72 



BULLETIN NO. 4, DIVISION OF ENTOMOLOGY. 



reported, 19° F., be correct, scale insects with only moderate protection 

 should have been killed, and all their eggs with them; but such was 

 not the case. Both thermometers and readings are often questionable. 

 Unreliability of graduation of common instruments, particularly below 

 the temperate figures, and readings made by parties unaccustomed to 

 accuracy, may be taken as a reasonable explanation of wide discrepan- 

 cies. 



There are conditions practically unattainable artificially, where the 

 coccids are protected from the effects of such temperature as under 

 favorable conditions would be fatal to them. The leaves of the tree, 

 the warm current rising from the ground around the trunk of the tree, 

 and the initial heat of the tree itself perform an important part in mod- 

 ifying temperature for these insects. In a still atmosphere this might be- 

 come a perfect protection against a temperature much lower than would 

 prove fatal in other conditions. Again, a cold, moist breeze following a 

 rain might lower this protection to a fatal point. Casual observation 

 warrants the supposition that these conditions do occur with the results 

 as supposed. Valuable information could be obtained by using regis- 

 tering thermometers within the protection of the head of the tree, and, 

 on the outer branches ; a comparison of records would indicate the 

 amount of protection, and give data for ascertaining approximately the 

 amount of cold required to reduce the temperature all over a tree to a 

 point absolutely fatal to coccids : probably a temperature fatal to the 

 tree also. 



The table has been arranged from the notes so as to present results 

 without unnecessary details. The experiments were repeated for veri- 

 fication, and also whenever any results were doubtful. 



The table may be regarded as an accurate exponent of the effect of 

 low temperature on orange coccids. 



Table showing results obtained by exposing orange scale insects to carious degrees of cold. 



Xo. of 

 experiment. 



Miniumm 

 tempera- 

 ture. 



Maximum 

 tempera- 

 ture. 



Time of 

 exposure. 



Result to 

 larva?. 



Result 

 to eggs. 



Time from 



exposure 



to final 



result in 



eggs. 



Remarks. 



1 



16 

 19 

 20 

 22 

 22 

 22 

 23 

 25 

 25 

 25 



24 

 32 

 25 

 22 

 22 

 22 

 23 

 34 

 25 

 34 



Hours. 



5 

 10 

 10 



5 



3 



1 



1 

 10 



5 

 16 



Dead . . . 

 . . do 



Dead ... 



..do 



Days. 

 31 



'1 





2 





3 ... 



. . do 



..do 





4 



..do 



..do 





5 





..do 



12 

 14 

 14 

 20 

 12 

 8 





6 



..do 



.do .... . 





7 



..do 



..do 





8 . 



. do 



do 





9 



..do do 





10 



3 eggs only out of a 



V 







large number. 



