Jeffrey D. Bradshaw

Stem-Boring Caterpillars of Switchgrass in the Midwestern United States

ABSTRACT Lepidopteran stem borers were collected from switchgrass, Panicum virgatum L., tillers showing symptoms of infestation at seven locations in Illinois and Iowa, with additional observations made on larval and adult activity. Blastobasis repartella (Dietz) (Coleophoridae), whose only known host is switchgrass, was common in plots grown for >5 yr, whereas the polyphagous stalk borer, Papaipema nebris (Guenée) (Noctuidae), was abundant in newly established (i.e., first- and second-year) switchgrass. Haimbachia albescens Capps (Crambidae) was collected from two locations in Illinois, making switchgrass the first known host for this species. Entry holes made by B. repartella and H. albescens were usually 1–2 cm above the soil surface, precluding discrimination between these species based on external appearance of damage. Although P. nebris often entered stems within 5 cm of the soil surface, they also seemed to move between stems and were the only species entering stems at heights >15 cm. Adults of B. repartella were active on and above the switchgrass canopy by 2130 hours, with peak activity at ≈0230 hours. Activity of B. repartella adults seemed greatly reduced on one night with relatively cool temperatures and low wind speeds. Data from switchgrass and giant ragweed, Ambrosia trifida L., suggest P. nebris larvae move out of switchgrass during July in search of hosts with larger diameter stems, although by then hosts such as corn, Zea mays L., or Miscanthus spp. may have outgrown the potential for serious damage. However, switchgrass could contribute to greater adult populations of P. nebris if thick-stemmed hosts such as giant ragweed are not managed.

Potential Biomass Reductions to Miscanthus × giganteus by Stem-Boring Caterpillars

ABSTRACT Injury from stem-boring caterpillars has been observed on the perennial grass Miscanthus × giganteus Greef and Deuter ex Hodkinson and Renvoize in both its native and introduced ranges. Because some species causing stem injury in the United States have not been identified, potential biomass reductions to M. × giganteus were measured using southwestern corn borer, Diatraea grandiosella Dyar (Crambidae), an insect pest of several related crops within the Andropogoneae. Results indicate D. grandiosella is capable of survival on whorl and stem tissue from hatch to 21 d in the laboratory, and field infestations with third instars support adult development, as exuviae were found during dissection of injured tillers. Relative to uninfested controls, M. × giganteus tillers with stem injury yielded 12–30% less dry mass in four infestations over 2009–2010. As in some D. grandiosella hosts, data indicate decreased susceptibility to stem-boring as tillers increase in size or age. Regressions of residuals (observed — predicted mass) for injured M. × giganteus tillers onto the cumulative length of tunnels per tiller also showed significant negative slopes (i.e., decreasing tiller mass with increasing tunnel length). Although D. grandiosella survival appeared low in both laboratory and field trials, results indicate that M. × giganteus productivity could become limited by other stem-boring caterpillars known to attack Andropogoneae, including the following: Elasmopalpus lignosellus (Zeller) (Pyralidae), Diatraea saccharalis (F.) (Pyralidae), and Eoreuma loftini (Dyar) (Crambidae). For perennial grasses grown exclusively for biomass, certain management strategies for stem borers or other pests may be uneconomical or impractical, suggesting long-term investment in breeding for host plant resistance may be needed.

Seed Reduction in Prairie Cordgrass, Spartina pectinata Link., by the Floret-Feeding Caterpillar Aethes spartinana (Barnes and McDunnough)

Insect damage to prairie cordgrass, Spartina pectinata Link., is conspicuously high in Illinois, where attempts to collect native seed show the majority of spikelets damaged with small holes. Dissection of spikes during summer reveals minute caterpillars boring though glumes and feeding on florets inside. In 2009–2010, panicles of prairie cordgrass from across its native range were used to estimate the percentage of insect-related damage and losses to seed production. Collections of caterpillars from panicles and stems were used to identify one floret-feeding species, estimate its distribution in the central USA, and assess its feeding patterns within spikes. Insect feeding damaged 38% of spikelets across eight states, though injury differed significantly between states. Regression of developed prairie cordgrass seeds onto insect damage suggests a 1:1 loss ratio (i.e., 50% damaged spikelets reduces seed production by 50%). Collections of caterpillars from six midwestern states suggest that larvae of a tortricid moth, Aethes spartinana (Barnes and McDunnough), are responsible for most insect damage to cordgrass spikelets. Larvae of A. spartinana generally feed on a series of consecutive spikelets, with high infestations (>50% insect damage) showing damage concentrated in the middle of spikes. Because larvae are concealed by moving into adjacent spikelets and later tunneling into cordgrass stems, they may be difficult to control using insecticides. While direct effects of the caterpillar on biomass yields for prairie cordgrass are not known, for states like Illinois (where damage to spikelets often exceeds 70%), breeding and seed production efforts may be severely limited without efforts to manage A. spartinana.

Landscape epidemiology of bean pod mottle comovirus: molecular evidence of heterogeneous sources

Bean pod mottle virus (BPMV) RNAs are grouped into subgroups (sgI and sgII). A BPMV partial diploid reassortant (IA-Di1) from the perennial Desmodium illinoense contained both RNA1 subgroups and an RNA1 recombinant. The RNA2 of IA-Di1 was characteristic of sgII. Additionally, ten BPMV isolates from a soybean field adjacent to the locality of IA-Di1 shared >98.5% nucleotide identity with RNA1 sgII of IA-Di1. The data demonstrate the co-existence of two differing consensus BPMV RNA1 subgroups in adjacent habitats and illustrate variation in virus genetic structure that can occur in a contiguous plant community.

Bean Leaf Beetle (Coleoptera: Chrysomelidae) and Bean Pod Mottle Virus in Soybean: Biology, ecology, and management

Bean leaf beetle, Cerotoma trifurcata (Forster), is a pest of soybean found in many production areas in the United States. The bean leaf beetle larvae feed on soybean root nodules, whereas the adults feed on the above ground parts of soybean such as cotyledon, leaves, and pods. Bean leaf beetle is also a very efficient vector of Bean pod mottle virus, a widespread virus of soybean in the south and southeastern United States with recent expansion into the north central region of the country. This article summarizes bean leaf beetle biology, ecology, and its impact on soybean production in the United States. The management of this insect and Bean pod mottle virus as recommended in the north central states is also presented.

Response of Pemphigus betae (Hemiptera: Aphididae) and Beneficial Epigeal Arthropod Communities to Sugarbeet Plant Density and Seed-Applied Insecticide in Western Nebraska

Abstract This study investigated the impact of a neonicotinoid seed-applied insecticide (Poncho Beta) and two plant densities (86,487 and 61,776 plants per hectare) on the sugarbeet root aphid (Pemphigus betae Doane), beneficial epigeal arthropods, and selected crop yield parameters in sugarbeet (Beta vulgaris L. var. vulgaris). Ground beetles and centipedes were the most commonly collected taxa during 2012 and 2013, respectively. Centipede, spider, and rove beetle activity densities were not affected by the seed-applied insecticide, whereas plant density had a marginal effect on centipede activity density during 2012. Ground beetle species richness, diversity, and evenness were also not impacted by the seed treatments. However, during 2013, ground beetle activity density was significantly higher in plots planted with untreated sugarbeet seeds due to the abundance of Bembidion quadrimaculatum oppositum Say. Sugarbeet root aphid populations were significantly higher in the untreated plots during both years. In 2012, sugarbeet tonnage and sugar yield were higher under the low plant density treatment, while higher sugar content was recorded from the seed-applied insecticide plots (2013). Seed-applied neonicotinoids and plant density had little impact on beneficial epigeal arthropod activity density. Seed treatment did result in decreased root aphid populations; however, these reductions were not sufficient to be considered as an adequate control. This limited aphid control likely contributed to inconsistent effects on yield parameters.

Impact of Grasshopper Control on Forage Quality and Availability in Western Nebraska

On the Ground Grasshopper outbreaks in Nebraska have resulted in losses over

Comparing the Effects of Two Tillage Operations on Beneficial Epigeal Arthropod Communities and Their Associated Ecosystem Services in Sugar Beets

2 million per year due to lost forage for livestock. As much as 23% of western U.S. forage is consumed by grasshoppers annually. Controlling grasshoppers reduced grasshopper numbers without negatively impacting beneficial insects. In 2011, 29 more 318 kg steers could have grazed a 1000 hectare pasture for a 5 month growing season due to grasshopper suppression. In 2012 (a drought year), 54 more steers could have been grazed if grasshoppers were controlled. Grasshopper infestation can result in significant reduction in livestock grazing capacity especially in dry conditions.

Evaluation of Greenbug and Yellow Sugarcane Aphid Feeding Behavior on Resistant and Susceptible Switchgrass Cultivars

Abstract Beneficial arthropods provide important ecosystem services in terms of arthropod pest and weed management, but these services can be adversely affected by farming practices such as tillage. This study investigated the impact of two tillage operations (zone tillage and moldboard plow) on the activity density of several beneficial, epigeal arthropod taxa, and postdispersal weed seed and prey removal in sugar beet agroecosystems. In addition, four omnivorous ground beetle species were selected for a weed-seed choice feeding assay, whereas a single species was selected for a weed-seed age preference assay. Ground beetles were the most commonly collected taxon (via pitfall sampling), with only a few dominant species. Tillage operation did not affect ground beetle activity density; however, spider, centipede, and rove beetle activity densities were higher in the reduced-tillage treatment. Live prey consumption was similar between tillage practices, with more prey consumed during nocturnal hours. More weed seeds were consumed in the reduced-tillage treatment, whereas weed-seed preference differed between the four weed species tested [Setaria pumila (Poir.) Roem. & Schult., Echinochloa crus-galli (L.), Kochia scoparia (L.), and Chenopodium album (L.)]. In the weed-seed choice feeding assay, significantly more broad-leaf weed seeds (C. album and K. scoparia) were consumed compared with grassy weed seeds (E. crus-galli and S. pumila). No preference for seed age was detected for E. crus-galli, but Harpalus pensylvanicus (De Geer) preferred old C. album seeds over fresh seeds. Zone tillage is compatible with ecosystem services, providing critical habitat within agricultural ecosystems needed to conserve beneficial, edaphic arthropods.

Reassessment of Resistance to Sunflower Stem Weevil, Cylindrocopturus adspersus LeConte (Coleoptera: Curculionidae), in Cultivated Sunflower Germplasm

Switchgrass (Panicum virgatum L.) is an emerging biofuel crop that serves as host for aphids. To discern the effects of plant age and possible resistance mechanisms, the feeding behavior of greenbugs (Schizaphis graminum Rondani.) and the yellow sugarcane aphid (Sipha flava Forbes.) was monitored on three diverse switchgrasses by the electrical penetration graph (EPG) technique. Callose deposition and genes associated with callose metabolism were also analyzed to discern their association with plant resistance. There was a strong host effect on greenbugs feeding on lowland cultivar Kanlow at the V3 stage of development, as compared to the greenbug-susceptible upland cultivar Summer and plants derived from Kanlow (♂) × Summer (♀) (K×S) crosses. These data confirmed that Kanlow at the V3 stage had antibiosis to greenbugs, which was absent in the Summer and K×S plants. In contrast, similar effects were not observed for yellow sugarcane aphids, excluding significant differences in the time to first probe on Kanlow plants at the V1 stage and reduction in time spent on pathway processes on Kanlow plants at the V3 stage. These data demonstrated that Kanlow plants may have multiple sources of resistance to the two aphids, and possibly some were phloem based. Microscopy of leaf sections stained with aniline blue for callose was suggestive of increased callose deposition in the sieve elements in Kanlow plants relative to Summer and K×S plants. RT-qPCR analysis of several genes associated with callose metabolism in infested plants was equivocal. Overall, these studies suggest the presence of multiple defense mechanisms against aphids in Kanlow plants, relative to Summer and K×S plants.