ROUNDHEADED APPLE-TREE BORER. 



11 



Table III.— Period of incubation of the roundheaded apple-tree borer at French 



Creek, W. Va. 



Dates on which eggs were laid. 



Dates on which eggs hatched. 



Number 

 of eggs. 



Number 

 of days re- 

 quired to 

 hatch. 





June 28 





14 



June 12 



do 



16 







16 



Do.. 



June 26. . . 



17 



June 10 



June 23. . „ 



June 29 



13 





16 



Do 



June 30 



17 



Do 



July 2 



19 









Average period of incubation 16 days. 



As is shown in Table III, the minimum and maximum periods of 

 incubation were 13 and 19 days, the average for the 8 eggs being 16 

 days. Evidence was obtained that hatching is retarded by low and 

 accelerated by high temperatures. 



THE LARVA. 



The larva (PL V, A, B) is a cream-colored, footless grub, with 

 brown head, blackish mandibles and a conspicuous patch of small, 

 brown tubercles on the posterior half of the broad, flattened dorsal 

 surface of the first thoracic segment. The intersegmental con- 

 strictions are deep and the dorsal and ventral surfaces of the first 

 seven abdominal segments are elevated and roughened. The sides 

 of the body are sparsely covered with short, stiff hairs. When full 

 grown, the length is from 30 to 40 mm., the females being consider- 

 ably larger than the males. According to Becker (14) there may be 

 as many as six larval instars. 



DEVELOPMENT AND FEEDING HABITS OF THE LARVA. 



The behavior of the larva varies as affected by individual char- 

 acteristics, difference in size, vigor, and species of host trees, and dif- 

 ference in localities, so that no one description of the larval develop- 

 ment will apply to all. In the latitude of West Virginia the activi- 

 ties and growth of the larva when feeding under normal conditions 

 in apple are about as follows : The larva begins to feed at once after 

 leaving the egg and soon eats out a broad, irregular, usually more 

 or less circular burrow around the point where the egg was laid. 

 At this stage of its life growth is rapid and the borer soon forms a 

 broad, elongate gallery under the bark which may extend in any 

 direction away from the point first attacked. As winter approaches 

 there is some tendency to burrow downward to or beneath the soil, 

 but this is by no means general. 



At first the feeding is all in the bark and the point of injury usu- 

 ally shows from the outside as a dark, slightly depressed spot from 



