Insecticidal activity of pyrethrum extract and its four insecticidal constituents against house flies. V. —knock‐down activity of the four constituents with piperonyl butoxide

The paralysis (knock‐down) and the subsequent recovery or death of female house flies treated by a measured drop method was studied with each of the four active constituents of pyrethrum extract alone and in the presence of piperonyl butoxide (1 part of pyrethroid + 10 parts of piperonyl butoxide) in n‐dodecane as solvent at 20°. Knock‐down was faster, lasted longer and the knock‐down end‐point was reached later when the flies were treated with the constituents in the presence of piperonyl butoxide. The synergist increased the overall efficiency of the constituents, probably because it inhibited the recovery mechanism of the flies. The effect of the synergist was least during the first few minutes after treatment; the synergistic factor increased most rapidly during the first 2 h, after treatment. Piperonyl butoxide changed the order and the magnitude of the relative toxicities from those obtained with the constituents alone. Four min. after treatment, when the effect of the synergist was very slight, the order of the relative toxicities of the mixtures, pyrethrin II, cinerin II, pyrethrin I, cinerin I, was the same as for the constituents alone. Three h. later it changed to (constituents alone in brackets) pyrethrin I (pyrethrin II), cinerin I (pyrethrin I), pyrethrin II (cinerin I), cinerin II (cinerin II) and it was the same at death (24 h. after treatment). Cinerin I and pyrethrin I were synergised most, cinerin II and pyrethrin II least, both during knock‐down and at death.