Ovicidal Properties of certain Insecticides of Plant Origin. (Nicotine, Pyrethrins, Deeris Products)

The pyrethrins, nicotine, rotenone and a derris resin have been tested in the laboratory under standard conditions for their ovicidal effect. The test-subjects were : Pieris brassicae, Plutella maculipennis, Aphis rhamni, Ephestia kühniella and Sitotroga cerealella . Notes on the technique of egg production are given for these species. In the majority of the tests made a water medium containing acetone together with sulphonated lorol as a wetting agent was used. It has been shown that all these products are toxic to the species on which they were tested. Lauryl thiocyanate, β-butoxyβ'thiocyanodiethyl ether and 3 : 5 dinitro- o -cresol were included as substances of recognised ovicidal value for purposes of comparison. All the above insecticides derived from plants compared favourably in their toxic action with the synthetics. In two instances during tests on eggs of Ephestia kiihniella , data were obtained enabling a satisfactory statistical comparisdn of relative potency to be made. In the first of these, the pyrethrins were found to be 8·45±1·47 times as toxic as 3 : 5 dinitro- o -cresol, while in the second the pyrethrins were found to be 2·66±0·26 times as toxic as a Derris elliptica resin (rotenone content 37–40 per cent.). It therefore appears that both the pyrethrins and the derris resin were more toxic, weight for weight, than 3 : 5 dinitro- o -cresol which is recognised as one of the most potent ovicides. The above vegetable poisons were found to be toxic not only to eggs developing in a few days without a diapause, but also to those of Aphis rhamni , a species of overwintering egg. The tests on A. rhamni were made at the time the eggs were just starting to hatch. The same result might not have been obtained with eggs at an earlier stage of development. Observations were made on the effect of the different insecticides on the development of the egg. This effect appeared to differ with each substance, either qualitatively or quantitatively, but within the limits of the experiment it seemed to be independent of the species of the egg.