Absorption and Translaminar Activity of Abamectin in Apple and Pear Foliage as Determined by Spider Mite (Acari: Tetranychidae) Mortality

Abstract

Translaminar activity of abamectin was studied during 1992-1994 on apple. Malus X domestica Borkhauser, and pear, Pyrus communis L. Field-aged residues were bioassayed from the top or bottom leaf surface of apple and pear after atomizer application to the top or bottom surface, or handgun application to both surfaces. Tetranychus urticae Koch was used as the test organism with the exception of 1 experiment, which included Panonychus ulmi (Koch). Abamectin showed little translaminar activity on apple regardless of the leaf surface to which it was applied. There was preferential absorption by the bottom leaf surface, which resulted in higher levels of mortality for mites feeding on the bottom surface when this was also the treated surface (bottom/bottom [surface treated/surface assayed]). Mortality caused by other combinations (bottom/top, top/bottom, top/top) was minimal. Mortality from assays conducted on the bottom surface was also higher in the apple/handgun experiments. Translaminar activity was greater on pear, but primarily through the bottom leaf surface. The degree of translaminar movement was sufficient to cause comparable levels of mortality on both the top and bottom surfaces when applied solely to the bottom surface. There was no difference in mortality between the 2 mite species when assayed on the same leaf surface. However, based on control mortality and runoff, the bottom leaf surface of apple and pear is a more favorable habitat for T urticae than the top surface, whereas the opposite is true for P ulmi. The implications of mite host preference, feeding behavior, and differential absorption of abamectin are discussed.