ROUNDHEADED APPLE-TREE BORER. 



13 



FORM OF BURROWS IN PEAR DIFFERS FROM THAT IN APPLE. 



It was frequently noted that the borers in pear trees formed dif- 

 ferently shaped burrows from those made in apple. In pear the 

 burrow is much more elongate, often being a slender gallery 6 or 8 

 inches in length and extending around the trunk, sometimes almost or 

 entirely encircling trees several inches in diameter. As the larva? in 

 pear near maturity they enter the wood and pupate much as in apple. 



PERIOD SPENT BY LARVA IN THE TREE. 



Ever since the roundheaded apple- tree borer began to attract the 

 attention of entomologists there has been some disagreement as to 

 the number of years spent by the larva in the tree. Practically all 

 writers have agreed that the life cycle requires either two or three 

 years for completion. Most of the well-known textbooks on general 

 entomology, as well as the systematic treatise on this particular 

 species, give three years as the life period. Comstock (4, p. 573) 

 says "It requires nearly three years for this larva to attain its 

 growth." Smith (5, p. 209-210) , speaking of the larva, says " In the 

 spring of the third year [it] changes to a beetle." Felt and 

 Joutel (6) give a three-year period in the tree. Saunders (8) says 

 " It is generally conceded that the larva is three years in reaching 

 maturity." Sanderson (12) says " The third spring the larvae trans- 

 form to pupae." Siingerland and Crosby (13) state, "It is generally 

 believed that it requires three years for this apple-borer to complete 

 its life cycle," Lutz (15, p. 359) says, "From egg to adult takes 

 three years." Chittenden (7) gives a three-year life cycle. O'Kane 

 (11) says "The larva requires three years for maturity." Both 

 Smith (10, p. 52-54) and Patch (9) give a three-year larval period. 

 Becker (14) says "Saperda Candida has a two-year life cycle in the 

 Ozarks," but points out that " There seems to be some indication that 

 occasionally a larva may require three years for its development." 



The present investigation has shown that the length of the life 

 cycle averages longer in the North than in the South and also that 

 this period may vary several years in length in a given locality. 

 Table IV shows the years required for 121 insects to reach maturity 

 at French Creek, W. Va. 



Table IV. — Period of life cycle of the roundheaded apple-tree borer at French 



Creek, W. Va. 





Year beetles issued. 



Number years in tree. 





1 



2 



3 



4 



5 



1913 





 



2 

 

 



9 

 11 



7 



36 

 40 





 2 



1 



10 

 2 





 

 

 1 

 







1914 







1915 







1916 







1917 













Total 



2 



1.7 



103 

 85.1 



15 



12.4 



1 

 0.8 















