December, '11] QUAYLE: SCALE INSECT PARASITISM 511 



been obtained from several different sections of the State during the 

 last five or six years does not show that the parasite in question is 

 an important factor in keeping the scale in check. 



Aphelinus fuscipennis How. is probably the commonest species 

 attacking the scale in the State, while A. mytilaspidis is also frequently 

 met with. Usually the number of these issuing has been small in 

 comparison with the number of scales. We have found no such 

 numbers, for instance, as Johnson found in Maryland some years 

 ago. Very large numbers issued from his material and it is pre- 

 sumed that the percentage ran high. 



It is true that in the Santa Clara Valley where the San Jds6 scale 

 first started in this country, it is no longer regarded as a serious pest, 

 but further data are necessary to prove that parasites are responsible 

 for this condition. A very considerable amount of the lime sulphur 

 spray is used in the State each year and chiefly against this scale, 

 and the general efficiency of this wash has done more than anything 

 else to allay the fears that were formerly held against the insect. 

 But where neither the parasites are present in sufficient numbers nor 

 has the wash been applied, the scale no longer occurs in alarming 

 numbers as formerly; and what is true of the Santa Clara Valley is 

 true in many other parts of the State. Again we have seen apple, 

 pear and plum trees practically killed by this scale as late as this 

 present year. 



THE RED SCALE 



{Chrysomphalus aurantii Mask.) 



At the present time Aphelinus diaspidis How. is the most widely 

 distributed and abundant parasite of the red scale in the State. Counts 

 made on large numbers of this scale show that the percentage para- 

 sitized varies from 1 or 2 per cent to 15 or 20 per cent. Aspidioti- 

 phagus citrinus Craw, also occurs in some numbers, but the highest 

 percentage found was with the yellow scale as given below. Other 

 parasites recorded from this scale in the State are: Prospaltella 

 aurantii How., Signiphora occidentalis How., and Aphycus immacu- 

 latus How. 



THE YELLOW SCALE 



(Chrysomphalus aurantii var. citrinus Coq.) 



The most important parasite of this scale is Aspidiotiphagus citrinus 

 Craw. While it attacks the red scale, it has been most frequently 

 met with and occurs in largest numbers on the yellow. Yellow scale 

 material has been obtained in several places in the southern Cali- 

 fornia citrus belt with no, or little, evidence of the parasite, while 

 in others as high as 40 per cent has been obtained. But it is on 



