Susceptibility of two strains of Amblyseius andersoni Chant. (Acari: phytoseiidae) to dithiocarbamate fungicides

The effect of five fungicides on adult female mortality, fecundity, egg hatch and on lan, al mortality was examined in the laboratory using a fungicide-susceptible and a fungicide-resistant strain of the predaceous phytoseiid mite, Amblyseius andervoni Chant. The combined effect of each fungicide was compared using a coefficient of toxicity computed using the above four toxicity factors. The susceptible and resistant strains were most affected by the bidithiocarbommate fungicides mancozeb, metirmn and propineb. Ziram and dithianon had little effect on the S strain and ziram had little effect on the R strain. The toxicity of dithianon was not tested using the R strain. A resistance factor (LCso R strain : LC~ S strain) of 6.13 for mancozeb was estimated for the R strain. Mancozeb resistance was a heritable trait and was primarily associated with the adult female.