K^ATUEAL CONTROL OF CITRUS MEALYBUG IN FLORIDA. 15 



fungi are antagonistic, and in view of the effect of fungicides upon the 

 latter, these facts should be kept in mind. It has been repeatedly 

 shown, for example, that Bordeaux mixture, when employed to de- 

 stroy the organisms causing citrus disease, at the same time de- 

 stroys the entomogenous fungi ; thus the natural balance that other- 

 wise exists, imperfect though it may be at times, but upon which 

 the grower, perhaps unconsciously, has relied, is upset to such a 

 degree that great injury results from attacks by insect pests. There- 

 fore a spray which may be of great importance as a control measure 

 for citrus diseases becomes to a large degree of no commercial im- 

 portance because the grower must choose either to control the diseases 

 or to permit the natural agencies to control the insects. If he feels 

 that the insects are more injurious than the diseases he will let the 

 entomogenous fungi control the insects, especially since their work is 

 performed at no expense whatever to him. The only alternative is 

 to follow the fungicide with an insecticide, or it may be possible to 

 apply the fungicide and insecticide in one mixture, but these are 

 expensive processes that may prove to be unjustifiable economically. 

 With regard to the effect of fungicides upon the mealybug fungus, 

 specific data are available in one instance. On August 11 and 12, 

 1921, a count was made of mealybugs in a grove in Orlando, a part 

 of which had been sprayed with fungicides by the Bureau of Plant 

 Industry, for the control of melanose, and a part of which had not 

 been thus treated. Although some plats were sprayed with Bordeaux 

 plus oil emulsion, some with copper soap, some with barium tetra- 

 sulphid, and some with lime-sulphur, for the present purposes all 

 the sprayed trees will be lumped together in one category as 

 " sprayed." While certain of the sprays employed contained an 

 insecticide, the presence of the latter has been entirely disregarded 

 because it has been repeatedly shown that such insecticides are 

 relatively impotent in so far as mealybug control is concerned. In 

 counting the mealybugs such arbitrary categories as " absent," " very 

 scarce," " scarce," " abundant," " very abundant," and " has been very 

 abundant" were employed; and, although crude, these will serve to 

 show the relative degree of infestation. Within the last-named 

 class were included those trees which showed evidences of a previous 

 heavy infestation, but which at the time of the count were free from 

 insects. The other terms are self-explanatory. There were 255 

 trees in the unsprayed area and 74 in the sprayed. Of the former, 

 4, or 1.6 per cent, were placed in the class " very abundant " and 6, 

 or 2.4 per cent, in the class "has been very abundant." Of the 

 sprayed trees 6, or 8.1 per cent, showed an infestation classed as very 

 abundant, whereas 1, or 1.4 per cent, in a plat sprayed with lime- 

 sulphur, showed evidences of having recovered from a past heavy 

 infestation. 



