Appendix. 135 



Even the moths are captured, while on the wing, by bats and probably 

 many fall a prey to birds, both while at rest during the day and while 

 on the wing at night. At least fifteen species of insects, one hair snake, 

 a fungous disease, a bacterial disease and many species of birds are known 

 to prey upon the codling moth during some stage of its existence, and yet 

 it ranks as the most destructive apple pest. 



The idea of controlling crop pests by their natural enemies is a popular 

 one; and there are not lacking enthusiasts who advocate, with little reason, 

 the introduction of this or that particular enemy, or the ai'tificial culture 

 and use of one already present, as a cheap and efficient method of con- 

 trolling the codling moth. 



In July, 1898, nearly eighty per cent of the larvae infesting the Waxen 

 apples on a certain tree were killed by disease. Two distinct types of 

 disease were noticeable; one a fungus which produced a solid or mummified 

 condition of the larvae; the other evidently a bacterium which induced 

 decay. I was, at first, impressed with the belief that organisms which 

 naturally produced such a great mortality among the larvae of the codling 

 moth might be successfully used in orchard practice; but when early in 

 August, the mortality diminished to about five per cent or less, while the 

 larvae were much more abundant, and there was thus more opportunity 

 for the spread of the contagion, I abandoned the idea. It was only too 

 evident that the organisms were too dependent upon favorable conditions 

 for their development, to be reliable agents in insect warfare. Spraying 

 the trees with cultures of these diseases might give good results under 

 certain circumstances; but the results, being so dependent upon conditions, 

 would be uncertain and the practice therefore unsafe. In all economic 

 work with diseases of insects, two conditions have been found essential 

 to success; the climatic conditions must be favorable for the development 

 of the disease and the insect must be gregarious. The first condition 

 cannot be controlled; the second does not exist in this particular instance, 

 the larvae being not only solitary .n their habits but deeply buried in the 

 fruit. I, therefore, do not believe the use of disease germs in controlling 

 codling moth can be made practical. 



I fully agree with Slingerland* that "the most eflicient aids to man in 

 controlling the codling moth are birds. * * * Any one who tries to 

 collect the apple worm on the trunks of trees in early spring, will be sur- 

 prised to find how many empty cocoons there will be. Usually, however, 

 a tell-tale hole through the back into the cocoon explains the absence of 

 its occupant. Our observations lead us to agree with Riley and Walsh 

 that 'almost all the cocoons of the moth that have been constructed in the 

 autumn on the trunks and limbs of apple trees, are gutted before the 

 spring opens.' * * * One finds such an astonishingly large number of 

 empty cocoons that it would seem as though the birds must get the larger 

 proportion of the worms which go into nibernation in the fall." Probably 

 the flickers and nuthatches should be given first rank as codling moth 



* Bui. 142, Cornell Expt. Sta. 



