554 THE MONTHLY BULLETIN. 



THE WALNUT MEALY BUG. 



(Pscudococcus hakeri Essig. ) 

 Order — Hemiptera. Family — Coccidse. 



By R. S. VailEj County Horticultural Commissioner, Santa Paula, Cal. 



In December, 1910, E. 0. Essig published a description of a new- 

 mealy bug, to which he gave the name Pseudococcus hakeri. Because 

 of its habit of feeding on the walnut trees in Ventura County it was 

 given the common name of walnut mealy bug. Since that time the 

 writer has collected additional specimens and data regarding the dis- 

 tribution of this insect which may prove of interest. 



The known host plant list at present is as follows: Walnut, apple, 

 pear, orange, lemon, pomelo, elder, cottonwood, southern California 

 black w^alnut, nightshade and a few of the ornamental shrubs. It has 

 been found in three localities in Ventura County infesting citrus 

 trees, but in two of these cases it occurs in much greater numbers on 

 the native elder and nightshade surrounding the trees. For at least 

 a portion of the year it lives primarily on the. roots of these two plants. 

 Numerous solanum bushes growing under orange trees have been found 

 with the roots thickly covered with all stages, from eggs to mature 

 adults. The same has been true of the elder, though so far no speci- 

 mens have been reported on roots of citrus or other fruit trees. 



The life history appears to be much the same as that of Pseudococcus 

 citri with this decided difference : the egg masses are much looser and 

 the number of eggs laid by a single female is much less. This is quite 

 a factor in the control of the insect, as it appears to have been present 

 in certain orchards for a good many years without at any time becoming 

 a damaging pest. Mr. J. J. Davis, in the Entomological News, XIX, 

 No. 8 (1908), gives the average eggs of Pseudococcus citri, per mass 

 counted, as 274 (twenty masses counted). Essig states, in commenting 

 on this count, that under field conditions around Santa Paula (1909), 

 the average was undoubtedly somewhat higher than this, reaching at 

 least five hundred eggs for some individuals. He further states (P. 

 C. Jr. Ent. II, No. 4) that practically all eggs of Pseudococcus citri 

 seem to be fertile. The writer has counted the eggs in ten masses 

 of Pseudococcus .hakeri with a range from forty-two to a hundred and 

 sixteen, and an average of sixty-seven eggs. In confinement in glass 

 jars these appeared to be from ten per cent to twenty per cent unfertile. 

 This may not hold true under field conditions, but we have observed 

 in numerous old egg masses a few shriveled eggs unhatched. We have 

 also seen appearances which lead us to believe that egg parasites play 

 a considerable part in the control, but, so far, we have been unable to 

 rear any. 



From all observations to date we do not feel that Pseudococcus hakeri 

 will ever properly be classed as a damaging insect, as it seems to 

 require no additional control measures. We have not seen it in suf- 

 ficient numbers to smut more than a very small percentage of the fruit 

 nor have we seen it to have any noticeable effect on the health of the 

 plant. Carbolic acid emulsion and other sprays which are effective 

 against Pseudococcus citri are equally so against Pseudococcus hakeri, 

 and fumigation seems much more efficient against the latter than the 

 former species. 



