Pear Slug

picture: bugguide
Pear Slug.
  • Binomial Name:                                           Caliroa cerasi.
  • Family:                                                       Tenthredinidae.
  • For the first couple of years my dwarf pear tree was infested with pear slugs, but last year after using a monthly aerated compost tea foliar spray on the plant, the pear slug stayed away.
  • This may have been a coincidence and some other factor caused the slugs to stay away.
  • I will take extra precautions this year including:-
    • Thoroughly cleaning up debris from beneith the tree, to remove pupating sawfly larvae in leaf litter and mulch.
    • Using horticultural glue to stop the female sawfly from crawling up the trunk to mate and lay eggs.
Why Pear Slug is a Pest.
  • The pear slug is the larva of the sawfly, Caliroa cerasi.  They are not slugs but are a kind of insect of the family Tenthredinidae. 
  • They eat the leaves of pear trees, leaving behind skeletonised foliage.  If left uncontrolled, this will eventually lead to a substantial stripping of the trees canopy and decline of the tree's overall health.
  • The larvae cover themselves in green slime, making themselves unpalatable to predators. 
  • When the larvae are fully grown, they drop off the tree onto the ground and pupate underground or in leaf litter/mulch. 
  • The adult sawfly emerges from the cocoon and climbs from the soil to mate.  It lays eggs on the leaves of the host plant, completing its lifecycle.
  • Because the female sawfly climbs the tree to mate and lay her eggs, horticultural glues can be used as a protective barrier.
Pest Control. 
  • The simplest think to do with sawfly larvae is to keep washing them of the trees foliage with a hose whilst still imature.  This is fine with a dwarf tree like mine, but a bit of a task with a full sized pear tree.
  • It is good practice to clear all debris from under the tree in winter.  Dispose of the debris in a hot compost or bury it 500mm under soil where it will not be disturbed for some time.  This will help remove some of the larvae pupating during the colder months.
  • Apply masking tape to the trunk of the tree about 100mm above the ground and apply a ring of horticultural glue around the tree on top of the masking tape.  This stops the adult female sawflies from crawling up the tree to mate and lay eggs.
  • The masking tape protects the bark of the tree from the glue, and makes it easy to replace the glue when it becomes covered in dust or dead insects. 
  • Spray the foliage with aerated compost tea every month during the growing season.  This seems to increase the plants resistance by toughening up the leaves or possibly supplying a microbial predator.  
  • It remains to be seen whether the good results last year were as a result of the compost tea spraying program or some other environmental factor.