93 
that each rain will wash down some of it, and thus keep the 
bark more or less coated with this offensive material to insects. 
Many complaints have been made about borers injuring the 
plum trees. Evidently several species are involved, but as only 
young caterpillars were received it is impossible to give the 
name of the culprits. These caterpillars injure not only large 
plum trees, but even the seedling plants one year old. The 
illustration (Fig. 47, Plate 8), shows the work of such a borer; 
the stem in this case was too small to permit it to burrow, but 
it had been forced to work from the outside. The still small 
worm was found in this partial burrow ready to hibernate. The 
largest number of borers work just below the surface of the 
soil. Others, and perhaps of a different kind, enter the trunk 
and even the larger branches. They are readily detected in 
such an exposed position, and as readily removed with a knife. 
In some cases, when the knife can not well be used, the borer 
can be reached with a piece of flexible wire and killed in its 
burrow; but this is not a wise plan to pursue, as the decaying 
insect below the bark is apt to badly affect the neighboring 
parts of the trunk. Remove the borer and cover the wounded 
spot with wax to prevent the growth of injurious fungi. 
The illustrations (Fig. 48 and 49), show two other borers, 
which are destructive in Minnesota. 
The Red oak borer, ( Trochilium luggeri H. Edw.) was very 
common some years ago, seriously injuring the red oaks in St. 
Anthony Park. Every tree would show numerous holes from 
which these moths had issued, and in many cases the empty 
chrysalids were still projecting from them. The moths issued 
towards the end of May and throughout the month of June, and 
as some trees harbored hundreds of 
such borers in the trunk and larger 
limbs, many were killed. The per- 
fect moth is a very beautiful insect, 
mimicking rather closely a wasp. 
It is very active, running rapidly 
over the trunk of the tree during 
the warmest part of the day, but it 
is very shy and difficult to capture. 
Strange to say, during the last four 
s years not a single moth has been 
Fig. 48.-Red oak borer, showing Seen, nor is any of their work to be 
eetenGempty pupabcase.\) Orlg- found in the same place where they 

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