FALL NUMBER oo 
rain. If this is the case, our problem is to induce this fungus 
to thrive during dry weather or find some parasite that will 
hold the mealybug in check until the rainy season begins. 
IT PAYS TO CONTROL RUST MITE 
J. G. GROSSENBACHER 
Strange to say, the rust mite is not an insect but is more 
closely related to spiders. It is a near kin of the itch mite, 
“red bugs,’ red spiders, and cattle ticks. It feeds on all new 
green growth of trees: leaves, fruit and twigs. It seems to live 
on juices taken from trees, particularly the oil. However, if 
these mites consumed all the oil from the glands they open we 
would have no real rusty fruit. In fact, the rusty appearance 
of fruit, leaves and twigs is due to the oil oozing from glands 
that had been tapped by the mites. The oil flowing from the 
punctured glands spreads out more or less over the rind of the 
fruit and during nights of heavy dew or light showers may run 
down the sides of the fruit in narrow bands; the exposure of 
these thin layers of oil to the air causes the oil to break down 
or oxidize and change to a dark color, thus resulting in rust and 
where it had run down the fruit in streaks to “‘tearstaining.” 
There is another effect that the exuding oil has on young fruit 
and other newly developed parts of trees that should be men- 
tioned in this connection. In 1914 and 1915, I punctured a large 
number of oil glands on newly hardened young twigs and half- 
grown oranges with a very fine pointed needle under a lens. 
The punctured areas were marked and kept under observation 
during some weeks. Small amounts of oil escaped from each 
pricked oil sack and spread over tiny spots and areas, the shape 
of which depended upon the action of gravity on the escaping 
oil. After a few days the distribution of the oil was definitely 
and clearly shown by brown spots of the exact size and shape of 
the oil-covered area. In order to make a further test of the 
effects of orange oil on the epidermal tissues of fruit, leaves 
and twigs of orange and grapefruit, a small quantity of this oil 
was obtained and applied with an atomizer so as to cover the 
surface with tiny spots of oil; in other cases the application was 
continued until the oil spots became so numerous and close to- 
gether that they eventually touched and thus covered consider- 
able areas completely with a continuous film of orange oil. The 
result was interesting in that in case of the light applications 
every point, formerly occupied by oil-dust particles delivered by 
