126 



PROTECTION OF PLANTS, 1916-17 



depends on the fact that the diameter of the heads of caterpillars increases 

 at successive ecdyses in geometrical progression. By measuring the diame- 

 ter of the heads at different peripds in the spring and summer and comparing 

 them with the geometric series of which .228 and .304 are the first and second 

 terms the writer reached the conclusion that there are seven larval instars. 

 The same result was obtained by Slingerland although his measurements 

 were throughout somewhat lower than those here considered. 



The following table giving these figures calculated and measured may 

 be of some interest. 



TABLE II. 



Method of Computing the Number of Instars of the Bud Moth Larva 



^ Each dimension given represents the actual measurement of a large number of cater- 

 pillars. 



Hibernation. — The bud-moth passes the winter as a half-grown cater- 

 pillar. The first cold spell towards the end of September drives the larvae 

 from their feeding nests to seek better protected quarters. It is generally 

 stated that the insect hibernates just beneath the leaf buds. While this is 

 often the case it is not invariably true, for the hibernacula may be constructed 

 in any well protected rough or angular spot on the twigs and smaller branches. 

 Old leaf scales at the base of the buds, rough scars, crotches of branches, 

 any position where bits of bark or scales afford protection, all serve as 

 convenient places for hibernation. From the cankered crotch of a small 

 branch I have collected as many as 16 hibernating larvae. Orchards there- 

 fore in which the trees are kept clean or in which varieties with naturalK' 

 smooth bark are grown offer less protection to hibernating larvae than 

 those in which the bark of the trees is rough. 



