22 BULLETIN 438, U. S. DEPARTMENT OF AGRICULTURE. 
diluted to 1 to 2,000. This time the check twig was sprayed with 
clear water. An examination on April 29 showed that all the larve 
sprayed with nicotine were dead, while those sprayed with water 
were alive. 
Control by cultivation is not successful. The Washington orchard 
in which the spraying was done was kept well cultivated all summer, 
the soil being in a finely pulverized condition and a dust mulch being 
maintained for the conservation of moisture. The orchard had been 
kept in this condition for several years. The cultivation evidently, 
as a measure of control, had but little effect on the cocoons in the 
soil. Many of the cocoons are located too near the trunk of the 
tree to be susceptible of mechanical injury by the teeth of the culti- 
vator, but aside from this they are tough and resist rough treatment, 
and moisture seems to be an indifferent agent, as indicated in Table 
I (p. 7), pertaining to moisture conditions. 
SUMMARY. 
The pear leaf-worm (Gymnonychus californicus Marlatt), so far as 
is known, is a native of the Pacific coast. 
Its original host is probably some one or more wild species of plants 
related to the pear, such as the service berry (Amelanchier), thorn 
apple (Crataegus), or mountain ash (Sorbus). As to cultivated plants, 
its selection of food is restricted to the different varieties of pears. 
There is only one generation each year. The adult or parent saw- 
flies issue in March and April, the female sex greatly predominating. 
Eggs are inserted into the pear leaves, the resultant larve or worms 
feeding upon the foliage for an average period of 3 weeks. The 
larve may be found on the leaves during April and May, and in 
Washington the season is perhaps 10 days or 2 weeks later than in 
California. Upon acquiring full growth the larve drop to the ground 
and bury themselves in the topmost inch of soil (a few go as deep as 3 
or 4 inches) and weave around themselves a brown, oval, tough cocoon 
in which the insect remains for slightly over 10 months, at first as 
larva and later for a period of 2 or 3 weeks as a pupa. At the end 
of the pupal stage the adult issues from the cocoon and comes forth 
from the ground, and thus the cycle is completed. 
Injury is confined to the foliage of the hosts and is done almost 
entirely by the larva or worm, the presence of which is readily 
detected by the characteristic circular holes it eats in the leaves. 
Generally it is of sight economic importance, but in cases of severe 
attacks trees have been defoliated and have suffered badly. 
What few natural enemies the insect has are quite unable to control 
it. Artificial remedies are correlative with those used against the cod- 
lng moth and also agaist the pear-thrips larva, and these are 
respectively as follows: 
