Effect of prey stages of the two-spotted miteTetranychus urticaeon functional response of the coccinellid predatorStethorus gilvifrons

Abstract

The effect of prey stages of the two-spotted spider mite Tetranychus urticae on the functional response of the coccinellid predator Stethorus gilvifrons was studied at 25±1 °C, 65±10% rh, and 16:8 h (L:D photoperiod). The functional response of S. gilvifrons female, to increasing prey stage density from 10–100 preys per patch, was of the curvilinear shape depicting Roger’s type II response with the highest consumption rate of larval prey stage. Results of the maximum likelihood analyses confirmed this type. By plotting a type II functional response model and polynomial logistic regression model to the numbers and proportions of consumed stages of T. urticae, respectively, the resulting regression lines fitted the data well. However, a composite waving form that appeared to be a decelerating (type II) response at low to medium prey densities and an accelerating (type III) response at high prey densities. We assume that the small size of experimental arena or predator feeding behaviour at low and high prey densities may have induced the modified type II response. A sensitivity analysis of the functional response model shows the crucial effect of prey stages on predation rates by S. gilvifrons. Theoretically, based on the lowest handling time for S. gilvifrons on larval stage of T. urticae, the maximum numbers of mites that could consume by a single female of S. gilvifrons within 24 h period were 77.42 larvae. These results improve our understanding of the interaction among S. gilvifrons and T. urtica stages and provide insights into the control of T. urticae.