Progress towards forest bug control

18 Mar 2024
2nd instar nymphs are camouflaged on tree bark copyright Jonathan Michaelson

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.

What damage does the forest bug cause?

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.

 Forest bug damage to Gala apples

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 (Figure 1).

They can also squeeze their 3 mm, 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 (Figure 2), 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.

There is only one generation of forest bug per year and only spring control measures are generally used before or after flowering, to target the overwintering nymphs before they start to feed. With fewer effective control products available than ever before, a novel management strategy needs to be found.

The project

Methods to rear forest bug in the laboratory have been developed

NIAB secured a Defra Farming Innovation Programme grant in 2022 to begin a two-year project to study the biology and control of forest bug. Collaborating with the University of Greenwich and industry partners Agrovista, Avalon Fresh and Russell IPM, orchards have been sampled for the pest and methods to rear it in the laboratory have been developed (Figure 3), whilst entrainment methods have been used to collect components of its sex pheromone. 

The University of Greenwich is analysing their composition with the intention of synthesising them for use as a chemical lure in monitoring traps.

Once synthesised, prototype dispensers for these lures will be manufactured and developed within a monitoring trap.

Additional work is in progress to develop the optimum design of trap which could be deployed once the lure is fully developed. The use of chemical repellents in the field is also being investigated. If successful, this might lead to the testing of a ‘push-pull’ approach to control which NIAB has previously achieved with capsid pests in strawberry.

This article originally appeared in the Autumn 2023 edition of NIAB’s Landmark magazine. Landmark features in-depth technical articles on all aspects of NIAB crop research, comment and advice. You can sign up for free and get Landmark delivered to your door or inbox:

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