The Bulletin. 15 



Natural Enemies. 



It is always of interest to know what forces Nature of her own accord 

 summons to aid us in the control of a destructive insect, and this knowl- 

 edge becomes the more important in the case of species like this, which 

 are ordinarily overlooked by the grower, or which, while capable of 

 great injury, do not usually appear to be of sufficient importance to 

 call for definite treatment. 



Weather. Probably the most important natural check to insect in- 

 crease generally, is the vagaries of the weather — the spells of heat or 

 cold, moisture or dryness. Just to what degree the weather controls 

 the Oyster-shell Scale we do not know, but we do know that in North 

 Carolina the chief month for the hatching of the spring brood of young 

 is April, and as April is notoriously a month of heavy showers, sudden 

 changes and frosts, we must believe that the newly-hatched young are 

 hampered considerably by the fickleness of the weather during their 

 early life. We believe that heavy showers at the time when the tiny 

 young are crawling wash off hundreds of them and leave them to 

 perish on the ground. Sudden gusts of wind must blow away many 

 more, and though by this means a few may find lodgment on other 

 trees (and thus spread the infection) still the majority which happen 

 to be blown off the trees must inevitably perish. But as before stated 

 the extent to which the weather conditions aid us is uncertain. 



Birds, like the winds, play a double role, some species devouring the 

 scale-insects, while the same birds (or others) serve as a means of 

 accidentally carrying the young crawling insects to new trees. Such 

 small tree-inhabiting birds as the chickadees, brown creepers, tufted tit, 

 kinglets, and warblers, are known to eat the seale-insects and individual 

 cases have been placed on record where single birds have eaten large 

 numbers of them. Yet so far as most of our birds are concerned the 

 Oyster-shell Scale is too small to be noticed, or is so concealed by the 

 scale itself that it is overlooked, and we can not regard birds as an 

 efficient means of controlling this pest. 



Fungous and Bacterial Diseases no doubt contribute somewhat to the 

 control of this scale, though to what extent Ave do not know. They are 

 known to exert some influence in the case of San Jose Scale and the 

 Gloomv Scale, but definite data as to their activity against the Oyster- 

 shell Scale is not known to the writer. 



Parasitic and Predaceous Insects, however, are known to play a very 

 definite part in the control of the species, and it is possible to form some 

 intelligent idea of their efficiency, which is certainly considerable at 

 times. We may divide these into three classes: (1) Parasitic insects of 

 the order Hymenoptera, (2) Lady-beetles and their larva?, and (3) 

 Mites. 



The exact species of parasites which infest the Oyster-shell Scale in 

 this State are not yet fully known,* but it is known that these parasites 

 are very actively at work, and that in some cases at least, they are a 



^Specimens of parasites bred from infested twigs and submitted to Washington proved to be ex- 

 clusively of the species Aphelinus mytilaspidis. Quaintance and Sasscer mention seven species among 

 those "more commonlv found." 



