This study was undertaken to identify, if possible, some morphological characteristics of the U. S. Sitona species that would help simplify the classification of this difficult group. Because of extreme difficulty in obtaining positively identified specimens of all species reported, the scope was limited to eight identified species and one unidentified series. External structures studied include mouth parts, appendages, eyes, wings, and genitalia. The spermathecae were the only internal structures analyzed. Mandibular profiles were compared throughout the species represented and variations were noted. Labia and maxillae were observed but no distinctive differences were noticed. Antennae were found to be quite uniform within the genus. Variations discovered in the thoracic appendages were limited to setae, pollexes, and corbels. These variations, though not too distinctive, appeared specifically consistent. Pollex variation within a species seemed correlated with sex and may well serve as a sex index. Variation of eye size within the genus was relatively large, but within each species it was more or less limited. Prominence of the mesal margins of the eyes followed a similar pattern. Eye characteristics, though consistent, were of a relative nature. Wing structures were found to exhibit great similarity in most respects. General contour and radial cell size and shape were recognized as possible taxonomic characters. The radial cell was emphasized as a wing character because of the ease with which it may be analyzed. The most important morphological taxonomic characters found, in the opinion of the writer, were those pertaining to the terminalia. On the basis of the shape of the apex of the median lobe, the species studied were keyed into two major divisions. Other terminal structures were employed in the key to separate the different species. The key was made to illustrate the ease with which some species may be distinguished. The spermathecae were found to vary around a generic mean. Specific characteristics were not arrived at because of variations. Sixty-seven illustrations were made of the mouth parts, appendages, wings, terminalia, and spermathecae.



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Plant and Wildlife Sciences



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