Life cycle

• Adults emerge on sunny days around the blossom time of apple.
• After mating, eggs are laid throughout the blossom period singly in the side of the receptacle of apple flowers.
• The eggs hatch in 1-2 weeks, longer in cold weather.
• The young larva burrows into the receptacle, often just beneath the skin causing characteristic ribbon scars.
• When larvae are semi-mature, they often move to another fruitlet (often within the same truss) boring into the ovary and feeding on the pips.
• When larvae are fully fed in late June or early July, they enter the soil to form a cocoon at depths down to 25 cm.
• The larvae overwinter in cocoons before pupating 3-4 weeks before emergence the following spring.

 

Pest status

Important pest of apple. Does not attack pear. A similar species, the pear sawfly (Hoplocampa brevis (Klug)) attacks pear, but is local and uncommon in the UK.

 

Other hosts

Apple sawfly is an obligate parasite of apple and related Malus species. It has no other hosts.

 

Varietal susceptibility

Some desert varieties are highly susceptible notably Charles Ross, Discovery, Ellison’s Orange, James Grieve and Worcester Pearmain. Culinary apples, with the exception of Early Victoria and Edward VII, are of lower susceptibility to attack.

 

Distribution

Widespread and common wherever apples are grown.

Damage

• The egg-laying slit in the side of the flower soon turns brown and this is readily visible as an early sign of infestation.
• Young larvae tunnel just beneath the surface of the skin of developing fruitlets leaving characteristic ribbon scars.
• Larvae bite large cavities inside fruitlets, consuming the flesh and the seeds and producing masses of wet, brown-black frass which is exuded through a large hole in the side of the fruitlet.
• Fruitlets with ribbon scars may remain on the tree until harvest but those with more severe damage fall from the tree.
• Losses can be severe, particularly when the amount of blossom or crop set is light.

Recognition

Adult
5.0-5.5 mm long. Body mainly orange with thorax and abdomen black above. Head with a conspicuous black central patch. Wings clear with brown veins.

Egg
0.8 mm long and slightly curved; white and translucent. Inserted in the receptacle of flowers and young fruitlets. Egg insertion scars are clearly visible on side of receptacle.

Larva
Up to 11 mm. Head black (early instars) to yellowish, body whitish, tapering with 7 pairs of prolegs. Produce a characteristic defensive odour.

Pupa
In soil-coloured, parchment-like cocoons in the soil.

Other pests with which apple sawfly may be confused

Codling moth
Codling moth larvae are also found commonly feeding in cavities in the centre of apple fruits.

• However, codling moth larvae tend to occur later in the season (apple sawfly larvae have vacated fruitlets to pupate in the soil by late June or early July) and codling moth larvae tend to produce dry frass at the entrance hole in the fruit surface.
• Codling moth larvae have 5 pairs of prolegs and their abdomens do not taper to the apex.
• Sawfly larvae have 7 pairs of prolegs and their abdomens taper towards their apex.

Monitoring

Adults
White, non-UV reflective sticky traps are attractive to apple sawfly adults and can be used to monitor populations in orchards.

• Place the traps in orchards at the late green cluster to pink bud growth stage of Cox.
• Examine the traps at least weekly throughout the blossom period and count the number of sawfly adults caught.
• No economic thresholds have been determined and, in any case, these will depend on many factors including the size, design and density of traps being used.
• However, on susceptible varieties, a catch of even one or two adults per trap per week can indicate that significant losses could occur if the crop set is light.
• If adult sawflies are caught, an assessment of the number of egg insertion scars should be made in the latter part of bloom to determine whether or not a post-blossom insecticide spray for control of sawfly is needed.

Egg insertion scars

Examine 100 trusses (5 from each of 20 trees) for egg insertion scars on the side of the receptacle.

• Treatment is likely to be justified if 11 or more scars are found.

Infestation and damage at and shortly after petal fall
Inspect the young developing fruitlets for signs of infestation or damage, such as ribbon scars.

• If infestation is caught early enough, the worst effects of damage can be avoided by prompt application of an insecticide spray.

Damage during the growing season, at harvest or during grading
If significant damage to fruits is seen one season, treatment the next season to avoid damage intensifying is justified.

Forecasting

The start of the flight of apple sawfly adults can be predicted using a temperature sum of 134 day-degrees above a threshold of 4 degrees C starting from 1 April.

• Soil temperatures at a depth of 5 cm must be used.
• Air temperatures are unreliable, though they can be used to predict the appropriate timing for trap installation for which the recommended temperature sum is 157 degree days above a threshold of 4 degrees C from 15 March.

Chemical control

Chemical control should be applied where a significant risk of infestation has been determined by monitoring and not as a routine.

• The main means of control is to apply an approved insecticide at or shortly after (within 10 days of) petal fall to coincide with the start of egg hatch.
• Thiacloprid (Calypso) which was previously approved for use on apples offered incidental control, but its approval was revoked in 2020.
• Synthetic pyrethoid insecticides such as deltamethrin may also give some control of apple sawfly but are not compatible with the IPM programmes employed by most growers because they are harmful to predatory mites and many other natural enemies.
• Growers should take advice from BASIS qualified agronomists before choosing a spray control product for apple sawfly.

Insecticide resistance

Resistance of apple sawfly to insecticides is not known to occur. However, repeated use of insecticides from the same group or with the same mode of action should be avoided.

Cultural and biological control

Hygiene
Infested fruitlets, or whole trusses, which show signs of damage, can be removed from the tree when seen during larval development. However, this is very labour intensive and unlikely to be economic.

Ground herbage
Circumstantial evidence suggests that some sites are prone to the pest, possibly due to soil type or possibly the absence of a ground cover of herbage under the tree.

Natural enemies

Parasitic wasps
The ichneumonid parasitic wasp Lathrolestes ensator is an important natural enemy of apple sawfly. The parasite often regulates the pest on unsprayed garden trees where almost cyclical flare-ups of the sawfly are controlled by attacks of the parasite in subsequent years.

• The parasite only attacks late first and second instar sawfly larvae.
• The comma-shaped, black eggs of the parasite can be seen through the skin of the sawfly larva. However, the parasite egg does not hatch until after the sawfly larva has entered the soil to form a cocoon.
• Feeding and development of the sawfly larva continues normally until that time.
• The parasite has only a narrow window of opportunity to parasitise its host and unfavourable weather conditions at this time greatly limit its effectiveness.

Another parasitic wasp, Aptesis nigrocincta, is an important parasite of larvae and pupae in the soil.

Ground beetles
It is probable that larvae moving over the surface and into the soil are vulnerable to attack by predatory ground beetles, especially larger species. However, whether or not ground beetles are able to locate larvae in cocoons deep in the soil is not known.

Biological control

Attempts have been made to control sawfly with entomopathogenic nematodes as they travel to the soil to pupate with limited success.

Biotechnological control

White non-UV reflective sticky traps can be used to mass trap adults. The higher the density of traps, the greater the effect. However, it has been demonstrated that economic damage cannot be prevented even if very high trap densities (1 per tree) are used.

 

Further reading

Cross, J. V. & Jay, C.N. 1998. Effects of fungicides against apple sawfly. Report to APRC 1998, 5pp.

Cross, J. V., Solomon, M. G., et al. 1999. Biocontrol of pests of apples and pears in Northern and central Europe. 2. Parasitoids. Biocontrol Science and Technology 9, 277-314.

Graf, B., Hopli, H. U. & Hohn, H. 1996. Modelling spring emergence of apple sawfly Hoplocampa testudinea Klug. Acta Horticulturae 416, 263-271.

Miles, H. W. 1932. On the biology of the apple sawfly, Hoplocmpa testudinea Klug. Annals of Applied Biology 14, 420-431.

Olszak, R. W. & Maciesiak, A. 1996. Preliminary investigations of the control of apple sawfly with fungicides. Brighton Crop Protection Conference – Pests and Diseases 1996, 331-336

Owens, E. D. & Prokopy, R. J. 1978. Visual monitoring trap for the European apple sawfly. Journal of Economic Entomology 71(4), 576-578.

Zijp, J. P. & Blommers, L. H. M. 1997. Prediction of the flight of apple sawfly, Hoplocampa testudinea, using temperature sums. Entomologia Experimentalis et Applicata 84, 71-75.