Forest bug
Progress towards forest bug control NIAB’s Francis Wamonje and Scott Raffle outline how a research project is developing new knowledge to improve its management in orchards. Since the withdrawal of the broad-spectrum insecticide chlorpyrifos in 2016, growers and agronomists have been finding increasing numbers of new insect pests in apple and pear that had previously been controlled. In some cases, insects that had not been considered as pests for a generation or more of fruit growers, have gradually been reappearing. The forest bug (Pentatoma rufipes) is one such pest. Like many other shield bug species, such as brown marmorated stink bug, forest bugs produce a sticky defensive secretion with a strong smell which can contaminate fruits such as raspberry and cherry, but the bug is considered to be harmless outside of harvest time. It may even provide benefits to growers through feeding on other pests, such as caterpillars and aphids. However, in apple and pear, the pest can be rather more damaging.
Overwintering forest bug nymphs (2nd instar) feed early in the season on developing buds, flowers, and fruits (shortly after flowering). The nymphs are particularly difficult to detect as their bodies appear similar to the tree bark and are well camouflaged. They can also squeeze their 3mm, small, flattened bodies into the cracks and crevices of tree bark to find some shelter from the cold. Their feeding only becomes apparent long afterwards when developing apples and pears become distorted and pitted, and the flesh becomes discoloured. Brown lesions develop in the fruit flesh at the site of the forest bug stylet insertion, and the lesions harden, giving the fruit a ‘stony’ texture at harvest. Fruit losses of 10% at harvest are common but occasionally, much higher levels of 40%-50% damage have been reported, so management and control measures are becoming increasingly necessary. 2nd instar nymphs are camouflaged on tree bark ©Jonathan Michaelson
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