CONTROL OF WATTLE «A(;\VORM. 2!M> 



moth larvae in Europe and to the polyhedral wilt disease of 

 g-ipsy moth larvae in America. Some specimens of diseased 

 bag'worms were sent to Dr. Glaser, the American authority on 

 wilt disease, and he wrote back to me that the larvae were 

 undoubtedly affected with polyhedral wilt disease. 



A larva aifected by thivS disease can be recognised by the 

 distended appearance of its body and by its pale colour. If 

 such a larva be pricked with a needle a drop of milky white 

 fluid will issue from the puncture thus made, quite different 

 in appearance from the colourless blood that issues from a 

 similar puncture made in a healthy individual. Under the 

 high power of the microscope this white fluid is found to 

 contain myriads of minute, highly refractive bodies known as 

 polyhedra. These polyhedra are mostly square or triangular 

 in outline, and have slightly rounded corners. They measure 

 0'5 ^ to 2'5 jj. across, the average breadth being about 1'5 p-. 

 They orig-inate in the nuclei of the tracdieal matrix, hypoder- 

 mal, fat and blood cells, and are, according to Glaser, probably 

 reaction bodies belonging' to the nucleoproteids. The nuclei 

 containing- these bodies swell up enormously and eventually 

 burst, setting' the polyhedra free in the blood. Thus the 

 tissues disintegrate and the blood becomes crowded with the 

 l)olyhedra, which gives it the milky appearance mentioned 

 above. At this stage the larva dies, the alimentary canal 

 disintegrates, the colour of the body changes to a deep brown, 

 and the corpse finally dries up until it is nothing but a scale 

 adhering to the side of the bag. At no stage in the disease 

 is the body filled with a brown fluid, the skin does not break 

 easily at a touch, nor does the diseased larva hang by its 

 prolegs. In these respects the disease differs from the wilt 

 disease of gipsy moth cater]nllars, silkworms and other larvae. 



Many experiments with this disease liaA^e been carried out 

 at Cedara, but only two will be mentioned here. The bodies 

 of several larvae that had died of wilt were emulsified in sterile 

 water, and this fluid was sprayed on to some wattle foliage by 

 means of an atomiser. This infected foliage was fed to fifty 

 bagworms, and in the course of three weeks all died of wilt. 

 In all these experiments only those caterjjillars Avhicli showed 

 typical polyhedral bodies in their blood were considered to 

 have died of wilt. The first larva to die of the disease died 

 ten days after being fed on the infected foliage, but the 

 majority of them died in the third week from the commence- 

 ment of the experiment. In a control cage containing fifty 

 bagworms that had been fed on cdean foliage only eight died 

 of wilt disease. 



In another experiment the emulsified bodies of ten larvae 

 in two hundred cubic centimetres of sterile water were filtered 

 first through a filter paper and then through a Berkefeld filter. 

 This filtrate, which was quite free of polyhedra and bacteria, 

 was sprayed on to wattle foliage as before and fed to fifty 

 bagworms. Within five weeks twenty-seven died of wilt, the 

 first one dying seventeen days after the commencement of the 

 experiment, Ijut the great majority died during- the fourth 

 week. In the control cage only ten of the larvae died of wilt. 



