12 



BULLETIN 1238, U. S. DEPARTMENT OF AGRICULTURE 



Table 2. — Hatching of eggs of the fall cankerworm from egg masses collected 

 in the field, Wallingford, Conn., 1919 and 1920. 



FROM 31 EGG MASSES, 1919. 



Date. 



May 1 



May 2 



May 3 



May 4 



May 5 



May 6 



Num- 

 ber of 

 eggs 

 hatched 



226 

 152 

 200 

 833 

 1,003 

 599 



Temperature. 



Maxi- 

 mum. 



F. 

 54 

 70 

 73 



77 

 89 

 66 



Mini- 

 mum. 



F. 



38 

 45 

 48 

 47 

 52 

 43 



Aver- 



' F. 

 46.5 

 57.4 

 58.1 

 61.4 

 65.2 

 53.0 



May 7. 

 May 8. 

 May 9. 

 May 10 

 May 11 

 May 12 



Num- 

 ber of 



hatched 



378 

 48 

 2 

 2 

 1 

 1 



Temperature. 



Maxi- 

 mum. 



F. 

 54 

 78 

 52 

 47 



Mini- 

 mum. 



F. 



45 

 52 

 47 

 40 

 41 

 42 



Aver- 

 age.! 



F. 



50.1 



62.0 



50.5 



42.6 



44.0 



46.0 



FROM 6 EGG MASSES, 1920. 



May 11 

 May 12 

 May 13 

 May 14 



150 



66 



49 



54.7 



190 



66 



44 



56.0 



168 



57 



47 



50.5 



88 



54 



45 



48.7 



May 15 

 May 16 

 May 17 



28 



64 



46 



12 



71 



43 



20 



74 



47 



54.8 

 58.1 

 60.6 



1 This column represents the average of hourly temperatures recorded by the thermograph. 



In hatching, the larva gnaws a hole in the cap of the egg, usually 

 including most of the area within the dark circle. Sometimes the 

 hole is eaten out nearly round, but more often a small segment of the 

 circle is left at one side. The opening through which the larva will 

 emerge is about two-thirds the width of the head, so that in leaving 

 the egg, the larva usually tips its head and works it through sideways. 



In many cases, for some unknown reason, quite a proportion of the 

 eggs failed to hatch. In 1920 five egg clusters, collected in the field 

 a short time before hatching, gave only about 53 per cent of the 

 possible number of larvae. None of these egg masses were para- 

 sitized. 



HABITS OF THE LARVAE. 



The newly hatched larvae make their way to the unfolding leaves 

 and buds and commence feeding. At first they gnaw small pits in 

 either surface of the leaves, but they soon eat all the way through, 

 making small perforations here and there. The younger larvae seem 

 to have a preference for the young, tender, newly formed leaves, and 

 do most of their feeding near the tips of the rapidly growing shoots. 

 When the larvae are numerous, the leaves may be skeletonized, little 

 being left except the veins and shreds of leaf tissue. 



After the first instar, larger and larger irregular holes are made 

 in the leaves, and when the larvae are nearly full grown, they may 

 consume almost entire leaves, leaving only the midribs and larger 

 veins with a few ragged shreds of leaf tissue. Unless the larvae are 

 numerous, however, the feeding is not likely to be very conspicuous, 

 as they have a strong tendency to wander, consuming a little here and 

 there as they go. The worms also feed occasionally in the blossoms. 



When disturbed, many of the larvae drop suspended on threads. 

 Those remaining on the leaves are often hard to find, because of their 

 similarity in color to the leaves. 



