8 BULLETIN 431, U. S. 0EPABTMKNT OF AGBICULTTJBE. 



APPEARANCE OF A HEALTHY LAKVA AT THE AGE AT WHICH IT DIES OF SACBKOOD. 



The symptoms which differentiate sacbrood from the other brood 

 diseases are to be found primarily in the post-mortem appearances 

 of the larvse dead of the disease. As an aid in interpreting the 

 description of these appearances a description of the healthy larvae 

 is first made. , 



Larvse ' that die of sacbrood do so almost invariably after capping 

 and at some time during the four days just preceding the change in 

 form of the maturing bee to that of a true pupa. 



During the first two days of this prepupal period the larva moves 

 about more or less in the cell and spins a cocoon. It is then com- 

 paratively quiet for about two days, lying on its dorsal side and ex- 



FiQ. ■!.— Lateral view of healthy worker larva showiug the nornial position within the cell. For oonTen- 

 ience of description the length is divided into thirds— anterior third (AT), middle third (MT) and 

 posterior tliird (PT). Enlarged about 8 diameters. (Original.) 



tended lengthwise in the cell. At the close of this two-day period of 

 rest, as a result of the metamorphosis going on, the larva changes 

 very rapidly to a true pupa, assuming the outward form of an adult 

 bee. 



Although many larvae die of sacbrood during the first two days 

 cr active period, of the 4-day prepupal period, by far the greater 

 number of deaths occur during the last two days, the period of rest. 

 A healthy larva at this resting period of its development is chosen, 

 therefore, for description. As dead worker larvae are the ones usually 

 encountered in sacbrood and the ones almost invariably chosen ia 

 discussing the symptoms of the disease, the worker larva is here 

 described. 



The normal larva lies extended in the cell (fig. 4) on its dorsal 

 side, motionless, and with its head poiating toward the mouth of the 

 cell. Its posterior or caudal end lies upon the bottom of the cell, 



' As beekeepers usually refer to the brood at this age as "larvse," the term is used here to designate the 

 developing bee at this stage of its growth. 



