Relative toxicity of nC24 agricultural mineral oil to Tetranychus urticae Koch (Acari: Tetranychidae) and Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae) and its possible relationship to egg ultrastructure

The relative toxicity (LC50 values based on mu g oil/cm(2)) is evaluated of aqueous nC24 agricultural mineral oil (AMO) emulsions to the egg, six-legged nymph (larva), eight-legged protonymph and adult stages of two-spotted mile (Tetranychus urticae) and its predator, Phytoseiulus persimilis, on French heart leaf discs. using it Potter spray tower to apply of the oil. The egg of P. persimilis was the least Susceptible stage (LC50 444.84) and its LC50 was significantly higher than all other stages tested of either P. persimilis or T. urticae. The LC50 for adult female T urticae (LC50 63.89) was significantly lower than the larva (LC50 93.86) however. there was no significant difference in response between the protonymph (LC50 70.44) and the larva, which were both higher than T urticae eggs (LC50 17.55.). LC(50)s for P persimilis larva (LC50 43.87), protonymph (LC50 41.55) and adult female (LC50 53.34) were similar. Scanning electron microscopy showed that the eo,, Surface of T. urticae is usually well covered with fine silk that may trap more oil and increase AMO efficacy. Other possible differences in AMO efficacy between T urticae and P. persimilis may be due to differences in egg size, egg incubation period. egg surface structure and the presence of vulnerable respiratory cones in T. urticae eggs. Dose of 0.2-0.3% (w/w) is considered to be the most appropriate for nC24 AMOs use against T urticae in combination with P persimilis in integrated pest management programs.