Density dependent prey‐feeding time of Stethorus bifidus (Coleoptera: Coccinellidae) on Tetranychus lintearius (Acari: Tetranychidae)

Abstract

The gorse spider mite, Tetranychus lintearius, a biological control agent introduced into New Zealand to control gorse, is often attacked by the endemic coccinellid, Stethorus bifidus. Predation by S. bifidus has been suggested as a reason why T. lintearius colonies collapse. For S. bifidus predation to regulate T. lintearius populations, at least one component of its numerical or functional response must result in an increased proportion of mites being killed as mite density increases. Laboratory experiments showed that feeding time (a sub‐component of the functional response) decreased markedly with increased T. lintearius density. An increase in available prey density from 3–25 mites/177 mm² led to an exponential decrease in mean feeding time from 870 s to 100 s. Furthermore, despite S. bifidus killing more mites, it extracted progressively smaller proportions of the contents of each mite killed as mite density increased.

Keywords:

• Stethorus bifidus
• beetle
• Tetranychus lintearius
• spider mite
• predation
• functional response
• feeding time
• prey density
• biological control