Operational and Biological Factors Influencing Responses of Spider Mites (Acari: Tetranychidae) to Propargite by Using the Petri Dish-Potter Tower Method

Abstract

A series of laboratory bioassays was done to determine the effects of various operational and biological factors on the responses of adult female twospotted spider mite, Tetranychus urticae Koch, and European red mite, Panonychus ulmi (Koch), to propargite when using the Petri dish—Potter tower method. The spray volume (1—5 ml) used to treat the petri dishes significantly influenced the responses of both species to propargite residues: a 5-ml spray volume was 6.7- and 4.7-fold more toxic than a 1-ml spray volume at the LC50 to twospotted spider mite and European red mite, respectively.To test the effectiveness of propargite residues over time, mites were exposed at intervals to treated petri dishes that were stored for up to 30 d at 4 ± 1oC. The toxicity of propargite remained constant throughout this period. When mites were retained in petri dishes in a manner that prevented contact with residues, no mortality of mites caused by the vapor action of propargite was detected at 23 and 30oC. However, the toxicity of propargite to mites in contact with residues increased 113- and 522-fold at the LC50 between 10 and 30oC for twospotted spider mite and European red mite, respectively. The age of adult females also influenced the response to propargite residues: 7-d-old twospotted spider mite females were 1.9-fold more tolerant than 1-d-old females at the LC50.The relevance of these findings to miticide bioassays using this method is discussed.