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

• Published in: Environmental entomology 1999-02, Vol.28 (1), p.72-80
• Main Authors: Lester, P.J, Pree, J, Thistlewood, H.M.A, Trevisan, L.M, Harmesen, R
• Format: Article
• Language: English
• Subjects: acaricide resistance; adverse effects; Amblyseius fallacis; Biological and medical sciences; Biological control; biological control agents; Control; cypermethrin; emulsifiable concentrates; functional responses; Fundamental and applied biological sciences. Psychology; Malus domestica; microencapsulation; mite control; nontarget effects; nontarget organisms; orchards; outbreaks; Phytopathology. Animal pests. Plant and forest protection; population density; predator conservation; predatory mites; Protozoa. Invertebrates; Tetranychidae; Tetranychus urticae; toxicity
• ISSN: 0046-225X; 1938-2936
• DOI: 10.1093/ee/28.1.72

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 micro-encapsulated sprayed trees this predator density, together with the stigmacid 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 EG 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.