Small fly ash settling ponds (e.g. 2-yr life time) should not be used after they are ~87–90% full when effluents are released into lotic systems. When our pond was > 90% full, mayflies (Stenonema, Heptagenia, Paraleptophlebia), stoneflies (Acroneuria), and caddisflies (Cheumatopsyche) were significantly (α = 0.05) reduced in density, number of taxa, and diversity in the stream receiving system. Highly resistant coleopterans (e.g. Psephenus herricki) became the dominant species. Two to 10 mo were required for the insect community to recover after cessation of ash effluent. Potential lethal effects of fly ash may result from ash particles, heavy metal, and other elements (especially As and Se), and alkaline pH increases above 9.0. Which fraction of fly ash is most limiting to each insect group or species needs far more examination. Ash particle concentrations (total suspended solids, [Formula: see text]) were not acutely toxic in 96-h laboratory bioassays to sensitive mayflies (Stenonema pudicum) or resistant coleopterans (P. herricki), nor were heavy metals (Cd, Cu, Zn) at concentrations similar to those found in the fly ash effluent, although data are lacking to evaluate long-term (e.g. [Formula: see text]) effects. Alkaline pH exposures need more research, since the 96-h LC50 of 9.5 for S. pudicum was similar to pH values observed in the receiving stream during summer low-flow, high-temperature conditions when the ash pond was > 95% full.
The life history of the giant stonefly Pteronarcys dorsata was investigated in a warm water fourth order river in southwestern Virginia. The life cycle of P. dorsata was univoltine with emergence occurring mid-March to 1st week of April. Adults lived up to 42 days in the laboratory. Mean fecundity was 242 eggs with up to four separate egg batches produced. Eggs hatched in 23 to 38 days. Early nymphal instars were collected in the river in mid-June. Nymphs reached maximum size by late November or December. During the warm months nymphs were found in mats of Podostemum ceratophyllum (river weed) and through the winter months under large unembedded rocks or leaf packs. The diet consisted of diatoms and detritus. Higher water temperatures of longer duration in the Little River probably allowed this species to complete its life cycle in 1 year rather than the 2 to 4 years previously reported.
Unstimulated fluid transport by everted locust ileal sacs in vitro was supported at 50% of control levels by the presence externally of any one of Na+, K+, or Cl−, whereas removal of all but trace levels of these ions reduced fluid transport to 25% of control transport rates. Stimulation of fluid transport by corpus cardiacum or fifth ventral ganglion extracts did not occur unless Cl− was present. The presence of Na+ or K+ was also required for maximum stimulation of fluid transport by these factors, the greatest stimulation occurring when the Na+:K+ ratio was 1:1. Cyclic AMP, and corpus cardiacum and fifth ventral ganglion extracts all stimulated Na+, Cl−, and K+ absorption across everted ileal sacs. Stimulation of fluid transport by these factors largely eliminated the anion deficit (Na+ + K+−Cl−) observed under unstimulated conditions. Stimulation caused large decreases in absorbate [Formula: see text] concentrations and pH concurrent with the increased absorbate Cl− levels. These results indicate a switch from low-capacity NaHCO3 plus NaCl transport under unstimulated conditions to high-capacity NaCl transport under stimulated conditions. Stimulation of fluid transport also causes a 3-fold increase in transepithelial potential (hemocoel negative), indicating stimulation of electrogenic anion (Cl−) movement to the hemocoel. These results provide the first direct evidence for hormonal control of Na+ reabsorption in insect excretory systems.
The rectum, the main reabsorptive site in the locust excretory system, actively transports Cl−. This Cl− absorption is electrogenie, not dependent on Na+or [Formula: see text] and insensitive to inhibitors of NaCl cotransport or [Formula: see text] exchange. To determine if active Cl− transport across rectal epithelia might be due to an anion-stimulated ATPase, a microsomal fraction was obtained by differential centrifugation. Microsomal ATPase activity was stimulated in the following sequence: sulphite > bicarbonate > chloride. Maximal ATPase activity was obtained at 25 mM [Formula: see text] or 25 mM Cl−. Thiocyanate (10 mM) inhibited 90% of the anion-stimulated ATPase activity. The microsomal fraction was enriched in the plasma membrane markers, leucine aminopeptidase, alkaline phosphatase, 5′-nucleotidase, and γ-glutamyItranspeptidase, and had little contamination of the mitochondrial enzymes, succinate cytochrome c reductase and cytochrome oxidase. Na,K-ATPase was enriched in the mitochondrial fraction. Microscopic examination confirmed that basolateral membranes were associated with mitochondria following differential centrifugation, while the microsomal fraction contained little mitochondrial contamination. These results indicate the presence of an anion-stimulated ATPase activity that could be responsible for active Cl− transport across locust recta.
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