1912] Etviitg and Webster — Mifes Associated zcith the Oyster-Shell Scale 123 



erable benefit occasioned by mites. Out of 100 scales counted 

 February 27, 1911, sixty-five showed indications of mite work. 

 Of the remainder, 32 scales were empty, while 3 were sound, i. e. 

 contained sound eggs quite unaffected by mites. Hemisarcoptes 

 malus was the mite concerned in this case. 



In this connection it must be mentioned that many oyster-shell 

 scales remain on the trees long after the insects themselves are 

 gone. The presence of 32 empty scales in the count just given 

 would refer to scales which had probably remained on the bark for 

 a year, or perhaps even more, rather than to those which had been 

 cleaned out by mites. 



From other counts made in 1911 it was found that a great varia- 

 tion existed in the condition of the scales at different places in the 

 state. In some of the infested orchards near Ames as low as 3.7% 

 of the scales contained sound eggs that spring. The remainder 

 were either empty, or had been gutted by mites. At this time in 

 the orchard at Ames that showed the scale in the best condition, 

 only 16.48% of the scales contained sound eggs. These last counts 

 were made for another purpose than to find mite injury, so that 

 this factor was disregarded in making them. If a scale had any 

 sound eggs in it, it was counted as such, so that a scale might be 

 half gutted by mites, and still contain sound eggs. Many of the 

 empty scales, however, were made so on account of mite attacks, 

 and so these counts are given here. 



At Northwood, Iowa, near the Minnesota line, a variety of con- 

 ditions were found. Much mite injury (Hemisarcoptes) was no- 

 ticed. From samples of scale collected in one orchard 82.4% of 

 the scales contained sound eggs; from another orchard 69%; from 

 a third, 34%) ; from a fourth, 23%. 



Samples taken from three orcliards near Iowa Falls cojitained 

 15.2%, 23.8% and 41.2% scales with sound eggs. Other samples 

 from additional places in the northern half of the state showed 

 that from 10% to 20% of the scales contained sound eggs, the 

 proportion occasionally running as high as 30%. 



Considering that a large proportion of the empty scales are left 

 over from the previous year, the percentage of scales not injured 

 must be larger than appears from the figures. A count made at 

 Ames, August 5, 1909, shows how these old scales remain on the 

 trees. Out of 500 scales from a mountain ash tree, 218 contained 



