Effects of residence time and webbing upon dicofol-avoidance behavior in two-spotted spider mites (Acari: Tetranychidae)

Two-spotted spider mites (Tetranychus urticae Koch) placed upon leaves treated with checkerboard-like discontinuous residues of 100 ppm dicofol were observed at time 0,3 h, 6 h and 24 h after application (h0,h3,h6 andh24, respectively). In one experiment, the mites were allowed to reside undisturbed upon a single leaf for the duration of the observations. In a second experiment, mites of one group were transferred to another webbing-free leaf with discontinuous dicofol residue for each observation period, while those of a control group were lifted off the leaf surface and returned to it (on the same leaf) prior to each observation period. The mites in all three groups eventually began to avoid the dicofol-treated squares during their nonlocomotory activities, in no instance was dicofolavoidance displayed by moving mites. Mites that lomained undisturbed upon leaves treated with discontinuous residue began to avoid the dicofol-treated squares byh3. The mites lifted above their leaf and replaced on it prior to each observation period did not begin to avoid the dicofol-treated squares untilh6. The mites transferred to a webbing-free leaf prior to each observation period did not begin to avoid the dicofol-treated squares untilh24. Attributes of tetranychid webbing, that may cause the last-mentioned group of mites to expend considerable energy in searching for a webbed area of leaf surface, are discussed.