Strains of Trissolcus basalis (Wollaston) Hymenoptera: Scelionidae, an egg parasitoid of the green vegetable bug, Nezara viridula (L.), were obtained from three regions of Australia and from Homestead, Florida (USA). Percent parasitoid emergence was approximately the same for freezer-stored (-75°C) and fresh eggs, and freezer-stored eggs were suitable hosts for a longer time.Optimum host age, oviposition and emergence patterns, mean number of progeny per female, sex ratio and longevity were examined and certain comparisons were made between the Australian and USA parasitoids. Genetic crosses made between males and females of each strain revealed that reproductive isolation did not occur.Higher fecundity of the Australian strains may make them more successful than indigenous (USA) strains for controlling pest populations of N. viridula in the southern USA.

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Samples of trout were exposed to flows of water containing constant low concentrations of oxygen (produced by equilibrating aerated water with nitrogen). At 9°–10 °C. minimum tolerance levels were defined by determining the lowest oxygen level permitting survival of 5%, 50% and 95% of the fish for a period of 5,000 minutes. Median resistance times for samples of fish exposed to lethal levels of oxygen were also determined. Within their first year, most trout reared in aerated water could withstand oxygen concentrations down to 1.9 mg.O2/1. The 50% tolerance level was 1.75 mg.O2/1. Most fish died at 1.5 mg.O2/1. Acclimation to low (but not lethal) oxygen levels occurred; for a drop of 1.0 mg.O2/1. in environmental oxygen concentration, the tolerance level decreased by approximately 0.09 mg.O2/1. and resistance times at given lethal levels increased up to five-fold. By acclimations trout could exist at 1.05 mg.O2/1. without direct lethal effects occurring. Between 20 and 33 hours were required for the fish to acclimate to a change of 1.0 mg. per liter in the oxygen concentration of the environment. Acclimation to low levels of oxygen was accompanied by an apparent increase in the ability of the animals to remove oxygen at low environmental oxygen concentrations, suggesting a physiological mechanism similar to that involved in acclimation of mammals to low oxygen. The tolerance levels of small fish were similar to those of large fish at similar acclimation levels, but small fish died more quickly than large fish when exposed to lethal concentrations.

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