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

Abstract

We examined the effects of a micro-encapsulated formulation of the pyrethroid cypermethrin on the predator Amblyseius fallacis (Garman) and the biological control of tetranychid mites. In functional response analysis, susceptible field-collected and mass-reared pyrethroid resistant strains of A. fallacis consumed similar numbers of Tetranychus urticae Koch eggs on unsprayed leaf-disks (14-16 eggs per day). Fewer prey were consumed on micro-encapsulated cypermethrin sprayed disks, but consumption was similar between strains (10.3-11.3 eggs per day). The functional response on cypermethrin EC (emulsifiable concentrate)-sprayed disks was associated with resistance. Susceptible 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 much less toxic to predators, and was similar in toxicity between strains (LC50 range = 87.0-100.4 ppm). In an experimental orchard, a commercial formulation of cypermethrin EC almost eliminated A. fallacis. On trees sprayed with the micro-encapsulated formulation, mean A. fallacis densities were reduced from 0.81 ± 0.26 per leaf to 0.26 ± 0.12 per leaf. On microencapsulated sprayed trees this predator density, together with the stigmaeid predator 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 trees. The micro-encapsulated cypermethrin formulation conserved natural biological control in pyrethroid sprayed orchards better than the cypermethrin EC formulation.