Mitochondrial DNA was amplified and sequenced from eastern, western, and Egyptian strains of alfalfa weevil, Hypera postica (Gyllenhal). Eastern and Egyptian weevils differed at only 2 nucleotide sites in 1,031 base pairs sequenced; western weevils differed by 5% sequence divergence. Three restriction sites were identified which separated eastern and western haplotypes. No intrastrain polymorphism was detected in 150 weevils from Nebraska. Collections from Lincoln in eastern Nebraska and Scottsbluff in western Nebraska were fixed for the eastern and western haplotypes, respectively. Eastern and western haplotypes were found together in the same fields in a broad overlap region in central Nebraska.

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a b s t r a c tIn recent decades, agricultural producers and non-governmental organizations have restored thousands of hectares of former cropland in the central United States with native grasses and forbs. However, the ability of these grassland restorations to attract predatory invertebrates has not been well documented, even though predators provide an important ecosystem service to agricultural producers by naturally regulating herbivores. This study assessed the effects of plant richness and seeding density on the richness and abundance of surface-dwelling (ants, ground beetles, and spiders) and aboveground (ladybird beetles) predatory invertebrates. In the spring of 2006, twenty-four 55 m × 55 m-plots were planted to six replicates in each of four treatments: high richness (97 species typically planted by The Nature Conservancy), at low and high seeding densities, and low richness (15 species representing a typical Natural Resources Conservation Service Conservation Reserve Program mix, CP25), at low and high seeding densities. Ants, ground beetles, and spiders were sampled using pitfall traps and ladybird beetles were sampled using sweep netting in [2007][2008][2009]. The abundance of ants, ground beetles, and spiders showed no response to seed mix richness or seeding density but there was a significant positive effect of richness on ladybird beetle abundance. Seeding density had a significant positive effect on ground beetle and spider species richness and Shannon-Weaver diversity. These results may be related to differences in the plant species composition and relative amount of grass basal cover among the treatments rather than richness.Published by Elsevier B.V.

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Although the alfalfa weevil Hypera postica (Gyllenhal)) is an important alfalfa (Medicago sativa L.) pest, relatively little is known about how defoliation at specific plant developmental stages affects yield. This study was conducted to characterize yield responses of alfalfa to simulated alfalfa weevil injury when injury was initiated at the early bud stage of the first growth cycle and to develop economic injury levels for the alfalfa weevil. The study was conducted on a silty clay loam (fine, montmorillonitic, mesic Typic Argiudoll) in a 3.6-ha alfalfa (cv. Haymaker) field near Walton, NE. Sixteen 1 by 1-m plots were arranged in a randomized complete block design with four treatments in each of four replicates. Treatments consisted of three levels of simulated alfalfa weevil defoliation and an undefoliated check. Leaflets were removed over 10 d. Dry matter yield and stem density responses were measured for both the first and second growth cycles. Simulated alfalfa weevil injury did not affect stem density before the first cutting or during the entire second growth cycle. When injury occurred during the early bud stage, the most significant effect was the loss of leaf tissue. Yield differences among treatments for the first growth were highly significant, and the relationship between percentage defoliation and percentage yield reduction was linear both years. Defoliation injury imposed during the early bud stage of the first growth cycle did not affect yields or stem densities of the second growth cycle. Dry matter yield responses of the first growth cycle were used to calculate economic injury levels for third and fourth instars feeding at the early bud stage of alfalfa development.

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Although the alfalfa weevil [Hypera postica (Gyllenhal)] is an important insect pest of alfalfa (Medicago sativa L.), relatively little is known about how larval defoliation affects growth processes at specific developmental stages. This study was conducted to characterize the developmental responses of alfalfa to simulated alfalfa weevil injury when injury was initiated at the early‐bud stage of the first growth cycle. The study was conducted on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic, Typic Argiudolls) in a 3.6 ha ‘Haymaker’ alfalfa field near Walton, NE. A total of 16 1‐by 1‐m plots were arranged in a randomized complete block design with four treatments in each of four replicates. Treatments consisted of an undefoliated check and three levels of simulated alfalfa weevil defoliation. Morphological effects of simulated alfalfa weevil injury were determined at five postdefoliation periods. Leaf area indices, leaf area to total dry weight ratios, and leaf dry weight to total dry weight ratios were reduced linearly as defoliation percentages increased. However, defoliation injury did not affect phenological development of the first growth cycle between the completion of injury and first harvest. Most growth rates were not different among treatments, indicating that there was no postdefoliation compensatory growth. Injury initiated at the early‐bud stage of the first growth cycle did not impact alfalfa regrowth after the first harvest. Consequently, the most important effect of defoliation initiated at the early‐bud stage of the first growth cycle was to reduce dry matter yield of the first growth.

Induced resistance in soybean, Glycine max (L.) Merrill, to the bean leaf beetle, Cerotoma trifurcata (Forster), was investigated in greenhouse experiments using the treatments of mechanical injury, a chemical inducer (Actigard™, Novartis Crop Protection Inc., Greensboro, NC) and defoliation by the bean leaf beetle and the soybean looper, Pseudoplusia includens (Walker). Experiments were conducted on soybean PI 227687, two soybean cultivars (Colfax and Williams 82) and a soybean germplasm line (HC95-24MB). Dual-choice feeding-preference tests with bean leaf beetle adults were used to assess induced resistance. Adult beetles were collected from soybean fields 2 to 5 d prior to the feeding preference tests. Pairwise comparisons of leaflets from treated and untreated (control) plants indicated that soybean looper herbivory was a better inducer than other treatments. Herbivory by bean leaf beetle feeding and Actigard following artificial defoliation also were found to induce resistance to the bean leaf beetle. Mechanical injury alone elicited a significantly lower induced response in plants than the other induction treatments.