Summary: OIKOS 103: 559565, 2003
Density dependent population growth of the two-spotted spider
mite, Tetranychus urticae, on the host plant Leonurus cardiaca
Karin A. Rotem and Anurag A. Agrawal
Rotem, K. A. and Agrawal, A. A. 2003. Density dependent population growth of the
two-spotted spider mite, Tetranychus urticae, on the host plant Leonurus cardiaca.
Oikos 103: 559565.
We observed Tetranychus urticae (Koch), a polyphagous spider mite herbivore, on
Leonurus cardiaca (L.) at several sites in eastern North America at variable density,
ranging from extremely dense to sparse. To understand the nature of T. urticae's
population dynamics we experimentally manipulated population densities on L.
cardiaca and assessed per capita growth after 1 to 2 generations in laboratory and
field experiments. In particular, we took a `bottom-up' approach, manipulating both
plant size and quality to examine effects on mite dynamics. Per capita growth was
strongly dependent on the initial density of the mite population. Spider mite
populations grew (1) in a negatively density dependent manner on small plants and
(2) unhindered by density dependence on large plants. Mean per capita growth was
59% higher on small plants compared to large plants, irrespective of mite density. We
also found evidence for density dependent induced susceptibility to spider mites in
small plants and density dependent induced resistance in large plants. Hence, spider