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The heaviest flights of beetles occurred late in May and early in June 
and, on occasions during this period, beetles concentrated on some kinds, of 
trees, as "bur oak, willow, and hickory, in such numbers that samples could he 
taken by shaking the branches over canvas. A few of these samples were used 
in attempts to estimate the proportions of various species present in the 
locality, but the accuracy of these estimates depended on the accuracy of an 
assumption (based on general observations) that most of the beetle population 
of the particular area was concentrated on these hosts. In most cases this 
assumption probably was correct, but at times temperatures and wind so affect- 
ed the movements of the beetles as to cause them to be widely scattered over 
a variety of plants and in- such numbers that, had they gone to these trees, 
they would have altered the proportions of the species actually found there. 
It seems difficult, therefore, to estimate the relative numbers of species 
present in a given area from the numbers found on any single host. Where many 
kinds of host plants are considered there are further complications, as nearly 
all the beetles can be collected from low-growing plants, whereas a relatively 
small proportion of the beetles on the taller types is accessible. 
The relative tenderneee of the leaves appears to influence the selec- 
tion of hosts by various species of beetles* Bur oak seemed to be the pre- 
ferred host of Phylophaga hirticula (Knoch) early in the season but later, 
when the oak leaves had become tough, hickory was preferred. For a consider- 
able period toward the end of the season P. tristis (F. ) was not found in the 
field, and it was concluded that this species had ceased emerging; but at Hipon, 
Wis., on July 10, large numbers were taken from tender second-growth leaves of 
bur oaks that had been stripped previously by beetles. 
..In certain areas beetles fed on species of plants that were not fed 
upon to any extent in other areas, and this feeding was not dependent on the 
presence or absence of other hosts. For example, there was in general practi- 
cally no feeding on boxelder, yet at Gays Mills this host was fed upon, even 
though other' hosts were abundant in the immediate vicinity. Air currents in- 
fluence the movements of beetles to or from hosts, therefore some beetles may 
go into the ground in different fields on different mornings and return to 
different hosts or different sides of the same host on different nights. 
These habits made it difficult to take any samples closely comparable with 
others, even in the same area. Temperatures seemed to determine the extent 
to which beetles fed on low shrubs or trees. On cool nights the beetles did 
not fly to any extent but issued from the ground and climbed and fed on the 
nearby shrubs. These observations show that care should be used in attaching 
much significance to counts made on various plants, no matter how accurate 
these may be, unless the counting be continued over a long period of time and 
under a great variety of conditions. 
