Further description of Helicoverpa zea (Lepidoptera: noctuidae) male genitalia and new genetic evidence of synonymy with respect to the anomalous form, “heliothis stombleri”

Abstract

The Helicoverpa/Heliothis complex can cause serious damage to agricultural crops. Phenotypic similarity makes it difficult to discriminate between closely related Helicoverpa species. Currently, morphology of the male genitalia complemented with molecular techniques constitutes the best approach for species identification. In this work, a broad microscopic examination of adult Helicoverpa zea (Boddie) males (n¼200) captured in central Argentina was carried out in order to provide a detailed description of the valvae and the phallus. A considerable degree of variability was recorded. Both rounded and sharp valve apices were observed and valvae were not always parallel-sided. Most evident differences were detected concerning the number of cornuti on the phallus. A range of 15–21 cornuti per phallus was recorded, the mode being 18. A significant minority of the samples (3.5%) displayed an abnormal genital condition showing a constricted phallus lacking cornuti, and pointed valvae. This form was initially attributed to a distinct species, Heliothis stombleri, and later proposed as a synonym of H. zea based on additional morphological observations and molecular studies. Here, a phylogenetic analysis combining mitochondrial (cytochrome oxidase subunit I) and nuclear (elongation factor –1 alpha) genes was performed on these and other Helicoverpa specimens collected in the same geographical region, in order to further verify the taxonomic status of H. stombleri. The tree topology clearly grouped H. stombleri with H. zea, supporting the assumption that the former represents, in fact, an anomalous form of the latter. Further experiments are needed to clarify the etiology of this anomaly and its persistence over time.

El complejo Helicoverpa/Heliothis produce graves daños a la agricultura. Las especies del género Helicoverpa son difíciles de diferenciar porque poseen un fenotipo similar. Actualmente, su identificación se basa en características morfológicas de la genitalia masculina y en el uso de marcadores moleculares. En este trabajo, se examinaron por microscopía machos adultos de Helicoverpa zea (Boddie; n = 200) capturados en la zona central de Argentina, a fin de detallar la forma y variabilidad de valvas y falo. Las valvas no siempre presentaron lados paralelos, y mostraron ápices agudos o redondeados. Las diferencias más evidentes se refirieron al número de cornuti del falo (15 a 21, moda = 18). Una minoría significativa de las muestras (3,5%) exhibió una fuerte anomalía en el aspecto del aparato reproductor: falo sin cornuti, estrechado en su extremo, y valvas terminadas en punta. Esta variante, que había sido atribuida inicialmente a una especie distinta, Heliothis stombleri, fue luego considerada como sinónimo de H. zea mediante estudios morfológicos y moleculares. Para verificar esta conclusión, se llevó a cabo un análisis filogenético que combinó genes mitocondriales (COI) y nucleares (EF-1α) a partir de especímenes de H. stombleri y otras Helicoverpa spp. provenientes de la misma región. La topología de los árboles agrupó claramente a H. stombleri con H. zea, permitiendo suponer que, en efecto, ambas formas constituyen la misma especie. Experimentos adicionales son necesarios para clarificar la etiología de esta anomalía, así como su persistencia en el tiempo.