534 ANNUAL. REPORTS OF DEPARTMENT OF AGRICULTURE. 



cation of poisonous spraj'S, are undertaken, the cultivation of this 

 important crop must be abandoned. The practice of growing onions 

 by starting them in sets seems to be one of the chief causes of injury 

 by thrips. Some injury may be prevented by dipping sets, before 

 transphinting, in nicotine sulphate at about the same strength as 

 used in spraying. Clean methods of cultivation, including prompt 

 destruction of remnants, and the stimulation of plants by means of 

 fertilizers and irrigation where possible, are among the best forms 

 of farm procedure. In some localities the observance of these meth- 

 ods serves to hold the insect in check; in others it is also necessary 

 to spray. 



Reports upon a number of Texas insects belonging to this class 

 have been submitted and accounts will be published. 



OTHER INVESTIGATIONS ON TRUCK-CROP INSECTS. 



The onion thrips just mentioned is by no means confined to Texas, 

 but occurs also in Colorado, and recent reports of injury have been 

 received from Stark County, Ind. The estimate of loss in the latter 

 locality was $30,000 for 1910 in the vicinit}'^ of the town of Knox 

 alone. The same insect also occurs in the vicinity of the District 

 of Columbia, and studies of its habits in this locality have been begun. 



WORK ON INSECTS AFFECTING CITRUS FRUITS. 



As during the previous year, the work on insects affecting citrus 

 fruits has been carried on under the supervision of Mr. C. L. Marlatt. 

 The principal items have been the continuation of the white-fly in- 

 vestigations, work upon the orange thrips in California, and the com- 

 pletion of the hydrocyanic-acid gas fumigation in California. 



WORK ON THE WHITE FLY IN FLORIDA. 



With the conclusion of the main features of the life-history studies 

 and fumigation experiments on the white fly, summarized in previous 

 reports, problems connected with insecticides and the mechanics of 

 spraying as adapted to Plorida conditions have been made the subject 

 of especial study. The agents of the Bureau, however, have con- 

 tinued the very important experiments leading to natural control by 

 bacteria and fungi, and have cooperated with growers in conducting 

 fumigation on a large scale. 



Experimental work and observations during previous years with 

 parasitic fungi have demonstrated that under normal climatic and 

 favorable grove conditions the fungi are capable of effecting in a 

 ^feries of years about one-third of a complete remedj'^, and that they 

 can be very readily introduced artificially into groves infested with 

 the white fly. The main line of investiL^ation during the past year 

 has been to determine to what extent the natural efficiency can be 

 increased by frequent artificial introductions of spores by spraying 

 at stated periods throughout the summer and early fall. This work 

 has not given encouraging results. The amount of fungus present 

 at the end of the season in no instance was enough greater than that 

 developing under normal conditions in unsprayed surrounding trees 

 to warrant from a practical standpoint the time expended in the 



