Acaricide-Mediated Suppression ofPanonychus Citri(Mcgregor) (Acari: Tetranychidae) in Pear Orchards in Japan

Abstract

Population density of the citrus red mite, P U I I O I~C~I I I Scirri (McGregor), in Japanese pear orchards remained low until mid-August, even after inoculation of pear leaves with a considerable number of adult female P. ciii-i from May onwards. This raised the possibility that pear leaves contain a natural compound that suppresses an increase of P. ciiri populations. The rate of development from larva to adult was significantly lower on leaves collected in July than on leaves collected earlier or later, in several years. The population suppression was caused by molting deterrent activity and ovicidal activity, according to our close observation in the laboratory. To clarify whether a natural pear compound caused this molting deterrence, a methanol crude extract of pear leaves was isolated and added to a newly developed artificial diet, consisting of sodium caseinate, sucrose, levulose, glucose and inositol. The compound extracted from pear leaves resulted in the molting deterrence as observed on pear leaves. Based on infrared and NMR spectral analysis, the compound extracted from pear leaves closely resembled the synthetic acaricide hexythiazox. Furthermore, the LC50 values of the compound extracted from pear leaves for ovicidal activity of P. citri eggs and for deterrence of molting to protonymphs were similar to those of hexythiazox. These results strongly suggest that the molting deterrent extracted from pear leaves was in fact hexythiazox, an acaricide in use on pear trees, rather than a natural product. This suggestion becomes even stronger, considering that the molting deterrence was observed in a hexythiazox-spray year, but not in a non-spray year.

A Leaf-Mimicking Method for Oral Delivery of Bioactive Substances Into Sucking Arthropod Herbivores

“…Mittler and Dadd (1962) later developed a membrane feeding device using an extensible and waterproof paraffin wax film (i.e., Parafilm) for the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae). Using the Parafilm membrane feeding method, many nutritional and pharmacological studies have been carried out on aphids, spider mites, planthoppers, thrips, bedbugs, whiteflies, and mosquitoes (Dadd and Mittler, 1966;Walling et al, 1968;Mitsuhashi and Koyama, 1969;Hanna and Hibbs, 1970;van der Geest et al, 1983;Montes et al, 2002;Gotoh et al, 2008;Upadhyay et al, 2011;Costada-Silva et al, 2013;Torres-Quintero et al, 2013;Suzuki et al, 2017a). Although the membrane feeding method was successfully used, the small specific surface area of the feeding arena that coincides with the liquid under the membrane limits the efficiency of the bioassays.…”

Protocols for the delivery of small molecules to the two-spotted spider mite, Tetranychus urticae

“…Most liquid diets formulated for mites and aphids [26,27,29] could keep mites alive, but did not facilitate progression through a full life cycle. Of the diets tested by us, only the diet described by Van Der Geest et al .…”

“…Artificial diets adequate to sustain TSSM have been published over 30 years ago [ 18 – 20 , 41 ] but have not been widely implemented. Most liquid diets formulated for mites and aphids [ 26 , 27 , 29 ] could keep mites alive, but did not facilitate progression through a full life cycle. Of the diets tested by us, only the diet described by Van Der Geest et al .…”

“…The first, has been formulated by Gotoh et al . [ 29 ] for Panonychus citri , a mite species belonging to the same Tetranychidae family as T . urticae .…”