Use of ITS 1 to identify Bactrocera dorsalis and Bactrocera occipitalis (Diptera: Tephritidae): a case study using flies trapped in California from 2008 to 2018

Authors

  • Norman Benjamin Barr USDA APHIS PPQ Mission Laboratory, 22675 North Moorefield Road, Edinburg, Texas 78541, USA
  • Martin Hauser California State Collection of Arthropods, Plant Pest Diagnostics Branch, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, California 95832–1448, USA
  • Jennifer Belcher USDA APHIS PPQ Mission Laboratory, 22675 North Moorefield Road, Edinburg, Texas 78541, USA
  • David Salinas Department of Biology, University of Texas Rio Grande Valley, 1201 West University Drive, Edinburg, Texas 78539, USA
  • Erin Schuenzel Department of Biology, University of Texas Rio Grande Valley, 1201 West University Drive, Edinburg, Texas 78539, USA
  • Peter Kerr California State Collection of Arthropods, Plant Pest Diagnostics Branch, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, California 95832–1448, USA
  • Stephen Gaimari California State Collection of Arthropods, Plant Pest Diagnostics Branch, California Department of Food and Agriculture, 3294 Meadowview Road, Sacramento, California 95832–1448, USA

Abstract

Molecular methods are necessary to diagnose immature life stages of the agricultural pest fruit fly Bactrocera dorsalis (Hendel), and are useful to corroborate identifications based on adults because morphological variation within the species can overlap with congeners. DNA sequencing of the nuclear ribosomal internal transcribed spacer 1 (ITS‑1) has been adopted by the International Plant Protection Convention as an internationally accepted method to distinguish between the 2 pestiferous fruit fly species Bactrocera dorsalis and Bactrocera carambolae (Drew & Hancock). Reported ITS‑1 sequences also are distinct and diagnostically informative to distinguish several other Bactrocera species related to B. dorsalis. In this study, we applied DNA sequencing of ITS‑1 to a collection of 513 adult flies trapped in California, USA, in the yr 2008 to 2018. Internal transcribed spacer 1 sequences were successfully recovered from 504 (98%) of these flies. One fly had an ITS‑1 sequence that matched B. occipitalis (Bezzi) records. Re-examination of that fly using cytochrome c oxidase I, elongation factor 1‑alpha, and morphology supports it as the second record of B. occipitalis trapped in California. The other 503 flies had ITS‑1 sequences consistent with B. dorsalis. Six unique ITS‑1 sequences (or DNA types) were observed in the collection of 503 B. dorsalis. Three of the ITS‑1 sequences (types A, B, and C) were present in 84% of the 503 flies and match ITS‑1 records reported in prior publications on B. dorsalis. The other 3 sequences (types D, E, and F) observed in 4% of the 503 B. dorsalis have not been reported in publications. Ambiguous nucleotides were observed from 12% of the 503 B. dorsalis flies, precluding designation of a sequence type. Including the 3 new types from the current study, a total of 15 unique ITS‑1 sequences now are known for B. dorsalis. The study, therefore, documents additional intraspecific variation of ITS‑1 that aids in future applications for species identification.

Resumen

Los métodos moleculares son necesarios para diagnosticar los estadios de vida inmaduras de la plaga agrícola mosca de la fruta Bactrocera dorsalis (Hendel) y son útiles para corroborar identificaciones basadas en adultos por la variación morfológica dentro de la especie puede superponerse con congéneres. La secuenciación del ADN del espaciador transcrito interno ribosómico nuclear 1 (ITS-1) ha sido adoptada por la Convención Internacional de Protección Fitosanitaria como un método aceptado internacionalmente para distinguir entre las dos especies de moscas de la fruta, Bactrocera dorsalis y Bactrocera carambolae (Drew & Hancock). Las secuencias de ITS-1 notificadas también son distintas y proporcionan información diagnóstica para distinguir varias otras especies de Bactrocera relacionadas con B. dorsalis. En este estudio, aplicamos la secuenciación de ADN de ITS-1 a una colección de 513 moscas adultas atrapadas en California, EE. UU. desde el 2008 hasta el 2018. Se recuperaron las secuencias espaciadoras transcritas internas1 con éxito de 504 (98%) de estas moscas. Una mosca tenía una secuencia ITS-1 que coincidía con los registros de B. occipitalis (Bezzi). El reexamen de esa mosca usando la citocromo c oxidasa I, el factor de elongación 1-alfa y la morfología lo respalda como el segundo registro de B. occipitalis atrapada en California. Las otras 503 moscas tenían secuencias de ITS-1 compatibles con B. dorsalis. Se observaron seis secuencias únicas de ITS-1 (o tipos de ADN) en la colección de 503 B. dorsalis. Tres de las secuencias de ITS-1 (tipos A, B, y C) estaban presentes en el 84% de las 503 moscas y coinciden con los registros de ITS-1 informados en publicaciones anteriores sobre B. dorsalis. Las otras 3 secuencias (tipos D, E, y F) observadas en el 4% de las 503 B. dorsalis no han sido reportadas en publicaciones. Se observaron nucleótidos ambiguos en el 12% de las 503 moscas B. dorsalis, lo que excluye la designación de un tipo de secuencia. Incluyendo los 3 nuevos tipos del estudio actual, ahora se conocen un total de 15 secuencias ITS-1 únicas para B. dorsalis. Por lo tanto, el estudio documenta una variación intraespecífica adicional de ITS-1 que ayuda en futuras aplicaciones para la identificación de especies.

Key Words: dorsalis complex; internal transcribed spacers; diagnostics; invasive species

Supplementary material for this article in Florida Entomologist 104(2) (June 2021) is online at http://purl.fcla.edu/fcla/entomologist/browse

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Published

2021-08-04

Issue

Vol. 104, No. 2 (June 2021)

Section

Research Papers

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