Horizontal and trophic transfer of diflubenzuron and fipronil among grasshoppers (Melanoplus sanguinipes) and between grasshoppers and darkling beetles (Tenebrionidae).

The possibility of horizontal transmission of diflubenzuron and fipronil was assessed in rangeland grasshoppers. Laboratory studies of Melanoplus sanguinipes demonstrated that fipronil was horizontally transferred at lethal levels (p < 0.05) via cannibalism through four passages when the initial dose applied to a food source was 250 times the label rate for rangeland grasshopper and locust control (label rate is 4 g AI/ha). Mortality was 100% on the first three passages through cannibalism. At 25 and 1 times the label rate, fipronil was lethal (p < 0.05) only on the first cannibalistic passage. Diflubenzuron generated significant (p < 0.05) mortality via horizontal transmission through two passages when the initial dose applied to a food source was 2,000 times the label rate for rangeland grasshopper control (label rate is 8.71 g AI/ha). There was 100% mortality in the first passage via cannibalism. At 250 and 25 times the label rate, diflubenzuron was lethal only on the first cannibalistic passage. Field applications of these two acridicides followed by collection of cadavers (Amphitornus coloradus and Ageneotettix deorum) that were fed to M. sanguinipes in the laboratory revealed that fipronil (25 times the label rate) generated significant (p < 0.05) mortality through two passages and diflubenzuron (label rate) caused no mortality via necrophagy. Tenebrionid beetles fed grasshopper cadavers collected from the field application of fipronil yielded 45% mortality, compared with 25% mortality in the controls. These findings suggest that horizontal and trophic transfer probably play a nominal ecotoxicological role in rangeland grasshopper control programs with diflubenzuron, but the transfer of fipronil to grasshoppers, scavengers, and natural enemies via necrophagy may increase both the efficacy of control programs and their environmental affects.

Cryopreservation of embryos of Culicoides sonorensis (Diptera: Ceratopogonidae).

The successful long-term storage of insects that are used for research purposes can eliminate the need for ongoing colony maintenance on a large scale. In addition, rare and valuable genotypes of insects can be preserved. This study was conducted to determine whether cryopreservation is a suitable means of storing embryos of Culicoides sonorensis Wirth & Jones, an important vector of animal pathogens. We determined that eggs of C. sonorensis can withstand vigorous treatments of dechorionation, permeabilization, and loading with the cryoprotectant, elthylene glycol. Although their viability was reduced, an average of 80.3% of the embryos developed into larvae. Dehydration in vitrification solution caused a much greater reduction in egg viability (42.7% survival), and freezing in liquid propane further reduced the number of eggs that developed into larvae (40.1%), pupae (22.9%) and adults (18.8%). This work demonstrated that this procedure may prove useful for the cryopreservation of standard laboratory colonies and genetic lines of C. sonorensis.

The effects of reduced agent-area insecticide treatments for rangeland grasshopper (Orthoptera: Acrididae) control on bird densities.

The effects of insecticidal control programs for grasshoppers on the population density of birds were assessed under operational conditions in two rangeland sites in Wyoming during an outbreak (19 to 56 grasshoppers m(-2) on >1,500 ha). Malathion, carbaryl, and fipronil were evaluated using large-scale (>/=260 ha) reduced agent-area treatments (RAAT), in which these chemicals were applied at 50% of the standard rate (except fipronil, for which there is no standard in North America) to 80, 50, and 33% of the areas (alternating treated and untreated swaths), respectively. Grasshopper population densities were reduced by 73 to 99%, at 14 and 28 days after treatment. Significant differences among treatments within the sites were apparent, and despite disparities in the vegetation, topography, and grasshopper populations between sites, some consistent patterns of response by bird populations were found. Relative to pretreatment densities and untreated plots, at 14 days after treatment, bird densities were enhanced at one site and suppressed at the other; at 28 days after treatment bird populations were generally suppressed at both sites. However, absolute densities increased in some plots, indicating that birds still had adequate food. There appeared to be no relationship between posttreatment grasshopper and bird densities, perhaps due to the large initial insect populations. Fipronil plots generally had higher avian population densities (nongregarious insectivores and total birds) than carbaryl plots, which had bird densities greater than or equal to malathion plots. These differences were probably a function of both the toxicological properties of the compounds and the proportion of the infested land that was treated. Based on these findings, we must consider the possibility that compounds with relatively high toxicity to birds and long residual effects applied to widely spaced swaths may cause no more (or perhaps less) environmental impact than less toxic and persistent insecticides that must be applied to large proportions of infested rangeland. http://link.springer-ny. com/link/service/journals/00244/bibs/37n4p519.html

COMPTEL measurements of the omnidirectional high-energy neutron flux in near-earth orbit.

On four occasions, twice in 1991 (near solar maximum) and twice in 1994 (near solar minimum), one COMPTEL D1 detector module was used as an omnidirectional detector to measure the high-energy (> 12.8 MeV) neutron flux near an altitude of 450 km. The D1 modules are cylindrical, with radius 13.8 cm and depth 8 cm, and are filled with liquid scintillator (NE213A). The combined flux measurements can be fit reasonably well by a product of the Mt. Washington neutron monitor rate, a linear function in the spacecraft geocenter zenith angle, and an exponential function of the vertical geomagnetic cutoff rigidity in which the coefficient of the rigidity is a linear function of the neutron monitor rate. When pointed at the nadir, the flux is consistent with that expected from the atmospheric neutron albedo alone. When pointed at the zenith the flux is reduced by a factor of about 0.54. Thus the production of secondary neutrons in the massive (16000 kg) Compton Gamma-Ray Observatory spacecraft is negligible. Rather, the mass of the spacecraft provides shielding from the earth albedo.

Applications of dot-blot, ELISA, and immunoelectron microscopy to field detection of bluetongue virus in Culicoides variipennis sonorensis: an ecological perspective.

An avidin-biotin complex (ABC) dot-blot, an antigen capture enzyme-linked immunosorbent assay (ELISA), and immunoelectron microscopy (IEM) were used to detect bluetongue (BLU) virus and viral antigen in field-collected C. varriipennis sonorensis Wirth & Jones from an enzootic BLU area in northeastern Colorado. This is the 1st attempt to apply these immunodiagnostic methods to an epidemiologically relevant, large-scale ecological system. One of the 1,800 midges (0.0005%) was positive by the dot-blot procedure, 2 (0.0011%) were positive by the ELISA, and BLU virus was identified in 8 midges (0.0044%) by IEM. These data are interpreted in context of the "whole system" of the disease to provide a framework for determining the knowledge gaps in our understanding and directing future studies in these areas. Our basic model of BLU ecology suggests that the infection rates found by the diagnostic methods are within expected ranges, thus strongly supporting the proposed ecological model and the work used to parameterize the model. This integration of immunodiagnostic methods and ecology makes it evident that further investigations of daily mortality during the extrinsic incubation period are vital to a better understanding of BLU virus occurrence in Culicoides vector and vertebrate host populations.

Pesticide labels: proven protection or superficial safety?

BACKGROUND: The readability of restricted-use pesticide labels is an important element in preventing misuse and unsafe application practices. METHODS: An optometric analysis of 54 pesticide labels was conducted to determine the visual acuity required to read the average general use label. Additionally, a survey of 1623 Wyoming residents was conducted to determine the extent label directions are read, understood, and adhered to. RESULTS: A visual acuity of 20/30 and 20/40 is required to read the average general use and restricted use pesticide label, respectively. The mean and mode cognitive reading level required is the 11th grade. About half of the sample population read the label and two thirds reported always following label directions. CONCLUSIONS: A significant proportion of the American public can not or does not read or understand pesticide labels and does not follow the label instructions. Essential pesticide use and safety information is not being effectively communicated to the public.

Olfactory basis of cannibalism in grasshoppers (Orthoptera: Acididae): I. laboratory assessment of attractants.

Two laboratory-reared and five field-collected species of grass-hoppers were assayed for behavioral responses to volatile chemicals emitted from grasshopper cadavers using a two-choice olfactometer with no stimulus as a control. Necrophilic and necrophobic responses to the stimuli were dependent upon species, sex, development, starvation, crowding, and attractant. Laboratory-rearedMelanoplus differentialis (Thomas) and field-collectedHadrotettix trifasciatus (Say) andAulocara elliotti Thomas exhibited significant responses to the cadavers. Females of these three species showed significant movement towards the cadavers, but males were not significantly necrophilic. All tested developmental stages ofH. trifasciatus (fourth-instar nymphs through adults) showed significant attraction to cadavers. FedM. differentialis adults andH. trifasciatus adults and nymphs were significantly attracted to cadavers, but starved individuals were either repelled or exhibited no significant response. Although femaleA. elliotti from an uncrowded population were significantly attracted to cadavers, females from a crowded population were significantly repelled from cadavers. Contraspecific cadavers more frequently elicited a measurable response in adultM. sanguinipes andH. trifasciatus than did conspecific cadavers, and only contraspecific cadavers yielded a significant (necrophilic) response. AlthoughM. differentialis was necrophilic, neither males nor females were significantly attracted to water.

Olfactory basis of cannibalism in grasshoppers (Orthoptera: Acrididae): II. field assessment of attractants.

The responses of rangeland grasshoppers to biologically and historically derived attractants were studied in a shortgrass prairie in southeastern Wyoming in July 1990. Seven long-chain fatty acids (C14-C20: singly and in combination), grasshopper cadavers, molasses, fruit extracts, and chloroform (solvent control) were tested. Each attractant was applied to filter paper and placed in an arena delimited by a 0.10-m(2) aluminum ring. Grasshoppers were most attracted to linoleic and linolenic acids, with significantly more grasshoppers found in these arenas than in those of the controls or other attractants. These two fatty acids alone and in combination were more attractive at 1 grasshopper equivalent (GE) than at 5 GE. The seed bug,Lygaeus kalmii Stål, and five species of ants were also attracted to these two fatty acids. Molasses had significantly more grasshoppers on the filter paper than did the other attractants, but molasses had significantly fewer grasshoppers in the arena than the fatty acids. Fruit extracts were not effective at attracting grasshoppers. Water extracts of cadavers attracted significantly more grasshoppers to the bait than did chloroform extracts. Because the assayed grasshopper community was dominated by the Gomphocerinae (a subfamily that includes many pest species that do not readily consume wheat bran bait), it may be possible to use fatty acids in conjunction with insecticidal bran baits for increased control of rangeland grasshoppers.

Olfactory basis of cannibalism in grasshoppers (Orthoptera: Acrididae): III. Use of attractants on carbaryl wheat bran bait.

Two known necrogenic attractants, linoleic acid (18:2) and linolenic acid (18:3), were added to carbaryl bran bait to enhance control of rangeland grasshoppers in southeastern Wyoming. The primary goal was to increase control of species of Gomphocerinae, which normally do not consume bran bait. Each attractant was applied at 1, 5, and 10 grasshopper equivalents (GE) (e.g., a 1-GE treatment had the amount of fatty acid per unit weight of wheat bran that would be found in one grasshopper). Controls included carbaryl bran with no attractant and no treatment. Bran was applied at a rate of 1 kg/ha to 1-ha blocks on June 6, 1992, with four replicates per treatment and control. Plots were sampled for grasshoppers and nontarget organisms one day prior to and one, two, and three days after treatment. The addition of linoleic acid (10 GE) resulted in significantly lower total grasshopper densities than carbaryl bran alone. None of the attractants significantly improved control of all Gomphocerinae due to inconsistent effects among species. Relative to carbaryl bait alone, all doses of both fatty acids significantly improved control ofAmphitornus coloradus (Thomas). However, the attractants did not change the level of control ofCordillacris occipitalis orAulocara elliotti, and linolenic acid (5 GE) and linoleic acid (1 GE) resulted in significantly poorer control ofAgeneotettix deorum (Scudder) than carbaryl bait alone. Nontarget arthropods were largely unaffected by the attractants, except for the spiders, which were significantly reduced in all linolenic acid treatments.