December, '10] quayle: scutellista cyanea 447 



black scale still remains the most important citrus insect pest in the 

 state. Taking the citrus belt over, more control work is directed 

 against the black than any of the other scale pests. And, with all 

 this control work, according to a statement by G. Harold Powell of 

 the Bureau of Plant Industry, in 1908, from 3^ to 3^ of the oranges 

 of California were washed because of the sooty mold fungus resulting 

 from black scale infestation. 



While, therefore, this parasite is well distributed, and the percent- 

 age of scales attacked is often large, as parasitization goes, yet, from 

 a commercial standpoint, at least, the Scutellista is not often a very 

 important factor in the control of the scale. Of course, in many places 

 the Scutellista may not be abundant enough to check the scales. But 

 again where they are most numerous the scale continues to thrive. 

 There is not, therefore, necessarily a direct relation between the 

 abundance of the parasite and the scarcity of the scale. It is not 

 unusual to find the greatest parasitization where the scales are most 

 abundant; and, again, where the scales are scarce there may be very 

 few Scutellista. This might be answered by the fact that the Scutel- 

 lista being an egg parasite affects only the progeny, and that the scar- 

 city of scales should be attributed to the abundance of the parasite 

 during the previous year. This may sometimes be the case, but there 

 are often other and less tangible factors at work. 



Many have been accustomed to judge of the efficiency of the Scu- 

 tellista on the basis of the number of scales with exit holes, but this is 

 not the only criterion. Since the Scutellista is an egg parasite, the 

 real test of its efficiency is in its ability to prevent young from appear- 

 ing. It might seem that this is directly related to the number of exit 

 holes in the parent scales, but this is not necessarily so. A black scale 

 may lay from 300 to nearly 3,000 eggs, the average number being 

 from 1,500 to 2,000. A Scutellista larva will mature on the minimum 

 number of eggs, but, if they are available, it will of course consume 

 many more. But the Scutellista larva often does not consume the 

 maximum number of eggs, so that in large health}' scales there may 

 be several hundred young that will appear in spite of the presence 

 of Scutellista larva. It is because of this failure to consume all of 

 the eggs, in the case of the larger scales, and the fact that from each 

 one of the 10, 15 or 25% of the scales not parasitized, there may appear 

 2,000 or more young, that a tree may continue to be badly infested, 

 notwithstanding the large number of scales with exit holes. This 

 may explain why more than 700 young black scales were counted on 

 a single orange leaf growing from a twig that had 75% of the parent 

 scales parasitized by Scutelhsta. On the other hand, where the scales 

 are small or of medium size, the Scutellista consumes all of the eggs, 



