POPULATION ECOLOGY Seasonal Dynamics of Mites and Fungi and Their Interaction with Southern Pine Beetle

We evaluated whether Dendroctonus frontalis Zimmermann populations were inßuenced by nontrophic interactions involving commensal mites, their mutualistic bluestain fungus Ophiostoma minus (Hedgc.) H. and P. Sydow, and beetle-mutualistic mycangial fungi. We tested for effects of delayed, nonlinear, or positive feedback fromO. minus and mites onD. frontalis population growth. We predicted that (1) high mite densities have demographic consequences for beetles by inßuencing the prevalence ofO.minus and antagonistic interactions betweenO.minus andmycangial fungi, and(2) inter-relations andabundancesofmites and fungidifferentially vary throughout theyear in a seasonally variable climate. Surveys ofD. frontalis populations revealed that temporal and spatial patterns in abundance of mites and their mutualistic fungus, O. minus were inversely related with beetle population growth. Negative demographic effects of O. minus on D. frontalis were nonlinear, only affecting beetle per capita reproduction when fungi colonized 35% of phloem habitat. Mite abundance was strongly correlated with O. minus and was an important driving force in promoting bluestain prevalence within trees. Spring abundances of mites and the prevalence ofO. minus during D. frontalis infestation formation were strong predictors of beetle population decline later that year. The twomutualistic fungi associated withD. frontalis cycled seasonally but did not seem to inßuence beetle population dynamics.