Responses of Susceptible and Resistant Myzus Persicae (Sulzer) to Ntn-33893, 1990

Abstract

Abstract An insecticide-susceptible strain of GPA (S) cultured under insecticide-free conditions for several years and a multiresistant strain (M-R) were tested. Strain M-R was field collected from a peach and nectarine orchard sprayed with twice the recommended rate of Pirimor. Prior to testing, both strains were maintained on potted cabbage in a mass culture laboratory under natural light at 25 ± 4°C. Neither strain had been previously exposed to NTN-33893, a nitromethylene. Initial laboratory screening categorized strain M-R with a 4 fold resistance to Monitor 580 (580 g/liter EC), a 17 fold resistance to Pirimor (500 g/kg W) and a 27 fold resistance to Meta- Systox (i) (250 g/liter EC) compared to strain S. Electrophoretic examination showed that 50 M-R individuals consisted totally of the R2 variant. Aphids were exposed to NTN-33893 by spraying directly with a 2 ml aliquot solution through a Potter spray tower producing a deposit of 1.6 mg/cm2. Apterous virginoparous adults from both strains were sprayed with a range of serially diluted concentrations of NTN-33893 (200 g/liter soluable liquid) in groups of 12-15 aphids on a 9 cm filter paper discs. Eight replicates were done at each concentration for strain S except the 8 mg/liter concentration which had 4 replicates. Four replicates were done at each concentration for strain M-R. All replicates included water-only sprayed controls. After being sprayed, aphids were transferred to cabbage leaves and held at 22°C ± 1°C under constant illumination. Knockdown, defined as the inability to walk in a coordinated manner, was assessed after 48 h and log dose probability (ld-p) curves were calculated using probit regressions after correcting for control mortality. Ld-p curves were compared to the KD50 level by relative potency analysis. Residual deviances were calculated and the changes in deviance compared to the relevant 5% value of X2 to determine if the lines were parallel.