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 larvse 

 sprayed with nicotine were dead, while those sprayed with water 

 were ahve. 



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 califomicus 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 larvas or worms 

 feeding upon the fohage for an average period of 3 weeks. The 

 larvse 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 l^arvse drop to the ground 

 and bury themselves in the topmost inch of soil (a few go as deep as 3 

 or 4 mches) 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 fohage 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 shght economic importance, but in cases of severe 

 attacks trees have been defohated 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- 

 ling moth and also against the pear-thrips larva, and these are 

 respectively as follows : 



