Comments on the ecology of grass grub and porina caterpillar

The object of this paper is to discuss the ecology of grass grub, Costelytra zealandica White, and porina, Wiseana cervinata (Walker), New Zealand’s most important pastoral insect pests, and to survey what has been achieved in ecological understanding of these insects. The biology and ecology of either or both insects have previously been reviewed by Dumbleton (1942), Miller (1945), Kelsey (1951a, b) and Hoy (1963). The lack of fundamental biological information on grass grub (and this is equally applicable to porina caterpillar) and the need for longterm team studies were stressed, although little sustained, co-ordinated research has since eventuated. Examination of the literature clearly indicates that the lack of fundamental ecological research on these pasture pests is directly due to the introduction of organochlorine insecticides, particularly DDT, to control both porina and grass grub. These insecticides proved cheap, persistent in soil, relatively safe to handle and easy to apply (Kelsey and Hay., 1950; Kelsey 1951a, b, 1952, 1959). DDT was so effective that it led to complacency, in spite of the warning by Miller (1945) that in his view no single control would suffice. There was failure to anticipate: (1) Development of insect resistance. to insecticides. (2) Possible alteration of tolerance limits for insecticides in foodstuffs, by countries importing New Zealand produce. (3) Failure of DDT to be effective in certain soils. (4) The need for fundamental knowledge, in case the efficacy of DDT and related insecticides diminished, and new methods had to be found

Rapid bioconcentration of steroids in the plasma of three-spined stickleback Gasterosteus aculeatus exposed to waterborne testosterone and 17β-oestradiol

The relationship over time between the concentrations of two steroids, singly and in combination, in a static exposure system and in the blood of three-spined stickleback Gasterosteus aculeatus, held within the exposure system was investigated. Groups of three-spined stickleback were exposed (nominally) to either 1000 ng l1 17β-oestradiol (E2), testosterone (T) or E2 and T in combination at the same concentrations for 6 days. Both water and fish were sampled at intervals and steroid concentrations in both compartments were determined. The plasma steroid time profile revealed a rapid bioconcentration within the first 6 h of exposure. The plasma steroid levels attained at this time point (20–90 ng ml1) were up to 50-fold (E2) and 200-fold (T) greater than the actual levels of steroid measured in the exposure water, while levels in the blood of control fish did not exceed 4 ng ml1. The substantial elevation of plasma steroid levels relative to the concentrations of steroid to which the fish were exposed in the ambient water gives scope for delivery of the steroids to target endocrine tissues at levels far in excess of what might be predicted on the basis of passive branchial uptake alone. These results are discussed in relation to endocrine disruption, and in particular the occurrence of effects in fish exposed to levels of endocrine active substances that are seemingly physiologically irrelevant

ACTH does not mediate divergent stress responsiveness in rainbow trout

Two lines of rainbow trout selected for high (HR) and low (LR) responsiveness to a standardised confinement stressor displayed a sustained divergence in plasma cortisol levels during a 3 h period of confinement (max.: HR: 167 ± 13 ng ml-1; LR: 103 ± 8 ng ml-1; P < 0.001). However, no significant difference in plasma ACTH levels was evident (max: HR: 153 ± 9 pg ml-1; LR: 142 ± 7 pg ml-1). Dexamethasone (DEX) was administered to HR and LR fish to block endogenous adrenocorticotropin (ACTH) release. Administration of a weight-adjusted dose of ACTH to the DEX-blocked fish elevated plasma cortisol levels to a significantly greater extent in HR (233 ± 24 ng ml-1) than LR (122 ± 14 ng ml-1) fish (P < 0.001). Plasma cortisol levels in DEX-blocked HR and LR fish after sham injection were low but also significantly different (HR: 6.7 ± 1 ng ml-1; LR: 2.2 ± 0.2 ng ml-1; P < 0.001). These results indicate that modulation of cortisol responsiveness to stressors in HR and LR fish resides, at least in part, downstream of the hypothalamic-pituitary axis

Assessment of the physiological impact of endocrine disrupting chemicals on salmonid fish from selected sites in Scotland and Northern Ireland

1. Recent research in the UK and elsewhere has demonstrated that industrial and domestic effluents may contain compounds of both natural and synthetic origin which are steroid estrogens, or mimic the activity of steroid estrogens. Although present in solution at very low concentrations the sensitivity of the endocrine system of animals to interference is such that these contaminants represent a potentially disruptive threat. 2. A survey of gonadal structure in roach populations in English rivers revealed that a high proportion (25% – 60%) of male fish within the sampled populations displayed evidence of abnormal gonadal development in the form of ovarian tissue within the testes. These effects were most pronounced at sites where discharged effluents represented a high proportion of total flow in the river. The functional significance of these observations has yet to be established. 3. Concerns have been raised regarding the possible susceptibility of valuable salmon and trout populations to endocrine disruptive processes. This report describes the results of a fieldbased investigation of indicators of estrogen exposure in salmonid fish exposed to potentially estrogenic effluent discharges at sites in Scotland and Northern Ireland. 4. This study addressed the possibility that native salmonid populations are being exposed to estrogenic contaminants via both domestic and industrial discharges and that this exposure may result in inappropriate and possibly detrimental physiological effects in exposed fish. 5. This objective was addressed by the sampling of brown trout and Atlantic salmon from sites receiving a STW discharge and from pristine sites. Blood levels of the estrogen-inducible yolk precursor vitellogenin were measured to assess whether there was evidence that the targeted populations were exposed to acute estrogen exposure. In addition, gonadal material sampled from each fish was examined microscopically for evidence of abnormal reproductive development, the presence of which would be indicative of early or possibly chronic exposure to estrogens. 6. A total of 209 fish were examined from four sites in Scotland [R. Teviot, Slitrig Water (tributary of the R. Teviot), Wilson Burn and Ale Water (pristine sites)]. Fish sampled from the R. Teviot were removed downstream of the Hawick STW discharge. In all the fish which were sampled blood vitellogenin levels were low, displaying no evidence of environmental estrogen-induced elevation. The gonadal structure of all the sampled fish was normal, with no evidence of ovarian tissue in male testes and no evidence of unusual ovarian development in female fish. 7. A total of 64 fish were examined from three sites in Northern Ireland (Minnowburn, Collin River and Ravernet River; all tributaries of the R. Lagan). As was the case for the Scottish sites, no evidence of gonadal abnormalities was obtained in fish from any site. 8. In addition to the field sampling, the estrogenicity of the effluents discharged at each site were evaluated by bioassay. In Northern Ireland, rainbow trout were held in cages submerged in the vicinity of the New Holland Sewage Treatment Works (STW) effluent discharge (R. Lagan). An aquarium-based exposure of rainbow trout to Hawick STW (R. Teviot) final effluent, at concentrations up to 100%, was employed. Analysis of blood vitellogenin levels after a period of or 11 – 14 days exposure in aquaria revealed that the Hawick STW effluent was not estrogenic. However, fish exposed to New Holland STW final effluent in situ for 3 weeks displayed elevated blood vitellogenin levels, relative to fish caged at control sites, indicating that the effluent contained estrogenic components. 9. Water samples collected from both study sites were analysed for total alkylphenols and alkylphenol ethoxylates (APEs; ubiquitous environmental contaminants and known estrogen mimics found in high concentrations in English rivers with a high incidence of intersexuality). Samples from the Hawick sites contained very low levels of APEs (< 3 :g l-1). Similar levels were found in samples from the sites in Northern Ireland with the exception of effluent samples taken downstream of the Barbour Campbell Linen Mill which contained 12 :g l-1 total APEs. Steroids were not quantified in these samples. 10. The microscopic examination of gonad structure, and analysis of blood vitellogenin levels, indicated that there was no evidence of exposure to estrogenic contaminants in the salmonid fish populations of the R. Teviot or R. Lagan. 11. A number of factors probably contribute to this result. Salmonid fish exhibit a life-history very different to that of cyprinid fish such as roach in which effluent-related intersexuality has been reported. Trout and salmon normally spawn in clean gravel beds in the upper reaches of a river system and newly-hatched and early juvenile salmonid fish remain in these relatively pristine stretches of river. They are therefore not usually exposed to point-source effluent discharges during critical early developmental stages when the reproductive system is particularly sensitive to external influences. In addition, both salmon and migratory brown trout (sea trout) are anadromous fish, spending a significant proportion of their lives at sea. These factors contrast with the potential for life-long exposure to contaminants displayed by non-migratory cyprinid fish which spawn in the main body of the river. Additionally, salmonid fish are less tolerant of poor water quality than cyprinid fish and even the nonmigratory brown trout are therefore not normally present in rivers subject to high effluent input. Most rivers which support populations of salmonid fish do not pass through heavily populated or industrialised areas. There is therefore less likelihood that these fish populations will encounter high concentrations of endocrine disrupting chemicals (EDCs). 12. Overall, these data do not provide absolute reassurance that salmonid fish are unaffected by estrogens and estrogen mimics present in effluent discharges but they do indicate that if a problem does exist it may be localised and on a smaller scale than has been reported for cyprinid fish. 13. Consideration should be given to a more widespread survey of gonad structure in salmonid fish populations in order to confirm these preliminary conclusions. It should also be considered whether reproductive performance of salmonid fish might be influenced by exposure to EDCs via mechanisms which do not involve alterations in gonadal structure (e.g. alterations in fecundity, gamete quality, behavioural changes). In addition, the possibility that aspects of the salmonid life-history other than reproductive development may be affected by EDCs should be examined. 14. For example, smoltification (pre-migratory sea water adaptation) is a critically important aspect of the salmonid life history. Smoltification is closely regulated by the endocrine system and may be susceptible to interference by chemicals which mimic or interfere with the activity of hormones other than estrogens. 15. It should also be considered whether sources of contamination other than effluent discharges (e.g. agricultural run-off) may expose salmonid fish to endocrine-disrupting chemicals

Brain monoaminergic activity in rainbow trout selected for high and low stress responsiveness

This paper investigates whether two lines of rainbow trout displaying genetically determined variation in stress responsiveness and behavior also show differences in brain monoaminergic activity. In several brain regions, strains of rainbow trout selected for consistently high or low post-stress cortisol levels displayed differences in tissue concentrations of monoamines and/or monoamine metabolites, or in metabolite/monoamine ratios. High-responsive trout reacted to stress by an increase in the concentrations of both serotonin (brain stem), dopamine (brain stem), and norepinephrine (optic tectum, telencephalon), whereas low-responsive fish did not. Brain stem and optic tectum concentrations of monoamine metabolites were also elevated after stress in high responders, but not in low-responsive fish. The simultaneous increase in the concentration of monoamines and their metabolites suggests that both synthesis and metabolism of these transmitters were elevated after stress in high-responsive trout. A divergent pattern was seen in the hypothalamus, where low-responsive fish displayed elevated levels of 5-hydroxyindoleacetic acid (a serotonin metabolite) and 3-methoxy-4-hydroxyphenylglycol (a norepinephrine metabolite). In the telencephalon, both populations had elevated concentrations of these metabolites after stress. These results clearly suggest that selection for stress responsiveness in rainbow trout is also associated with changes in the function of brain monoaminergic systems. The possible functional significance of these observations is discussed with respect to the physiological and behavioral profile of these strains of fish. Literature is reviewed showing that several factors affecting brain monoaminergic activity might be altered by selection for stress responsiveness, or alternatively be under direct influence of circulating glucocorticoids

Electrically Mediated Plasmid DNA Delivery to Hepatocellular Carcinomas in Vivo

Gene therapy by direct delivery of plasmid DNA has several advantages over viral gene transfer, but plasmid delivery is less efficient. In vivo electroporation has been used to enhance delivery of chemotherapeutic agents to tumors in both animal and human studies. Recently, this delivery technique has been extended to large molecules such as plasmid DNA. Here, the successful delivery of plasmids encoding reporter genes to rat hepatocellular carcinomas by in vivo electroporation is demonstrated

Direct thrust measurement of a permanent magnet helicon double layer thruster

Direct thrust measurements of a permanent magnet helicon double layer thruster have been made using a pendulum thrust balance and a high sensitivity laser displacement sensor. At the low pressures used (0.08 Pa) an ion beam is detected downstream of the thruster exit, and a maximum thrust force of about 3 mN is measured for argon with an rf input power of about 700 W. The measured thrust is proportional to the upstream plasma density and is in good agreement with the theoretical thrust based on the maximum upstream electron pressure