Sue L. Blodgett

Alfalfa Weevil (Coleoptera: Curculionidae) Larval Sampling: Comparison of Shake-Bucket and Sweep-Net Methods and Effect of Training

Abstract Two field-sampling methods, shake-bucket and sweep-net, were compared for use in monitoring alfalfa weevil, Hypera postica (Gyllenhal), larvae in alfalfa hay of the high plains and intermountain region of North America. In this region, alfalfa grows to sufficient height to use both methods before the more damaging late instars peak in abundance. Both methods also were compared with extracting larvae by using Berlese funnels in the laboratory. The shake-bucket method was more sensitive in detecting small larvae (first and second instars) than large larvae (third and fourth instars), and the sweep-net method detected a lower proportion of small larvae. The number of larvae collected with the shake-bucket method was strongly correlated with number of larvae recovered from Berlese funnels (total larval counts, R2 = 0.85). Correlation of the sweep-net samples with the Berlese extraction was also significant but less strong (R2 = 0.56). In addition, sampler instruction was evaluated to determine whether demonstration training affects performance of inexperienced samplers using the two field-sampling methods. Training did not significantly change sampler performance in using the shake-bucket but did increase the number of large larvae when using the sweep-net. In addition, less variability was associated with the shake-bucket sampling method than with the sweep-net method for samplers who only had access to written sampling instructions. Therefore, when estimation of small larval abundance is desired for economic decision-making and sampling is performed by people with little or infrequent sampling experience, such as growers, the shake-bucket method is the preferred field-sampling method in the high plains and intermountain region of North America. Sweep-net sampling is more variable than shake-bucket sampling, although demonstration training improves the usefulness of the sweep-net.

Impact of livestock grazing on abundance of Miridae and Reduviidae (Hemiptera) in crested wheatgrass pastures.

Abstract Miridae of the genera Labops and Irbisia, collectively referred to as “black grass bugs,” can cause significant damage to wheatgrasses (Poaceae) of several genera on western North American rangeland. Another mirid in the same area, Capsus cinctus (Kolenati), causes damage to bluegrass (Poa spp.). Previous studies suggest that grazing management may reduce mirid populations on rangeland by eliminating preferred oviposition sites and reducing accumulations of litter that provide diurnal refuges for nymphs. We tested the hypothesis that grazing reduces mirid populations, along with those of Reduviidae, during a controlled grazing experiment. Densities of mirids and reduviids declined with increasing intensity of grazing, even though grazing occurred after the peak of mirid abundance each year. This suggests that declines in hemipteran densities resulted from grazing that occurred during previous years, perhaps because the most heavily grazed plots had the least plant litter. The results further confirm that grazing has the potential to control black grass bug populations, although the benefits could be potentially offset by negative impacts on beneficial insects such as reduviids.

Evaluation of Alfalfa Weevil (Coleoptera: Curculionidae) Densities and Regrowth Characteristics of Alfalfa Grazed by Sheep in Winter and Spring

Fall regrowth of alfalfa, Medicago sativa (L.), serves as a major source of winter pasture for Montana sheep producers. In years of drought, alfalfa fields are extensively winter/spring grazed; how...

Efficacy of Imidacloprid for Control of Cereal Leaf Beetle (Coleoptera: Chrysomelidae) in Barley

Abstract The toxicity of imidacloprid to the cereal leaf beetle, Oulema melanopus (L.), was measured under laboratory and field conditions. Insect mortality and plant damage were determined from artificial and natural infestations of O. melanopus applied to various growth stages of barley. All rates of imidacloprid formulated and applied as a seed treatment caused >90% mortality to cereal leaf beetle larvae when barley was infested with eggs at the 4-leaf stage, but were ineffective when barley was infested with eggs at the early tillering or flag-leaf stages of barley. This window of susceptibility influenced results obtained in field trials where peak larval emergence did not occur until the early tillering stage of barley. The resulting mortality in plants from treated seeds never exceeded 40% in the field. Foliar imidacloprid, however, caused >90% mortality in the field, and may be another option in the management of the cereal leaf beetle.

Diversity of Flower-visiting Bees and their Pollen Loads on a Wildflower Seed Farm in Montana

Abstract During a two-year survey on a wildflower seed farm in southcentral Montana, we collected ∼50 species of bees from 18 genera in sweep samples on cultivated wildflowers and weeds. The two cultivated plant species most intensively sampled attracted different assemblages of bee visitors. Slender white prairie clover (Dalea candida) attracted 27 species, 94% of visitors being Apis mellifera (73%), Lasioglossum spp., Colletes phaceliae, and Bombus spp. Prairie coneflower (Ratibida columnifera) attracted 20 species, the majority being Halictus rubicundus and three Melissodes species; only 3% of visitors to this plant were A. mellifera, despite the fact that the coneflower field was closer to an apiary than were the prairie clover fields. Other apparently non-random plant-bee associations included A. mellifera on Onobrychis viciaefolia, Bombus spp. on Astragalus cicer, and Halictus ligatus and a Melissodes sp. on Symphyotrichum chilensis. Analysis of pollen loads suggests high flower constancy for A. mellifera, Bombus spp., and many of the native solitary bee species foraging on cultivated plants. The low numbers of honey bees on certain plants suggest that native, non-managed bees of such genera as Bombus, Melissodes, Halictus, and Lasioglossum may be critical for plant species for which honey bees show relatively low preference (especially when highly-preferred species such as D. candida are abundant).

Durum Spring Wheat Susceptibility to Wheat Stem Sawfly (Hymenoptera: Cephidae)

The wheat stem sawfly, Cephus cinctus Norton, is the primary arthropod pest of wheat, Triticum aestivum Thell, in the Northern Great Plains. Yet, information is unavailable on wheat stem sawfly inf...

Regional assemblages of Lygus (Heteroptera: Miridae) in Montana canola fields.

Abstract Sweep net sampling of canola (Brassica napus L.) was conducted in 2002 and 2003 to determine Lygus (Heteroptera: Miridae) species composition and parasitism levels in four regions of Montana. Regardless of region or seasonal change, Lygus elisus (Van Duzee) was the dominant species in all canola fields sampled, averaging 60–99% of the total adult populations. Lygus borealis (Kelton), Lygus keltoni (Schwartz) and Lygus lineolaris (Palisot) were detected at much lower levels. Total lygus population density was greatest in the southwest and central regions. The northeast and southwest regions had the greatest lygus species diversity. The proportion of L. elisus increased from early to late crop maturity stages in the southwest and central regions while there was no change in northeast and southwest canola production regions. Nymphal stages III–V were dissected to detect parasitism in 2003 only. Parasitism was found to be negligible in the dissection of 1,230 nymphs. Lygus population densities in canola indicate the potential for economic impact on Montana canola, especially in years when moisture is limited.

Influence of tillage system, oilseed species, and insecticidal seed treatment on flea beetle (Coleoptera: Chrysomelidae) damage, oilseed production, and postharvest residue cover.

The influence of tillage system and imidacloprid seed treatment on flea beetle (Phyllotreta cruciferae (Goeze)) damage, oilseed production, volunteer barley density, and post harvest residue cover was determined for Polish canola (Brassica rapa L.) and yellow mustard (Sinapis alba L.). Field trials were conducted at Moccasin, MT, USA, from 1998 through 2000. Flea beetle damage was assessed on cotyledon and first true leaf stage plants using a numerical damage rating. Flea beetle damage was low in both tillage systems and on both plant species when imidacloprid seed treatment was applied. In the absence of seed treatment, seedlings of both plant species in conventionally tilled plots usually suffered more damage than did seedlings in zero tillage plots. Canola often sustained more damage than yellow mustard. Across tillage system and insecticidal seed treatment, yellow mustard produced significantly greater (P> 0.01) seed yields than canola. Density of volunteer barley was significantly greater (P > 0.01) ...

Spring Wheat Production and Associated Pests in Conventional and Diversified Cropping Systems in North Central Montana

Producers in the northern plains are diversifying and intensifying traditional wheat (Triticum aestivum L.)-based cropping systems by reducing summer fallow and including legume and oilseed crops. This study examined the influence of diversification and intensification on spring wheat yield and quality and associated insects, diseases, and weeds. Research was conducted during the 1998 through 2000 period in farm fields in north central Montana. Conventional rotations included either hard red spring wheat–spring barley (Hordeum vulgare L.)–fallow or spring wheat–fallow. Diversified rotations included replacement of fallow with either annual pulse crops or cool-season oilseeds. Preplant soil water was less in diversified rotations, but residual nitrate was not influenced by rotation type. Insect pests and beneficial arthropods were in greater numbers in conventional rotations. Incidence and severity of crown and root rots of wheat were similar between rotation types, but foliar leaf spot diseases were greater for wheat in conventional rotations. Weed densities were not influenced by rotation type. Spring wheat yield, tiller density, and test weight were greater in conventional rotations. Spring wheat in diversified rotations had greater drought stress. Diversification and intensification of spring wheat systems may reduce pests and decrease wheat productivity, particularly when precipitation is inadequate.

Black Grass Bug (Hemiptera:Miridae) Damage to Intermediate Wheatgrass Forage Quality

The black grass bug, Labops spp. (Hemiptera: Miridae), is native to the western U.S. and was first observed damaging range grasses in the western U.S. coincident with the increase in seeded acreage of wheatgrasses (Agropyron and Thinopyrum spp. (Poaceae)) (Bohning and Currier 1967, J. Range Manage. 20: 265-267). Black grass bug refers to a complex of species belonging to genus Labops spp. and (rb/s/a spp., though in this study Labops was the predominant genera represented. Differences in grass species susceptibility to black grass bug damage have been studied (Bohning and Currier 1967, Todd and Kamm 1974, J. Range Manage 27: 453-458; Higgins et al. 1977, J. Range Manage. 30: 380-384). Black grass bug has been documented damaging crested wheatgrass (Agropyron cristatum (L.) Gaertn.) (Bohning and Currier 1967), mixed crested and intermediate wheatgrass (Elytrig/a intermedia (Host) Nevski (Poaceae)) (Todd and Kamm 1974), wheat (Triticum aest/vum L.) fields in Montana (Bohning and Currier 1967), pubescent wheatgrass (formerly Agropyron trichophorum) = intermediate wheatgrass (formerly Agropyron intermedium) now Thinopyron intermedium ( Host) Barknight and Dewey, and other wheatgrasses (Bohning and Currier 1967). Higgins et al. (1977) ranked susceptibility of several grasses to black grass bug feeding (most to least susceptible): intermediate wheatgrass, Kentucky bluegrass (Poa pratensis L. (Poaceae)), slender wheatgrass (Elymus trachycaulus (Link) Gould ex Shinners (Poaceae)), orchardgrass (Dactyl/s glomerata L. (Poaceae)), smooth brome (Bromus inermis Leyss. (Poaceae)), mountain brome (Bromus marginatus Nees ex Steud. (Poaceae)), and a mixture of native grass species including Lettermans needlegrass (Achnutherum letterman/i (Vasey) Barkworth (Poaceae)), sheep fescue (Festuca ovina L. (Poaceae)), and mountain muhly, (Muhlenbergia montana (Nutt.) A. S. Hitchc. (Poaceae)). Black grass bug overwinters as an egg within grass stems, which hatch in the spring, completing one generation per year. Piercing-sucking mouthparts of immature