explain why scientists have previously been able to find egg-infested fruitlets in the orchard. They drop to the ground and the larvae must develop inside.

The latest work is concentrating on collecting volatiles from males and females to see whether any sex-specific compounds that might be pheromones are produced.

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