FUMIGATION OF CITRUS TREES. 63 



efficiency between December and April, provided the work be per- 

 formed by careful men who observe the various factors affecting 

 these two considerations. These factors are given at various places 

 throughout this bulletin. 



FUMIGATION FOR THE MEALY BUG. 



Considerable excitement has been aroused in some parts of southern 

 California during the last year or so over a so-called threatened 

 invasion of the citrus mealy bug (Pseudococcus citri Risso) . This 

 insect has been known in this region for at least 15 years. Its 

 greatest injury has been done in the vicinity of National City, San 

 Diego County; along the Sierra Madre foothills, near Monrovia, Los 

 Angeles County; and very recently at Santa Paula, Ventura County. 

 There have also been sporadic occurrences in many other sections. 

 This sporadic activity has been of a somewhat puzzling nature. A 

 tree severely infested with the mealy bug one day might be found to 

 be practically free of this insect a month later, though no artificial 

 measures of control had been applied. The mealy bug might reap- 

 pear on this same tree the following year, or even sooner. The 

 writer is inclined to attribute this disappearance largely to the 

 activity of parasitic and predaceous insect enemies. The general 

 appearance of the remains of the mealy bug, as well as the rear- 

 ing of several beneficial insects therefrom, including two or three 

 species of Hymenoptera, a brown lace wing (Hemerobius sp.), and a 

 syrphus fly, lead the writer to this conclusion. Several species of 

 Coccinellidse also have been found present in severe infestations of 

 this insect. Undoubtedly climatic conditions as well as fungous and 

 bacterial diseases produce some effect. 



The recent prominence of this insect in the immediate vicinity of 

 Santa Paula, Ventura County, is well worthy of mention. Its infes- 

 tation here has been so severe that the proportion of fruit in some 

 orchards ruined by this insect during 1909 was very great. The 

 large amount of damage caused there, together with the difficulties 

 experienced in destroying the mealy bug, has led to agitation for its 

 control in several other localities. 



At various times during this investigation a few trees infested with 

 mealy bugs have been treated. The usual dosage has been 1J to 2 

 times schedule No. 1. The results have been variable. Some trees 

 would appear to be entirely freed, while on others many live insects 

 would remain. 



During the autumn of 1909 a prominent orchardist of Santa Paula 

 carried on some very extensive fumigation work against this insect, 

 partly according to the writer's directions. Some trees were treated 

 with 2, 2§, and 3 times schedule No. 1 for from one to one and one- 

 half hours without eradicating the scale in any case. The results 



