FURTHER OBSERVATIONS ON THE BIOLOGY OF THE CABBAGE ROOT FLY, ERIOISCHIA BRASSJCAE BCHÉ

In 1951, eggs of Erioischia brassicae were first found in the field on 2 May, and the peak period of egg-laying occurred 19–31 May. This was up to a month later than in the period 1948-50.
The periodic removal and examination of the surface soil showed that eggs of E. brassicae were continuously present on the host plants from mid-June to early November. Plants under observation during this period showed an average of 285 eggs per plant and other plants exposed to attack from July to November showed an average of 162 eggs per plant. Peak periods of egg-laying, as indicated by numbers of eggs per plant per day, occurred in late June and early July, in mid-August and, to a less extent, in the first half of October. The plants showed no increase in the rate of infestation as the season advanced, although E. brassicae has a reproductive capacity of about 100 eggs per female and three to four generations a year.
The difference between the observed egg populations and pupal populations indicated that E. brassicae had a heavy mortality rate in its immature stages. The condition of puparia showed that the species was subject to a high degree of natural control, a fact for consideration when direct control measures are formulated.
Pupal diapause extending from October 1949 to May 1951 was observed in one specimen of E. brassicae and from October 1949 to August 1951 in one specimen of its Hymenopterous parasite, Trybliographa rapae Westw.
Tests with tar-oil winter wash showed that at a concentration of 1 1/4% it killed eggs of Erioischia brassicae and repelled gravid females for approximately a week. Laboratory tests with BHC indicated that it had no adverse effects on the eggs but was larvicidal.     

Regulation of Turgor Pressure by Suspension-Cultured Tobacco Cells

Turgor regulation and effects of high NaCl and water deficiton growth and internal solutes were studied after transferringtobacco cells from control culture medium (osmotic pressure= 0.13–0.15 MPa at time of transfer) to culture mediumcontaining either 82 mol m^–3 NaCl or 150 mol m^–3melibiose (osmotic pressure of media = 0.62 MPa). Followingtransfer to media with higher osmotic pressure, expansion rateand turgor pressure were reduced. Within 24 h of imposing thewater deficit, expansion rate had returned to that of cellsin control culture medium. However, by 24 h, turgor pressurehad only risen from 0.2 MPa to 0.65 MPa in the NaCl treatmentand to 0.53 MPa in the melibiose treatment, while it was 0.73MPa in the control treatment. Furthermore, turgor pressure remainedwithin 0.05 MPa of these respective values for the rest of the(75 h) experiment. These results suggest differences in bothcell wall properties (extensibility and/or threshold turgor)and the level at which turgor is maintained for cells in thevarious treatments. Solutes contributing nearly all (82–97%) of the osmoticpressure in cells were identified. The initial (up to 24 h)increases in turgor pressure were mainly due to increases insolute concentrations caused by relatively slow expansion rates.However, increased Na⁺ and Cl ^– uptake contributed toincreased turgor pressure in the NaCl treatment and caused turgorpressure of cells in this treatment to increase faster thanin the melibiose treatment. Likewise, expansion rate rose morequickly in the NaCl than in the melibiose treatment. After 24h, maximum expansion rate was reached and concentrations ofmost internal solutes began to decrease. Nevertheless, turgorpressure remained relatively constant. The constancy of turgorpressure was due to increased glucose uptake rates relativeto controls, with consequent increases in concentrations ofsucrose, glucose and fructose and, in cells in the melibiosetreatment, of organic acids. Glucose uptake was slower in theNaCl than in the melibiose treatment but higher turgor pressurewas maintained in the NaCl treatment due to high uptake of Na⁺and Cl^–. Glucose uptake appears to respond to a systemof turgor regulation, but further experiments are required toconfirm this and to determine whether Na⁺ and Cl^– uptakealso respond to a system of turgor regulation. Key words: Salinity, water deficit, growth     

Melanin Standard Method: Titrimetric Analysis

Melanin isolated from the ink sac of Sepia officinalis (Sepia melanin) has been proposed as a standard for natural eumelanin, and a standard mild isolation and purification protocol for Sepia melanin has been developed (Zeise, doctoral dissertation, Johns Hopkins University, 1991). The goal of the present work, developed using Sepia melanin, was to quantify the bioavailable carboxylic acid groups present in melanin particles. Bioavailability is governed by the accessibility of carboxy groups to the surrounding biological milieu, and is expressed as microequivalents of carboxy group per gram of melanin. The present work was carried out using an heterogeneous slurry of melanin in a nonaqueous system. A standard acidic titrant, and an automatic titrator operating in an equilibrium titration mode were used to characterize and quantify the carboxy group content of Sepia melanins and several other commonly used melanins purified by a standard method (Zeise et al., Pigment Cell Res. [Suppl] 2:48–53, 1992).