The Functional Responses of Stethorus punctum 1 to Densities of the European Red Mite 234

Abstract

The functional response of the predator Stethorus punctum (LeConte) was tested at various densities of the European red mite, Panonychus ulmi (Koch). Overwintered S. punctum adult females were tested at a range of densities from 4–30 mites/cage, whereas, the 2nd and 3rd generation larvae, female and male adults were tested at a range of densities from 4–80 mites/cage. Various types of mathematical models were fit to the data, using weighted regression analysis, to estimate the relationship between the number of prey eaten and prey density. Three types of functional response curves were exhibited by the different stages and sexes of S. punctum , a linear response, a negatively accelerated curve and an S-shaped rise to a plateau. Two factors partially responsible for these 3 types may be the different environmental conditions for each test and the replenishment of prey on an hourly basis. S. punctum was found to stop feeding at dusk and to resume ca. 2 h after sunrise. The feeding of S. punctum increased as temperatures rose during the day with a maximum consumption occurring during the warm afternoon hours.