| Abstract: | The effects of synthetic pyrethroids on the feeding behaviour of the two-spotted spider mite Tetranychus urticae (Koch) were studied using a modified leaf disc technique. Four different concentrations of the pyrethroids fenvalerate and permethrin and of the organophosphorous insecticide phosmet were sprayed on to Henderson lima bean plants in the laboratory. A water spray was used as a control. Leaf discs were taken from each treatment, including the control, at 2h, 1, 2, 4, 7, 11 and 14 days after treatment. One mite was placed on each disc, allowed to acclimatise and then observed for 1 h. Experiments were conducted under laboratory light at 25 (±1.5)°C and 30 (±2)% r.h. Mites on untreated and phosmet-treated discs spent an average 70–95% of the time feeding; mite behaviour appeared to be unaffected by phosmet. In contrast, mites often spent only 5–40% of the time feeding on discs treated with fenvalerate or with the higher rates of permethrin. In response to pyrethroid residues mites exhibited hyperactivity, longer search periods and reduced feeding, reduced oviposition and a preference for areas with lower residues. These changes in mite behaviour may partially explain mite outbreaks in the field on apple trees following treatment with pyrethroids. |
