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Ministry of Agriculture, Food and Rural Affairs

Pear Slug

Pear slug and damage Pear slug and damage Pear slug and damage Pear slug damage Pear slug and damage Pear slug and damage Click to enlarge.

Beginner

This pest affects:

Pear;

Scientific Name
 Caliroa cerasi

Identification
Eggs

  • Pale to almost colourless
  • Oval, sometimes slightly flattened at one side
  • 0.9 mm long and 0.5 mm wide
  • Laid just under the leaf surface, appearing like a small blister on the leaf

Larvae

  • When first hatched 1.2 mm long and 0.5 mm wide at the broadest portion; body pale and free from slime; the head light brown
  • As soon as the small slug begins to eat, the particles of green leaf tissue show through its body
  • The slug secretes a coat of slime soon after hatching and then appears dark olive-green, with a dark brown head
  •  Newly moulted larvae are yellow until the slime is secreted
  • Growth is very rapid at first
  • When fully mature, the larva loses the slimy covering and is orange-yellow. At this stage, it is 8-12 mm long and has 10 pairs of legs

Pupae

  • 5.8 mm long, 2.4 mm wide and lemon-yellow

Adults

  • Glossy black and yellow wasp-like insect, about 5 mm long
  • Four transparent wings

Damage
The first signs of damage are little yellow spots on the leaves of the tree from young larvae feeding. With continual feeding, these spots will merge together causing the leaf to look bleached. Eventually, mature larvae feed on the surface of the leaves and skeletonise them by removing all leaf tissue except the fine network of veins. On heavily infested trees, the leaves will turn brown, wither and drop.

Damage from both generations can reduce fruit size at maturity. If the second generation causes extensive defoliation of trees, bloom may be reduced the following spring.

Often confused with
Wasp –Sawflies belong to the same family as wasps and bees. The adult is small, black-bodied with the ventral side and legs yellow in colour

Slug –Larvae of pear sawfly secretes a slimy olive-green coating over its slug-shaped body, though not a true slug

Moth (Lepidoptera) caterpillars –Sawflies have five or more pairs of abdominal prolegs, while caterpillars have four or fewer. These prolegs do not have rows of hooks on the bottom as do the prolegs of caterpillars. Sawflies also have only one pair of ocelli (primitive eyes), whereas caterpillars can have more than one pair

Period of Activity
Adults emerge in late spring. Feeding damage can occur summer to early fall.

Scouting Notes
In spring, shortly after pears or cherries have come into full leaf, examine leaves for olive-green, slug-like larvae covered with slime on the leaf. Re-inspect in late July or August for the summer generation.

Thresholds
No thresholds currently established in Ontario.  This is considered a minor pest of pears.

Advanced

This pest affects:

Pear;

Scientific Name
 Caliroa cerasi

Identification
Eggs

  • Pale to almost colourless
  • Oval, sometimes slightly flattened at one side
  • 0.9 mm long and 0.5 mm wide
  • Laid just under the leaf surface, appearing like a small blister on the leaf

Larvae

  • When first hatched 1.2 mm long and 0.5 mm wide at the broadest portion; body pale and free from slime; the head light brown
  • As soon as the small slug begins to eat, the particles of green leaf tissue show through its body
  • The slug secretes a coat of slime soon after hatching and then appears dark olive-green, with a dark brown head
  •  Newly moulted larvae are yellow until the slime is secreted
  • Growth is very rapid at first
  • When fully mature, the larva loses the slimy covering and is orange-yellow. At this stage, it is 8-12 mm long and has 10 pairs of legs

Pupae

  • 5.8 mm long, 2.4 mm wide and lemon-yellow

Adults

  • Glossy black and yellow wasp-like insect, about 5 mm long
  • Four transparent wings

Damage
The first signs of damage are little yellow spots on the leaves of the tree from young larvae feeding. With continual feeding, these spots will merge together causing the leaf to look bleached. Eventually, mature larvae feed on the surface of the leaves and skeletonise them by removing all leaf tissue except the fine network of veins. On heavily infested trees, the leaves will turn brown, wither and drop.

Damage from both generations can reduce fruit size at maturity. If the second generation causes extensive defoliation of trees, bloom may be reduced the following spring.

Biology
Hosts include American mountain-ash, cherries / plums, common pear, hawthorns, plum, quince, serviceberries.

Adults usually emerge over a prolonged period in the late spring. After mating, the female pear sawfly inserts eggs into the lower surface of the leaf tissue. The eggs hatch 9-15 days later and the larvae begin feeding on the upper surface of leaves. It takes 3-4 weeks for the larvae to pass through five instar stages. Each larva has the capacity to damage many leaves before they become adults, though the 5th instar larvae do not feed. Before pupation, the head of the larva widens and the body tapers toward the back. The larvae secrete a slimy green substance which covers the entire body; this is what gives it the slug-like appearance. When mature, larvae drop to the soil and overwinter as pre-pupae in a cocoon. There is usually one generation of pear slug; however, in some years, a  second (summer) generation may finish development before winter.  The damge from this generation is usually more severe, sometimes retarding tree growth the following year.

Period of Activity
Adults emerge in late spring. Feeding damage can occur summer to early fall.

Scouting Notes
In spring, shortly after pears or cherries have come into full leaf, examine leaves for olive-green, slug-like larvae covered with slime on the leaf. Re-inspect in late July or August for the summer generation.

Thresholds
No thresholds currently established in Ontario.  This is considered a minor pest of pears.

Management Notes
No special sprays are needed – the cover sprays applied for the common pests of pears will control it. This insect does not cause direct fruit damage.

Some information included above excerpted from: