28 
EASTERN SHADE TREE CONFERENCE 
So far there is close similarity in the outbreak of forest tent caterpillar 
just preceding the turn of the century and that beginning in 1935. 
There was one point of difference which I have not mentioned. In the 
earlier outbreak and in the milder one which occurred around 1912— 
1915, the infestation, though spotty, was fairly evenly scattered over 
the state. In the past four years I have known of no defoliation by the 
forest tent caterpillar in the northeastern quarter of the state. 
Why ? I don’t know. But here is what I consider a strong probability. 
The build-up of numbers in both species of tent caterpillars resulting in 
the present outbreak had been occurring generally throughout Vermont 
up to 1934. It was more obvious, of course, in the case of the eastern 
tent than of the forest species, because the tents make a noticeable index 
of prevalence, even where defoliation is not common, but both species 
had become fairly plentiful after several years of obscurity during which 
it had been hard to find egg masses of either. Then came the severe cold 
of the winter of 1934. In the southern and western parts of Vermont, 
the caterpillars apparently continued on their course. In the northern 
regions before referred to, tents of the eastern caterpillar were almost 
a rarity the next spring, even in sections where the roadside cherry and 
apple trees had been covered by them the year before. Disease and 
parasitism should be considered in this connection, of course, but judg¬ 
ing by the usual “run” of these things and also by conditions elsewhere, 
I do not think it was time for them to assert themselves. What I do 
think happened was that the temperature in these colder sections of the 
state went just below the hair line standing between mortality and sur¬ 
vival of the eggs. I think that the great majority of eggs, certainly of 
the eastern species, were killed in these cold sections and if that were the 
case it seems reasonable to suppose that eggs of the forest caterpillar 
went with them. This isn’t backed by check and definite record and I 
realize that it would not stand in the court of scientific experiment, but 
the winter killing theory does have some backing by observations of John 
Schaffner of the U. S. Bureau of Entomology and Plant Quarantine and 
probably of others. 
It would make little difference, anyway, were it not for the disquieting 
possibility it presents. From past experience we have reason to hope 
that the present outbreak where it has been running for the past four 
years will subside before very long as the result of natural control agen¬ 
cies. But what of this northern section? If my thesis is correct, and 
the insects were cut off by something outside the usual control agencies, 
