Hibernation of the corn earworm in the central and northeastern parts of the United States Page: 11
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HIBERNATION OF THE CORN EARWORM 11
FACTORS INDIRECTLY AFFECTING HIBERNATION
The number of larvae that enter hibernation successfully in the
field and the likelihood of pupal survival are affected indirectly by
a number of factors. Among these are time of corn planting, rapidity
of drying of the corn, and the time of first frost in the fall.
Time of planting of the corn is dependent to a considerable extent
on the amount of rainfall in the spring as well as the soil type. A dry
spring allows corn to be planted at an early date, especially in
well-drained, sandy soils. Such soils warm up and dry to a good
tillable condition earlier than do the heavier soils. Also farmers
as a rule plant corn in sandy soils as early as possible to take advantage
of the moisture that has accumulated during the winter and
early spring, as such soils tend to dry out too rapidly during the
late summer months to produce a good crop. It has been observed,
therefore, that in general the late-maturing corn is found on the
heavier, less drained clay or river-bottom soils. It is here that
earworm larvae enter hibernation in greatest numbers, and yet such
locations offer the poorest chances for survival owing to excess moisture,
heaving of soil, and accumulation of weed growth before the
land can be plowed for a crop. In some market-corn areas late
crops of corn are planted on the sandier soils, thereby affording
suitable food for larvae to hibernate under optimum conditions, but
taken over a large area this is not the general situation.
The rate of maturing or drying of corn is the result of several
factors, among which are variety, time of planting, amount of rainfall
late in the summer, and time of first frosts. Long-season, slowmaturing
varieties, which remain in the dough stage a considerable
length of time, provide the best foods for larvae that are to enter
hibernation. Ample rainfall in the late summer and early fall also
increases the time the corn remains in the dough stage, thereby
allowing larvae to enter hibernation in good condition in large
numbers. Dry, warm weather in the fall, on the other hand, results
in earlier drying of the corn, which in turn has been observed to
result in desiccation of a large percentage of the larvae that are
attempting to feed on it.
Frost not only hastens the drying of late-planted corn but has
been observed to kill many of the larvae that were feeding on the
ears. This occured in central Illinois in the fall of 1937 and in
northern Illinois in 1938. Even where mild weather in northern
latitudes allows larvae to develop late in the fall, the chances of their
being able to pupate normally are reduced. This was mentioned
previously in discussing cages established at La Fayette, Ind., and
Toledo, Ohio, between October 11 and November 4, 1935, in which
only a very small percentage of the larvae placed in them were able
to form pupae.
CONCLUSIONS
The limits of successful hibernation reach much farther north
after dry, mild winters than after those during which the weather is
more severe. Likewise, the chances for successful hibernation are
much greater in well-drained, sandy soil than in heavier soils. Certain
protected locations, such as those around cannery buildings,
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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/m1/11/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.