Pear or Cherry Slug
Caliroa cerasi (L.)
Family: - Tenthredinidae
Order: - Hymenoptera
Description: It is a larvae of the sawfly family. The larvae cover themselves in green slime, so they look like slugs and make themselves unpalatable to predators. The name sawfly refers to the saw like ovipositor they use to slice leaves iso the eggs may be laid inside the leaf.
Colour - Shiny black
Body - 5-6.5 mm long
Wings - Transparent
Thorax - Divided from the abdomen by a distinct waist.
Colour - Yellow-green covered in shiny black slime
Body - Covered in slime. 7 pairs of prolegs. Final length 10 mm.
Pupa - Underground in an earthen cell.
Eggs - Oval. Hyaline yellowish. About 0.5 mm long.
The fully grown larvae drop from the tree to the ground and pupate underground. The adult sawfly emerges from the pupal case and climbs from the soil to mate and lays eggs on the leaves of the host plant. The female uses its terebrant ovipositor to lay its eggs below the upper epidermis of the leaf. Usually only one egg is laid per leaf but there may be up to 3 or more. Each female can lay 150 eggs. The egg absorbs moisture from the leaf and swells to form a white blister. The larvae hatches about a week later and breaks out of the egg case and leaf blister. The larvae are yellow and about 1 mm long at this stage. One to two days later it starts secreting the shiny blackish slime that smells like ink. The slime covers the dorsal surface giving it the appearance of a slug. The larva browses the upper surface of the leaf without perforating it, leaving veins and lower epidermis intact. The leaf becomes completely skeletonised. When crowded the larvae may also feed on the underside of leaves. The larva develops over 3-4 weeks and may consume 4 leaves. The last instar is not covered with slime and when fully grown drops to the ground. It penetrates the soil and pupates inside a brown earthen cell a few centimetres below ground level. A week or two later the adult sawfly emerges. They quickly mate and the female makes it to the tree to start ovipositing. There are more females than males and they live for about a week to a fortnight. There is often about 5 generations per year. In spring a generation takes about 6 weeks and the final generation hibernates.
Some believe the adult sawflies can fly from the ground to the tree tops.
Habitats:Stone fruit and pear orchards.
Origin and History:Distribution:
Significance:Worldwide pest of Pears, Cherries, Plums, Almonds and stone fruit.
Also feeds on Birch, Oak, Roses and Willow.
Skeletonise leaves of trees.
May reduce growth of trees, defoliation and cause premature fruit drop.
Management and Control:Historically lead arsenate and cryolite was used for control. A range of insecticides including spinetoram, carbaryl, methidathion and azinphos-methyl are used for control these days
Thresholds:Pear slug infestations can often be seen from the distance by the light coloured feeding patches contrasting with the green leaves.
Related Species:Perga species are the large black or brown grubs that cluster on eucalypts.
Ants, bees and wasps are in the same Hymenoptera order.
CSIRO. The Insects of Australia. Melbourne University Press. (1991)
Avidov, Z. and Harpaz, I. (1969) Plant Pest of Israel. Israel University Press. P459
Evans, J.W. (1943) Insect pests and their control. P23, P58
Acknowledgments:Collated by HerbiGuide. Phone 08 98444064 for more information.