The five nymphal instars of Mesouelia mulsanti can be separated by the number of rows of setae on the second abdominal tergum. Fifth instars can be separated from younger instars and from each other by the degree of development of the external genitalia

McPherson, J. E

Taylor, Steven J

English

Valparaiso University

The Great Lakes Entomologist Volume 26 Number 3 - Fall 1993 Number 3 - Fall 1993 Article 5 October 1993 Distinguishing Nymphal Instars of Mesovelia Mulsanti (Heteroptera: Mesoveliidae) J. E. McPherson Southern Illinois University Steven J. Taylor Southern Illinois University Follow this and additional works at: https://scholar.valpo.edu/tgle  Part of the Entomology Commons Recommended Citation McPherson, J. E. and Taylor, Steven J. 1993. "Distinguishing Nymphal Instars of Mesovelia Mulsanti (Heteroptera: Mesoveliidae)," The Great Lakes Entomologist, vol 26 (3) Available at: https://scholar.valpo.edu/tgle/vol26/iss3/5 This Peer-Review Article is brought to you for free and open access by the Department of Biology at ValpoScholar. It has been accepted for inclusion in The Great Lakes Entomologist by an authorized administrator of ValpoScholar. For more information, please contact a ValpoScholar staff member at scholar@valpo.edu. 1993 THE GREAT LAKES ENTOMOLOGIST 233 DISTINGUISHING NYMPHAL INSTARS OF MESOVELIA MULSANTI (HETEROPTERA: MESOVELIIDAE) J.E. McPherson and Steven J. Taylorl ABSTRACT The five nymphal instars of Mesouelia mulsanti can be separated by the number of rows of setae on the second abdominal tergum. Fifth instars can be separated from younger instars and from each ther by the degree of develop­ment of the external genitalia. Life history studies require reliable separation of nymphal ins tars. In Heteroptera, these instars can often be distinguished by structural characters that change during development, often becoming more complex. For example, pigmentation pa terns can change, punctures become more numerous, sderi­tes increase in size and occasionally fuse, and wing pads progress from a simple arcuate pat rn along the posterior margin of the mesonotum to well defined mesonotal pads that extend onto the abdome  in the last instar (metanotal wing pads are almost or quite covered by those on t e mesonotum). In addition, the sexes can be determined in the last instar. Mesouelia mulsanti White shows little change in color pattern during development, and little variation in sclerotization. Hungerford (1917,1919), in his study of this insect, used lengths of the third and fourth antennal seg­ments and metatibia among several structures he selected to distinguish the nymphal instars. Subsequently, Hoffmann (1932), i  his study of this insect. used Hungerford's characters but added length of body. In 1988. one of us (JEM) reported on the life history of M. mulsanti in southern Illinois. Although the various nymphal i stars have abdominal sclerites, these structur s show almost no progressive change during develop­ment. Punctation is minimal. color is primarily greenish, and markings are absent. Mo t adults are apterous (less than 1% were macropterous in the above life history study [unpublished data]). Galbreath (1975), In her study of thoracic polymorphism in M. mulsanti, found that nymphal wing pads mayor may not be present in the fourth and fifth ins tars. If ab ent in the fourth (and resulting fifth), adults will be apterous. If present in the fourth, then the wing pads in the resulting fifths vary from well developed to absent. If wing pads in the fifth nstar extend to at least the third abdominal tergum, the adults w ll be macropterous. If they extend only to the sec d abdominal tergum or are shorter or lacking, the resulting adults will vary from micropterous to apter­ous. Since the presence of wing pads and their shape cannot be relied upon as diagnostic characters to distinguish nymphal instars in field samples. other diagnostic characters must be used. Nonmacropterous adults are easily sepa-JDepartment of Zoology, Southern Illinois University, Carbondale, IL 62901. 1McPherson and Taylor: Distinguishing Nymphal Instars of <i>Mesovelia Mulsanti</i> (HetePublished by ValpoScholar, 1993234 THE GREAT LAKES ENTOMOLOGIST Vol. 26, No.3 A B E 0.1 mm Figure lA·E. Setal pattern of second abdominal tergum in nymphs of M. mulsanti. A, First instar. B, Second instar. C, Third instar. D, Fourth ins tar. E, Fifth instar. rated from nymphs by several characters (e.g., adults have two tarsal seg­ments, nymphs have only one). Of several nymphal cha cters evaluated in the southern Illinois life his­tory study (unpublished information) and present study, th  number of rows of setae on the second abdominal tergum and, in the fifth instar, the presence of well defined ext rnal genitalia proved particularly useful as diagnostic characters. The differences in these characters for the various ins tars, and their reliability, are discussed below. 2The Great Lakes Entomologist, Vol. 26, No. 3 [1993], Art. 5https://scholar.valpo.edu/tgle/vol26/iss3/51993 THE GREAT LAKES ENTOMOLOGIST 235 A B O.5mm Figure 2A-B. External genitalia of fifth instar of M. mulsanti. A, Male. B, Female. MATERIALS AND METHODS We collected nymphs from a pond on the Southern Illinois University at Carbondale campus (President's Pond) throughout the active season (ca. April to November) during 1989 and randomly selected 30 of the first four nymphal instars and 60 of the fifth instar (30 of each sex) for comparison; wing padswere not readily apparent in any specimens. All specimens were preserved in 70% alcohol. Illustrations were made with e aid of an ocular grid. RESULTS AND DISCUSSION Number of rows of setae on the second abdominal tergum changed during nymphal development and corresponded roughly to the number of the instar (Le., one row in the first instar, two rows in the second, etc.) (Fig. lA-E). Setae can sometimes be pale and care must be taken to insure they are not over­looked. Sexes can be distinguished in fifth ins tars (Fig. 2A-B); the genitalia are not developed enough in the fourth instar to allow the sexes t  be reliably separated. Thus, external genitalia can be used to distinguish fifth instars from younger instars and from each other. ACKNOWLEDGMENTS We thank Karen Fiorino, Research Photography and Illustration Facility, SIUC, for the final illustrations and photographs of the figures. 3McPherson and Taylor: Distinguishing Nymphal Instars of <i>Mesovelia Mulsanti</i> (HetePublished by ValpoScholar, 1993236 THE GREAT LAKES ENTOMOLOGIST Vol. 26, No. 3 LITERATURE CITED Galbreath, J. E. 1975. Thoracic polymorphism in Mesovelia mulsanti (Hemiptera:Me­sovellidae). Univ. Kansas Sci. Bull. 50:457-482. Hoffmann, C. H. 1932. The biology of three North American species of Mesovelia (Hemiptera-Mesoveliidael. Canadian EntomoL 64:88-95,113-120, 126-134. Hungerford, H. B. 1917. The life-history of Mesovelia mulsanti White. Psyche 24:73-84. Hungerford, H. B. 1919. The biology and ecology of aquatic and semi aquatic Hemiptera. Univ. Kansas Sci. Bull. 11:3-328. McPherson, J. E. 1988. Life history of Mesovelia mulsanti (Hemiptera:Mesovelidae) in southern Illinois. Great Lakes EntomoL 2:19-23. 4The Great Lakes Entomologist, Vol. 26, No. 3 [1993], Art. 5https://scholar.valpo.edu/tgle/vol26/iss3/5

Distinguishing Nymphal Instars of \u3ci\u3eMesovelia Mulsanti\u3c/i\u3e (Heteroptera: Mesoveliidae)

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Distinguishing Nymphal Instars of \u3ci\u3eMesovelia Mulsanti\u3c/i\u3e (Heteroptera: Mesoveliidae)

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