Genetic characterization of a putative Densovirus from the mealybug Planococcus citri.

Total genomic DNA preparations from the citrus mealybug, Planococcus citri, contained a DNA band corresponding to 5.5 kilobases. This DNA was a linear molecule and was cloned into pUC18. Nucleotide sequence determination indicated that it was the replicative form of a densovirus, most closely related to the virus from Periplaneta fuliginosa (smokybrown cockroach).

Stress and growth response of juvenile crayfish to rhythmic and arrhythmic temperature fluctuations.

Growth, molting, and survival of juvenile crayfish, Procambarus a. acutus, were recorded under constant and variable temperature regimes. Crayfish, were exposed to four rhythmic regimes: Constants temperatures of 10, 17.5, and 25 degree C, and a daily square-wave cyclic regime of 10 to 25 degree C (mean = 17.5 degree C); and to one arrhythmic temperature regime: A daily square-wave acrylic regime varying within 10 to 25 degree C limits (mean = 17.8 degree C). The direction and magnitude of temperature changes in the acyclic variable temperature chamber were selected randomly to make temperature changes unpredictable within the specified range. Rhythmic and arrhythmic temperature regimes had different effects on growth, molting, and survival of crayfish. Growth under both variable regimes was similar to growth at a constant temperature (17.5 degree C) equal to the mean of the variable regimes. Molt frequency was directly related to temperature. Growth rates approximately paralleled changes in the adjusted molt rate for each regime. Mortality under variable regimes approximated mortality at a constant temperature (25 degree C) equal to the upper extreme of the variable regimes. The cyclic regime tended to be less optimal for growth and survival than the acyclic regime, possibly because of differences in average daily temperature fluctuations and relative time spent at temperature extremes.

Effects of chronic cadmium exposure on crayfish survival, growth, and tolerance to elevated temperatures.

Crayfish Cambarus latimanus were subjected over a 5-month period to 0.02, 5, and 10 microgram Cd/L in a continuous flow system at ambient winter temperatures. Uptake of cadmium, growth, and mortality were measured. One-half of the surviving crayfish were analyzed for Cd after completion of the 5-month experiment, while the remaining half were removed from the contaminated water and subjected in a static laboratory experiment to stepwise, daily increases in temperature. The results indicated that (1) the rate of Cd uptake in crayfish was positively related to external concentration, (2) mortality increased significantly with higher Cd concentrations, and (3) neither growth nor thermal tolerance was significantly related to the Cd concentration in the crayfish tissues. The importance of chronic, low-level studies is discussed.