8 BULLETIN 1032, V. S. DEPARTMENT OF AGEICULTURE. 



another by these leaves drifting from place to place over the bog in 

 and on the water which sometimes collects during the winter time. 

 Instances were noted in which numerous egg-bearing leaves had been 

 washed into a corner of a bog, where they almost covered the vines. 

 These eggs, being the first affected by rising temperatures, were the 

 first to hatch in the spring, and the young larvse had almost com- 

 pletel}^ destroyed the surrounding uprights before eggs elsewhere in 

 the bog had hatched. 



It^cubatiox and Hatching. 



The first signs of incubation are noted as the black head and tho- 

 racic shield of the developing lar\^a begin to show through the chor- 

 ion or eggshell. As development progresses the young lars^a may be 

 seen to move within the egg and finally, as it grows in vigor, to rup- 

 ture the egg wall at a j)oint over its mandibles and gradually escape 

 by means of a wriggling sidewise motion through this slitlike open- 

 ing, which is near the top of the upper surface of the egg. (Fig. 

 1, 5, c.) It usually takes from about 3 to 5 minutes for the larva to 

 free itself entirely from the eggshell. 



Factors IxMFLrENciNG Hatching and Development. 



(a) Temperature. — Temperature has the greatest influence on the 

 fireworm eggs as well as on the other stages. This varies more than 

 is generally supposed among different bogs, depending upon location. 



(5) Depth of vines. — Another very important factor which tends 

 to retard or hasten development of fireworm eggs is the depth of the 

 vines in which they are deposited. A bog with thin vines will warm 

 up more readily in the spring and maintain a higher temperature 

 generally throughout the season than a bog with rather thick vines. 

 Observations show, for instance, that on bogs with thin vines, hatch- 

 ing generally starts during the first warm, days of spring (sometimes 

 late in March or in early or mid- April), reaches its maximum early 

 (say towards the latter part of April), and produces moths in maxi- 

 mum numbers in the middle or late part of June. On a thickly vined 

 bog, in the same locality, however, and under similar conditions of 

 temperature and moisture, hatching, while it may start about the 

 same time as it does on the thinly vined bog, will be only desultoiy 

 until the vines have warmed up considerably. Hatching in maximum 

 numbers may not take place then until the middle or latter part of 

 May. This in the absence of a winter flooding distributes hatching, 

 on bogs with a medium or heavy growth of vines, over a considerable 

 period. 



(c) Drainage. — During the winter or rain}^ season more or less 

 water usually accumulates on the majority of the cranberry bogs 



