308 Report of the Department of Entomology of tut; 



NATURAL ENEMIES. 



Plant lice have a number of predaceous and parasitic enemies and 

 fungus diseases which exert a marked restraining influence upon the 

 increase of the pests. The twice-stabbed lady-beetle 

 (Plate XXIV, figs. 5, 8), aphis lions (Plate XXIV, figs. 

 9, 10) and the larvae of syrphus flies (Plate XXIV, 

 figs. 6,7) are common and efficient enemies of the insects. 

 Aphids are also subject to the attacks of a parasite which 

 develops within the body of the host. Under favorable 

 weather conditions fungus attacks appreciably reduce 

 the numbers of the lice. During periods of inclement 

 weather the work of the insect enemies of plant lice is 

 noticeably retarded and the aphids increase rapidly, 

 but with the advent of fair weather the insect enemies 

 become abundant and the aphids are correspondingly 

 lessened in numbers. Useful as are these predaceous 

 and parasitic insects they only limit the extent of the 

 damage and do not prevent the aphids from developing 

 in destructive numbers. If perfect immunity is de- 

 sired, the work of these natural agencies should be 

 supplemented by active measures on the part of the 



Fig. 4i.- Aphids on grower 



o p e n i n g bud; 

 period for spray- 

 ing. 



SPRAYING DIRECTIONS. 



Experiments conducted by this Station during the 

 last three years indicate that plant lice are most vulnerable to sprays, 

 (1) when the aphids are appearing on the green tips 

 of the buds, and (2) when the leaves have unfolded 

 but have not been curled by the lice, which is usually 

 just before or immediately after blossoming. In some 

 of the tests thorough applications of sprays during 

 these periods have afforded protection to the trees. 

 To what extent these treatments will afford immunity 

 from later attacks of the insects in years when lice 

 are superabundant has not so far been determined. 



This phase of the problem is still under investigation. 

 But on the basis of the experimental work conducted 

 in the past, the following suggestions are offered to 

 fruit-growers as a guide for future spraying operations 

 in an effort to protect their orchards from these insects. 

 1. Spraying for newly hatched lice. — Especial pains 

 should be taken to destroy the pest at this stage as 

 thorough work greatly reduces the subsequent 

 numbers of the lice and may simplify later spraying 

 operations. The best means of killing the newly 

 hatched lice is a treatment during a period when the 

 tips of the buds show green and while the buds are still 

 compact. (Fig. 41.) It is important to spray early, for if the treat- 

 ment is delayed the aphids obtain protection in the fuzzy, unfolded 



Fig. 42. 



Ap 



too far advanced 

 for aphis spraying. 



