258 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 1 



an important bearing on the comparative immnnity of this territory 

 from serions injnry. " Doctor Chittenden reported the species rare 

 on corn at Washington, D. C. in 1899 following — 15°F. in February, 

 where it is usually very abundant. 



Eggs of H. ohsoleta were laid at Newark. Del., about June 12, 1900, 

 and moths from them emerged July 15, at a mean temperature of 

 about 73°F., thus requiring approximately 900° above 43°F. Quain- 

 tance (1. c.) found the average effective temperature in Texas to be 

 1417 °F. He also shows (1. c. p. 86) that the sum of the effective 

 temperatures for pupal development are more nearly equal for dif- 

 ferent temperatures when computed above 58° or 60° than above 

 43° F. He also shows that at Boston, Mass., there could be two gen- 

 erations with a total effective temperature of 2967 °F. over 43°, 

 commencing when the monthly mean has reached 62°F., or ]\Iay 1. 

 Further, if 58°F. were taken as the critical point, there would have 

 been required in 1900 only 450° at Newark, Del., while there were 

 801° at Boston and 525° at Durham, N. H. Yet the species breeds 

 only rarely in eastern Massachusetts, according to Dr. H. T. Fernald, 

 and is practically unknown at Durham. The summer temperature 

 evidently does not control the northern limit in this case, though the 

 distribution of the species is practically that of the Austral zones. 

 May not the minimum temperature be the controlling factor? 



Prof. F. ^I. Webster records^ that the West Indian Peach Scale 

 (Aiilacaspis pentagona Targ.) withstood — 9° during 1897-'98 suf- 

 ficiently to increase in numbers the next season at Wooster, Ohio, but 

 that in 1899 the temperature fell to — 21° one night and to — 12° to 

 — 18°F. in several successive nights, with the result that all of the 

 scales succumbed. 



]\[r. C. L. ^larlatt'- calls attention to the influence of the minimum 

 of 1899 (— 15°F.) at Washington, D. C, on scale insects, 95 to 100%, 

 of such species as Diaspis pentagotia, D. rosae, Aspidiotus perniciosus, 

 and others being killed. He points out that such mortality is more 

 likely to occur at AA^ashington where the hibernation of these scales 

 is short and where low temperatures are rarer thaii further north.'' 



At Nashua and IManchester, N. H., during the past winter some- 

 thing over 60 per cent of the scales were killed by — 13°F.. but are 

 breeding abundantly now. 



The northern limit of the San Jose Scal-e is shown on map 7. The 



iCaiiaflian Entomologist, XXXI, p. 130 (1899). 

 -Bulletin 20, n. s., Division Entomology, U. S. Dept. Agr., p. 76. 

 3See also Voyle, Bulletin 4, old ser., Div. Entomolojjy, U. S. Dept. Agr., p. 

 70-75, "Low Temperatures vs. Scale Insects." 



