Effects of Orchard Pesticides on Galendromus occidentalis (Acari: Phytoseiidae): Repellency and Irritancy.

The effects of repellency or irritancy in Galendromus occidentalis (Nesbitt) were studied for three rates of 16 pesticides commonly used in apple production. Adult female mites were exposed to residues in a series of choice bioassays (treated and untreated half of bean leaf disks). Novaluron, carbaryl, mancozeb+copper hydroxide, and sulfur were the most repellent materials to G. occidentalis, with females consistently avoiding the treated side of the leaf disk. Spirotetramat, flubendiamide, and cyantriniliprole caused an intermediate or inconsistent degree of repellency; azinphosmethyl, lambda-cyhalothrin, acetamiprid, thiacloprid, imidacloprid, spinetoram, spinosad, and chlorantriniliprole caused little to no repellency. Irritancy (running off of the disk, as opposed to resting on the untreated half) was the most pronounced in the acetamiprid and lambda-cyhalothrin treatments. Acute toxicity (within the 6 h test period) was highest in the lambda-cyhalothrin and spinetoram treatments; in the former case, the mortality at all rates tested was substantial enough to interfere with the measurement of behavioral effects. Although irritancy may be considered the more extreme form of repellency, there were several pesticides (carbaryl, cyantraniliprole, mancozeb+copper hydroxide, novaluron) where a moderate to high degree of repellency did not correspond to a high degree of irritancy. Similarly, repellency was not consistently related to acute toxicity; one of the most repellent materials (novaluron) was not acutely toxic. Behavioral effects may help explain instances where lethal or sublethal bioassays do not fully predict the effects of pesticides seen in orchard use.