12 DECTDUOITS FRUIT INSECTS AND INSECTICIDES. 



METHODS AND NATURAL FACTORS IN CONTROL. 



The study oi the hfe habits of the pear thrips, as already given in 

 detail, explains why certain artificial remedies are not entirely effect- 

 ive, and it also suggests other methods. Adults ai)pear suddenly in 

 late February and early March. They enter the opening buds and 

 feed largely in protected places, and always on newly developing plant 

 tissue. Destruction to buds can be accomplished in aver}" few days — 

 it may be in less than a week. The fully developed wings of the 

 insect permit of active flight and widespread distribution. Ovipo-. 

 sition, extending through several weeks, permits of a widespread and 

 a continuous feeding period for the new brood. Eggs are safely placed 

 within the plant tissue. Larvse feed largely in protected places while 

 on the tree, and then seek shelter and spend many months in the 

 ground. An individual of the species will spend about eleven months 

 in the ground and one on the tree, although the whole period of infes- 

 tation cf trees by adults and larvse may be about three months. 



SPRAYS. 



Exposed thrips, both adults and larva^, can be killed by several of 

 the contact insecticides, but sprays have not proved successful, be- 

 cause the spray mixture can not be forced into the very tender l)uds 

 and blossoms where the thrips are, without injuring the plants, and, 

 besides, all of the thrips can not be reached by a single spraying. It 

 was found in the limited experiments of 1905 that thrips could be 

 killed over any given area, but that within a few days the infestation 

 would be as bad as though no spraying had been done. This is 

 accounted for by the presence of those thrips which escaped the spray 

 and by the new individuals which had migrated into the orchard. 



It would be impossible for all persons to accomplish their spraying 

 within the few days when the thrips are arriving on the trees. Larvae 

 are more easily killed than adult thrips, but as they feed largely within 

 the leaf clusters they, too, are protected. Spraying to kill larva^ would 

 necessarily be done after the serious injury from adults had been 

 efl'ected. It might be possible to obtain some results by applying a 

 poisonous spray, but the ever newly unfolding leaf surface, upon 

 which the insects could feed and which would not be poisoned, would 

 render this kind of spraj^ almost useless. 



CULTIVATION. 



There is some ground for believing, although the evidence is not 

 conclusive, that thorough cultivation will figure largely as a mea,ns of 

 control for the pear thrips; but even here the treatment must cover 

 areas of considerable extent. Thrips larva^ in the ground are mostly 

 within reach of the plow, bemg usually found within 5 inches of the 

 surface, although a few may go deeper. On uncultivated areas they 



