A preliminary study of the chorion design in the micropyle area of noctuid eggs (Lepidoptera)
Seamans, Howard L.
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The family Noctuidae is the largest family of the Lepidoptera and includes all those forms the larvae of which are commonly known as "cutworms". These larvae are the generally hairless caterpillars of the heavy-bodied "owlet moths" or "millers" which are so abundant around lights on summer evenings. The name "cutworm" has been applied to the larvae because the more common forms feed on the lower stem portions of plants, cutting them off close to the soil surface. The feeding habits of the larvae of this family are variable. Many species confine their activities to the soil, and can only be found by digging. Some species remain in the soil during the day but come up at night and climb the food plant, feeding entirely on the upper leaves. Other species are never found in the soil and remain on the food plant during their entire development. The economic importance of some species of noctuids has resulted in extensive studies on the biology and control of the larvae. The abundance of species and the variations in the adult markings within species have complicated the systematic study of the family. The great mass of published material dealing with the Noctuidae has dealt with these phases and ignored the eggs except for occasional brief descriptions or to note that they occur in the life history. General entomological texts frequently refer to the great variety of shapes and chorion designs which occur in insect eggs. Metcalf and Flint (17 - p.133) state "Of special usefulness is the sculpturing of the egg shell as seen under the microscope. A great variety of impressions, elevations or depressions are found, the exact shape and arrangement of which will often serve to distinguish one species from another." Illustrations of noctuid eggs are common in literature but with the exception of Henneguy (11 - p.297), Parker, Strand and Seamans (19 - p.314) and Strickland (27 - p.9) no detailed illustrations of the micropyle area have been found. In all other cases the chorion reticulations are shown with a more or less blank area labelled "micropyle" in the center. Crumb (4) has published egg descriptions which refer particularly to the size of the egg and the number of "ribs". He also notes the presence or absence of "transverse lines' but usually refers to the micropyle area as being reticulated. Much misinformation has been published regarding the oviposition habits of the noctuid moths. The general statement, "the adult moths lay their eggs on vegetation which will be suitable for larval food" is far from correct. Observations in the field and experiments with caged moths show that many noctuid species lay their eggs in bare soil whether vegetation is present or not. Of 39 species which have been observed ovipositing in the field or in cages, 30 deposited eggs in the soil, even though larval food plants were available. This indicates that the hours which have been spent in fruitless searching of larval food plants for eggs, have been largely wasted and that eggs found in soil may belong to anyone of a great number of species. The present study is an attempt to illustrate and define the chorion markings surrounding the micropyle in the hope that they may be of value in determining the species to which the egg belongs. No attempt is made to use the egg design as a basis of noctuid classification although a study of the eggs may show resemblances which would assist in definitely placing a doubtful species. This study is not concerned with the histology or function of the chorion or micropyle although some discussion as to the formation of the chorion and the source of the chorion markings is necessary.