Concentrations Of Pyrethrins Research Articles

Aqueous formulations of pyrethrum for controlling phytophagous Arthropoda—an evaluation using bioassay techniques

SUMMARYBioassay techniques were used to compare the toxicities of formulations of pyrethrum containing different amounts of surface‐active agents (mainly non‐ionic condensates of ethylene oxide) and synergists (Bucarpolate, piperonyl butoxide, S 421 and Sulfoxide). Phytophagous species of Arthropoda used in the tests were: Acyrtho‐siphon pisum Harris (Aphididae); Phaedon cochleariae F. (Chrysomelidae); Pieris brassicae L. (Pieridae); and Tetranychus telarius L. (Acarina, Tetranychidae).The insects were dosed by spray tower, and the mite by dipping infested leaves. The LC50 pyrethrins with unsynergized formulations were: aphid (adult), 150 p.p.m.; beetle (adult), 50,910 p.p.m.; caterpillar (third instar), 325 p.p.m.; mite (adult) 1168 p.p.m. Formulations whose wetting powers were increased by adding surface‐active agents were more toxic to the aphid and caterpillar (LC50 of 20 and 50 p.p.m., respectively). Addition of piperonyl butoxide or Sulfoxide to formulations, at up to 8 times the concentration of pyrethrins, increased their potencies for the aphid, beetle and mite by factors of 7–10 times, but were ineffective with the caterpillar. Bucarpolate and S 421 were poor synergists.A detailed study was made, using Acyrthosiphon pisum, of the synergizing effect of surface‐active agents on formulations of pyrethrum. Hypotheses for their modes of action suggest that toxicity is influenced by the fineness of dispersion of pyrethrum emulsions, and by the improved coverage and penetration of spray on insects, which results from increased wetting power.The results of bioassay studies are interpreted to indicate that a formulation of pyrethrum synergized with both surface‐active agent and piperonyl butoxide would be a very effective aphicide, with some ovicidal and larvicidal properties, when applied to infested plants as a high‐volume spray.

Substantivity of pyrethrins I and II to cattle skin and hair: Behaviour of pyrethrins in a cattle spray race

AbstractLaboratory experiments have shown that the pyrethrins are substantive to cattle skin and hair. When cattle are passed through a spray race, the concentration of pyrethrins in the circulation liquor decreases. The adsorption rate constant has been calculated for standard conditions and an equation derived for calculation of the concentration after passage of cattle through the spray race. The use of this equation in veterinary practice is discussed.

Insecticidal activity of pyrethrum extract and its four insecticidal constituents against house flies. III.—Knock‐down and recovery of flies treated with pyrethrum extract with and without piperonyl butoxide

AbstractThe influence of concentration and of time after treatment on knock‐down and recovery from the action of pyrethrum extract alone and with piperonyl butoxide at 2 : 1 and 1 : 5 w/w, was studied on house flies (Musca domestica L.) by a measured drop method. The unanaesthetised flies, held by suction during dosing, were inspected after treatment at frequent intervals for 5 h. and once on the following day. The tests were done at 20† with the materials tested dissolved in n‐dodecane.Most of the flies treated with a fixed dose of pyrethrum extract alone or with piperonyl butoxide remained normal for a very short time (the latent period). The number of flies knocked down increased very rapidly during the knock‐down period and reached a maximum at the knock‐down end‐point. Past this point a proportion of the flies knocked down recovered, the rest died. The relative and absolute durations of each of these periods were influenced by the concentration of pyrethrins and the presence of piperonyl butoxide. The interval of time between treatment and knock‐down end‐point was the same (10 min.) over a wide range of concentrations when the flies were treated with pyrethrum extract alone, and the flies treated with the extract alone recovered rapidly after knock‐down end‐point. The synergist inhibited recovery, so that more flies died, increased the toxicity of the extract during knock‐down and prolonged the duration of knockdown. The influence of piperonyl butoxide, small initially, increased with the passage of time after treatment.Attention is drawn to some of the shortcomings of methods commonly used to compare the knock‐down action of insecticides.

Development of Resistance to Synergized Pyrethrins in Body Lice, and Cross Resistance to DDT

A strain of body lice maintained in the laboratory for 14 years without exposure to any insecticides was subjected to progressively increased concentrations of pyrethrins plus sulfoxide for 56 generations. Resistance to the synergized pyrethrins gradually developed to about seven or eight times that of the parent colony. Cross resistance to DDT developed slowly at first, but in later generations increased rapidly until the lice could no longer be killed by exposure to doth treated with 10% of DDT in an acetone solution. There was little or no resistance to lindane, two- to four-fold resistance to synergized allethrin, and none to malathion.

THE LOSS OF WEIGHT OF PYRETHRIN‐TREATED FLOUR BEETLES, TRIBOLIUM CASTANEUM (HERBST), AND ITS APPLICATION TO BIOASSAY

Pyrethrin‐treated flour beetles, Tribolium castaneum (Herbst), lose weight rapidly. The weight lost by batches of beetles, a readily determined graded response, has been investigated with a view to its use in bioassay. Strong evidence was obtained that (1) in pyrethrum extracts only the pyrethrins cause the loss, and that (2) the other extractives do not modify the loss caused by the pyrethrins. Allethrin also caused a rapid weight loss; piperonyl butoxide, by itself producing little loss, greatly increased the loss caused by pyrethrum solutions and by allethrin, paralleling its effects on toxicity. The pyrethrin content of solutions appeared to account quantitatively for their weight‐reducing activities; irradiation of pyrethrum solutions that destroyed their toxicity also destroyed their weight‐reducing properties; and neither pyrethrum oleoresin heat‐treated to destroy the pyrethrins, nor irradiated solutions, modified the weight loss due to allethrin.Factors influencing weight loss were investigated. Beetles were exposed, mostly for 3 hr. at 25°C., on hard filter‐papers treated with solutions of pyrethrins in a non‐volatile oil (Shell Risella oil 17, formerly called P31). At fixed deposit the loss rose sigmoidally with increasing pyrethrin concentration from about 0.7 % for zero concentration to an upper limit of about 6.5 % of initial beetle weight. A log‐logit transformation made the sigmoid curve linear. The carrier oil and the length and temperature of the exposure to the pyrethrins influenced the weight loss. At 25°C, the rate of air movement and the relative humidity between 40 and 90% did not. Pyrethrins in Risella oil 17 could be applied satisfactorily to the filter‐papers by means of a spraying tower, or by pipette if the solutions were first diluted with a volatile solvent, which was allowed to evaporate subsequently. Deposits of given pyrethrin content were about 1.3 times as active in producing a weight loss if prepared by spraying than if prepared by solvent evaporation.The technique, design, and analysis of results, for bioassays based on weight loss are described. The most elaborate method of analysis ever likely to be needed is given, with a worked example, but a considerably simpler method, only slightly longer than the probit analysis for quantal‐response assays, would probably suffice normally.For a given number of beetles used, the weight loss method of assay has about the same inherent precision as the film method of Parkin & Green (1943), but is less precise than the direct spray method of Hewlett (1947). However, larger numbers of beetles can be used in the new method, the assessment of the insecticidal effect is more objective, and results are obtained more quickly y‐BHC and DDT cause T. castaneum to lose weight less rapidly than do pyrethrins.