- 560 - 
readily from a hand duster. It would therefore appear that with 
hydrated lime as a carrier, a 3 percent dust is as high a percentage 
as is practical and economical. The mortality among flea-beetles 
with varying strengths of nicotine dust ran in a fairly regular 
progression, the average percentages killed being 44 for 1 percent 
dust, 63 for 2 percent and 91 for 3 percent. 
"Length of exposure to the fumes appears to be the most im- 
portant factor in the 'control of Aphids. In dusting for P. hamuli, 
slight air movements could be largely overcome by extra heavy applica- 
tions, but this very greatly increases the cost. In the case of 
Phyl lotreta albionica , the air movement seemed to be of less importance, 
flea beetles being apparently peculiarly susceptible to nicotine fumes. 
It was found that exposure for 15 seconds at least is necessary to 
kill Phorodpn humuli, while Phyllotreta albionica and the hop flea- 
beetle ( Psylliodes p unctulata l.Iels.) are killed after an exposure of 
3 seconds, the different results being probably due to the varying 
rates of respiration; flea-beetles lose all power of movement after 
15 seconds, while the hop aphis often remains alive from 12 to 24 
hours after dusting. Variations in temperature are only of importance 
when hand operated machines or power machines without agitators are 
used; with these machines a minimum shade temperature of 70 P-. was 
necessary for an effective kill, but otherwise, owing probably to the 
fact that the agitators raise the temperature of the dust to about 
130° P., a 100 percent mortality of P. humuli was obtained at an 
air temperature of 50° F. During the course of these experiments dust- 
ing was found to be as effective on dry as on damp days, taking the 
temperature into consideration; the addition of 6 percent moisture 
to the dusts did not produce a markedly different result. 
"Though dusts can be applied at a rather lower cost than sprays, 
it is unlikely that dusting will supplant spraying in British Columbia, 
owing to the limited period during which the atmospheric conditions 
are favorable, Nicotine dust will, however, continue to be used on 
hops, especially if outbreaks of red spider ( Tetranychus t elar ius L.) 
occur, as a combination dust of ground sulphur, hydrated lime, and 
nicotine sulphate has been found most effective in destroying both 
mites and aphids at one operation. It has also proved to provide 
the only satisfactory method of controlling P. albi onica . " 
HULL, P. M. .' (2341) 
1929. THE PLAET LOUSE PROBLEM OP THE TEXAS GULP COAST. Jour. Econ. 
Ent. 22: 774-777. [Abstract in Rev. Appl. Snt. (A) 18: 65. 1930.] 
Low temperatures and high winds render ineffective standard 
control measures against various aphids including Aphis pseudo - 
brassicae Davis and Pemphigus populit ra nsversus Riley which seriously 
damage crucifers. A method of heating nicotine sprays and dusts by 
means of a small petrol heater attached to the spray tank or dust gun 
