Biodiversity Data Journal :
Taxonomic Paper
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Corresponding author: Maria Lourdes Chamorro (lourdes.chamorro@ars.usda.gov)
Academic editor: Li Ren
Received: 02 May 2018 | Accepted: 16 Oct 2018 | Published: 02 Nov 2018
This is an open access article distributed under the terms of the CC0 Public Domain Dedication.
Citation:
Chamorro M, Barclay M (2018) On the identity of a U.S. intercepted Conotrachelus Dejean (Coleoptera: Curculionidae) with avocado (Persea americana). Biodiversity Data Journal 6: e26362. https://doi.org/10.3897/BDJ.6.e26362
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The multimillion-dollar avocado industry is threatened by a number of serious insect pests, including at least seven species of Curculionidae. Of these, three Conotrachelus species are known to develop and feed on avocados: Conotrachelus aguacatae Barber, Conotrachelus perseae Barber and C. serpentinus (Klug); the first two are of economic importance. Recently, a series of unrecognised Conotrachelus was intercepted with avocado and other commodities by the USDA at various southern U.S. ports of entry. The species most closely resembled the U.S. native Conotrachelus posticatus Boheman. Given the threat posed by certain species of Conotrachelus to avocado, the identity and biology of intercepted unknown Conotrachelus species becomes a matter of much concern for regulators due to the potential risk posed by non-native species to local agriculture. This study aims to determine the identity, which in turn may shed light on the biology and native distribution, of possible new non-U.S.-native weevils and provide the tools necessary to distinguish amongst phenotypically similar native species.
Amongst the unknown Conotrachelus weevils intercepted with avocados at certain U.S. ports of entry is Conotrachelus lobatus Champion. This poorly known species resembles a commonly collected, phenotypically variable indigenous U.S. species, Conotrachelus posticatus, which, on occasion, is also intercepted with avocado. Conotrachelus lobatus has been collected, since the early 1900s until today, along a narrow corridor in the southwest Mexican states of Michoacan, Jalisco and Nayarit. Specimen label data in natural history collections suggests the presence of this species in large numbers in early July in the avocado growing region of Mexico and, based on notes from former curators, appears to breed in acorns of the Mexican endemic oak species Quercus obtusata. The interception of C. posticatus and C. lobatus wth avocado does not imply strict biological association, however it reveals an important pattern of a non-native species' potential for introduction and its potential vector. Understanding all aspects of an organism's biology will better equip growers, as well as regulators, with effective and well-informed management strategies. Characters are imaged and discussed in order to help distinguish some Conotrachelus species belonging to Conotrachelus group II designated by
Food security, weevils, Molytinae, avocado seed weevils, oak, natural history collections
Avocados (Persea americana Mill.) are lucrative. Between the years 2015-2016, the U.S. state of California produced 401.4 million pounds (~182 million kilograms) of avocados yielding more than $412 million dollars in crop value (
A number of insects species are considered serious pests of, and present a potential threat to, the multibillion dollar national and international avocado industry. Within Curculionidae (Coleoptera), known avocado pests include at least seven species: five species of seed weevils, Heilipus lauri (Boheman, 1845), Heilipus apiatus (Olivier, 1807), Conotrachelus aguacatae Barber, 1924, C. perseae Barber, 1919 and C. serpentinus (Klug, 1829) (Molytinae); one species of stem weevil, Copturus aguacatae Kissinger, 1957 (Conoderinae) (USDA 2012); and the recent invasive Redbay Ambrosia Beetle, Xyleborus glabratus Eichhoff, 1877 (Scolytinae), vector of the laurel wilt fungus, Raffaelea lauricola T. C. Harr (Ophistomatales: Ophiostomataceae) (
In July of 2016 and 2017, the senior author received, for urgent identification from the United States Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) Plant Protection and Quarantine (PPQ), more than 10 Conotrachelus Dejean, 1835 (Curculionidae: Molytinae) adults intercepted with various commodities, mainly avocados, at U.S. ports of entry. These specimens were not the three Conotrachelus species currently associated with avocados: C. aguacatae (Fig.
Conotrachelus is a New World molytine weevil genus with approximately 1,200 described species (
In this study, we determine the identity of more than 10 specimens of unfamiliar Conotrachelus intercepted with avocado over the course of two growing seasons (2 years).
Material examined is deposited in the following institutions:
BMNH – Natural History Museum (formerly British Museum of Natural History), London, U.K.;
CWOB – Charles W. O'Brien Collection, Green Valley, Arizona, USA;
NHRS – Naturhistoriska riksmuseet, Stockhom, Sweden;
USNM – National Museum of Natural History, Washington, DC, USA.
Specimens were examined with a Zeiss Discovery v8 stereomicroscope. Multiple habitus images were taken with the Macropod (Macroscopic Solutions) at different focal distances and combined with Zerene Stacker to achieve a greater depth of field. Images of detailed morphological features and of types were taken with an Olympus PEN5 camera mounted on a Zeiss Discovery v8 and combined with Zerene Stacker. Minor editing of the final stacked images (rotation, sharpening) was achieved using Adobe Photoshop (Adobe Products). Terminology follows
Adults were compared with the male and female type specimens of C. lobatus Champion, C. squamifrons Champion and C. scoparius Champion housed at BMNH. Locality information on the labels was supplemented with the gazetteer by
Males can be distinguished from females by the more distal insertion of the antennae on the rostrum, whereas in females, the antennae arise more proximad on the rostrum, approximately 1/5th from the apex. In weevils generally, males and females may be readily distinguished by the presence in males of a concavity on the metasternum and on the first (and sometimes second) visible abdominal ventrite. The male genitalia characters for C. posticatus and C. lobatus were examined, compared and checked against Schoof's work.
Conotrachelus lobatus Champion, 1904 –
Conotrachelus lobatus (Figs
Of the species from North America north of Mexico, Conotrachelus lobatus is most similar to C. posticatus Boheman, C. carinifer Casey and C. naso LeConte. These species all have a longitudinal median prothoracic carina (Figs
Conotrachelus lobatus resembles C. posticatus in the presence of white to fulvous setae concentrated in a few scattered patches, but mainly in a narrow, posteriorly curved, postmedian elytral band (on the declivity) (Figs
Male Conotrachelus lobatus, which have elongate fulvous setae ventrally on the fore femur and insertion of antennae subapically on the rostrum (Fig.
Sexual dimorphism is minimal in C. lobatus compared to C. posticatus. As in the majority of Conotrachelus, the rostrum in the female is longer, the antennae are located more proximad and the sternum is not concave. Conotrachelus females are more challenging than the males to distinguish.
Mexico
Conotrachelus posticatus Say, 1831 in
One of the salient features of C. posticatus (Figs
Conotrachelus posticatus syntype, NHRS-COLE000008467. Photographed by Johannes Bergsten (© 2018 Naturhistoriska riksmuseet). Made available by the Swedish Museum of Natural History under Creative Commons Atribution 4.0 International Public License, CC-BY 4.0.
Conotrachelus posticatus male, syntype? NHRS-JLKB000027565. Photographed by Johannes Bergsten (© 2018 Naturhistoriska riksmuseet). Made available by the Swedish Museum of Natural History under Creative Commons Atribution 4.0 International Public License, CC-BY 4.0.
Canada, Guatemala, Mexico, Panamá, U.S.A.
It is not uncommon in collections to find Conotrachelus naso misidentified as C. posticatus. The fore-femora of C. posticatus are distally excavate ventrally and bear a tooth, while in C. naso, the ventral margin of the fore-femora is largely entire. During the course of this study, we came across multiple species that resemble C. posticatus (e.g. elytral maculation, males with metauncus dentiform and first and second striae costate); however, upon dissection of males, differences in the median lobe confirmed these to be different species. Careful examination of the metauncus reveals additional diagnostic characters. While many of these superficially similar C. posticatus males possess a dentiform metauncus, slight differences exist, such as the presence of tufts of setae on the denticles themselves. Other species, in what is here termed the C. posticatus complex, share many characteristics with C. naso; for example, the ventral margins of the fore-femora are entire with either a small spine or altogether lacking one. In addition, the shape of the apex of the median lobe resembles that of C. naso. A revision of C. posticatus and related species is needed.
Conotrachelus scoparius Champion, 1904; –
Size: 4.5 mm. Currently, only the male is known for this species, which can be distinguished from other species included in this study by the presence of elongate, fulvous setae apically on all tibiae (Fig.
Mexico
Conotrachelus squamifrons Champion, 1904; –
Male C. squamifrons (Fig.
Guatemala, Panama
In addition to the general remarks above on ways to differentiate males from females, males of C. squamifrons can be distinguished from females by interstice 3 being sharply costate, while in some females, it may be subapically interrupted. Males are generally narrower-bodied than females.
Females in the paralectotype series differ from each other in the presence of a subbasal interruption of striae 3 and greater pronotal lateral expansion, resulting in a cordate pronotum e.g. in specimen number NHMUK010801264.
The specimens intercepted most closely resemble Conotrachelus posticatus Boheman, 1837, a widespread species in the U.S. with a distribution extending beyond the U.S. border south as far as Panama (
The identity of the male Conotrachelus, treated in this study, can be unequivocally determined to be Conotrachelus lobatus Champion (Figs
Establishing the correct identity of organisms, intercepted at border protection points, has direct implications for food security. Political boundaries do not reflect biological realities and species may or may not occur on both sides of the border. The accidental introduction of a non-native species has the potential to destabilise the delicate balance of natural and agricultural systems. The identification of this weevil, Conotrachelus lobatus, putatively associated (loosely or not) with avocado as non-native is significant, since this species closely resembles and may be easily confused with a U.S. native species, Conotrachelus posticatus. The risks posed by the non-native weevil C. lobatus to U.S. agriculture, particularly commercial U.S. groves of avocados or other resources, are not yet understood, given the limited knowledge we have of the life history of this species. However, some inferences may be made based on historical data.
The identity of C. lobatus was confirmed through collaboration between scientists from two museums with extensive and historical research collections, the Natural History Museum in London and the U.S. Museum of Natural History in Washington, DC. The linking of the newly intercepted species to an older, already described taxon provides valuable baseline data, especially as it pertains to the original native range of the species, or at least its area of occurrence more than a century ago. This type of historical information is often poorly known or unknown for invasive/alien organisms, but is crucial for prospecting for natural enemies for possible implementation of biological control programmes (e.g.
In addition to the 120 year-old specimens described by Champion, two addtional series of Conotrachelus lobatus collected in the 1970s and 80s are confirmed. One is a series of specimens in the USNM weevil collection, identical to the intercepted specimens, which were tentatively identified by Donald Whitehead (USDA, SEL, deceased) as C. lobatus.
The second is a series of specimens in the Charles W. O'Brien collection (CWOB). O'Brien confirmed the identity of these specimens based on comparison with images sent to him of the type, which are the same images included in this manuscript. O'Brien sent the following information when the label data was requested: "One important specimen says 'Uruapan Mich [Michoacán, Mexico],/ Junio – 1989/ 1600 M/ Leon Llandera' // 'Hosp. Persea americana'. Some from Nayarit say 'pine/oak', one 'oak' only, which probably refer to habitat.".
Conotrachelus posticatus and species in this complex are known to be associated with acorns of Quercus spp. (
In summary, the following information is known about Conotrachelus lobatus:
- collected approximately 120 years ago in west-central Durango state, Mexico;
- collected between 43-27 years ago in/near avocado groves in the west-central Mexican states of Nayarit and Michoacán, the latter being the heart of the avocado growing region of Mexico;
- collected in/near oak stands;
- putative sister species associated with oaks (Conotrachelus posticatus complex);
- belongs to a group of weevils that are readily attracted to lights;
- intercepted (possibly incidentally) with at least two different types of commodities: avocados and papaya;
- usually collected/intercepted during the months of June and July.
Given the resemblance between Conotrachelus lobatus and several Conotrachelus species native to the U.S.A., we have provided numerous distinguishing features to prevent type I and II errors (false positives and false negatives). Sexual dimorphism makes identification of single specimens challenging and one must exercise caution when only a single sex is present, particularly the female.
While
We are indebted to Dr. Johannes Bergsten, NHRS Curator of Coleoptera for generating multiple images of two Conotrachelus posticatus types (possible type in the case of the second specimen) housed in the NHRS collection in Stockholm, Sweden. We thank Charles W. O'Brien for providing locality data for Conotrachelus lobatus from his collection and for discussion on the identity of this species. Special thanks to Thomas T. (Tad) Dobbs, Clarissa J Maroon-Lango and David S. Neitch (USDA, APHIS-PPQ) for discussion about this species and the staff of the Coleoptera Section of the Natural History Museum, London, for helpful discussions. We thank the following reviewers for their helpful comments and suggestions: Robert Anderson, Matthew Buffington, Christopher Lyal, Gary Miller, Li Ren, Gregory P. Setliff, Mike Skinner, and Antonio J. Velazquez. Images of some of the species were generated by Ms. Alyssa Seeman and Mr. Ashton Smith and their assistance is appreciated. In addition, the work of U.S. port inspectors and identifiers is greatly appreciated and their initial discovery of this species led to the present work. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the USDA. The USDA is an equal oppportunity provider and employer.