-72- 
carefully "but thoroughly sprayed or dusted. The materials used were" 
corrosive sublimate solution 1:1,000, Derrisol spray 1:250, bordeaux - 
oil emulsion (l-percent oil) , 4-percent calomel-lime dust, and un- 
diluted ground derris root (5 percent rotenone) . No larvae hatched 
from eggs exoosed to any of these treatments, but about 20 percent 
hatched from the untreated eggs. Luring 1928, 1929, and 1930 about 
300 newly. emerged flies were confined in groups of 10 in lantern 
-globe cages over potted carrots that had been sprayed or dusted with 
various insecticides. Where dusts were used, the flies were confined 
with the treated plants immediately after application, except in special 
experiments; but the liouid sprays were allowed to dry on the plants 
before the flies were caged with them. Derris killed the flies with 
unusual speed and consistency. Applied as a dust, derris mixtures 
killed all flies within 2 days. Another series of tests indicated that 
undiluted derris dust killed all the flies in 24 hours when they were 
confined with the plants 4 days after the dust was applied, but it was 
only partially effective 5 or 6 days after application. Derris-gyosum 
dusts containing 75 and 50 percent of derris killed all the flies with- 
in 3 days after application, but a dust containing 33 percent of derris 
killed only 70 percent of the flies exposed to it immediately. In 
field experiments derris and cube have been the most consistently 
effective materials, especially to control the first-generation flies 
on early carrots. Good results with derris were also obtained by G-orham 
(reported by correspondence) in New Brunswick, Canada. 
In the first work with derris, the undiluted derris root was superior 
to any mixture of it with gypsum. In fact, the greatest commercial 
damage by the flies where this treatment was used was 13.2 percent in 
1928, which represented a gain of 64.4 percent over the check; and the 
average loss in 3 years was only 7.73 percent. However, ground derris 
root costs at least 40 cents a pound and, undiluted, is much too expensive 
for commercial use on carrots. Since 1933, derris and cube powders have 
been improved by careful grinding and handling. In 1937 four applications' 
of a oube-clay dust containing 0.6 percent of rotenone gave complete pro- 
tection from a 14-percent infestation in an adjacent check; and in 1932 
and 1933 a similar commercial dust containing 0.55 percent of rotenone 
permitted an average damage of only 3.5 percent, m hich represented the 
greatest gain from any treatment with a contact insecticide against the 
second generation. This dust is now readily available for about 13 cents 
a pound, and used at the rate of 50 to 75 pounds per acre it would cost 
from $6.50 to $-10 for each application. This expense has not been 
justified in the last few years; but with a heavier infestation and a 
yield of 500 bushels or more ner aere, it might be practical on early 
carrots. On small plantings and home gardens it can be recommended. 
Sprays containing rotenone have been effective but in most cases are 
more difficult to apply. Pyrethrum as a dust or spray was less effective 
than derris or cube. 
Scatophegidae 
Scatophaga stercoraria L. 
According to De Pussy et al. (48) the full-grc-n flies ere much more 
