Assessment of Repellency of Nine Phthalates against Red Imported Fire Ant (Hymenoptera: Formicidae) Workers Using Ant Digging Behavior

Repellency of nine phthalates against red imported fire ant workers, Solenopsis invicta Buren, was evaluated using ant digging behavior. Test compounds included dimethyl, diethyl, dipropyl, dibutyl, dipentyl, dihexyl, diheptyl, dioctyl, and dinonyl phthalates. The active ingredient was incorporated into sand within a liquid scintillation vial with an entry hole on the cap. Fire ant workers dug and removed sand from the vial through the entry hole. The differences in amount of sand removed from the treated and control vials were used to evaluate chemical repellency. Of the 9 phthalates, dimethyl and diethyl phthalates were most repellant to red imported fire ant workers. The minimum repellant concentration within 24 h was 100 ppm for both dimethyl and diethyl phthalates.

Pollen Viability of Clerodendrum

The genus Clerodendrum belongs to the family Verbenaceae of which there are over 400 tree, shrub, and vine species. Species of Clerodendrum vary in leaf size, shape and texture; inflorescence shape; and flower shape, size and color. There is commercial interest in developing hybrids with desirable floricultural attributes. Interspecific hybridization could be used to increase variability in flower color, inflorescence shape, plant vigor, leaf color and shape for selection. Pollen viability among species is in question because of absence of seed set on many selected plants. The need for assessing viability of pollen used is important in determining the strategies to be used in hybridization. Clerodendrum floribundum, C. speciosissimum, C. splendens, C. × speciosum (C. thompsonia × C. splendens) and C. quadriloculare grown in a greenhouse under natural daylight were used as pollen sources. Pollen was collected from recently opened anther, placed in a scintillation vial on ice, and brought into the laboratory. A peroxidase test, dehydrogenase test, and the fluorescein diacetate procedure were used to determine percent viability of pollen before, during and after anthesis for each Clerodendrum species.

Toxicological Assays in Bemisia tabaci (Genn.) from Cabbage Plots in La Paz, Baja California Sur, Mexico

The sweetpotato whitefly [Bemisia tabaci (Gennadius)] has become a high-risk insect pest in Mexico as well as in other countries, causing serious damage to several crops. Control of whitefly in Baja California Sur, ,Mexico, is usually done by intense insecticides applications, either alone or in mixtures of several kinds. The aim in this work was to determine its susceptibility to cypermethrin, endosulfan, methamidophos, and methyl-parathion. LC50 was obtained to identify the resistant and susceptible populations. A group of 20 whiteflies were introduced in a 20-ml scintillation vial coated in the inner surface with a known concentration of the insecticide. Mortality readings were obtained 3 h after exposing the insects to the residual activity at five concentrations. Five replications and control were run in different consecutive days for each bioassay. Results indicated that cypermethrin was the most toxic to B. tabaci and metamidophos the least. Data will be considered for further evaluations.

An Inexpensive Combustion Apparatus for Preparation of Radioactive Samples

The combustion apparatus described provides a rapid and inexpensive alternative for measurement of radioisotopes in plant parts. The apparatus utilized a nickel-chromium resistance wire connected to a low-voltage transformer to generate the heat required to ignite the plant tissue. The nickel-chromium wire also served as the sample holder. Combustion was performed in an O2-flushed liquid scintillation vial, and the combustion gases containing either 14CO2 or 3H2O were trapped in situ, scintillant was added, and the vials assayed for radioactivity. The percentage of the radioactivity recovered after combustion was 96.0 for 14C and 93.4 for 3H with standard deviations of 6.8 and 3.0%, respectively.

A Simple and Economical Method for the Radioimmunoassay of Cortisol in Serum

Summary A simple, economical method is described for the radioimmunoassay of cortisol in serum. Extraction is avoided by heating the diluted serum to inactivate cortisol-binding globulin. The radioimmunoassay is carried out in a single disposable scintillation vial without centrifugation. Free and bound steroid is separated by partition between ammonium sulphate solution and liquid scintillation fluid. Accuracy, precision and sensitivity are satisfactory. Normal ranges obtained are comparable to those obtained by other radioimmunoassay methods for cortisol.

A Simple Method for the Differential Measurement of 125I and 3H by Liquid-Scintillation Spectrometry

1. A method is described for the differential radioactivity counting of 125I and 3H in a liquid-scintillation spectrometer without a separate gamma counter. 2. The sample was contained in a polyethylene miniature vial placed centrally in a standard 20 ml glass scintillation vial containing a tin-loaded scintillant. 3. A direct measure of the 125I radioactivity at an efficiency of 30% was then obtained by radioactivity counting in the pre-set 3H window of a scintillation spectrometer. No counts for 3H radioactivity were registered at this stage because of the barrier to the passage of the low-energy β-particles provided by the wall of the polyethylene vial. 4. After mixing the sample and scintillant both 125I and 3H were detected at efficiencies of 73 % and 29% respectively. Subtraction of the 125I contribution from the combined radioactivity count rate then gave the net 3H count.

Automatic Quantitative Radiometric Assay of Bacterial Metabolism

In a two-compartment scintillation vial, suspensions of bacteria were cultured with 1 µCi of [U-14C] glucose and the released 14CO2 was measured continuosly, cumulatively, and automatically in a liquid-scintillation counter modified to maintain sample temprature at 37 °C. We could follow the metabolism of bacterial populations through their early phase of exponential growth with good precision. The data were obtained conveniently, with use of conventional regents, glassware, and counting equipment. From analysis of the exponential portion of the curves for cumulative activity vs. time, we could measure cell replication rate precisely in units of time. The resulting values were demonstrably independent of some common experimental variables, including the number of bacteria in the inoculum and counting system sensitivity. Sensitivity of the bacteria to antibiotics was measured to within a few percent by noting the relative prolongation of replication time in the presence of those inhibitors. The digital data from the scintillation counter are susceptible to on- or off-line computer analysis, thus providing the prospect for a totaly-automated analytical system. The method shows promise for the mechanized quantitative analysis of bacterial growth, and its inhibition.