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.

Effects on litter-dwelling earthworms and microbial decomposition of soil-applied imidacloprid for control of wood-boring insects.

BACKGROUND: Imidacloprid is an effective, systemic insecticide for the control of wood-boring insect pests in trees. Systemic applications to trees are often made by soil injections or drenches, and the resulting imidacloprid concentrations in soil or litter may pose a risk of harm to natural decomposer organisms. The authors tested effects of imidacloprid on survival and weight gain or loss of the earthworms Eisenia fetida (Savigny) and Dendrobaena octaedra (Savigny), on leaf consumption rates and cocoon production by D. octaedra and on microbial decomposition activity in laboratory microcosms containing natural forest litter. RESULTS: Dendrobaena octaedra was the most sensitive of the two earthworm species, with an LC(50) of 5.7 mg kg(-1), an LC(10) of about 2 mg kg(-1) and significant weight losses among survivors at 3 mg kg(-1). Weight losses resulted from a physiological effect rather than from feeding inhibition. There were no effects on cocoon production among survivors at 3 mg kg(-1). The LC(50) for E. fetida was 25 mg kg(-1), with significant weight losses at 14 mg kg(-1). There were no significant effects on microbial decomposition of leaf material at the maximum test concentration of 1400 mg kg(-1). CONCLUSION: The results indicate that, when imidacloprid is applied as a systemic insecticide to the soil around trees, it is likely to cause adverse effects on litter-dwelling earthworms if concentrations in the litter reach or exceed about 3 mg kg(-1).

A refined method for the detection of baculovirus occlusion bodies in forest terrestrial and aquatic habitats.

A sensitive and efficient method was developed for the detection of genetically modified and wild-type baculovirus occlusion bodies (OB) in forest terrestrial and aquatic habitats. The protocol facilitates the analysis of a large number of samples collected and frozen to maintain viral integrity. Lyophilization was used to standardize the size of both field-collected soil samples and test substrates inoculated with OBs for the determination of minimum detection threshold. To simulate natural conditions, terrestrial test substrates were inoculated at a standardized moisture content determined using a soil pressure plate apparatus. OBs, extracted from lyophilized test substrates by washing, sieving and centrifugation, were subjected to alkaline lysis and viral DNA isolated using a purchased DNA purification kit. PCR amplified DNA was visualized using agarose gel electrophoresis. Minimum detection thresholds in terrestrial substrates were 10(3), 10(2), 10(2) and 10(1) OBs from 0.5 g of lyophilized L, F-H and mineral soil horizons, and 1.0 ml of leachate, respectively. Detection thresholds in aquatic substrates were 10(0) and 10(3) OBs from 1.0 ml of pond water and 1.0 g of bottom sediment, respectively.