Stephen B. Holmes

Leaf-litter decomposition and macroinvertebrate communities in boreal forest streams linked to upland logging disturbance

Abstract Leaf-litter decomposition and associated macroinvertebrate communities were compared in standardized leaf packs across forest streams in recently clearcut (n = 9) and reference (n = 12) low-order catchments on the Boreal Shield in northeastern Ontario, Canada. Logging was conducted under best management practices that included application of 30- to 100-m-wide no-harvest buffer zones on both sides of each stream. No significant differences were detected between sites in logged and reference streams for any reach- or catchment-level characteristics (except % area logged) or water-quality variables. Coarse-mesh leaf-pack mass loss was significantly lower (t-test, p = 0.003), and the ratio of fine-mesh to coarse-mesh leaf-pack mass loss was significantly higher (t-test, p = 0.008) in logged than in reference streams, but no difference in fine-mesh leaf-pack mass loss was detected between logged and reference streams. A stepwise multiple regression model of coarse-mesh leaf-pack mass loss on 15 reach- and catchment-level characteristics indicated that only logging presence/absence (r = −0.524) and average reach velocity (r = 0.397) were significantly and independently associated with leaf-litter decomposition. Macroinvertebrate communities on leaf packs in logged streams were different from those in reference streams. Taxonomic richness was significantly lower in logged than in reference streams. A multivariate ordination and analysis of similarity separated logged from reference streams, and abundances of the 3 most discriminating taxa were significantly lower in logged than in reference streams. A multivariate BVSTEP routine indicated that macroinvertebrate community structure was most strongly associated with logging presence/absence among the suite of site characteristics. Leaf-litter decomposition and aquatic macroinvertebrate community structure were successful bioindicators of catchment logging impacts, even when logging was conducted under best management practices. Effects on litter decomposition and leaf-pack macroinvertebrate communities seem to have been caused by upland logging disturbances because riparian areas were undisturbed in logged catchments.

Environmental persistence and impact of diflubenzuron in a forest aquatic environment following aerial application

Dimilin® WP-25 (diflubenzuron) was applied at a rate of 70 g active ingredient (AI) in 10, 5, and 2.5 L/ha to three spray blocks in a mixed boreal forest near Kaladar, Ontario, Canada. Water, sediment, and aquatic plants were collected from two ponds and a stream at intervals up to 30 days post-treatment for analysis of diflubenzuron (DFB) residues. The duration of detectable residues was different for each substrate, but in all cases was less than two weeks. Zooplankton and benthic invertebrate populations were monitored for up to 110 days post-spray in two ponds in the high volume rate block and in control ponds. Significant mortality occurred in two groups of caged macroinvertebrates (amphipoda and immature corixidae) 1 to 6 days after the ponds were treated with Dimilin. Three taxa of littoral insects (Caenis, Celithemis andCoenagrion) were significantly reduced in abundance in the treated ponds 21 to 34 d post-treatment, but recovered to pre-treatment levels by the end of the season. Of the six remaining groups studied, only one (immature corixidae), may have been slightly affected by treatment. Zooplankton (cladocera and copepoda) populations were reduced 3 days after treatment and remained suppressed for 2–3 months.

Influence of exposure duration on the toxicity of triclopyr ester to fish and aquatic insects

Flow-through toxicity tests were conducted to determine the effects of exposure time on the toxicity of triclopyr butoxyethyl ester (Garlon® 4) to fish (rainbow trout and chinook salmon) and stream insects (Hydropsyche sp. and Isonychia sp.). The toxicity of triclopyr ester to fish increased with exposure time, but the rate of increase in toxicity declined with increasing exposure duration. Median lethal concentrations for rainbow trout exposed for 1, 6, or 24 h were 22.5, 1.95, and 0.79 mg/L triclopyr ester (expressed as acid equivalent, nominal concentrations), respectively. Comparable values for chinook salmon were 34.6, 4.7, and 1.76 mg/L. The toxicity of triclopyr ester to aquatic insects also increased with increasing exposure time, but was considerably less than the toxicity to fish. There was no significant mortality (chi-square p>0.05) of insects following 3-h exposures to the maximum test concentration of approximately 110 mg/L. Median lethal concentrations following 9- and 24-h exposures were 14.9 and 4.0 ml/L for Hydropsyche sp., and 37.0 and 8.8 mg/L for Isonychia sp., respectively. At each exposure time in the toxicity tests, there was a sharp increase in mortality over relatively small increases in concentration, resulting in extremely steep slopes of the probit lines (6.3–33.8), and indicating an apparent response threshold. The herbicide exhibited delayed lethal effects, particularly in fish, but only at short term exposures to higher concentrations. The risk of adverse effects on fish and aquatic insects from triclopyr ester contamination, based on the results of these time-toxicity tests, is discussed.

Effects of the herbicides hexazinone and triclopyr ester on aquatic insects

Experiments were conducted to measure acute lethal response of aquatic insects to hexazinone (Velpar L) and triclopyr ester (Garlon 4) in flow-through laboratory bioassays, and to determine lethal and behavioral effects of these herbicides on insects in outdoor stream channels. No significant mortality (chi 2 P greater than 0.05) occurred in 13 test species exposed to hexazinone in laboratory flow-through bioassays (1-hr exposure, 48-hr observation) at the maximum test concentration of 80 mg/liter. The survival of insects exposed to 80 mg/liter hexazinone in outdoor stream channels was likewise unaffected. Significant drift (chi 2 P less than 0.001) of Isonychia sp. occurred during a hexazinone treatment of the stream channels, but only at the maximum concentration of 80 mg/liter, and survival of the displaced Isonychia sp. was not affected. In flow-through bioassays with triclopyr ester, 10 of 12 test species showed no significant mortality at concentrations greater than 80 mg/liter. Survival of Isogenoides sp. and Dolophilodes distinctus was significantly affected at less than 80 mg/liter. Lethal concentrations were estimated by probit analysis of concentration-response data (1-hr exposure, 48-hr observation) for Simulium sp. (LC50 = 303 mg/liter), Isogenoides sp. (LC50 = 61.7 mg/liter), and D. distinctus (LC50 = 0.6 mg/liter). Triclopyr ester applications to the stream channels resulted in significant drift and mortality of D. distinctus at 3.2 mg/liter (no effects at 0.32 mg/liter), Isogenoides sp. at 32 mg/liter, and Hydropsyche sp. and Epeorus vitrea at 320 mg/liter. The risk to aquatic insects of these herbicides used in forest vegetation management is discussed.

Lethal and sublethal effects of Bacillus thuringiensis var. kurstaki on aquatic insects in laboratory bioassays and outdoor stream channels

The microbial insecticide Bacillus thuringiensis is generally considered to be more environmentally acceptable than many broad-spectrum chemical insecticides (Laird et al. 1990), and Bacillus thuringinesis var. kurstaki (Btk) is now widely used in forest management for controlling defoliating insects (van Frankenhuyzen 1990). Broadscale applications of Btk to forested areas may result in contamination of watercourses, and may pose some hazard to aquatic organisms. Although the impact of B. thuringiensis var. israelensis (a dipteran-active serotype used for biting-fly control) on non-target aquatic fauna has been extensively investigated (e.g., Merritt et al. 1989), few published studies have reported the effects of Btk (the variety used in forest pest management) on aquatic invertebrates. Previous risk assessments of Btk to aquatic invertebrates have been largely based on static bioassays (Eidt 1985) and unpublished data from field investigations (Surgeoner and Farkas 1989). Our objective was to improve the risk assessment for stream insects exposed to Btk by providing further toxicity data for an array of insect taxa under more natural exposure regimes and environmental conditions. We conducted experiments to measure the acute lethal response of aquatic insects to Btk (Dipel 8AF) in recirculating laboratory bioassays, and to determine lethal and behavioural (drift) effects of Btk on aquatic insects in outdoor stream channels. MATERIALS AND METHODS Test organisms were collected from streams with an electroshocker and acclimated at the test sites for 24 hr before the treatments. No attempt was made to determine specific stages of development for the specimens, but most (except Taeniopteryx nivalis and some groups of Lepidostoma sp.) were in late or final instar. Btk was applied as formulated product (Dipel 8AF, Abbott Laboratories, Chicago, IL) at a maximum concentration of 600 IU/mL. As a means send reprint requests to D.P. Kreutzweiser at above address

Persistence of naturally occurring and genetically modified Choristoneura fumiferana nucleopolyhedroviruses in outdoor aquatic microcosms.

BACKGROUND To assess the persistence of genetically modified and naturally occurring baculoviruses in an aquatic environment, replicate (three) outdoor, aquatic microcosms were spiked with spruce budworm viruses [Ireland strain of Choristoneura fumiferana multiple nucleopolyhedrovirus (CfMNPV) and the recombinant CfMNPVegt(-)/lacZ(+)] at a rate of 1.86 x 10(10) occlusion bodies (OBs) m(-2) of surface area. The presence of virus in water samples collected at various times after inoculation was determined by PCR amplification of baculoviral DNA extracted from OBs. RESULTS Although UV radiation rapidly degrades baculoviruses under natural conditions, both viruses persisted above the level of detection (>100 OBs 450 microL(-1) of natural pond water) for at least 1 year post-inoculation, with little difference between the viruses in their patterns of persistence. CONCLUSION The present microcosm study suggests that occlusion bodies of baculoviruses can persist in the flocculent layer of natural ponds. On disturbance, OBs could re-enter the main water column and thus be available for transport to new locations. Implications for environmental risk assessment are discussed.

An interlaboratory comparison of data on brain cholinesterase activity in forest songbirds exposed to aerial application of zectran

Zectran® (4-dimethylamino-3,5-xylyl N-methyl-carbamate), a carbamate insecticide (active ingredient [AI] mexacarbate), was aerially applied to two 300 ha plots of coniferous forest at dosage rates of 70 and 140 g AI/ha, respectively. The brains of 288 birds collected from the treated areas and 84 birds from untreated areas were sagittally sectioned into approximately equal halves. Each of the laboratories participating in the study, the Forest Pest Management Institute (FPMI) and the Canadian Wildlife Service, Atlantic Region (CWS), assayed one half of each brain for cholinesterase (ChE) activity and the results were compared. The ChE estimates of the two laboratories on half brains from the same birds were poorly correlated (R=0.136, P<0.05) and differed significantly (P<0.00005). The reasons for this are uncertain. Despite the discrepancy in ChE estimates, however, separate statistical analysis of each data set produced the same general conclusion: the ChE response to Zectran® exposure was statistically significant but biologically unimportant. In both data sets, statistically significant ChE responses by niche and time since spraying were found. The dosage rate emitted from the airplane was a better predictor of ChE activity in the canopy niches than was volume deposited at ground level, but volume deposited was a more useful predictor for ground birds in most situations. These results are discussed in the context of a proposal to develop a reference file of normal brain ChE activities of common wildlife species.

Host-Range Testing of a Mixture of Two Nucleopolyhedroviruses of Choristoneura fumiferana (Lepidoptera: Tortricidae)

Abstract The host range of a mixture of Choristoneura fumiferana (Clemens) nucleopolyhedroviruses (CfMNPV and CfDefNPV) was investigated using a per os bioassay of larvae of 29 species of Lepidoptera and adult males of Megachile rotundata (F.) (Hymenoptera: Megachilidae). Using a whole-genomic DNA probe, positive results were obtained in 8 of 10 Tortricidae: Archips cerasivorana (Fitch), Choristoneura fractivittana (Clemens), C. fumiferana, Choristoneura occidentalis Freeman, Choristoneura pinus pinus Freeman, Choristoneura rosaceana (Harris), Clepsispersicana (Fitch), and Cydia pomonella (L.); one Crambidae: Ostrinia nubilalis (Hübner); one arctiine Erebidae: Estigmene acrea (Drury); and two Noctuidae: Oligia illocata (Walker) and Pyrrhia exprimens (Walker). Mortality rates were highest among C. fumiferana, C occidentalis, C. pinus pinus, A. cerasivorana, and C. pomonella. Sequenced polymerase chain reaction (PCR) amplicons from infected individuals from several species confirmed that the primer sets amplified the target viruses. CfMNPV was consistently found in virus-fed C. fumiferana; whereas, CfDefNPV was present only occasionally. The presence of CfMNPV and CfDefNPV in A. cerasivorana was confirmed by PCR and DNA sequencing. Significant treatment-mortality rates were induced in the noctuids P. exprimens and Acronicta impleta Walker; PCR determined that both viruses were present in treated P. exprimens but only CfMNPV was present in A. impleta. No virus was detected in M. rotundata.

EFFECTS OF LETHAL AND SUBLETHAL CONCENTRATIONS OF THE HERBICIDE, TRICLOPYR BUTOXYETHYL ESTER, IN THE DIET OF ZEBRA FINCHES

Lethal and sublethal effects of dietary triclopyr butoxyethyl ester (TBEE) on zebra finches (Poephila guttata Gould) were determined in laboratory experiments conducted between 8 January and 1 May 1991. The 8-day median lethal dietary concentration, LC50 (95% confidence interval), of TBEE to zebra finches was 1,923 (1,627 to 2,277) mg/kg. In the sublethal effects experiment, when birds were exposed to 500 mg/kg TBEE in the diet for 29 days, food consumption and body weight were significantly depressed (P < 0.05). Similar prolonged exposures to 50 and 150 mg/kg TBEE in the diet had no significant effect on food consumption or body weight (P > 0.05). Perch-hopping activity was depressed relative to controls in the 500 mg/kg group, and elevated in the 150 mg/kg group, but neither of these differences was significant (P > 0.05). Disappearance of TBEE residues from treated seeds over the 29 day experimental period followed an exponential decay model, with half-lives in the order of 15 to 18 days. On the basis of our observation that TBEE had no significant adverse effects at a concentration greater than the maximum expected environmental concentration, we propose that forestry applications of triclopyr at registered dosage rates pose little risk to wild songbirds.

Insecticide residues and cholinesterase inhibition in zebra finches orally dosed with fenitrothion

Abstract Fenitrothion residues and cholinesterase (ChE) activities were measured in zebra finches given acute, oral doses of fenitrothion insecticide. Dosage rates were 1.04, 3.80, and 11.36 mg/kg. Residues declined rapidly but were still detectable at trace levels (<0.005 mg/kg) 96 h after treatment. Peak brain and plasma ChE inhibitions averaged between 50–76% and 79–89%, respectively. Plasma ChE recovered more rapidly (1–4 days) than brain ChE (10 days or more). Brain and plasma ChE inhibitions were positively, but weakly, correlated with fenitrothion body burden.