The uptake of fluorescent particles by protists and filter-feeding metazoa is being used increasingly by microbial ecologists to study feeding behavior and measure grazing rates. Recent studies of microflagellate uptake of these inert particles have yielded inconsistent results. In particular. grazing rates determined from fluorescent particle uptake are often less than rates measured using other techniques. These low uptake rates have been attributed to osmotrophy, food quality or size selection, rapid egestion of inert particles, and the slower feeding by free-living, as opposed to attached, protists. We have found that a variety of flagellates egest food vacuole contents upon fixation with several commonly used agents including glutaraldehyde and formaldehyde. During time course experiments, the observed microsphere uptake rate for a small chrysomonad flagellate using 1 % glutaraldehyde was only 6 % of the rate obtained by using the fixation method of van der Veer (1982) (2 '10 acrolein, 2 % glutaraldehyde and 1 % tannic acid), modified for epifluorescence microscopy. Uptake rates of several mixed flagellate populations also were 2.4 to 3.1 times higher using the modified van der Veer method than with 1 % glutaraldehyde. The average number of ingested microspheres cell-' using this method was simllar to that observed in live cells immobilized with NiS04. Glutaraldehyde also caused the egestion of Synechococcus sp. cells and fluorescently labelled bacteria from the chrysomonad flagellate. We conclude that previous studies using common aldehyde fixation wlth particle uptake for measunng rates of microflagellate bacterivory have significantly underestimated actual rates of consumpt~on, and that these studes must be re-evaluated, and perhaps repeated, using effective fixation methods.

The toxic dinoflagellate Pfiesteria piscicida Steidinger & Burkholder has recently been implicated as the etiologic agent of acute mass mortalities and skin ulcers in menhaden, Brevoortia tyrannus, and other fishes from mid-Atlantic U.S. estuaries. However, evidence for this association is largely circumstantial and controversial. We exposed tilapia (Oreochromis spp.) to Pfiesteria shumwayae Glasgow & Burkholder (identification based on scanning electron microscopy and molecular analyses) and compared the resulting pathology to the so-called Pfiesteria-specific lesions occurring in wild menhaden. The tilapia challenged by high concentrations (2,000-12,000 cells/mL) of P. shumwayaeexhibited loss of mucus coat and scales plus mild petecchial hemorrhage, but no deeply penetrating chronic ulcers like those in wild menhaden. Histologically, fish exhibited epidermal erosion with bacterial colonization but minimal associated inflammation. In moribund fish, loss of epidermis was widespread over large portions of the body. Similar erosion occurred in the mucosa lining the oral and branchial cavities. Gills exhibited epithelial lifting, loss of secondary lamellar structure, and infiltration by lymphoid cells. Epithelial lining of the lateral line canal (LLC) and olfactory organs exhibited severe necrosis. Visceral organs, kidney, and neural tissues (brain, spinal cord, ganglia, peripheral nerves) were histologically normal. An unexpected finding was the numerous P. shumwayae cells adhering to damaged skin, skin folds, scale pockets, LLC, and olfactory tissues. In contrast, histologic evaluation of skin ulcers in over 200 wild menhaden from Virginia and Maryland portions of the Chesapeake Bay and the Pamlico Estuary, North Carolina, revealed that all ulcers harbored a deeply invasive, highly pathogenic fungus now known to be Aphanomyces invadans. In menhaden the infection always elicited severe myonecrosis and intense granulomatous myositis. The consistent occurrence of this fungus and the nature and severity of the resulting inflammatory response indicate that these ulcers are chronic (age >1 week) and of an infectious etiology, not the direct result of an acute toxicosis initiated by Pfiesteria toxin(s) as recently hypothesized. The disease therefore is best called ulcerative mycosis (UM). This study indicates that the pathology of Pfiesteria laboratory exposure is fundamentally different from that of UM in menhaden; however, we cannot rule out Pfiesteria as one of many possible early initiators predisposing wild fishes to fungal infection in some circumstances.

Bacterioplankton abundance and production were examined over the course of a destratification event in the lower James River, Virginia, USA. Goals of the study were to determine if destratification would influence temporal patterns of bacterioplankton parameters and relationships between bacterioplankton and other biological and abiological parameters. Mean bacterial abundance grouped over stations did not change over the course of the study, and were characterized by much smaller coefficients of variation than all other planktonic constituents. However, bacterial production measured by 3H-thymidine (3 H-~d r) incorporation decreased significantly from a stratified (324 pg C I-' d-l) to a destratified (187 pg C I-' d-l) hydrography. The importance of bacterial-autotrophic coupling was also suggested from oxygen metabolism experiments, which indicated substrate limitation of bacteria, and the existence of a rapidly utilized photosynthetically produced substrate. Correlative relationships between bacterial parameters with chlorophyll a were significant during stratified hydrography, but diminished or became non-significant during destratified hydrography. Estimates of microzooplankton grazing rates upon bacteria decreased significantly during the onset of destratification. During the stratified hydrography, bacterial parameters displayed highly significant negative correlations to ammonium, however these relationships disappeared during the destratified hydrography. Results of this study indlcate that destratification changes the trophic interactions of bacterla within the microbial loop, however these changes are not necessarily reflected by temporal patterns of bacterial abundance.

Fifteen insecticide treatments were tested at the MSU Montcalm Research Farm, in Entrican, MI, for their control of Colorado potato beetles (CPB). ‘Snowden’ potatoes were planted 12 inches apart with a 34 inch row spacing on 10 May. Treatments were replicated four times and assigned to plots in a RCB design. The plots measured 40 feet long and were three rows wide. There were at least two rows of bare ground between plots and five feet of untreated potatoes between plots in the same rows. The Admire and Mocap treatments were applied in furrow at planting. The first foliar treatment was applied, at 25% CPB hatch, on 18 June using a tractor-mounted sprayer (30 gal/acre, 40 psi). Subsequent first generation sprays were applied on 29 June and 7 July. Light rain occurred on 7 July before the insecticides had a chance to dry. Insecticide effectiveness was determined by counting the various stages of CPB on two randomly chosen plants from the middle row of each plot. Counts were done on 12 and 23 Jun and 3 and 12 July. Second generation methods were the same as for the first generation with sprays occuring on 19 July, 26 July and 2 Aug and counts on 18, 24 and 31 Jul. All plots other than the two Trigard treatments were sprayed with a maintenance spray of Imidan and PBO. Each plot was assessed for percent defoliation on 3 July and 9 August. The middle row of potatoes from each plot was harvested on 22 August, separated by size and weighed.

‘Snowdon’ variety potatoes were used to test nineteen insecticides for control of Colorado potato beetle (CPB) at the MSU Montcalm Research Farm in Entrican, MI. Potatoes were planted 12 inches apart with a 34 inch row spacing on 4 May. Plots were 40 feet long by three rows wide and arranged in a randomized complete block design with four replications. Plots were separated by at least 5 feet of bare ground. Fosthiazate in-furrow treatments were incorporated into the soil through rototill on 3 May. An Admire treatment was applied in furrow on the potato seed with a CO2 backpack sprayer (8005 flat fan single nozzle, 30 psi) on 4 May. Foliar treatment applications were applied on 16, 23 Jun, 1 and 7 Jul using a tractor-mounted sprayer (30 gal/acre, 40 psi). Preplant Fosthiazate treated plots also received foliar treatments of Asana and piperonyl butoxide (PBO). Rain occurred on 24 Jun and 7 Jul within hours after spraying. Insecticide effectiveness was determined through postspray counts for all stages of CPB (small larvae = 1 st and 2nd instar, large larvae = 3rd and 4th instar) by searching two randomly selected plants from the middle row of each plot on 21, 28 Jun, 5 and 12 Jul. Plots were assessed for percent defoliation on 28 Jun, 5, 8 and 12 Jul. Plots were sprayed 13 Jul with Imidan and PBO (except for two of the Agrimek plots) to control summer adults emerging from poor treatments and migrating toward other research plots. All plots were sprayed for the same reason with Agrimek on 23 Jul and 11 Aug. Potatoes in the middle row of each plot were harvested on 2 Sept. Potatoes were separated by size.