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Rhynchites weevil (Rhynchites aequatus (Linnaeus))

Adult Rhynchites weevil

Fruitlet showing characteristic feeding damage caused by an adult apple fruit Rhynchites weevil

The apple fruit rhynchites is a local but destructive pest of apples which has been increasing in importance  in recent years so monitoring is advisable. Hawthorn is the normal host but apple and occasionally pear, plum and cherry can be attacked.

Adults are readily recognised  being reddish-brown and having a typical long weevil snout. 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.

At the base of some holes, single eggs may be laid. These hatch after a week or so and the larva feeds on the surrounding flesh, becoming fully grown in about 3 weeks. They then drop to the ground and eventually pupate in the soil, each within an earthen cell. There is apparently one generation per annum.

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.

Control 

  • Experience has shown that a spray of thiacloprid (Calypso) at late blossom or early fruitlet gives good control of adults and prevents further damage.
  • It is probable that other insecticides such as indoxacarb (Steward or Explicit) are also effective but the efficacy of different products has not been explored.
  • Sprays of other broad-spectrum insecticides that control adult weevils are also likely  to be effective if applied at this time.
  • Use of synthetic pyrethroid insecticides should be avoided as they are harmful to the orchard predatory mite Typhlodromus pyri and other natural enemies.
  • If effective control measures are not applied, the apple fruit rhynchites weevil can build up to high levels and cause serious damage (> 50% fruits infested).
  • It can be very destructive in organic orchards where the only effective control measure is likely to be a spray of pyrethrins (Spruzit).

 

Insecticides approved for use on apple that are likely to offer incidental control of apple fruit rhynchites weevil adults. No products have a specific label recommendation for the pest.

Choice of insecticides – efficacy factors

Active ingredient Trade name (examples) Class Recommended by the manufacturer for control of – Safety to Typhs 
deltamethrin Decis etc. pyrethroid Aphids, suckers, capsids, caterpillars, codling and tortrix moths, sawfly harmful
pyrethrins Spruzit extract from pyrethrum Aphids, apple blossom weevil, caterpillars, scale insect, spider mites harmful
thiacloprid Calypso chloronicotinoid aphids safe

Choice of insecticides – Safety factors

  Hazards1 Harvest interval(days)  Max. no. sprays Buffer zoneWidth (m)
Anticholin-Esterase?  Humans Fish &aquatic life Bees
deltamethrin no h,i ed d 0 none stipulated 50
pyrethrins no h,i ed d 0 4 50
thiacloprid no h, i h h 14 2 30
Key:     1d=dangerous, ed=extremely dangerous, h=harmful, i=irritant

 

Control in organic orchards

If effective control measures are not applied, the apple fruit rhynchites weevil can build up to high levels and cause serious damage (> 50% fruits infested).

  • It can be very destructive in organic orchards where the only cultural control  measure is to manage alternative hosts. However, it seems that although infestations are often associated with adjacent hawthorn, this is not always the case.
  • It is probable that apple fruit rhynchites weevils may be controlled in organic orchards by one or more sprays of pyrethrins (Spruzit) targeted against adults after blossom. Pyrethrins (Spruzit) is approved for use in organic orchards but permission should be sought from certification bodies before use.