Pyrethroid Encapsulation for Conservation of Acarine Predators and Reduced Spider Mite (Acari: Tetranychidae) Outbreaks in Apple Orchards

Abstract

We examined the effects of a microencapsulated 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 microencapsulated 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 microencapsulated 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 microencapsulated cypermethrin formulation conserved natural biological control in pyrethroid sprayed orchards better than the cypermethrin EC formulation.