ORCHARD INSECTS OF THE PACIFIC NORTHWEST 



43 





■'■■ :~i. 



Pear Slug 



The pear slug (Caliroa cerasi (L.)) feeds on the foliage of pear and 

 cherry trees, skeletonizing the leaves by eating the upper surfaces 

 (fig. 51). The larvae are slimy and sluglike in appearance, olive green 

 or almost black, and about 

 one-half of an inch long when 

 full-grown. When they are 

 numerous the whole tree be- 

 comes brown, as though 

 swept by fire. This should 

 not be allowed to happen to 

 valuable trees, as the reduc- 

 tion in the leaf surface seri- 

 ously interferes with the 

 growth of the fruit and with 

 the development of fruit 

 buds. This insect is widely 

 distributed in the United 

 States, having come in from 

 Europe. 



LIFE HISTORY 



::;-- 



miner. 



The adult insects are glossy FlGURE 50> __ Work of the apple fruit 

 black, lour - winged flies, 

 about one-fifth of an inch long. They are known as sawflies because 

 the}^ cut slits in the upper surface of the leaves, in which the eggs 

 are laid. The eggs in the leaves have the appearance of small blisters. 



The young slugs hatch in a week or two 

 and feed almost altogether on the upper 

 surface, usually avoiding any leaves that 

 may have been attacked by aphids or 

 blister mites. Just after molting the slugs 

 are yellow, but they soon secrete a slime 

 which gives them the characteristic olive 

 green or black color. Their bodies are 

 somewhat enlarged in front and taper 

 behind. The slugs complete then* growth 

 in less than a month, drop to the ground, 

 and form cells hi the soil, within which 

 they transform to adults in a couple of 

 weeks. The second brood of slugs appears 

 on the trees in August, and these, when 

 full-grown, spend the winter in earthen 

 cells from which the adult sawflies emerge 

 the following spring. 



CONTROL 



Figure 51 . — Pear slug and its 

 injury. About X 2. 



The pear slug is very easily controlled 

 and does not become a pest if any arseni- 

 cals are used on pear trees in the spring for other insects. If the slug 

 is the only insect present, an application of lead arsenate in the pro- 

 portion of 2 pounds to 100 gallons of water is very effective, or lead 

 arsenate or hydrated lime may be used as a dust. If it is necessary 



