RELATIVE SUSCEPTIBILITY TO ARSENIC IN SUCCESSIVE INSTARS OF THE SILKWORM
The susceptibility of the silkworm to arsenic decreases during its larval development. Relative susceptibility may be expressed numerically as a ratio of areas under dosage-effect curves.
The relative Susceptibility to Pyrethrum in Oil of Coleoptera and Lepidoptera infesting Stored Products.
With a view to providing information useful in practical control, the relative susceptibility to pyrethrins, and to pyrethrins plus piperonyl butoxide, of a series of stored product insects has been determined. Adult moths and beetles of 31 species were investigated, together with the larvae of 16 of these, and that of one other. The insects were treated with 1.3 per cent, pyrethrins, and 0.3 per cent, pyrethrins plus 3.0 per cent, piperonyl butoxide, in a heavy, highly refined mineral oil (Shell Risella 17). Both formulations were applied in two ways: insects were exposed on sprayed filter papers or were directly sprayed. Insects were also treated with the oil alone by both techniques. While confined on films, and after being sprayed, the insects were kept at 25°C. and 70 per cent. R.H. Large differences in susceptibility were encountered. The adult moths and Bruchids were susceptible, the adult Ptinids rather resistant, but otherwise susceptibility showed little correlation with systematic classification. The larva of a given species was usually more resistant than the adult. Among the adults of the different species, susceptibility to pyrethrum appeared to be correlated with high activity of the normal insect. On the whole, 1.3 per cent, pyrethrins and 0.3 per cent, pyrethrins plus 3.0 per cent, piperonyl butoxide were of about equal toxicity.
A Simple Method of Measuring the Rate of Respiration of Small Organisms
IN view of the widespread interest at. the present time in the subject of respiration in the lower organisms, it is thought that the following simple method of measuring the rate of carbon dioxide production in small non-aquatic animals and plants may be found useful not only by teachers who desire a quantitative method suitable for class instruction but also by investigators who wish, without any material sacrifice in accuracy, considerably to simplify the various procedures at present followed in making determinations of small amount of CO,. The apparatus required may readily be constructed by anyone in a few minutes out of materials easily obtainable, and with it, it is possible to measure, with a probable error well within the normal uncontrollable range olf variation of the material likely to be studied, a few thousandths of a milligram of carbon dioxidean amount equal to that given out at ordinary temperatures by a sprouting grain of wheat in perhaps three or four minutes and by a house-fly in one or two minutes. It. would be relatively easy still further to increase the delicacy of the method, though the gain in sensitiveness would be at the expense of the simplicity which in its present form is its chief recommendation. 'The method is based upon the well known indicator methods of Haas1 and of Osterhout,2 but unlike the first, it is applicable to small non-aquatic organisms, and unlike the second, it involves the use of apparatus so simple in construction that it can be duplicated any desired number of times and can therefore be used even by large classes of elementary students. Furthermore, provision is made not only for the comparison of relative rates of carbon dioxide production but also for the measurement of absolute amounts. Simplicity is secured by taking advantage of