The taxonomic status of Xyonysius major (Berg) (Hemiptera: Lygaeidae), an occasional pest of sunflower in Brazil

A situação taxonômica de Xyonysius major (Berg) (Hemiptera: Lygaeidae), uma praga ocasional no Brasil

SYSTEMATICS, MORPHOLOGY AND PHYSIOLOGY

The taxonomic status of Xyonysius major (Berg) (Hemiptera: Lygaeidae), an occasional pest of sunflower in Brazil

A situação taxonômica de Xyonysius major (Berg) (Hemiptera: Lygaeidae), uma praga ocasional no Brasil

Carl W. Schaefer^I

^IDepartment of Ecology and Evolutionary Biology University of Connecticut, U-43 75 North Eagleville Road, Storrs CT 06278-3043, USA

ABSTRACT

Specimens of a species of the orsilline genus Xyonysius have been collected on sunflower (Helianthus annuus) in Londrina, Paraná. The specimens appeared to be X. major (Berg), but this species has been synonymized with X. californicus (Stål). Here I show the two species should be considered distinct, at least until the concept "Xyonysius californicus" has been clarified. The sunflower lygaeid is X. major.

Key words: Insecta, Lygaeidae, Orsillinae, sunflower.

RESUMO

Exemplares de uma espécie de Orsillinae do gênero Xyonysius foram coletados em girassol (Helianthus annuus) em Londrina, Paraná. Os exemplares parecem ser da espécie X. major (Berg), mas essa espécie foi colocada como sinônimo de X. californicus (Stål). Demonstra-se aqui que as duas espécies devem ser consideradas distintas, ao menos até que o conceito "Xyonysius californicus" seja esclarecido. Desta forma, o ligeídeo do girassol deve ser considerado X. major.

Palavras-chave: Insecta, Lygaeidae, Orsillinae, girassol.

Sunflower, Helianthus annuus, is grown commercially in the Brazilian states of Paraná, São Paulo, Mato Grosso, and Goiás. About 25,000 hectares are planted to the crop each year, yielding some 40,000 tons of seed (Regina V. C. Leite, personal communication).

In February, 1997, several specimens of a species of Xyonysius (Orsillinae: Metrargini), were collected on sunflower grown in the greenhouse, in Londrina, Paraná State, Brazil. Because of the commercial importance of sunflower in Brazil, these specimens should be identified. Accurate identification is especially important because what is probably this species has already been reported as a minor sunflower pest: by Boiça et al. (1984) (as "Nizius" sp.), in Mato Grosso State; and by Zucchi et al. (1993) (as Nysius sp.), more generally.

Of the Xyonysius species recorded from Brazil (Ashlock 1967), the Londrina specimens are too large (5.6-6.8 mm long) to be X. ellipticus Berg—spelled "elypticus" in Ashlock (1967),— described by Berg (1892) as 3.7-4.3 mm long. The sunflower Xyonysius closely resembles X. volxemi (Distant), but the rostrum reaches between the hind coxae, whereas in X. volxemi it "almost reachy [sic] the intermediate coxae" [Distant 1888]); the antennae are less infuscated in the sunflower specimens than in X. volxemi; and the latter insects are somewhat smaller (5 mm long) (Distant 1888). The Londrina specimens most closely resemble X. californicus (Stål). And herein lies a problem.

Xyonysius californicus was described by Stål in 1859 (as Nysius), and X. major was described by Berg in 1879 (again, as Nysius). In 1947, Barber synonymized major with californicus. Ashlock and Lattin (1963) separated from Nysius those species with both costal and abdominal stridulitra into a new genus, Xyonysius. Ashlock and Lattin listed both X. californicus and X. major, and wrote further, "For the present state of synonymy of these names, see Barber (1947)" (p. 702). In his 1967 revision of orsilline genera, Ashlock again listed both species. Thus it is unclear whether Ashlock - the authority on the lygaeid subfamily Orsillinae - meant to remove X. major from synonymy or not; he did not do so explicitly either in 1963 or in 1967, and the catalogs of the Lygaeidae (Slater 1964, Slater and O'Donnell 1995) quite properly list only the synonymy of Barber (1947). Nevertheless, by referring the reader to Barber (1947), Ashlock and Lattin (1963) seemed to be accepting Barber's synonymy. Yet, by not mentioning that synonymy, and listing major as a species of Xyonysius like the others, Ashlock (1967) implicitly rejected Barber's synonymy.

Material and Methods

In order to determine whether the Londrina specimens are Xyonysius californicus, it becomes necessary to determine if this species and X. major are the same. To do this, I have compared specimens of X. major determined by P. D. Ashlock (in J. A. Slater Collection), with specimens of X. californicus determined by H. G. Barber, P. D. Ashlock, and M. H. Sweet (J. A. Slater Collection, and mine); P. D. Ashlock was the authority on orsilline lygaeids, and M. H. Sweet is a leading authority on Lygaeidae. The X. major specimens were collected "nr. Campo Grande," Mato Grosso State, Brazil, and in Carmen and Independencia, Paraguay; the X. californicus are from Illinois (U.S.A.) south through central Mexico and the Dominican Republic. I compared these specimens also with those from sunflower in Londrina.

Results and Discussion

In general, X. major specimens are uniformly darker than are X. californicus, whether from Mexico and the United States southwest or from the less dry midwestern United States. The Brazilian specimens from sunflower are also dark. The thoracic and abdominal venters of X. major and the sunflower specimens are mostly black; those of X. californicus are pale, although occasionally dark.

In males, the ventral rims of the genital capsules of X. major and the Brazilian sunflower specimens are more broadly rounded than are those of the capsules of X. californicus. The blade of the latter's parameres is slightly longer than those of the parameres of X. major and the Brazilian specimens (Table 1). These differences are slight, however.

At its base, the corium is contracted, that is, it curves medially (Table 1). The sunflower specimens and X. major have a sharper contraction than does X. californicus, although Barber (1947) says this sharper contraction occurs in X. californicus (with which he synonymizes X. major). The costal (outer) margin of the corium is straight in X. major, but that of X. californicus and of the sunflower specimens is slightly curved (Table 1); Ashlock (1967), however, says this margin is straight in both X. major and X. californicus (which - significantly - he lists as apparently of equal rank).

Ashlock (1967) suggests that the relative lengths of antennal segments may help separate species of Xyonysius; the relative lengths of the three groups here are the same (Table 1). However, from the measurements Barber (1947) gives, the relative lengths of X. californicus should be 2=4>3>1; and, of his subspecies X. californicus alabamensis Barber, the relative lengths should be 4>2>3>1, 2 being only slightly greater than 3. I have measured three U.S.A. specimens in the J. A. Slater Collection, all identified by Barber, as follows (in millimeters): specimen from Illinois: 0.36, 0.99, 0.82, 0.82; specimen from North Carolina: 0.36, 0.73, 0.63, 0.66; specimen from Arizona: 0.36, 0.82, 0.66, 0.63. Thus the relative lengths of antennal segments of specimens identified by Barber as X. californicus are the same as I give in Table 1. The North Carolina specimen is X. californicus alabamensis, an eastern North American subspecies which is smaller than the typical subspecies. But the similar specimen from Arizona is presumably the typical subspecies, as is also the Illinois specimen. The concept "Xyonysius californicus" is clearly a confused one.

In general, the differences between X. major and X. californicus are ones of degree, not of kind. X. major is darker and larger than X. californicus, except specimens of the latter from Arizona and Texas (U.S.A.). With respect to structural characteristics, the two species either differ slightly or not at all (Table 1). In addition, the ambiguities mentioned above suggest that it is not clear just what "Xyonysius californicus" is.

Until the concept "Xyonysius californicus" is clarified, via a thorough analysis of variation within both species, I believe the two should be treated as separate. Therefore I explicitly remove X. major (Berg) from synonymy with X. californicus (Stål), just as, it appears, Ashlock had already implicitly done.

The Brazilian specimens, collected in Londrina on sunflower, are X. major.

Very little is known about the biology and ecology of Xyonysius. Therefore, and because this species may become a pest on sunflower in southern Brazil, its biology and life history should be studied.

Acknowledgments

I am very grateful to Ms Andréa B. Malaguido (EMBRAPA/ Soja, Londrina), who told me about these insects and generously collected them for me. I am indebted to J. A. Slater (Prof. Emeritus, University of Connecticut) for much (and much needed) taxonomic advice, and for open access to his collection of Xyonysius. Dr. A. R. Panizzi (EMBRAPA/ Soja) was a most gracious host during my stay in Brazil, which was sponsored by IICA/ EMBRAPA PROMOAGRO. Finally, I thank A. R. Panizzi for furnishing the Portuguese abstract, and an anonymous reviewer for several references.

Literature Cited

Received 24/IX/97. Accepted 29/I/98.

• Ashlock, P. D. 1967. A generic classification of the Orsillinae of the world (Hemiptera-Heteroptera: Lygaeidae). Univ. Calif. Publ. Entomol. 48: 1-82.
• Ashlock, P. D. & J. D. Lattin. 1963. Stridulatory mechanisms in the Lygaeidae, with a new American genus of Orsillinae (Hemiptera: Lygaeidae). Ann. Entomol. Soc. Am. 56: 693-703.
• Barber, H. G. 1947. Revision of the genus Nysius in the United States and Canada (Hemiptera Heteroptera: Lygaeidae). J. Wash. Acad. Sci. 37: 354-366.
• Berg, C. 1879. Hemiptera Argentina enumeravit speciesque novas. Pauli E. Coni, Bonariae, 316p.
• Berg, C. 1892. Nova Hemiptera faunarum Argentinae et Uruguayensis. Lygaeidae. An. Soc. Cient. Argent. 33: 151-165.
• Boiça, A. L., Jr., A. C. Bolonhezi, & J. Paccini Neto. 1984. Levantamento de insetos-praga e seus inimigos naturais em girassol (Helianthus annuus L.), cultivado em primeira e segunda época, no município de Selvíria-MS. An. Soc. Entomol. Brasil 13: 189-196.
• Distant, W. L. 1888. Enumeration of the Van Volxem Collection of Rhynchota contained in the Brussels' Museum. Part III. Ann. Soc. Entomol. Belg. 32(3): 1xxviii-lxxxiii.
• Slater, J. A. 1964. A catalogue of the Lygaeidae of the world. University of Connecticut, Storrs, 1668p.
• Slater, J. A. & J. E. O'Donnell. 1995. A catalogue of the Lygaeidae of the world (1960-1994). N. Y. Entomol. Soc., New York, New York, 411p.
• Stål, C. 1859. Hemiptera. Species novas descripsit. Kongl. Svenska Fregatten Eugenies Resa Omkring Jorden, Entomol. Bidrag. 1859: 219-298.
• Zucchi, R. A., S. Silveira Neto, & O. Nakono. 1993. Guia de identificação de pragas agrícolas. FEALQ, Piracicaba, SP, 139p.

Publication Dates

• Publication in this collection
  03 Aug 2006
• Date of issue
  Mar 1998

History

• Received
  24 Sept 1997
• Accepted
  29 Jan 1998