400 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 15 



obtained, however. Lime-sulphur alone can not be regarded as a 

 satisfactory remedy. The addition of arsenate of lead (neutral or 

 basic) or nicotine sulphate to lime-sulphur, and this mixture applied as 

 near the pink stage as possible is considered to be the best control for the 

 peach twig-borer at the present time. If lime-sulphur spraying is not 

 necessary for fungous diseases, nicotine sulphate sprayed at blooming 

 time is recommended. 



On account of the fact that there is a second generation, one spraying 

 may not be sufficient. If complete control is not secured in a given 

 district, the flight of surviving moths may scatter and multiply the in- 

 festation and "wormy fruit" will be the result. A spray applied the 

 middle of May will probably reduce the fruit damage. The writer is 

 testing the effectiveness of nicotine sulphate and arsenate of lead against 

 the second generation of larvae and will be able to report results at the 

 end of this season. 



RESISTANCE OF CERTAIN SCALE INSECTS IN CERTAIN 

 LOCALITIES TO HYDROCYANIC ACID FUMIGATION 



By H. J. QuAYLE, Citrus Experiment Station, Riverside, California 



In 1915 my attention was called to the unsatisfactory results of 

 fumigation for the citrus red scale, Chrysomphalus aurantii Mask., that 

 had been obtained in the vicinity of Corona, California. The red scale 

 was very abundant in several groves in spite of the fact that the trees 

 had been fumigated not only regularly in the fall but the more severely 

 infested trees had been fumigated also in the spring. This condition is 

 known to have prevailed for some years previous to 1915 and still pre- 

 vails. 



Ordinarily, the so-called 100- or 110-percent schedule of dosage is 

 effective in controlling the red scale, but this schedule was considerably 

 increased in the commercial fumigation work in the Corona district 

 with the result as indicated above. In our experimental fimiigation 

 work there since 1915, dosages varying from 100 to 200 per cent for the 

 regular period of 45 to 50 minutes, and dosages of from 75 to 100 per 

 cent repeated at the end of the regular period, were given with unsatis- 

 factory results. This experience, together with that of several differ- 

 ent commercial firms, led us to suspect that the red scale is actually 

 more difficult to kill in that district, rather than to ascribe the poor 



Paper No. 103 University of California, Graduate School of Tropical Agriculture 

 and Citrus Experiment Station, Riverside, Cal. 



