December, '22] quayle: scale resistant to fumigation 401 



results to insufficient dosage, leaky tents, or lack of attention to the 

 details of the work. 



The time and place may very materially affect the results of fumigation, 

 hence in any comparative work it is necessary to eliminate these two 

 variable factors. This was done in the case in question by taking in- 

 fested fruits from two localities and fumigating them under the same 

 tent in a third locality. The fruits infested with red scale were picked 

 from two localities on the same day, or from one of the localities on the 

 day following. They were placed in the same basket, or two baskets 

 were placed together under the tent, in order to guard against variation 

 in gas concentration in different parts of the tent. Different series of 

 such tests have been made repeatedly since 1915 under tents over "form 

 trees," under tents in experimental fumigation work in the field, and 

 under tents operated in commercial ftmiigation practice. Since 1915 

 it has been determined that the red scale in certain districts in Orange 

 County manifests the same apparent resistance to hydrocyanic acid. 



In the comparative tests reported below the dosage was varied con- 

 siderably, but in all cases the scales from the different localities were 

 under essentially identical conditions. 



The stimmary results of a few representative tests are given below in 

 table 1. 



Table 1. The Effect of Fumigation on Red Scale from Different Localities 



No. of scales No of scales Percentage of 



Locality fumigated alive scales alive 



Orange 

 Corona 



La Habra 

 Corona 



Riverside 

 Corona 



Redlands 



Highgrove 



Corona 



La Habra 

 Corona 



The fact that we have evidence extending over a period of seven 

 years of exceptional resistance in the red scale at Corona, and in a 

 district in Orange County extending over four or five years, would in- 

 dicate that it is not necessarily a seasonal condition. If it is a case 

 of acquired immunity and the factor of resistance is hereditary, it is 

 necessary that this factor be transmitted through two or three genera- 

 tions of scales since this niunber intervenes between fumigations. We 

 have some evidence to indicate that the individuals that are alive after 



