Sipha flava (Forbes) (yellow sugarcane aphid) and Rhopalosiphum maidis (Fitch) (corn leaf aphid) (Hemiptera: Homoptera: Aphididae) are common aphids occurring throughout North America on many host plants, most of which are grasses (Blackman & Eastop 2006). Both aphids are pests of several important food crops, e.g., Sorghum bicolor (L.) Moench (sorghum), Saccharum officinarum L. (sugarcane), Triticum spp. (wheat), and Zea mays L. (corn) (Blackman & Eastop 2000). Additionally, both aphids are vectors of potyviruses and R. maidis is a vector of luteoviruses in these crops. Until now, to our knowledge, no natural infestations of these aphids have been reported on the grass genus Miscanthus.
Miscanthus spp. is a common grass throughout the United States, with ornamental varieties of M. sinensis Andersson being the most frequently cultivated species. However, M. × giganteus Greef and Deuter ex Hodkinson and Renvoize (Liliopsida: Poaceae: Andropogonaeae: Saccharinae) is being evaluated in the United States as a cellulosic feedstock crop (Heaton et al. 2008) primarily to meet production targets for advanced biofuels (e.g., cellulosic ethanol; Energy Independence and Security Act of 2007, 42 U.S.C. §17001). Miscanthus × giganteus is a perennial, sterile hybrid (possibly between M. sinensis and M. sacchiflorus (Maxim.) Hack.) and may exist in nature within a sympatric zone of these 2 species in southeastern Asia (Clifton-Brown et al. 2008).
More than 1,500 insect species reportedly feed on Saccharum officinarum (sugarcane) (Long & Hensley 1972), a sister genus of M. × giganteus (Hodkinson et al. 2002); however, very few insects have been reported to feed on M. × giganteus (Prasifka et al. 2009). The lack of reported insect herbivory on M. × giganteus may be related to few extensive survey efforts. However, in a 3-year intensive survey of invertebrates of M. × giganteus in the United Kindom, Semere & Slater (2007) found “no major pests.” A similar 2-year survey in Germany noted 1 arthropod pest, Tetranychus urticae Koch (twospottted spider mite), a polyphagous, widespread species that causes damage during dry and hot weather (Gottwald & Adam 1998). The only documentation of an aphid feeding on M. × giganteus is from a laboratory study of aphid transmission of Barley yellow dwarf virus (BYDV) (Huggett et al. 1999); however, they suggest that the genus Miscanthus is “nutritionally insufficient” for aphids.
Visual observations and samples were taken from managed M. × giganteus plots from locations in Illinois, Indiana, Kentucky, and Nebraska in 2008. Samples were collected by hand or by vacuum sampler, (Burd & Porter 2009), and transported to the laboratory for species confirmation.
Sipha flaya was collected from 7 locations from 4 states in 2008 (Table 1) and was found on the lower leaves of both young and old plants, from 1to 21-year old plantings (Fig. 1A). Some populations appeared to be large enough to cause leaf death (Fig. 1B). Generally, leaves infested with S. flava were yellow to reddish in color; similar symptoms have been noted in sugarcane (Nuessly 2005) and sorghum (Costa-Arbulú et al. 2001). Ants, Crematogaster cerasi (Fitch), were observed tending S. flava on 14 Jul 2008 in Champaign, IL, and similar tending activity was observed elsewhere throughout Illinois.
Rhopalosiphum maidis, collected from 4 locations from 4 states (Table 1), was found only within the whorls of young M. × giganteus in first-year plantings (Fig. 1C, white arrow). In Champaign, IL, R. maidis populations occasionally co-infested M. × giganteus tillers with other recently-identified M. × giganteus herbivores, e.g., Spodoptera frugiperda (J. E. Smith), (Prasifka et al. 2009) (Fig. 1C, black arrow). No conspicuous symptoms were associated with these infestations; however, very young tillers (4–6 expanded leaves) showed some yellowing of uppermost leaves.
Multistate agronomic trials of M. × giganteus (as well as other bioenergy feedstock grasses) are underway in the United States with a renewed interest in both economically and environmentally sustainable energy production. Crops attacked by S. flava and R. maidis contributed to more than $6.4 billion of the 2007 U.S. sugar and grain production value (about 4% of the 2007 total U.S. crop production value) (USDA 2009).
The broader purpose of this survey was to sample for common insect herbivores from known field establishments of M. × giganteus in North America. Twenty-one aphids are known to use Miscanthus (mostly M. sinensis) as a host; therefore, there is potential for aphid damage on M. × giganteus. This damage potential is especially concerning because most plant viruses are transmitted by aphids (Hull 2002) and R. maidis can transmit the RPV strain of BYDV to M. × giganteus (Huggett et al. 1999). However, expectations for sampling potential pests of M. × giganteus were reduced because of repeated references indicating that none should be found (e.g., Semere & Slater 2007; Atkinson 2009).
LOCATION, COLLECTION DATE, CROP STAND SIZE, AND CROP AGE FOR SIPHA FLAVA AND RHOPALOSIPHUM MAIDIS COLLECTED IN 2008 FROM MISCANTHUS × GIGANTEUS.
Captures of alate S. flava occur about 14 d earlier in the growing season than captures of alate R. maidis (David Voegtlin, unpublished data); however, infestations of S. flava are likely to occur even earlier, relative to R. maidis, because S. flava overwinter in northern latitudes. Such infestations of S. flava in M. × giganteus appear to have the potential to damage young plants, similar to infestations of S. flava in other crops (Long & Hensley 1972; Starks & Mirkes 1979; Breen & Teetes 1990). Indeed all of the surveyed plots, including young, small stands (Table 1), were infested with S. flava. Therefore, since aphids can locate these small plots of M. × giganteus, they inevitably will find larger, commercial-scale fields as well. Broadly speaking, this may result in a need for insect management decisions for this bioenergy feedstock and related crops; potentially resulting in a reevaluation of the input costs for economical bioenergy-crop production.
Miscanthus × giganteus Greef and Deuter ex Hodkinson and Renvoize is being evaluated as a cellulosic feedstock for energy production in the United States. This is the first field report of Sipha flava (Forbes) and Rhopalosiphum maidis (Fitch) (Hemiptera: Homoptera: Aphididae) on M. × giganteus and the first report of these aphids on Miscanthus in the Western Hemisphere. A qualitative survey of managed M. × giganteus stands revealed S. flava or R. maidis populations at 7 sample locations in 4 states. The large populations of S. flava observed on young stands of M. × giganteus suggests their potential for economic importance.
We thank David Voegtlin and Doris Lagos, University of Illinois Natural History Survey, for helpful discussion and aphid identification. We thank Dr. Gregory Evans and one anonymous reviewer for their constructive comments. Additionally, we are grateful to Tom Voigt, Energy Biosciences Institute, University of Illinois, for assistance in locating M. × giganteus plots.
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