Symbiosis and competition: complex interactions among beetles, fungi, and mites
Symbioses among bark beetles and their fungal and mite associates involve complex, multi-level interactions. Dendroctonus frontalis attacks and kills southern pines, introducing fungi into the tree. Ophiostoma minus may initially aid beetles in killing trees, but later this "bluestain" fungus becomes an antagonist, competing with larvae for host phloem. Two additional fungi, Entomocorticium sp. A and Ceratocystiopsis ranaculosus are carried within a specialized mycangium and inoculated into phloem where they are fed upon by beetle larvae. The beetle also vectors several species of phoretic mites, which transport spores of O. minus, and C. ranaculosus and can complete their life cycle upon these two fungi. A similar interaction occurs between Ips avulsus and its fungal (Entomocorticium spp.) and mite (Elattoma bennetti) symbionts. Larval beetles feed on fungus, as do the mites. Female mites feed on fungus growing within beetle galleries, swelling to many times their normal size. Larval mites develop and mate within the females who burst open, giving birth to reproductively mature females. These relationships may be best understood by considering the manner in which symbioses vary with time and resources, and the degree to which other species may affect interactions among symbionts.