24 CIRCULAR 3 92, U. S. DEPARTMENT OF AGRICULTURE 



bees have been flying freely and dysentery has subsided. Infected 

 bees usually perform their normal duties until they are too weak to 

 continue. The shortened life of infected bees weakens or kills the 

 colony. 



SYMPTOMS SHOWN BY THE COLONY 



The first noticeable symptoms shown by a colony heavily infected 

 by Nosema apis are increasing restlessness of the bees and a weaken- 

 ing of the colony. When only a small number of bees are infected, 

 the loss may be so gradual that it is not noticed. At other times the 

 death rate among adult bees is very high, and the colony dwindles 

 rapidly. The queen usually is among the last handful of bees to 

 die. Nosema disease may appear annually at about the same time. 

 During any time of year, however, colonies with bees infected by 

 N. apis may be found that show no noticeable loss. 



SYMPTOMS SHOWN BY INFECTED BEES 



In the individual bee the symptom most commonly observed is 

 inability to fly more than a few yards without alighting. Many bees 

 will be seen crawling on the ground, on the bottom board, at the 

 entrance, and on the top of frames when the cover is removed. Some- 

 times infected bees crawl actively long distances from the hive, or they 

 may crawl up blades of grass in an effort to fly. At times they collect 

 in small groups on the ground in front of the hive. 



It is mostly the older workers that are killed, although drones, 

 queens, and young workers may be attacked. At times the disease 

 seems to be aggravated by periods of cold, damp weather, particu- 

 larly in the spring when the bees cannot fly freely. 



The legs of affected bees may be dragged along in crawling, as 

 if paralyzed; and the rear wings may be unhooked from the front 

 wings and held at abnormal angles. Such bees are capable of only 

 feeble fanning with the wings. The abdomen is often distended 

 with feces and may appear shining or greasy. 



APPEARANCE OF THE INTESTINAL TRACT 



The intestinal tract of bees infected by Nosema apis is frequently 

 swollen and discolored. When favorable specimens are at hand, this 

 symptom can be used for diagnosis in the apiary. If the bees are alive, 

 or have just died, the entire intestinal tract can be removed as follows: 

 Remove the head and hold the thorax with the thumb and forefinger, 

 then grasp the tip of the abdomen with a pair of forceps and pull 

 gently. By this procedure the entire intestinal tract can frequently 

 be withdrawn from the abdomen. 



In healthy bees the long, cylindrical mid-intestine is usually of a 

 brownish-red, yellowish, or grayish- white color. Circular constric- 

 tions show for nearly the entire length of the intestine and the tissues 

 are fairly tough and of a healthy appearance. When Nosema disease 

 is present, the mid-intestine swells but finally shrinks to about normal 

 size. Heavily infected intestines are usually of a dull grayish white, 

 and some or all of the circular constrictions disappear. The tissues 

 become soft and watery and are more easily crushed than are the 

 tissues of healthy intestines. The fluid that flows from heavily in- 



