Structure and development of the alimentary canal of the southern armyworm larva. Page: 2
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2 TBmHNoAL BU;LLETIN 762, U. S. DEPT. OF AGRIULTURE
The southern armyworm is a typical lepidopterous larva and one
of a heterogeneous group of noctuid larvae known as armyworms.
The group has been reviewed by Crumb (8, 9).1 A technical description,
by Dyar, of the egg and larval stages is included in a paper
by Chittenden and Russell (7). The species occurs in the lower
Austral faunal area and is probably of tropical origin. It is destructive
to various field and truck corps in the southern part of the
United States (7, 31).
The larvae are about 1.2 mm. long at hatching. Mature larvae
range in length from about 39 to 46 mm., and in breadth from about
6 to 7.5 mm. The average weight of such larvae is about 960 mg.
About half of this weight is due to ingested material within the alimentary
canal. The larvae develop in six stadia, requiring about
17 days at 27 C.
An examination of the few detailed accounts of the anatomy of
the alimentary canal of lepidopterous larvae reveals a diversity of
structure even among closely related species. Especially helpful is
a comparative study of the morphology of the alimentary canal of
lepidopterous larvae, including species of Noctuidae, given by Dauberschmidt
(10). Bordas (6) described the alimentary canal and
the Malpighian tubules of the larva of each of several representative
species of Lepidoptera, including four species of the family Noctuidae,
and Snodgrass (24, 26) has described the alimentary canal
of noctuid species. Shinoda (83) made a comparative study of the
histocytology of the midgut of several species of Lepidoptera. There
is no report in the literature on the alimentary canal of the larva of
the southern armyworm. In its general features it is similar to the
alimentary canals of other lepidopterous larvae that have been
described.
MATERIALS AND METHODS OF STUDY
The larvae used in this study, with the exception of the late sixth
instars, were reared on fresh turnip foliage in an incubator at 27 C.
The late sixth instars (60 or more hours past the fifth molt) were
reared on the foliage of living turnip plants in a greenhouse insectary.
Actively feeding larvae were selected and conserved for a
time on fresh, clean leaves in a clean culture dish, in order that sand
grains or other hard objects that may have been present in the lumen
of the gut would be eliminated.
For the study of tthe microanatomy the paraffin method was employed.
Larvae for study were selected and fixed during and immediately
after the hatch, before and immediately after each molt,
at 8, 12, 24, 36, and 48 hours after each molt, and at other suitable
times. Larvae of the first four instars were killed and fixed in Carnoy
and Lebrun's mixture. Larvae of the fifth and sixth instars
were killed by immersion in hot water (at 600-70 C.) and immediately
dissected, and the desired tissues were removed and dropped
into Bouin's picro-formol-cetic fixative Serial sections of whole
larvae and of isolated gut tissues were cut from 3 to 10& in thicknss,
in both the transverse and the longitudinal planes. A thickness
of 5 to 7, was usually most satisfactory. The sections were stained
1ItaIic nombn In parenthe refer to Literature Cited, p. 27.
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Woke, Paul A. Structure and development of the alimentary canal of the southern armyworm larva., book, March 1941; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc3506/m1/2/: accessed May 4, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.