Pyrethroid encapsulation for conservation of acarine predators and reducedspider mite (Acari : Tetranychidae) outbreaks in apple orchards

We examined the effects of a micro-encapsulated formulation of the pyrethro id cypermethrin on the predator Amblyseius fallacis (Garman) and the biolog ical control of tetranychid mites. In functional response analysis, suscept ible field-collected and mass-reared pyrethroid resistant strains of A. fal lacis consumed similar numbers of Tetranychus urticae Koch eggs on unspraye d leaf-disks (14-16 eggs per day). Fewer prey were consumed on micro-encaps ulated cypermethrin sprayed disks, but consumption was similar between stra ins (10.3-11.3 eggs per day). The functional response on cypermethrin EC (e mulsifiable concentrate) sprayed disks was associated with resistance. Susc eptible A. fallacis mites (cypermethrin LC50 = 7.2 ppm) consumed a maximum of 1.0 eggs per day; field-collected predators (LC50 = 13.3 ppm) consumed a maximum of 4.0 eggs per day, and mass-reared A. fallacis (LC50 = 28.2 ppm) consumed a maximum of 4.33 eggs per day. Encapsulated cypermethrin was muc h less toxic to predators, and was similar in toxicity between strains (LC, , range = 87.0-100.4 ppm). In an experimental orchard, a commercial formula tion of cypermethrin EC almost eliminated A. fallacis. On tt ces sprayed wi th the micro-encapsulated formulation, mean A. fallacis densities were redu ced from 0.81 +/- 0.20 per leaf to 0.26 +/- 0.12 per leaf. On microencapsul ated sprayed trees this predator density, together with the stigmaeid preda tor Zetzellia mali (Ewing), appeared to regulate Panonychus ulmi Koch to a peak density of 21.7 +/- 11.7 per leaf, compared to 87.2 +/- 15.6 per leaf on cypermethrin EC treated trees, and 10.4 +/- 4.6 per leaf on unsprayed tr ees. The micro-encapsulated cypermethrin formulation conserved natural biol ogical control in pyrethroid sprayed orchards better than the cypermethrin EC formulation.