Rhynchites weevil – additional information
The apple fruit rhynchites weevil is a local but destructive pest of apples which has been increasing in importance in recent years.
Hawthorn is the normal host but apple and occasionally pear, plum and cherry can be attacked.
Many commonly grown apple varieties are susceptible. The scab resistant apple variety Saturn is highly susceptible.
- It is widespread and though local in apple orchards is normally associated with hawthorn. The pest is more common in organic orchards and orchards that do not receive regular insecticide treatments at or after blossom
2.5-4.5 mm long; wing cases (elytra) reddish brown and hairy; head and thorax darker, strongly punctured and with a purplish to bronzy sheen.
Up to 4 mm long; whitish, with the brownish head retracted into the swollen prothoracic region.
0.7×0.5 mm; whitish and translucent.
Other pests with which rhynchites weevil may be confused
Apple blossom weevil (Anthonomus pomorum)
The adult apple blossom weevil is a small beetle, 3.5-6.0 mm long, with a long snout, dark brown to black, covered with brown, greyish and whitish hairs and mottled, with a V-shaped mark across the elytra and a prominent whitish spot between the elytra and thorax.
- It does not have the chestnut red colouring of apple fruit rhynchites.
- It tends to occur earlier in the year though adults can persist through blossom and the new generation of adults emerges in mid-summer.
Apple bud weevil (Anthonomus piri)
The adult of the apple bud weevil is very similar in appearance to the adult apple blossom weevil, but is a lighter, brown colour, and lays its eggs in the autumn and early spring.
- The apple bud weevil is local and rare in the UK and until recently was only recorded on apple though a recent local outbreak has occurred on pear in north Kent.
- It is an important pest of pear in continental Europe.
- The larva infests buds which are hollowed out remaining as dead husks in which the larva is found.
Apple twig cutter (Rhynchites caeruleus)
- A locally common weevil that occurs on apple but the adult is metallic blue in colour and appears much later in May and June causing characteristic shoot severing damage.
- During blossom and early fruitlet development, the adult weevils drill small cylindrical holes into the flesh with their rostrum.
- Numerous holes may be made in one fruitlet or in a group of adjacent fruitlets by a single weevil. Feeding can continue till July.
- In AHDB Horticulture Project TF 209, adult females were found to lay single eggs inside apple fruitlets. After laying an egg in a fruitlet, the female weevil then partially severs the fruitlet stalk with her rostrum, rather like the strawberry blossom weevil does to strawberry.
- These hatch after a week or so and the larva feeds on the surrounding flesh, becoming fully grown in about 3 weeks. The fruitlets then drop to the ground, leading to yield loss.
- Fruitlet damage can be serious and is very characteristic.
- On apple there may exceptionally be 100 or more holes in a single fruitlet but more likely several or many neighbouring fruitlets will each have a small number of holes, each damaged fruit potentially being down graded.
- Attacked apples remain marked and distorted, although the holes tend to close up as the fruitlets grow.
- Adults can be seen feeding on fruitlets during and after blossom and are readily collected by beating.
- Growers should also tap-sample nearby hawthorn and blackthorn hedgerows, to assess the risk of weevil damage.
Damage to fruits during the growing season, at harvest or during grading
- Damage occurs gradually as weevils feed over a period of weeks during and following flowering.
- Fruitlets can be readily inspected for damage.
- If significant fruit puncturing damage to fruits is seen one season, treatment the next season to avoid damage intensifying is likely to be justified.
No forecasting methods have been developed for this pest.
- Targeted control measures, levelled at both males and females as they prepare to mate, would reduce rhynchites numbers at the beginning of the season.
- Experience has shown that a spray of thiacloprid (Calypso) at late blossom or early fruitlet gives good control of adults and prevents further damage, but Calypso is no longer authorised for use on apple. Another neonicotinoid acetamiprid (Gazelle) can still be used on apple and may give some incidental control when applied against aphids, but this has not been fully explored.
- As weevils are still found in the trees until fruit have reached about 20mm, treatments could also target females looking for sites to lay eggs. Most of the feeding damage would have already been caused by this stage for the current year, but such treatments could reduce the numbers of weevil offspring emerging the following year.
- Fatty acids (Flipper) has an EAMU approval on apples and is recommended to control apple blossom weevil so it is likely that it would offer incidental control of rhynchites weevil when applied for blossom weevil.
- It is probable that other insecticides are also effective but the efficacy of different products has not been explored.
- Use of synthetic pyrethroid insecticides should be avoided as they are harmful to the orchard predatory mite Typhlodromus pyri and other natural enemies.
Resistance of apple fruit rhynchites weevil to insecticides is not known and is unlikely to occur.
- Trees could be carefully searched and adults removed and destroyed after blossom but this would be labour intensive.
- Hawthorn is the main host but the weevils are only able to complete their development on trees/hedges that flower and bear haws.
Around the world several organisms are know to attack various Rhynchities spp.
- In the USA, Rhynchities spp. larvae are parasitized by ichneumonid wasps of the genus temelucha.
- In laboratory studies it has been possible to infect Rhynchities spp larvae with the nematode Steinenernema feltiae.
- The larvae died within 3 days.
Both trichogrammatid and braconids have been reared from the eggs of Rhynchites spp.
- Parasitized eggs change in appearance, the chorion becoming opaque, yellowish, thickened and wrinkled.
- The existence of these parasitoids of Rhynchites spp. provides potential biological control agents.
However, as there is a lack of biological and ecological information on these parasitic species and how to exploit them, it may be difficult to apply them in a practical situation.