16 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE, 1952 
thiol) powder containing 3-percent parathion per LOO gallons; or of a 
dust containing 1 percent parathion. Inclusion of Bordeaux mixture 
in the second application did not decrease the effect iveness of the mate- 
rials against the mites. 
A single application of DDT in combination with 1 pound of 15- 
percenl parathion or 25-percent EPN, or 2% pound- of 3-percent 
parathion per LOO gallons gave an acceptable degree of control of the 
grape mealybug and of another mealybug, Ferrisiana virgata Ckll., 
when applied while second-brood crawlers were active on the grape-. 
Chlordane was ineffective. 
Newer Miticides Tested Against Citrus Red Mite 
As part of the work to develop better methods for controlling mites 
that infest citrus, special consideration is being given to the citrus 
red mite. In California, p-chlorophenyl ©-chlorobenzene sulfonate 
(Ovotran) at 8 pounds per acre was one of the best of the newer acari- 
cides and had considerable commercial usage. Control by parathion 
was of short duration. Result with parathion plus Ovotran varied 
in different locations. In some cases the combination was as effective 
a- the full dosage of oil. In one experiment, benefits from the addi- 
tion of (hot ran were of short duration. The combination of 1 per- 
cent of oil plus parathion was superior to larger amounts of parathion 
alone. 
Work in Florida sought to develop hot-weather combination sprays 
that would be less expensive than the separate oil emulsion sprays 
formerly necessary for red mite control. The new miticides bis- 
(p-chlorophenoxy) methane (Neotran), K-242, EPN, p-chlorophenyl 
p-chlorobenzene sulfonate (Ovotran). compound ( .>:23, and Aramite 
were found to be effective for control of the red mite on Temple orange 
trees in April or in May. These were compatible with basic copper 
sulfate fungicide, with wettable parathion, and with wettable sulfur. 
They were more effective in dry weather. Oil emulsion spray gave 
better control when heavy rains followed the applications. 
Marked increases in red mite infestations followed sprays of Meta- 
cide plus wettable sul 1'nr or parathion plus wettable sulfur applied late 
in March. Inclusion of bis(p-chlorophenoxy) methane in June com- 
bination sprays containing wettable sulfur or parathion plus wettable 
sulfur controlled these heavy infestations on Ruby grapefruit trees. 
Physiological Study of Red Scale Discloses Resistance Factors 
I nvesl igations of the reactions of different strains of California red 
scale to IK "X and other Liases were made to find the physiological basis 
of resistance to HCN. Resistance of some strains has increased until 
sal isfactory control cannot be obtained with dosages that the tree will 
tolerate. Resistance was not caused by tracheal closure on exposure 
to HCN. Resistance was associated with a difference in the respira- 
tor} enzyme systems, susceptibility being dependent on a heavy metal- 
containing respiratory enzyme system and resistance on metal-free 
enzymes, possibly of the navoprotein type. These findings, which 
came a Iter a Long series of studies, offer an explanation of the physio- 
logical basifl of one of the earliest known and most studied case 
insect resistance to an insecticide. 
