POPULATION ECOLOGY Components of Antagonism and Mutualism in Ips pini–Fungal Interactions: Relationship to a Life History of Colonizing Highly Stressed and Dead Trees

Efforts to describe the complex relationships between bark beetles and the ophiostomatoid (stain) fungi they transport have largely resulted in a dichotomous classiÞcation. These symbioses have been viewed as either mutualistic (i.e., fungi help bark beetles colonize living trees by overcoming tree defenses or by providing nutrients after colonization in return for transport to a host) or antagonistic (i.e., fungi compete for a limited resource and reduce brood development with no apparent beneÞt to the beetle). We investigated several components of one beetleÐfungus interaction. SpeciÞcally, we addressedwhether beetle entry into, and developmentwithin, a host tree varywith the degree of colonization by ophiostomatoid fungi. Ips pini (Say) transports several species of ophiostomatoid fungi, themost commonbeingOphiostoma ips(Rumbold)Nannfeldt, in theprocess of colonizing its host, Pinus resinosa Aitman. We introduced this fungus 0, 3, 7, and 10 d before beetle entry to characterize its effects on I. pini colonization and development. This sequence allowed quantiÞcation of temporal effects and comparison of results with other systems. Fungal growth was greatest when inoculated before beetle colonization. Fungal colonization reduced beetle entry into logs, but increased brood production. Mate capture was not signiÞcantly affected by fungal growth. The beneÞts imparted by O. ips to its beetle vector during brood development are compared with results from other systems. This differencemay in part be related to the exploitation of highly stressed and dead trees, rather than vigorous hosts, by I. pini.