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The western corn rootworm, Diabrotica virgifera virgifera LeConte, is one of the most economically important insect pests threatening the production of corn, Zea mays (L.), in the United States. Throughout its history, this insect has displayed considerable adaptability by overcoming a variety of pest management tactics, including the cultural practice of annual crop rotation. Since first reported in Illinois in the late 1980s, populations of the rotation-resistant western corn rootworm have spread over a wide area of the eastern Corn Belt. Currently, little information is available concerning the interaction of rotation resistance with the use of genetically modified corn expressing insecticidal toxins from Bacillus thuringiensis Berliner (Bt), a popular tactic for preventing larval injury and its associated yield loss. The goal of this greenhouse experiment was to determine whether rotation-resistant and rotation-susceptible western corn rootworm larvae differ with respect to survival or development when exposed to single- or dual-toxin (pyramided) Bt corn. Individual corn plants were infested with 225 near-hatch eggs at the V5 (five leaf collar) growth stage. Larvae developed undisturbed on the root systems for 17 days, after which they were recovered using Berlese-Tullgren funnels. Surviving larvae were counted to estimate mortality, and head capsule widths were measured to assess development. Rotation-resistant and rotation-susceptible larvae had statistically similar mean levels of mortality and head capsule widths when exposed to both single-toxin (Cry3Bb1 or Cry34/35Ab1) and pyramided (Cry3Bb1+ Cry34/35Ab1) Bt corn, suggesting that these two populations do not differ with respect to survival or development when exposed to Bt corn. Additionally, the statistically similar mean levels of mortality for larvae exposed to single-toxin and pyramided Bt corn suggest that pyramided Bt hybrids containing the Cry3Bb1 and Cry34/35Ab1 toxins do not result in additive mortality for western corn rootworm larvae. Implications for management of this economically important pest are discussed. [ABSTRACT FROM AUTHOR]

Injury from stem-boring caterpillars has been observed on the perennial grass Miscanthus x giganteus Greef and Deuter ex Hodldnson 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. x 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. x 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. x 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. x 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. [ABSTRACT FROM AUTHOR]

Observations of fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), larvae infesting plots of Mi.scanthus X giganteus Creef and Deuter ex Hodkinson and Renvoize prompted laboratory-based tests of survival, development, and feeding preferences on leaf tissue from M. X giganteus and switchgrass, Panicum virgatum L. Survival from hatch to pupation was >70 and 50% for fall armyworms reared on switchgrass and M. X giganteus, respectively, although survival of the S. frugiperda rice strain was significantly greater than the corn strain on both crops. Developmental times from hatch to pupation or adult emergence showed effects of crop and S. frugiperda host strain, but analysis of an interaction revealed developmental times for the rice strain were similar on both crops, whereas corn strain larvae showed delayed development on M. X giganteus relative to switchgrass. Analysis of larval (10 d) and pupal masses showed a similar pattern, with effects of crop and an interaction (at 10 d), but only the mass of corn strain larvae feeding on M. X giganteus was reduced relative to the other crop and strain combinations. In choice tests, neonates of both corn and rice strains showed a strong preference for feeding on young tissues rather than mature leaves of M. X giganteus or switchgrass, but they also clearly favored corn, Zea mays L., leaves over either of the perennial grasses. Results indicate both plants are potential hosts for S.frugiperda, but additional information is needed to understand under which scenarios and to what degree fall armyworms may damage perennial grasses grown for biofuel production. [ABSTRACT FROM AUTHOR]

Monitoring for resistance to Bacillus thuringiensis Berliner (Bt) toxins in transgenic crops is challenging, in part because alleles conferring resistance appear to be rare. Consequently, several complementary methods are used to identify, collect and test putatively resistant individuals. A series of experiments conducted at commercial seed production facilities explored an alternative sampling method. Larvae of the European corn borer, Ostrinia nubilalis Hübner, were collected from bins containing Bt hybrid seed corn and their inbred progeny (both F2 and backcross- F2 larvae) were tested for resistance to the Bt toxin Cry1Ab. Marked, laboratory-reared O. nubilalis larvae also were placed beneath drying corn ears to evaluate potential contamination of samples by larvae developing on non-Bt corn. Both feral and laboratory-reared larvae were used to examine the causes and levels of mortality of larvae in drying bins. Screening of larvae on diet containing Cry1Ab failed to provide evidence of resistance, although insufficient inbred lines survived to make conclusions about the presence of resistance alleles in larvae originally collected beneath Bt corn. Both larvae from previously dried non-Bt corn and O. nubilalis moving between adjacent bins are potential sources of contamination of larvae collected beneath drying Bt corn. Exposure to conditions inside seed corn drying bins for 3 d significantly increased O. nubilalis mortality. Larvae collected beneath seed corn also showed infection by the pathogens Nosema pyrausta (Paillot) and Beauveria bassiana (Balsamo) Vuillemin, with significant mortality apparently caused by B. bassiana. While contamination and mortality may limit the application of sampling beneath drying bins, several modifications could improve the potential utility of the technique. [ABSTRACT FROM AUTHOR]

Applications of entomopathogenic nematodes in the families Steinernematidae and Heterorhabditidae have traditionally been targeted against soil insects. Nonetheless, research over the last two decades highlights the potential of such agents against above-ground pests under certain circumstances. A general linear model was used to test for patterns in efficacy among 136 published trials with Steinernema carpocapsae Weiser, the most common species applied against foliar and other above-ground pests. The focus was on field and greenhouse assessments, rather than laboratory assays where relevant ecological barriers to infection are typically removed. The model showed differences in nematode treatment efficacy depending on the pests' target habitat (bore holes > cryptic foliage > exposed foliage) and trial location (greenhouse > field studies). Relative humidity and temperature during and up to 8 h post-application were also predicted to influence rates of nematode infection obtained. Conversely, spray adjuvants (both wetting agents and anti-desiccants) and nematode dosage applied (both concentration and use of consecutive applications 3-4 days apart) did not explain a significant amount of variance in nematode performance. With reference to case studies the model is used to discuss the relative importance of different factors on nematode efficacy and highlight priorities for workers considering using entomopathogenic nematodes to target pests in novel environments.