42 



CIRCULAR 270, U.S. DEPARTMENT OP AGRICULTURE 



Figure 50.— "Work of the apple fruit miner. 



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 



The pear slug is very easily controlled and does not become a pest 

 if any arsenicals are used on pear trees in the spring for other insects. 



If the slug is the only insect 

 present, an application of 

 lead arsenate at the rate of 2 

 pounds to 100 gallons of wa- 

 ter is very effective, or lead 

 arsenate or hydrated lime 

 may be used as a dust. 



PEAR LEAF WORM 



Round or oval holes, half 

 an inch or more m diameter, 

 are sometimes found in pear 

 leaves in late April or in 

 May. A close examination 

 will usually show a green 

 worm stretched along the 

 edge of each hole, feeding 

 on the leaf (fig. 52). This 

 is a pear leaf worm (Gym- 

 nonychus californicus Mar- 

 latt). The young worms first make small holes in the leaves, grad- 

 ually enlarging the holes as they feed around and around them. A 

 single worm will consume about one fourth of a Bartlett pear leaf 

 during its fife, and when the worms are 

 numerous the trees may be partially de- 

 foliated. This insect occurs throughout 

 the Pacific Northwest and in California. 



LIFE HISTORY 



The adult insects are sawflies similar in 

 appearance to those of the pear slug, but 

 somewhat more slender and with some 

 yellowish markings. They emerge from 

 the ground early in April and cut slits in 

 the lower surfaces of the partly unfolded 

 leaves, in which the eggs are laid. The 

 wounds often cause the leaves to become 

 deformed. The small green worms hatch 

 in 10 days or 2 weeks and feed as described 

 above. Growth is attained in about 4 

 weeks, when the mature worms, which 

 are about one half inch long, drop to 

 the ground and spin tough brown cocoons 

 among the leaves or in the soil within an 

 inch or so of the surface. Here they remain until the following 

 April, as there is only one generation a year. 



Figure 51.— Pear slug and its injury. 

 About twice natural size. 



