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The systemic insecticide imidacloprid may be applied to deciduous trees for control of the Asian longhorned beetle, an invasive wood‐boring insect. Senescent leaves falling from systemically treated trees contain imidacloprid concentrations that could pose a risk to natural decomposer organisms. We examined the effects of foliar imidacloprid concentrations on decomposer organisms by adding leaves from imidacloprid‐treated sugar maple trees to aquatic and terrestrial microcosms under controlled laboratory conditions. Imidacloprid in maple leaves at realistic field concentrations (3–11 mg kg−1) did not affect survival of aquatic leaf‐shredding insects or litter‐dwelling earthworms. However, adverse sublethal effects at these concentrations were detected. Feeding rates by aquatic insects and earthworms were reduced, leaf decomposition (mass loss) was decreased, measurable weight losses occurred among earthworms, and aquatic and terrestrial microbial decomposition activity was significantly inhibited. Results of this study suggest that sugar maple trees systemically treated with imidacloprid to control Asian longhorned beetles may yield senescent leaves with residue levels sufficient to reduce natural decomposition processes in aquatic and terrestrial environments through adverse effects on non‐target decomposer organisms.

Abstract A forest headwater stream was manipulated (logging road-crossing amended) to induce fine sediment inputs. Benthic inorganic sediment concentrations .particles 1.5–250 μm increased from a 2-year pre-disturbance average of about 800 g m–2 to over 5000 g m–2 that persisted for 3 years. Aquatic insect communities were examined over the 5-year study period in the manipulated and nearby reference streams. Overall, the effects of the fine sediment increases on aquatic insect communities were minimal. There were no significant effects of sedimentation on total aquatic insect abundance or biomass. An index of multivariate dispersion gave no evidence of community stress at the manipulated site. Multivariate ordination plots and time trends among univariate community metrics indicated only subtle changes in community structure. Among the univariate metrics (16 time series analyses in total), six gave evidence of a sediment impact on aquatic insect communities. Of those, the clearest indications of an effect were small reductions in diversity and richness of spring communities. These resulted from a significant decline in the proportion of spring shredders, accompanied by a significant increase in the percent Chironomidae. This large-scale experimental approach integrated the realism of a whole-stream study with the control of a manipulative study by including pre-manipulation measurements and excluding other confounding catchment disturbances. In this regard, it may provide a more realistic measure of benthic community level responses to sedimentation in streams at a magnitude associated with logging activity than many previous studies.

The effects of a genetically engineered insect baculovirus on indigenous aquatic microbial communities were determined in closed, recirculating aquatic microcosms, and compared with the effects of a natural strain of the virus and of a growth-regulating insecticide, Dimilin. The recombinant virus was a nuclear polyhedrosis virus (NPV) of the spruce budworm (Choristoneura fumiferana(Cf)) with a lacZ marker gene inserted into the egt region of the CfNPV. The natural virus was Ireland strain CfNPV. Microbial measurement endpoints included decomposition activity (mass loss of organic material), respiration on two different substrates (O2consumption), heterotrophic bacterial abundance (plate counts), and microbial community metabolic profiles (carbon source utilization patterns in Biolog GN microplates). Viral DNA of both the natural strain and the recombinant viruses, detected by polymerase chain reaction techniques, settled out of the microcosm water and accumulated on bottom substrates within 3 days of the microcosm inoculations. The viral DNA persisted in bottom substrates for the duration of the 21-day experimental period, although there was some evidence that the recombinant virus was less stable than the natural strain in particulate organic matter. No significant changes in microbial decomposition or respiration activity, bacterial abundance, or average metabolic responses were detected by a time trend analysis in microcosms inoculated with either the lacZ recombinant virus or the natural Ireland strain CfNPV. Significant effects on microbial decomposition and respiration activity were detected in microcosms treated with the growth-regulating insecticide at, and above, the expected environmental concentrations. Despite significant effects on microbial community functional attributes in Dimilin-treated microcosms, there were no detectable changes in community structure in terms of metabolic profiles or bacterial abundance.

A potent ecdysone agonist, tebufenozide, has recently been developed as a molt-inducing insecticide to control defoliating lepidopterans. As part of continuing research efforts to assess the effectiveness and environmental safety of this material for insect pest management in Canadian forests, tebufenozide (RH-5992-2F) was applied to large lake enclosures and the effects on zooplankton communities were evaluated. There were significant treatment effects at all test concentrations (0.07–0.66 mg L-1 tebufenozide). Concentration-dependent reductions in the abundance of cladocerans indicated that there were direct toxic effects of tebufenozide on this group of macrozooplankton. There were no indications of direct toxic effects on copepods. Significant increases in abundance of rotifers in treated enclosures at the three higher test concentrations were coincident with reductions in cladocerans and indicated secondary effects of the insecticide on the abundance of microzooplankton. There were no significant differences among treated and control enclosures in chlorophyll a concentrations, indicating that tebufenozide did not have direct effects on phytoplankton biomass, nor did the alterations in the zooplankton communities of treated enclosures have measurable secondary effects on phytoplankton biomass. Daytime dissolved oxygen concentrations were significantly higher in treated enclosures than in controls, indicating that the perturbation to biotic communities of some treated enclosures was sufficient to induce measurable changes in system-level functional attributes. Recovery of zooplankton communities in the enclosures occurred within 1–2 months at 0.07 and 0.13 mg l-1 and by the following summer (12–13 months) at 0.33 and 0.66 mg l-1.

Previous field studies have demonstrated that residues of the herbicide, triclopyr butoxyethyl ester (3,5,6‐trichloro‐2‐pyridinyloxyacetic acid, butoxyethyl ester) (TBEE), can accumulate in submerged leaf material of aquatic systems at concentrations up to 20 times the maximum aqueous concentrations. Accumulated TBEE residues may pose a risk of adverse effects to detritivorous invertebrates inhabiting and using natural leaf packs. We examined the dynamics of TBEE accumulation and persistence in leaf materials of laboratory and outdoor aquatic systems, and determined the ecological significance of this in terms of effects on detritivorous insects and organic matter processing. Accumulations of TBEE in leaf packs of semi‐static laboratory microcosms were up to 80 times aqueous concentrations, and residues persisted for 4 to 5 d. Leaf material of flow‐through laboratory microcosms accumulated TBEE at much higher rates (up to 1000 times aqueous concentrations), but residues were cleared by 48 to 72 h. Accumulation and persistence in flow‐through units were dependent on water depth, velocity, and exposure duration. Accumulated TBEE residues were less in outdoor stream channels than in laboratory flow‐through units, probably because of losses through sorption to natural benthic material in the stream channels. Despite accumulations of TBEE in leaf packs at up to 90 mg kg−1in systems treated at or near expected environmental concentrations, there was no significant mortality of detritivorous insects and no significant reductions in leaf consumption. Significant mortality and reduced feeding occurred only in systems treated at concentrations well above (up to 10 times) expected environmental concentrations.

Epilithic microbial communities were colonized on leaf disks and exposed to commercial preparations ofBacillus thuringiensisvar.kurstaki(Btk) in aquatic microcosms. Responses in terms of microbial respiration, bacterial cell density, protozoan density, and microbial decomposition activity were measured. Test concentrations for treatments with Dipel 64AF and Dipel 8AF in microcosms were the expected environmental concentration (EEC) of 20 IU/ml, 100× the EEC, and 1000× the EEC. Bacterial cell density in the biofilm of leaf disks was significantly increased at concentrations as low as the EEC. There were no concomitant alterations in protozoan density. Microbial respiration was significantly increased, and decomposition activity was significantly decreased, but only at the artificially high concentration of 1000× the EEC. This effect was attributed to the spore–crystal component rather than formulation ingredients. Microbial decomposition of leaf material was also determined in outdoor stream channels treated at concentrations ranging from the EEC to 100× the EEC. Although there tended to be reduced decomposition activity in treated channels, there were no significant differences in mass loss of leaf material between treated and control channels. Various regression, classification, and ordination procedures were applied to the experimental data, and none indicated significant treatment effects. These results from laboratory and controlled field experiments indicate that contamination of watercourses with Btk is unlikely to result in significant adverse effects on microbial community function in terms of detrital decomposition.

Neem-based insecticides are being investigated as alternatives to synthetic insecticides for the control of forest insect pests in Canada. Because the proposed use pattern against forest defoliators often necessitates spraying near shoreline areas, an assessment of adverse effects of neem on nontarget aquatic invertebrates was warranted. Acute lethal effects of two neem-based formulations on eight species of macroinvertebrates were determined in flow-through screening tests at 10 times the expected environmental concentration (0.35 mg/liter). Significant mortality occurred only in the mayflyIsonychia bicolor/rufaexposed to one formulation, and further tests were conducted to determine a concentration-dependent response. The LC50forI. bicolor/rufawas estimated at 1.12 mg/liter; the LC10was 0.63 mg/liter. Three detritivorous species were tested at expected environmental concentrations (0.035 mg/liter) at longer exposures in aquatic microcosms to determine effects of the two formulations on feeding rates and survival. Neither formulation caused significant mortality or antifeedant effects after a 28-day exposure. The implications of these results for forest pest management operations are discussed.

Rainbow trout fingerlings were fed dried krill injected with gypsy moth or spruce budworm nuclear polyhedrosis virus (LdNPV and CfNPV, respectively) at a total dose of 1.4 × 107occlusion bodies (OBs) per fish. By the end of the 21-day experimental period there were no adverse effects on fish survival or behavior and no significant differences in feeding rates or growth between treated and control fish. The internal organs of all fish were examined at the end of the experiment and there were no signs of lesions, discoloration, swelling, hemorrhaging, or other aberrations. Visceral tissues were analyzed with a horseradish peroxidase-labeled whole genomic DNA probe (enhanced chemiluminescence procedure) to detect infection by the NPVs. There were no indications of NPV infection (no positive signals) in stomach and intestinal tract tissues of treated fish. High background signals were obtained from liver samples, but further analyses indicated that these were not due to the presence of LdNPV or CfNPV. The protocols outlined here should be applicable to determining infectivity and effects of genetically modified insect viruses on fish.

Conventional statistical approaches rely heavily on the properties of the central limit theorem to bridge the gap between the characteristics of a sample and some theoretical sampling distribution. Problems associated with nonrandom sampling, unknown population distributions, heterogeneous variances, small sample sizes, and missing data jeopardize the assumptions of such approaches and cast skepticism on conclusions. Conventional nonparametric alternatives offer freedom from distribution assumptions, but design limitations and loss of power can be serious drawbacks. With the data-processing capacity of today's computers, a new dimension of distribution-free statistical methods has evolved that addresses many of the limitations of conventional parametric and nonparametric methods. Computer-intensive statistical methods involve reshuffling, resampling, or simulating a data set thousands of times to empirically define a sampling distribution for a chosen test statistic. The only assumption necessary for valid results is the random assignment of experimental units to the test groups or treatments. Application to a real data set illustrates the advantages of these methods, including freedom from distribution assumptions without loss of power, complete choice over test statistics, easy adaptation to design complexities and missing data, and considerable intuitive appeal. The illustrations also reveal that computer-intensive methods can be more time consuming than conventional methods and the amount of computer code required to orchestrate reshuffling, resampling, or simulation procedures can be appreciable.