108 THE MONTHLY BULLETIN. 



INSECT PARASITES AND PREDATORS AS ADJUNCTS 

 IN THE CONTROL OF MEALYBUGS. 



By Hafrt S. Smith, Superintendent State Insectary. 



In recent years the mealybugs have been growing increasingly 

 important as pests of citrus fruits and at the present time they are per- 

 haps attracting more attention than any of the true scale insects attack- 

 ing the same host plant. There are about twenty different species or 

 kinds of mealybugs in California, but only three occur commonly on 

 citrus. The most numerous of these is what is known as the citrus 

 mealybug, Pseudococcus citri, which is found pretty generally distrib- 

 uted over the warmer parts of the state. It feeds on a large number of 

 host plants, although various kinds of citrus seem to be preferred. 

 Clausen states that it was apparently first found in California orchards 

 about 1880, in San Diego County. 1 It was introduced into Ventura 

 County on nursery stock in 1897, and was a serious pest during 1908 

 and 1909. It is at the present time an important enemy of citrus trees 

 in Los Angeles and San Diego counties. 



The Baker mealybug, Pseudococcus bakeri, was first described by 

 Essig from Santa Paula, where he found it attacking alder and various 

 deciduous fruit trees. It has since become of some importance as a 

 citrus pest and occurs rather commonly over the citrus growing sections 

 of southern California, as well as at numerous places north of the 

 Tehachapi Mountains. It has a large number of host plants besides 

 citrus. 



The citrophilus mealybug, Pseudococcus citrophilus, was first found 

 at Upland in a number of citrus groves, and was thought at that time 

 to be the Baker mealybug. It was later found on further study by 

 Clausen to be a new species, which he described under the above name. 

 At the present time its distribution covers several hundred acres of citrus 

 near Upland and one hundred acres near Riverside, and also occurs in 

 Los Angeles County and around San Francisco Bay. Like the other 

 species infesting citrus it has a number of host plants. 



All three kinds of mealybugs are quite resistant to fumigation as 

 ordinarily practiced, and this treatment, if made strong enough to kill 

 the pest, results in serious injury to the trees. Some success has been 

 attained by spraying, especially with water under high pressure, but 

 even this method has not always proven satisfactory, because so many 

 applications are necessaiy that the labor cost is almost prohibitive. On 

 account of the difficulties in the way of combatting these pests artificially, 

 as pointed out above, the natural enemies of mealybugs have attracted 

 much attention. The Insectary has devoted a considerable portion of its 

 time and funds to an attempt to secure new parasites from foreign 

 countries, with a certain measure of success, and to the study of the 

 natural enemies already occurring in California. 



This importation and study of the insect enemies of mealybugs has 

 been more than justified, as is proven by the results secured by Mr. Rus- 

 sell S. Woglum, of the U. S. Bureau of Entomology, during the past 

 season. His work may be summarized briefly as follows: 



Mr. Woglum has found that with certain exceptions the outbreaks 



"Curtis P. Clausen, Mealybugs ot Citrus Trees, University of California, Exp. Sta. 

 Bui. 258. 



