BUREAU OF ENTOMOLOGY. 535 



work. In several instances more fungus developed on unsprayed 

 trees. Observations and experiments have led to the conclusion that 

 losses resulting from the white fly attacks will be greatly reduced 

 if, in the majority of cases, the parasitic fungi are disregarded and 

 the use of direct remedial measures extended as fast as possible. 



While no specific bacterial disease of the citrus white fly or spotted- 

 wing white fly has yet been discovered, it became evident very early 

 in the present investigation that mortality among larvae and pupae 

 resulting from causes other than those recognized as attacks by 

 insect and known fungus enemies, and from overcrowding, was the 

 most important element of natural control affecting these species. 

 This heretofore unappreciated check effected by nature has been cred- 

 ited to the fungi, greatly enhancing the value of the latter. In sev- 

 eral instances the fungi have been credited with controlling the fly in 

 groves in which none of the known fungi was present, or in which 

 they were present in too small numbers to bring about the great 

 reduction in the numbers of flies. This phase of natural control is 

 still under investigation. 



Fumigation experiments were conducted only in cooperation with 

 the Tangerine Citrus Association of Tangerine and the growers of 

 Arcadia. In each instance an agent of the Bureau gave assistance 

 in securing the necessary apparatus and chemicals and in the general 

 methods of procedure. The fumigation of over one thousand trees 

 under varying conditions thoroughly demonstrated the value of the 

 method of control in isolated groves, as well as its nselessness in 

 groves closely surrounded by untreated infested groves. 



The experimental work of the previous year to determine the cost 

 and effect of various insecticides has been continued, together with 

 an extensive study of the mechanics of spraying as adapted to the 

 peculiar conditions presented by the problem in hand. It has been 

 found that by a careful application of knowledge gained by life- 

 history studies the cost of insecticides can be reduced about two-thirds 

 during late spray; while experiments have shown that their cost can 

 be safely reduced about one-half during the summer months, due to 

 the greater susceptibility of the larva? and pupae at this season. The 

 control of the fly by spraying has been undertaken in several groves, 

 consisting of several thousands of trees of all sizes, and data are 

 accumulating to warrant the statement that spraying, when once 

 given an intelligent continued trial, will be found a much more 

 promising method of control than is generally believed. 



THE OIIANGE THRIPS. 



The orange thrips, a serious insect enemy of orange in the south- 

 ern San Joaquin Vallej^ in California, has been under investigation 

 for about two years, and most gratifying progress has been made in 

 the determination of control measures. Large-scale experiments with 

 various sprays have been continued, and on the whole the pest has 

 proved to be less resistant to the sprays than was found to be true of 

 its near relative, the pear thrips. Two or three applications, how- 

 ever, appear to be necessary, since there is a series of generations oc- 

 curring (luring the year. The actual area of orange groves under ex- 

 periment by the Bureau in 1910 is approximately HO acres, the grow- 

 ers cooperating in allowing the use of the trees. The destructiveness of 



