Insect Pests of Saskatoons

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This Week
  Apple curculio | Saskatoon sawfly | Wooly elm aphid | Prairie tent caterpillar | Leaf rollers |Saskatoon bud moth | Plant bugs | Cherry shoot borer | Hawthorn lace bug | Cecidomyiid midges | Pear slug

An important part in the production of any fruit crop is to know what type of insects could cause production losses. A crop is at risk throughout the fruiting cycle. Insects can attack plants during flowering, fruit formation or just before harvest of the plump, juicy berries. A successful pest management program includes: insect identification; pest number and damage monitoring; what population numbers warrant control and knowing when the pest can be effectively controlled.

Apple Curculio
(Tachypterellus quadrigibbus)


  • 5 mm long, reddish brown weevil with a long curved snout
Life cycle
  • adults appear 5-10 days after petal fall
  • adults lay eggs, one per fruit, about 28-33 days after the peak flowering period
  • egg laying punctures on the young fruit are at the base close to the stem
  • the puncture is sealed with excrement
  • larval development takes less than 31 days, pupation less than 7 days
  • larva feed on the developing seed in the fruit
  • adults emerge from fruit mid July
  • adults drop to ground and overwinter in leaf litter
  • there appears to be no feeding after emergence
  • misshapen, hard fruit

Apple Curculio on a Saskatoon

Apple Curculio egg in a
Saskatoon berry

Saskatoon Sawfly
(Hoplocampa montanicola)

  • adults are a 6 mm long sawfly with yellow with brown markings
  • mature larvae are 6 mm long with yellow-brown head
Life cycle
  • appears in May, just prior to maximum flowering (25% bloom)
  • lay eggs in the nectaries of flower blossoms, the position is marked externally by a dark scar along the calyx of the flower
  • one egg is laid in each flower
  • eggs hatch after petal drop
  • the larvae feed on the top of developing fruit
  • on average, one larva will ruin 2 fruit per cluster
  • the last fruit attacked is completely hollow
  • mature larva drop out of the fruit at the end of June
  • overwinters in the soil
  • pupates in the spring

Immature sawfly larva

  • can cause large numbers of fruit to drop
  • more than 90% of the potential fruit crop can be lost
  • causes fruit to be hollow and mummified

Wooly Elm Aphid
(Eriosoma americanum)

  • blue-black in color with white woolly masses on posterior end
Life cycle
  • overwinters on an elm tree as an egg
  • the egg hatches into a "stem" mother; which moves to the leaves, where she starts feeding
  • without mating, the stem mother gives birth to live young
  • while feeding, the aphid injects fluid into the elm leaves, causing the leaves to curl and galls to form
  • approximately the time the wild roses and lilacs bloom, aphids move from the elm tree to the roots of the saskatoon and establish colonies there
  • in the fall, the aphids return to the elm tree to lay eggs for overwintering
  • heavily infested saskatoons may fail to leaf out in spring
  • moderately infested saskatoons may leaf out in spring, but will not grow vigorously
  • may have small chlorotic leaves
  • once exposed to hot weather, the plants die
  • seedlings and plants less than 5 years old seem to be most affected

Winged Wooly Elm Aphid

Wooly Elm Aphid in roots of Saskatoon

Prairie Tent Caterpillar
(Malacosoma c. lutescens)

  • adults are stout bodied moths, chocolate brown to dark buff in color with two whitish bands across the front wings
  • wingspan of 30-40 mm
  • the caterpillar has a black back with a whitish middorsal stripe
  • the sides of the caterpillar body are light blue with sparse hairs
  • the cocoon is multi-layered and yellowish white
Life cycle
  • the eggs are laid at the base of host plant, within 30 cm of ground
  • they are covered with a frothy substance
  • they hatch in the spring with a flushing of host foliage
  • the caterpillar construct silken nest near fork in stem
  • when feeding, the caterpillar move out from nests leaving a trail of silk behind
  • they return to the nests at night or during bad weather
  • they feed for 6-8 weeks, depending on the weather
  • then spin a cocoon and emerge in about 3 weeks
  • one generation per year
  • the caterpillars spin webbed tents around leaves and branches of host plant
  • they feed inside the tent
  • repeated defoliation results in a setback of fruit production

Leaf Rollers
(Archips argyrospilus/Choriostoneura rosaceana)

  • a diverse group of moths
  • the caterpillar is slender, green to brown, 12 mm in length with a dark-brown or black head
  • usually very active and moves backwards when disturbed
Life cycle
  • the eggs are laid on leaves
  • the larvae change from pale green to greyish brown as they mature
  • the larvae roll a leaf around their body to pupate
  • could be 2 generations per year
  • holes are eaten in leaves, later the leaves are folded in half and webbed together, which causes the leaves to turn brown and die
  • leaf rolling includes the fruit, resulting in lower yields

Fruit-tree Leafroller

Fruit-tree Leafroller in pupate

Saskatoon Bud Moth
(Epinotia bicordana)

  • the adult is a small greyish-black moth with tinges of brown
  • the larva is a light green to whitish worm, with dark head
Life cycle
  • adult emerges in April, lays eggs at bud base and in crevices of bark
  • larvae hatch in late April to early May
  • larvae burrow into the buds around the time of flower bud break (green tip) to tight bud cluster
  • they feed on the interior of flower buds
  • as the insect matures, they web individual flowers in the flower cluster together and continue feeding
  • larva numbers of 1 or more per bud cluster are common
  • larva development is complete shortly after the flower petals fall

Bud Moth

Bud Moth Larva

Plant Bugs
(including the tarnished plant bug Lygus lineolaris)

  • adults are 5-6 mm long, 2.5 mm wide and flattened
  • they are pale green to reddish-brown in colour with a distinct triangle or "V" mark 1/3 way down back
  • they are difficult to see because they fly or move rapidly
  • young nymphs are dull blue-green
  • they look similar to aphids, but lack cornicles and move much faster
Life cycle
  • adult overwinters under debris or plant cover along fence lines
  • in the spring, they feed on early growing plants
  • they mate, then migrate to crops suitable for feeding
  • egg laying begins as early as mid May (in south) to mid June (in Peace country)
  • nymphs develop into adults in 12-34 days, depending on the temperatures -- the hotter the weather, the faster they develop
  • they are strong flyers
  • when feeding, the Tarnished Plant Bug punctures the plant tissue and sucks the sap

Cherry Shoot Borer
(Argyresthia oreasella)

  • small, silver white moth with dark gold markings
  • present in June and again in late July to mid Aug
  • the light green caterpillar is 7 mm when full grown
Life cycle
  • overwinters as an egg on leaf buds
  • the larva tunnel into young shoots in May
  • the larva exits the stem, then pupates
  • late May or early June--new green shoots wither and die
  • look for a small hole at the base of the stem and cut open, then look for light a green caterpillar

Hawthorn Lace Bug
(Corythucha cydoniae)

  • the adult is oval or rectangle in shape
  • it has a lace-like appearance and the head is covered with a hood
  • the larvae are identical to the adults, just smaller

Hawthorn Lace Bug eggs on Saskatoon leaf

Life cycle
  • the eggs are laid in early spring on leaf underside
  • the eggs hatch in 3 weeks, then the larvae feed on the leaves
  • the adults emerge in mid summer
  • the second generation completes its development by early fall
  • overwinters as adult in leaf litter
  • mottling of foliage
  • leaves become leathery and tend to drop prematurely
  • will also leave dark, tarry excrement drops on the leaf underside

Cecidomyiid midges
(Cecidomyia sp.)

  • the adult is a slender fly
  • the larvae are small, legless maggots
Life cycle
  • little is known of the life cycle
  • finger-like galls on the leaves
  • they do not cause serious damage to the host plant

Pear Slug
(Caliroa cerasi)

  • green-black, slug-like larva
  • adults are a shiny black sawfly and house fly size

Pear Slug damage to Saskatoon

Life cycle
  • two generations per year
  • adults lay eggs in slits in leaves
  • larvae rasp away the leaf surface
  • skeletonized leaf turns brown and dries up
  • feeding damage occurs in June and again in late August
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For more information about the content of this document, contact Shelley Barkley.
This information published to the web on November 27, 2001.
Last Reviewed/Revised on November 14, 2017.