Patch residence by aphidophagous ladybird beetles: Do specialists stay longer?

Aphidophagous ladybird beetles are perceived as highly mobile organisms, with adults frequently moving between patches containing ephemeral aphid prey. Nonetheless more specialized ladybirds are likely to be more sedentary due to their greater tolerance of lower aphid densities. We tested the hypothesis that a conifer specialist, Mulsantina picta, would remain in patches (individual pine trees) longer than the generalist Harmonia axyridis. One hundred marked M. picta and H. axyridis were released onto single isolated Austrian pines infested with the aphid Eulachnus rileyi once in 2006 and once in 2007. On both occasions marked H. axyridis left the pine trees almost immediately, but marked M. picta continued to be detected for periods in excess of 10 days. Unmarked H. axyridis continued to be observed on the trees after the marked ladybirds had dispersed and in 2006 H. axyridis oviposition also continued after dispersal of marked individuals. In 2007, M. picta oviposition was observed to continue after H. axyridis oviposition had ceased. The factors that might be responsible for the differential dispersal of the two species from the pines either do not appear to satisfactorily explain the difference between them or are directly related to their degree of specialization. We therefore conclude that M. picta’s longer patch residence time is a consequence of it being more specialized. In the habitats in which they occur, longer patch residence times of specialist ladybirds and a tolerance of lower densities of their preferred prey are likely to make specialists better aphid biocontrol agents than generalists.