Hibernation of the corn earworm in the central and northeastern parts of the United States Page: 8
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8 TECHNICAL BULLETIN 838, U. S. DEPT. OF AGRICULTURE
vival and adult emergence. As is shown in tables 2 and 3, pupae
survived the winter at Arlington Farm during the entire period, at
Carlisle in the winters of 1936-37 to 1938-39, inclusive, and at Manhattan
in the winter of 1938-39, whereas there was no, survival at
Urbana or Toledo in any season. No adults emerged in the cages at
Arlington Farm in 1936, but from 0.75 to 2.3 percent of the larvae
entering the soil to pupate produced adults the following spring during
the years 1937 to 1939, inclusive. No adults emerged in the spring
in cages at any of the other localities during any of the years included
in this study.
Since it has been shown that under dry cage conditions earworm
pupae can survive exposure for several days to temperatures as low
as 10 to 14 F.,5 it would appear that lethal temperatures were not
reached at any of the places shown in table 3. Salt (9, p. 31) states,
as has also been shown by other investigators, thatExcluding
contact moisture as a factor, there are certain types of insects which
are killed by low temperatures without being frozen, provided the time of exposure
is of sufficient length. The lower the temperature, the shorter is the
exposure necessary to kill them, and vice versa.
Length of time the pupae were exposed to low temperatures would
seem to explain lack of survival in areas like Manhattan, where winter
rainfall does not appear to be an important factor in causing death
of the pupae. During 1938-39, however, 2 percent of the pupae survived
the winter at Manhattan both in the clay loam and sandy silt
soils. Six percent of the pupae in the sandy silt soil produced adults,
whereas no adult emergence occurred in the clay loam soil. The temperature
in the clay loam soil reached a minimum of 18 F. 21/ inches
below the surface and was 32 or lower for a total of 73 days. In
1936-37 at the same location no pupal survival or adult emergence
occurred in the clay loam soil. The temperature that winter reached
a minimum of 16 2/2 inches below the soil and was 32 or lower
for 73 days. At Toledo in 1938-39 the minimum temperature at the
6-inch level in uncovered sand was 36, and yet no pupal survival
occurred. These facts suggest that there are differences in the physiological
condition of the pupae in different years or localities and perhaps
even in different lots of pupae collected in any single year.
Moisture content of the soil is no doubt an important factor.
Barber and Dicke (2) have shown that more pupae survive in cages
cn dry soil or sand than on moist soil or sand. The fact that the
soil is frozen to a depth below the pupal cells in the more northern
areas tends to maintain the soil surrounding the pupae in a much
moister condition as spring thawing takes place in those areas than in
areas farther south where soil is not frozen so deeply or for so long a
period. This may be an important reason for the difference in survival.
Salt (9, p. 14), in his studies on the freezing process in insects,
states:
* * * This [moisture] is obviously of importance also in nature, since hibernacula
of insects are frequently wet or icy, and the contact of such moisture
with the insect body produces a center of ice formation which may inoculate
or seed the body fluids. * * * If the insect were dry, or if inoculation failed
to occur, freezing would not take place until the temperature dropped to the
Unpublished data supplied by Dwight Isely of the Arkansas Agricultural Experiment
Station and F. F. Dicke of the Arlington, Va., laboratory of the Bureau of Entomology and
Plant Quarantine.
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Blanchard, R. A. Hibernation of the corn earworm in the central and northeastern parts of the United States, book, December 1942; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc5968/m1/8/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.