MOLECULAR ENTOMOLOGY Is There a Cryptic Species Within Aulacorthum solani (Hemiptera: Aphididae)? 1,2 1 1 3 GARY L. MILLER, COLIN FAVRET, ANDREW CARMICHAEL, AND DAVID J. VOEGTLIN J. Econ. Entomol. 102(1): 398Ð400 (2009) ABSTRACT Examination of DNA sequences of the 5Ј end of the mitochondrial cytochrome oxidase I gene of Aulacorthum solani (Kaltenbach) (Hemiptera: Aphididae) reveals little variation between samples from broad geographic provenances. The apparent genetic similarity despite A. solaniÕs morphological and biological differences contrasts with the species complexes of other aphid pests. KEY WORDS foxglove aphid, glasshouse potato aphid, cytochrome oxidase I Most aphids are host specialists, but of the nearly 4,700 solani may represent more than one species and that species of aphids (Remaudie`re and Remaudie`re its global movement should be more carefully moni- 1997), 18Ð35 species are highly polyphagous (Black- tored and controlled. The present study was con- man and Eastop 1994, 2000, 2006). One of these ducted to ascertain whether there is molecular evi- polyphagous species is Aulacorthum solani (Kalten- dence for cryptic species within what is currently bach) (Hemiptera: Aphididae). Considered native to recognized as A. solani. Europe, A. solani is nearly cosmopolitan in its distri- bution. This aphid was Þrst described on potato (So- Materials and Methods lanum tuberosum L., Solce), but it has since been recorded from an extremely large range of both mono- Specimens were collected by hand at various sites and dicotyledonous, herbaceous, and woody plant in the United States, China, and Japan. Other sites (i.e., families (Blackman and Eastop 1994, 2000, 2006). The Colombia, The Netherlands, New Zealand, and Pan- basic life cycle of A. solani is also variable, the species ama) are represented by specimens intercepted at exhibiting both holocycly and anholocycly. Along quarantine facilitates in the United States (Table 1). with this range in the life history, there is an equal Because The Netherlands is a re-exporter of cut ßow- amount of morphological variability. This combina- ers for the worldwide market, this country may or may tion of variability has led some to propose additional not represent the actual point of origin for the perti- species and subspecies (Blackman and Eastop 2006, nent samples. Damsteegt and Voegtlin 1990, Mu¨ ller 1976) or to sug- Using the technique described by Favret (2005), we gest that A. solani be treated as a species complex extracted whole genomic aphid DNA nondestruc- (Mu¨ ller 1985). With all of these complications, it is no tively from a single individual in each collection sam- surprise that A. solani ranks third among aphids for ple using kits from QIAGEN (Valencia, CA). Speci- most recognized junior synonyms, with 37 (Re- men body contents are cleared via this system and maudie`re and Remaudie`re 1997). individuals were subsequently preserved on micro- Clearing the taxonomic difÞculty associated with A. scope slides in Canada balsam. Specimens were de- solani is of great economic importance considering the termined as A. solani by using standard identiÞcation its combination of extreme polyphagy and its known keys and then deposited in the National Aphidoidea transmission of 45 plant viruses (Chan et al. 1991). Collection of the U.S. National Museum of Natural Despite damaging crops in Asia, Australia, and Europe History, located at the USDA, Systematic Entomology (Southall and Sly 1976, Hwang et al. 1981, Johnstone Laboratory (Beltsville, MD). and Rapley 1981), A. solani is generally not considered A portion of the mitochondrial cytochrome oxidase a serious pest on Þeld crops in North America, and in I (COI) gene was ampliÞed by polymerase chain re- particular rarely colonizes soybean, Glycine max (L.) action (PCR) using aphid-speciÞc primers (Favret Merr. However, there have been recent out breaks of and Voegtlin 2004). The fragment of DNA was se- A. solani on soybean in Asia (Nagano et al. 2001, Saito quenced in both directions using these same primers et al. 2001). This difference in host use suggests A. with BigDye kits, version 3.1 (Applied Biosystems, Foster City, CA) and read on an Applied Biosystems 1 Systematic Entomology Laboratory, PSI, USDAÐARS, Bldg. 005, sequencer. Sequences were assembled and aligned BARC-W, Beltsville, MD 20705. with BioEdit version 7.0.8. The number of base pair 2 Corresponding author, e-mail: [email protected]. 3 Illinois Natural History Survey, 1816 S. Oak St., Champaign, IL differences was hand-counted, and sequences were 61820. deposited in GenBank (accession nos. FJ009047, February 2009 MILLER ET AL.: CRYPTIC SPECIES WITHIN A. solani 399 Table 1. Sample origins, variable sites, and accession numbers between specimens from The Netherlands, western United States, and Australia. Selected sequence position GenBank Origin If A. solani does not represent a complex of cryptic 918336876342348accession species, why is it a pest on soybean in Asia but not in United Statesa A G C C T C C FJ009047 North America? One possibility is that of biotypes that Chinab C A T C C C C FJ009046 are sometimes recognized and labeled for morpho- Japanc C A T C C C C FJ009045 New Zealand (1)d A G C C T C C FJ009044 logically indistinguishable insect populations harbor- New Zealand (2)d A A C C C T A FJ009043 ing biological differences with usually the presence or Netherlands (1)d A G C C T C C FJ009040 absence of virulence on a particular host variety. Of Netherlands (2)d A A C C C T A FJ009042 the described biotypes of insect pests of agricultural Netherlands (3)d A A C C T C C FJ009039 Netherlands (4)d A A T T T T A FJ009041 crops, nearly half are aphids (Saxena and Barrion Portugald A A T C T T A FJ009035 1987). Along with biotypes, it is possible that host plant United Kingdomd A G C C T C C FJ009037 use may be tied to facultative endosymbionts as has d Colombia A G C C T C C FJ009038 been shown with the pea aphid, Acyrthosiphon pisum Panamad A G C C T C C FJ009036 (Harris) (Tsuchida et al. 2004). In this case, the pres- a Ten collections from nine host genera in the Great Smoky Moun- ence of the U-type symbiont provided its aphid host tains National Park in North Carolina and Tennessee, U.S.A. improved Þtness on certain plant hosts (Tsuchida et al. b Two collections from soybean in Xiuyan, Liaoning Province, 2004). Alternately, different host cultivars may react China. differently to aphid clones. For example, Shufran et al. c Two samples from soybean in Morioka, Iwate Prefecture, and one sample from soybean in Tsukuba, Ibaraki Prefecture, Japan. (2007) demonstrated the ability of different aphid d Intercepted at ports-of-entry in the United States. clones to cause varying degrees of plant damage to the same aphid-resistant crop variety. Whatever may be the causes of variation in the FJ009046, FJ009045, FJ009044, FJ009043, FJ009040, biology of A. solani, our current species concept of A. FJ009042, FJ009039, FJ009041, FJ009035, FJ009037, solani remains intact based upon our collected spec- FJ009038, and FJ009036). imens. This is important from a taxonomic and regu- latory point of view. However, our sampling was lim- ited and more genetically divergent lineages of A. Results and Discussion solani may yet be found. Even with a broad range of host plants (we col- lected A. solani on 23 host species in the Great Smoky Mountains National Park alone) and the great geo- Acknowledgments graphic range from which we obtained specimens, we We thank Discover Life in America (Gatlinburg, TN) for observed very little COI sequence variation, because funding to sample aphids in the Great Smoky Mountains only Þve different genotypes were found. In the 551 bp National Park (Tennessee and North Carolina). We ac- sequenced, only seven were variable (Table 1), with knowledge J. Lozier (Illinois Natural History Survey, Cham- no more than Þve base pair differences between any paign, IL) and J. Prena, and R. Ochoa (USDA, Systematic two individuals. Sequences from the specimens from Entomology Laboratory) for manuscript reviews. the Americas, the United Kingdom, and one of The Netherlands samples and one of the New Zealand specimens were identical, and another pair of samples References Cited from New Zealand and The Netherlands was identical to each other. Sequences from the Japanese and Chi- Blackman, R. L., and V. F. Eastop. 1994. Aphids on the nese samples were identical. This divergence of 0.7% worldÕs trees: an identiÞcation and information guide. is far lower than the 2% sequence divergence often CAB International, Wallingford, United Kingdom. cited for species level differences (Hebert et al. 2003). Blackman, R. L., and V. F. Eastop. 2000. Aphids on the worldÕs crops: an identiÞcation and information guide, However, a Templeton, Crandall, and Sing (TCS) 2nd ed. Wiley Ltd., Chichester, West Sussex, England. analysis suggested that the Southeast Asian haplotype Blackman, R. L., and V. F. Eastop. 2006. Aphids on the was not nested with the other haplotypes. worldÕs herbaceous plants and shrubs, 2 vols. Wiley Ltd., Numerous other aphids have been considered as Chichester, West Sussex, England. part of species groups or complexes (e.g., A. frangu- Chan, C. K., A. R. Forbes, and D. A. Raworth. 1991. Aphid- lae), which has confused their taxonomy and rendered transmitted viruses and their vectors of the world. Agric. species identiÞcations difÞcult. Taxonomic resolution Canada Res. Branch Tech. Bull. 1991-3E. has been achieved with some of these complexes by Clements, K. M., B. M. Wiegmann, C. E. Sorenson, C. F. using molecular techniques (e.g., Lozier et al. 2008) or Smith, P. A. Neese, and R. M. Roe.