Hymenoptera : Tenthredinidae : Caliroa cerasi

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Pear and Cherry Slug (Caliroa cerasi) is a worldwide pest that originated in Europe. Pear and Cherry Slugs aren’t Slugs − they are the larvae of a type of sawfly in the family Tenthredinidae. The larvae are leaf-chewing pests that when in large numbers, may defoliate their host plants.

Pear and Cherry Slugs are pests of several fruit trees including Cherry, Pear and Plum, as well as several ornamental plants including Cotoneaster and Hawthorn. The pest is widespread across southern Australia including New South Wales, Australian Capital Territory, Victoria, Tasmania, South Australia and south-west Western Australia.

Best Treatment for Pear & Cherry Slugs

Pear and Cherry Slugs are covered in slimy mucous to prevent them drying out (desiccating) in warm dry air. Knowing they are prone to desiccation can be your best weapon against them. If you dust Pear and Cherry Slugs with some kind of dry powder, such as wood ash, talcum powder or lime, you will see them shrivel up immediately and later die.

The trick with this pest is to try to take action against the first generation, which peaks in about November. If you act from September onwards you will be able to prevent most of the damage they are likely to cause later. You can either use the dusting method described here or if treatment is required, try Yates Success Ultra Insect Control. Mix up the product in a sprayer and apply thoroughly over the tree, ensuring spray coverage is to the point of runoff. Whichever method you choose, you need to do it early to prevent the much larger second generation of Pear and Cherry Slugs damaging your plants.

Pear and Cherry Slug attack won’t kill a tree but may significantly reduce yield in fruit trees and totally ruin the appearance of ornamental trees. Once the leaves are skeletonised and the tree is partly defoliated that tree won’t grow new leaves until the following spring. Your best bet is to act early to prevent such damage.

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What are Pear & Cherry Slugs, &
How to Get Rid of Them

You can be forgiven for thinking that Pear and Cherry Slugs are some kind of mollusc because of their slimy appearance. They are the larvae of a species of sawfly from the family Tenthredinidae, which are members of the insect order Hymenoptera – so Pear and Cherry Slugs are actually related to ants and wasps.

Description

Adult

Adult Caliroa cerasi sawflies are winged, black, glossy, wasp-like insects about 8 mm long with a wingspan of about 10 mm. They have two pairs of transparent wings.

Larva

Pear and Cherry Slugs are slimy olive-green larvae that are not obviously segmented, and their legs aren’t visible when viewed from above. They actually have 10 pairs of legs hidden under their bodies – 3 pairs of true legs and 7 pairs of prolegs. The front end of a larva is where the head is and the front end is wider than the rest of the body.

Life Cycle

Male Caliroa cerasi sawflies do not occur in Australia, so all female sawflies reproduce by parthenogenesis. All offspring produced are females, which means that every Caliroa cerasi sawfly you see can produce Pear and Cherry Slugs.

Females cut slits in leaves with saw-like ovipositors (hence ‘sawfly’) and deposit their eggs inside. Eggs on leaves look like small blisters of about 1-2 mm diameter. Larvae hatch out as tiny pale larvae and they eventually grow to their full size of about 12 mm after about 5 moults. Mature larvae usually become yellowish-orange in colour, stop feeding, and drop to the ground. Larvae dig into the soil and pupate in the ground at a depth of about 7 cm. When adults (females) emerge from the soil, they fly up into the tree and begin laying eggs almost immediately. Females lay about 50 eggs each on average.

There are usually two generations per year. Adult females emerge in the spring and lay their eggs, which gives rise to the first generation of larvae that peaks from November to December. These larvae pupate and emerge as adult females in late summer and their offspring are usually more numerous and damaging than the first generation. The larvae of the second generation may remain on the tree until the weather becomes too cold for them, which prompts them to drop to the soil and make overwintering pupation cells.

What Plants are Impacted by Pear & Cherry Slugs

 
Symptoms of Pear & Cherry Slugs

  • Upper surfaces of leaves skeletonised.
  • Damaged leaves shrivel and fall. Trees may look like they have been scorched.
  • Damage occurs first in late spring and again during late summer/autumn.

 

How to Prevent Pear & Cherry Slugs Appearing

Monitor

  • Keep an eye out for glossy black sawflies on susceptible plants.
  • Look for eggs on leaves.
  • Try to spot the first generation of larvae as soon as possible.

Prevent

  • Keep the ground under trees clear of weeds and debris, making Pear and Cherry Slugs dropping to the ground more visible to predators such as birds.
  • Pick off leaves with eggs.
  • Squash small larvae.
  • Prune off minor infestations of larvae.
  • Pear and Cherry Slugs are prone to desiccation − dust infested trees with wood ash, talcum powder or lime. You may have to do this a couple of times as it is difficult to dust all the larvae in one hit.
  • Avoid wetting leaves of susceptible plants when watering.
  • When pruning trees in winter, open up the middle of the tree to maximise air circulation.
  • Try Yates Success Ultra Insect Control that is registered for use in home gardens against Pear and Cherry Slugs. Remember to follow label directions.

Natural Enemies

  • There are no known parasites of Pear and Cherry Slug in Australia.
  • Predators such as Paper Wasps, Spiders and Birds may help reduce numbers of Pear and Cherry Slug.

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