Effects of pesticides on the functional response of predatory thrips,Scolothrips takahashiitoTetranychus viennensis

Abstract

Abstract: It is of importance to integrate the biological control of hawthorn spider mite,Tetranychus viennensis, by predatory thrips in commercial orchards in north China. In this study, a leaf disc bioassay was employed to investigate the effects of two insecticides, i.e. abamectin and fenpropathrin, and two fungicides, i.e. mancozeb and carbendazim, on the functional response of an acarophagous thrips,Scolothrips takahashiiPriesner, to eggs of the mite at the conditions of 25 ± 1°C, 60 ± 10% relative humidity, and a 16 : 8 h (L : D) photoperiod. Results indicated that the type of functional response in predatory thrips differed depending on the types and doses of the pesticides exposed. Holling‐II type responses were exhibited by all predatory thrips but females that were exposed to labelled dose of abamectin and half‐labelled dose of fenpropathrin exhibited the Holling‐III type responses. Parameters of random predator equation for both exposed and unexposed predators were estimated and compared with an equation with indicator variables. Both doses of both fungicide treatments did not have any impact on the attack rates of the thrips. Handling time (Th) estimates for males exposed to both doses of both fungicides were similar to that of the control, but there seemed to be a trend towards prolonged handling times for females in these exposures with a significantly prolonged Thfound in labelled dose of mancozeb. Exposures of both doses of fenpropathrin and labelled dose of abamectin produced significantly lower attack rates and significantly prolonged handling times in both males and females, whereas an exposure of half‐labelled dose of abamectin had no obvious influence on the attack rates of the predator, but the handling time in females prolonged significantly. The theoretical maximum number of prey attacked by the thrips were 59.81 eggs per day per female and 23.21 eggs per day per male in the control, but it reduced by 57.03–71.41% and 6.03–36.75% for females and males in the insecticide exposures and 23.91–44.26% and −5.13–11.55% in the fungicide exposures, respectively. The finding implies that the natural control effects ofS. takahashiiwould be weakened by the application of the pesticides such as fenpropathrin, abamectin and mancozeb, which are often used to control insect pests and fungal diseases in apple orchards.