16 BULLETIN" 1117, U. S. DEPARTMENT- OF AGRICULTURE. 



It is evident, therefore, that so far as mealybugs were concerned 

 the trees in this grove were in better condition in the unsprayed areas 

 than in the sprayed; in fact, there was 5.5 per cent more injury in the 

 sprayed plats. 



Observations on the prevalence of the mealybug fungus were made 

 in connection with this count. A dead infected individual here and 

 there in unsprayed areas showed that the fungus had been respon- 

 sible for the destruction of the colonies included under the caption 

 " has been very abundant." In those colonies classed as " very abun- 

 dant" the fungus was very noticeable at the time the count was 

 made. On the other hand, in the sprayed area, except for one tree 

 sprayed with lime-sulphur, no fungus was observed, and there were 

 no indications that it had been there previously. A few dead infected 

 mealybugs, however, were found upon the tree sprayed with lime- 

 sulphur. 



In brief, this experiment shows that fungicides, with the possible 

 exception of lime- sulphur, prevented the development of the mealy- 

 bug fungus, which in turn permitted an unrestrained development 

 of the mealybugs. In the grove where this experiment was per- 

 formed the infestation was very scattered, as shown by the fact that 

 of the 255 unsprayed trees, 185, or 72.5 per cent, were free from the 

 insect. 



Considered from the standpoint of a period of years, the mealy- 

 bug is relatively innocuous as a citrus pest, and it is believed that its 

 commercial control during such periods is brought about by the 

 natural enemies, chiefly the fungous parasite herein described. Sea- 

 sons obtain, however, such as the summer of 1921, and to a certain 

 extent that of 1920, in which this insect appears in numbers suf- 

 ficient to arouse the attention of the citrus grower. There seem to 

 occur more or less lengthy periods in which control exists to all in- 

 tents and purposes, alternating with periods of much shorter dura- 

 tion, lasting but one or two seasons, in which the insect threatens to 

 become a serious pest. Numerical fluctuation of the mealybug is 

 natural and unavoidable, for its control is largely brought about by 

 natural enemies which are dependent for the perpetuation of their 

 own species upon the presence of the hosts which they parasitize, the 

 lack of which, particularly if the parasites are more or less specific, 

 will cause them to disappear. It is very probable in the present in- 

 stance that a great part of the fungus, which is extremely prevalent 

 when the mealybugs are abundant, dies out for this reason, and in 

 the period of recovery which follows, the host has the advantage 

 and therefore increases in numbers until the parasite once again be- 

 comes sufficiently abundant to check it. The grower is concerned 

 only with those periods in which the insect threatens to injure hi& 

 fruit and trees. At such periods he can either resort to the employ- 



