Beginner

Scientific Names
Dogwood borer, Synanthedon scitula, and, apple clearwing moth, Synanthedon myopaeformis

Identification
Eggs:

• Laid singly on the trunk of the tree,
• Very difficult to see.

Larvae:

• Dirty white with a reddish-brown head and thoracic shield (area behind the head),
• 15 mm in length.

Pupae:

• Small,
• Yellow-brown,
• Sometimes observed as pupal cases partially protruding from the adult exit holes in the trunk or infested burr knots.

Adults:

Damage:

• Sloughing-off of bark,
• Crown die-back,
• General decline,
• Presence of borers is indicated by reddish brown frass and pupal cases on the surface of burr knots.

Often Confused With

• Wasps - Adults resemble wasps. 
• Peachtree borer - Larvae resemble the Peachtree borer which are much larger and do not attack apple.

Period of Activity
Dogwood borer begins emerging in June, with flight continuing through August and early September. Peak flight typically occurs during July. There is limited information on the life history of apple clearwing moth in North America, but data collected in Ontario (2007, 2008) indicate the moth has a single flight period beginning in late May or early June, reaching a peak in mid to late July, and ending abruptly following peak activity. 

Scouting Notes
Currently apple clearwing moth is only present at a single site in Ontario, while dogwood borer can be found in most apple growing regions.

To check for larval infestations, examine the bases of trees for 2-3 mm-wide holes and tunnels under the bark or in burr knots. Pupal cases and/or frass may be evident at the tunnel exits.

Place pheromone traps in orchards that had borer problems in previous years. Commercial lures often capture other clearwing moths, making identification critical for successful management.

Use pheromone traps to monitor for adult activity of these pests. Hang pheromone traps in the orchards before the first flight begins (mid June for dogwood borer, and mid May for apple clearwing moth). Four traps per site, placed in low scaffold limbs, are recommended. Use a minimum distance of 50 m between traps, and monitor traps twice a week.

Thresholds
Record the number of adults captured – graphing the results – to identify peak flight times. For dogwood borer apply insecticides at peak pheromone trap catch.  Currently there are no thresholds for apple clearwing moth.

Advanced

Clearwing moths are the most common borers seen in commercial apple orchards in Ontario. The dogwood borer, and recently introduced apple clearwing moth are all clearwing moths in the Sesiidae family.

Clearwing moth species attacking apple have a relatively wide host range including apple, pear, oak, dogwood, plum, apricot, peach cherry, quince, hawthorn, willow, birch and other hardwoods.

Scientific Names
Dogwood borer, Synanthedon scitula, apple clearwing moth, Synanthedon myopaeformis

Identification
Eggs are very difficult to see and are laid singly on the trunk of the tree. Larvae are 15 mm in size, dirty white with a reddish-brown head and thoracic shield (area behind the head). Pupae are small, yellow-brown and sometimes observed as pupal cases partially protruding from the adult exit holes in the trunk or infested burr knots. Adult clearwing moths possess transparent wings with striking dark markings along the margins. They are daytime flyers. There are numerous species of clearwing borer males, which are attracted to and can be caught in commercial pheromone traps. Fortunately, they are relatively easy to distinguish from one another with little training.

Moths are most active at dusk and dawn. Females lay eggs on the surface of burr knot formations, pruning cuts, and wounded bark. Once hatched, tiny larvae bore into burr knots and create shallow, irregular, winding galleries. As they feed, reddish brown frass is pushed towards the entry hole where it collects, held together by silken threads.

Larvae bore into burr knots or adventitious roots just below the graft union. Apple clearwing moth larvae tunnel under the bark anywhere on the tree where tissues have been previously damaged, including branches. Infestations are found below the graft union and under burr knots or around cankers above the graft union.

Sloughing-off of bark, crown die-back and general decline are symptoms of infestations in older trees. The presence of the borers is indicated by reddish brown frass and pupal cases on the surface of burr knots. Cut away the outer layers of bark to reveal discolouration of the underlying cambium where larvae have fed. Clearwing borers cause a slow decline in tree health and reduced yields due to the girdling cause by larvae feeding in the cambium layer. Trees are increasingly susceptible to attack by other insects and may have reduced longevity.

Often Confused With

• Wasps- Adults resemble wasps. 
• Peachtree borer - Larvae resemble the Peachtree borer which are much larger and do not attack apple.

Biology
Borers overwinter as larvae in hibernaculae within feeding galleries under the bark. Pupation occurs in the spring, emergence is often extended over several months.

Period of Activity
Dogwood borer begins emerging in June, with flight continuing through August and early September. Peak flight typically occurs during July. There is limited information on the life history of apple clearwing moth in North America, but data collected in Ontario (2007, 2008) indicate the moth has a single flight period beginning in late May or early June, reaching a peak in mid to late July, and ending abruptly following peak activity.

Scouting Notes
Currently apple clearwing moth is only present at a single site in Ontario, while dogwood borer can be found in most apple growing regions.

Check for larval infestations by examining the bases of trees for 2-3 mm-wide holes and tunnels under the bark or in burr knots. Pupal cases and/or frass may be evident at the tunnel exits.

Place pheromone traps in orchards that had borer problems in previous years. Commercial lures often capture other clearwing moths, making identification critical for successful management.

Use pheromone traps to monitor for adult activity of these pests. Hang pheromone traps in the orchards before the first flight begins (mid May for apple clearwing moth and mid June for dogwood borer. Four traps per site, placed in low scaffold limbs, are recommended. Use a minimum distance of 50 m between traps, and monitor traps twice a week. Record the number of adults captured – graphing the results – to identify peak flight times. This information is used to time insecticide sprays.  

Thresholds
Record the number of adults captured – graphing the results – to identify peak flight times. For dogwood borer apply insecticides at peak pheromone trap catch. Currently there are no thresholds for apple clearwing moth.

Management Notes

• The best way to reduce apple borers is to minimize burr knot development on trees. If possible, select rootstocks with a lower tendency for burr knot formation to reduce attractiveness to dogwood and apple bark borer. Rootstocks particularly susceptible to burr knot formation – and attack by borers – are M.9, M.26 and Mark.
• Some agricultural products such as naphthalene acetic acid (NAA) – used in thinning – increase the development of burr knots. Several cultural practices deter egg-laying activity of clearwing moths and round-headed apple tree borers.
• Use wire mesh mouse guards rather than solid guards. Borers prefer shaded, protected habitat. Solid guards restrict air circulation and prevent bark hardening, predisposing the tree to winter injury and providing good borer egg laying sites.
• Apply undiluted external white latex paint to the trunk area (by brushing, not spraying) to deter female moths from laying eggs. Paint must be reapplied annually. If applied thick enough, paint will also suffocates borers already in the wood.
• Removal of adjacent wild hosts may be required where borers have become a problem near established apple orchards. Remove and burn trees that are severely weakened or killed by borer infestations to eliminate insects still present in those trees.
• Another alternative is to insert a small length of wire into feeding holes to kill boring larvae inside. This process is very time consuming and must be repeated annually in blocks where the pest is a problem.
• Larvae feed in well-protected areas and are difficult to manage using insecticides. Pheromone traps may help time insecticide sprays used against clearwing moths.
• Refer to OMAFRA Publication 360, Fruit Crop Protection Guide - Chapter 2 Apples or Apple Calendar only :
  • Recommendations for clearwing moth/dogwood borer at Special sprays.