315 



is only rarely, however, that any of the scale insect pests of 

 citrus plants there become numerous enough to require spraying 

 or other remedial treatment, and this is due to the presence, 

 under suitable conditions, of the natural enemies which are 

 able to keep these pests within bounds. 



The purple scale {Lepidosaphes heckii Newman), the white 

 scale {Chionaspis citri Comstock), and the green scale [Coccus 

 viridis Green) are the principal scale insect pests of citrus plants. 

 These of course are attacked to a considerable extent by parasitic 

 and predaceous insects, but it seems likely at the present time 

 that the completeness of their control is more largely due to 

 the activity of the red-headed fungus {Sphœrostilhe coccophila 

 Tul.), white-headed fungus {Ophioncctria coccicola E. and I'2.), 

 and the shield scale fungus {Cephalosporium lecanii Zimmermann). 

 The belief that the parasitic fungi are the more efficient or- 

 ganisms in the control of scale insects in Dominica is based on 

 the fact that in that island the climatic conditions are generally 

 very favourable to the development of fungi, and as a result 

 the natural control of scale insects is fairly complete. In those 

 islands possessing a drier climate the fungi have less favourable 

 opportunities for growth and development, and the control 

 by natural enemies is much less complete, even though parasitic 

 insects may occur to the same or even to a greater extent than 

 in Dominica. In wet seasons and in damp situations, however, 

 instances have been found, even in the dry islands, of fairly 

 complete control of scale insects by these parasitic fungi. 



Another very interesting example of complete control is 

 to be found in the case of the cotton worm {ÄIaba)na argillacca) 

 in St. \'incent." During the past ten years a very consider- 

 able area has been planted in cotton in St. Vincent, and 

 although the cotton worm has been known to be present in 

 that island for the greater part of that time, there is no record 

 of its ever having become numerous enough to cause any loss 

 to cotton planters or serious injury to cotton plants. This 

 is rather remarkable, since in the adjoining small islands of the 

 Grenadines and in St. Lucia, wiiere cotton has been grown on 

 only a comparatively small scale, the cotton worm has appeared 

 as a serious pest. 



The insects which appear to be responsible chieth" for the 



