August, ’24] 
BLACKMAN: HICKORY BARK BEETLE 
469 
normally and as there is a fairly definite relation between the length of 
the gallery and the number of eggs deposited, a smaller number of 
progeny came from each pair than is normal. In addition to the trees 
killed this year many others were attacked but were not killed. In 
these, many burrows were started only to be abandoned before a single 
egg was laid. In other burrows a few eggs had been laid but did not 
hatch. In still others the egg-gallery had been continued for a distance 
of one or two centimeters upon the sapwood, eggs had been laid in 
niches on each side and the young larvae hatching from them had 
started their mines at right angles to the egg-gallery. However, in 
most of the burrows, either all or a greater number of the larvae had 
soon succumbed. Thus while many trees were attacked by the beetles 
in numbers sufficient, under normal conditions to have insured their 
death, only four trees outside of the immediate center of infestation were 
killed. The flight of the beetles in a northerly direction could be readily 
traced for more than a mile by the presence of aborted brood burrows 
in the trees attacked. 
The writer explains these various facts as follows. The frequent 
rains during the first half of July destroyed a number of the adults while 
these were feeding upon the twigs and petioles. However, a considerable 
number of these survived in spite of the adverse conditions at this time 
and the continued excess in rainfall during the following month. Many 
of these beetles attacked the trees in swarms, and started their burrows. 
Where the beetles were present in excessively large numbers, their 
attack was successful and the trees were killed. Those emerging later, 
however, found practically all of the trees in the vicinity already fully 
stocked and were forced to migrate. Dozens of pasture hickories were 
attacked during late July and August but this was successful on only 
four trees. We have already seen that there was an excess in rainfall 
during August and—which is of at least equal importance—this month 
was excessively cloudy, there being only three clear days. The result of 
this was an excess of sap held in the living tissue of the tree—an in¬ 
crease in sap-pressure. Thus the adult in making the brood burrow 
was subjected to an excessive flow of moisture into her burrow and this 
moisture on account of the cloudy and humid conditions did not evapo¬ 
rate from the burrow entrance as rapidly as normally. Also during the 
frequent rainstorms the female was twice subjected to the danger of 
being washed away for every egg deposited. Doubtless also many 
females were never fertilized on account of the high mortality of the 
males, which remain outside of the burrows most of the time. Thus the 
