A Potter spray tower bioassay of two petroleum spray oils against adult female Panonychus ulmi (Koch) and Tetranychus urticae Koch (Acari: Tetranychidae)

A Potter spray tower was used to determine the susceptibility of adult female European red mites (Panonychus ulmi (Koch)) and two-spotted spider mites (Tetranychus urticae Koch) to suffocation by petroleum spray oils (PSOs). The LC₉₅ values calculated for P. ulmi against C23 Ampol D-C-Tron NR and C21 Caltex Lovis were 104 and 165 g cm^-2, respectively. For T. urticae the values were 169 and 207 g cm^-2, respectively. The results are consistent with established relationships between PSO efficacy and increasing PSO molecular weight. The results are discussed in relation to previously reported bioassays on spider mites and to concurrent evaluations of PSOs for use in pome fruit integrated pest management programmes in Australia.