Frequency of resistance to Bacillus thuringiensis toxin Cry1Ab in an Iowa population of European corn borer (Lepidoptera: Crambidae).

The refuge plus high-dose strategy for resistance management assumes that the frequency of resistance alleles is low. We used an F2 screen to estimate the frequency of resistance to transgenic corn that produces Bacillus thuringiensis Berliner Cry1Ab toxin (Bt corn) in an Iowa population of European corn borer, Ostrinia nubilalis (Hübner). We also proposed a modification to the statistical analysis of the F2 screen that extends its application for nonuniform prior distributions and for repeated sampling of a single population. Based on a sample of 188 isofemale lines derived from females caught at light traps during the 2nd flight of 1997, we show with 95% confidence that the frequency of resistance to Bt corn was <3.9 x 10(-3) in this Iowa population. These results provide weak evidence that the refuge plus high-dose strategy may be effective for managing resistance in O. nubilalis to Bt corn. Partial resistance to Cry1Ab toxin was found commonly. The 95% CI for the frequency of partial resistance were [8.2 x 10(-4), 9.4 x 10(-3)] for the Iowa population. Variable costs of the method were 14.90 dollars per isofemale line, which was a reduction of 25% compared with our initial estimate.

Clinical, serologic, and histopathologic characterization of experimental Borna disease in ponies.

Borna disease was originally described as an equine neurologic syndrome over 200 years ago, although the infectious etiology of the disorder was unproven until the early 20th century. Borna disease virus (BDV) was finally isolated from horses dying of the disorder, and that virus has been used to experimentally reproduce Borna disease in several species of laboratory animals. However, BDV has never been inoculated back into horses to experimentally and etiologically confirm the classic clinical, pathologic, and serologic characteristics of the disease in that species. Three ponies were intracerebrally inoculated with different amounts of BDV and were evaluated clinically, serologically, and neurohistopathologically. All 3 animals developed the clinical signs characteristically described for naturally occurring Borna disease, including ataxia, torticollis, postural unawareness, rhythmic repetitive motor activities, muscle fasciculation, and cutaneous hyperesthesia and hypoesthesia over several body surfaces. Two ponies died after rapid onset of these signs 28-30 days postinoculation. The third animal made a nearly complete clinical recovery. Seroconversion occurred only after the onset of signs and to a marked degree only in the convalescent animal. Virus was recovered postmortem from 2 of the 3 ponies, and a BDV-specific nucleic acid sequence was detectable in all 3 animals using a reverse transcription-polymerase chain reaction procedure. Gross neural lesions were absent, but histopathologically there was generalized intense mononuclear perivascular cuffing, glial nodule formation, and astrocytosis in all 3 brains. Confirming a diagnosis of Borna disease is difficult and perhaps best accomplished using a combination of the clinical, serologic, and histopathologic indicators of this unusual disease supported by positive reverse transcription-polymerase chain reaction findings.

Managing the evolution of insect resistance to transgenic plants.

The evolution of resistance in pests such as the European corn borer will imperil transgenic maize varieties that express insecticidal crystal proteins of Bacillus thuringiensis. Patchworks of treated and untreated fields can delay the evolution of pesticide resistance, but the untreated refuge fields are likely to sustain heavy damage. A strategy that exploits corn borer preferences and movements can eliminate this problem. Computer simulation indicates that this approach can delay the evolution of resistance and reduce insect damage in the untreated fields of a patchwork planting regime.

Diagnostic analysis of the prolonged bluetongue virus RNA presence found in the blood of naturally infected cattle and experimentally infected sheep.

Bluetongue virus (BTV) RNA was detected by the polymerase chain reaction (PCR) in the blood of 24 naturally infected cattle as long as 160 days after the estimated date of infection. Blood samples from these animals and from 10 experimentally BTV-infected sheep, which also exhibited a prolonged hematologic BTV RNA presence, were concurrently evaluated for viral infectivity. Infectivity analyses were conducted using the sentinel sheep inoculation and embryonated chicken egg inoculation procedures. Blood specimens from the experimental sheep 50, 56, 71, and 89 days after BTV inoculation were uniformly negative for viral infectivity despite their uniformly positive status with PCR evaluation. Three collections of blood from the naturally infected cattle at least 100, 135, and 160 days after infection also revealed no recoverable viral infectivity but an initially high and progressively decreasing prevalence of BTV with the PCR technique. These retrospective epidemiologic and prospective experimental approaches were concordant in that both studies demonstrated consistent discrepancies between the viral infectivity and the PCR diagnostic data. The significance of these discrepancies is discussed with respect to Koch's postulates and with respect to the possibility that the biological vector of BTV (Culicoides variipennis) may recover BTV infectivity from PCR-positive but virus isolation-negative blood.

A capture-rate model of net-spinning caddisfly communities.

Empirical research suggests that net-spinning caddisflies require two basic resources, suspended particulate foods, and the currents which deliver them. I present a theoretical model of caddisfly communities based on quantitative differences in the capture rate produced by different catchnet designs. It assumes that catchnet architecture reflects a tradeoff between water filtration rate (flux through the net) and capture efficiency (the proportion of suspended items retained), and that the marginal resource concentration required by species with different catchnet morphologies should reflect the product of these parameters. The model hypothesizes a) that downstream changes in the physical morphology of the stream channel cause a shift in the relative importance of population limitations imposed by food and current-substrate availability, b) that the interaction of these physical changes with the filtering biota results in a seston resource gradient, and c) that the distribution of each taxon along this resource gradient reflects a marginal resource requirement determined by the functional morphology of its catchnet.

Particle size, resource concentration, and the distribution of net-spinning caddisflies.

The dimensions of net meshes constructed by hydropsychid Trichoptera vary both within and between species. Despite these catchnet differences, the diets of most Hydropsychidae studied in Utah streams were statistically indistinguishable. There was no relationship between the size of available resources and catchnet construction among species assemblages inhabiting 10 different localities. A particle-size model of caddis communities, suggesting that taxa feed selectively on particle sizes corresponding to the dimension of catchnet meshes, is not supported by these data.Diatom concentration increased regularly with downstream passage in two different drainages. The identity and number of coexisting hydropsychid species and the size of their catchnets were strongly correlated with diatom concentration. Taxa with large catchnet mesh were the only residents at sites where diatom concentration was very low; as resource concentration increased downstream, species with successively smaller mesh joined the coexisting guild. Together, the broad dietary similarities and distributional pattern from Utah streams suggest that resource concentration, rather than particle size, is the basis of community organization among the hydropsychid Trichoptera.

Selection, outbreeding depression, and the sex ratio of scale insects.

The black pineleaf scale insect has haploid males and diploid females. Ratios of males to females late in development ranged from 0.005 to 0.320 among insect subpopulations that were infesting different host trees. Demes well adapted to an individual ponderosa pine had a higher proportion of males than did demes that were poorly adapted to the host. Ratios of males to females rose in successive annual samples as natural selection increased insect adaptation. Gene flow between demes on different host trees produced predictable changes in the sex ratio.

Current speed and filtration rate link caddisfly phylogeny and distributional patterns on a stream gradient.

Patterns of body size and net construction suggest that current speed and food-particle concentration (not size) influence the distribution of suspension-feeding caddisflies on a downstream gradient. Large ancestral taxa with high filtration rates occur in resource-poor upstream habitats; more derived members of the phylogeny enter successively in downstream reaches with slower current and greater concentrations of particulate food.