FUNCTIONAL RESPONSE OF THE COCCINELLID PREDATOR Stethorus gilvifrons MULSANT FEEDING ON THE TWO SPOTTED SPIDER MITE, Tetranychus urticae KOCH: THE EFFECT OF DIFFERENT PREY STAGES

The functional response of a ladybeetle, Stethorus gilvifrons Mulsant, to increasing density of two spotted spider mite, Tetranychus urticae koch, was of the curvilinear shape depicting Holling’s type II response with larval stage being the most voracious stage when compared with nymphal and adult stages. 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. 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 be consumed by a single female of S. gilvifrons within 24 h period were 77. 42 larvae. Based on the inversely density-dependent predation rate for S. gilvifrons on different prey stages, it seems to be more effective in low prey densities and this result has to be considered in future inundative biological control programs. These results might be a better strategy for developing mass rearing of S. gilvifrons and biocontrol program of T. urticae.