A QUANTITATIVE EXAMINATION OF THE TOXI‐CITY OF 3:5‐DINITRO‐O‐CRESOL AND OTHER COMPOUNDS TO INSECT EGGS, UNDER LABORATORY AND FIELD CONDITIONS

SUMMARY1 The toxicity of 3: 5‐dinitro‐o‐cresol and its sodium salt to eggs of the moth Selenia tetralunaria Hüfn, has been determined quantitatively under controlled conditions in the laboratory. The figures obtained confirm earlier results and show ( a ) that these compounds have a very high toxicity to insect eggs, and ( b ) that the sodium salt of dinitro‐o‐cresol is only slightly less toxic than dinitro‐o‐cresol in the uncombined state. The relationship between concentration and toxicity is expressed by means of diagrams. 2 Preliminary laboratory experiments indicate that dinitro‐o‐cresol is also highly toxic to insect eggs of a more resistant type than those of S. tetralunaria.3 Spray fluids containing dinitro‐o‐cresol or the sodium salt showed a high efficiency against eggs of the Hop‐Damson Aphis ( Phorodon humuli Schr.) on plum trees on a larger scale under field conditions. The trees sprayed with these compounds remained almost free from aphides during the following spring when the control trees were badly infested. 4 A quantitative method for judging the results of the field experiments was worked out. This involved recording details of large numbers of eggs on selected shoots on sprayed and control trees before and after spraying, a numerical measure of the effect of the various treatments being thus obtained. The method gave consistent and reliable results. 5 The spray fluids containing dinitro‐o‐cresol and its sodium salt had a marked general cleansing effect on the trees. No injury to the trees was observed.