Pear Slug,Caliroa cerasi (L.)

I. Introduction: While the larva of pear slug (PS) resembles a slug, it is actually a type of sawfly (Hymenoptera). It is usually seen in backyard or other low-spray situations.

II. Hosts: Pear, cherry (including flowering cherry); apple and plum are attacked occasionally.

III. Description: The larva of PS appears as a shining black, slug-like insect, reaching a length of ca. 1/3 inch (8-10 mm). When larvae hatch from eggs, they are white with a brown head, but soon secrete a dark coat, creating the slug like appearance. The head end is somewhat wider than the rest of the body. Larvae have seven pairs of prolegs, separating them from caterpillars, but these are obscured by the slime covering. Full-grown larvae become yellow-orange in color. The pupa is 2/10 inch long and 1/10 inch wide (5.8 mm x 2.4 mm), and lemon yellow in color. The adult is black, with four transparent wings, and about 1/5 inch (4-6 mm) long.

IV. Biology: Pupae overwinter in the soil. Adults emerge in the spring and begin oviposition on leaves. Females usually reproduce parthenogenetically. Eggs are inserted into small slits in the leaves, often 2-5 per leaf. Larvae skeletonize upper leaf surfaces. Upon completion of development (after 2-3 weeks), larvae drop to the soil and tunnel to depths of 4 inches (10 cm). Here black cocoons are formed. A second generation occurs in late summer. The second generation is most important. In some regions a partial third generation may develop.

V. Injury: Larvae feed only on pear foliage, causing a skeletonizing injury which leaves a thin area of brown tissue, often with a network of fine veins. Such injury may be extensive, especially after the second generation. If injury is severe, tree growth may be reduced in the following year.

VI. Monitoring: Observe skeletonizing injury in mid- to late-summer. No thresholds are currently available. Minor injury is acceptable.

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