57 



the scale insect eggs and feeds upon them. Generally, only 

 one parasite grub is to be found under each scale, but in a 

 few instances two have been seen. 



When its growth is finished, the parasite changes from 

 a fat, whitish grub to a pupa which, when first formed, is 

 light-coloured, and later is almost black. At the completion 

 of the pupal stage the adult Zalophothrix emerges through 

 a round hole in the back of the scale insect. 



An abundance of scales punctured in this way indicates 

 an efficient percentage of parasitism, but it must be remem- 

 bered that such scales are dead and that the parasites have 

 left them. Other full-grown scales on the same plant will 

 probably contain the grub or pupa of the parasite. 



In the event of an attack of black scale occurring 

 in a field of young cotton, it would be advisable to 

 introduce the parasite in order that the control of the scale 

 might be begun as soon as possible. Old cotton plants in 

 which there is an abundance of black scale should be pulled 

 up after the cotton is reaped, and piled in the field for two 

 weeks before they are burned or otherwise destroyed. This 

 will give the nearly mature parasites an opportunity to 

 emerge, and being winged, they will be able to fly into 

 adjoining wild land in search of scales in which to deposit 

 eggs ; many of the scale insects will die for want of food as 

 the plants become dry, since they are not able to travel far, 

 and the few that succeed in establishing themselves on other 

 plants will in all probability become so severely attacked 

 by parasites that they will be practically killed out. 



Fig. 56. White scale on cotton. 

 About 1% times natural size. (Original.) 



