Association of declining red pine stands with reduced populations 4 of bark beetle predators , seasonal increases in root colonizing 5 insects , and incidence of root pathogens

9 10 Abstract 11 12 Declining red pine, Pinus resinosa (Aitman), stands in the Great Lakes region appear to arise from a complex of biotic and 13 abiotic factors. We monitored stem and root colonizing beetles in declining and healthy plantations in Wisconsin from 1997 to 14 1999. We also conducted systematic field excavations and laboratory isolations of various root pathogens. Multiple funnel 15 traps were baited with the synthetic aggregation pheromones of the two most common bark beetle (Coleoptera: Scolytidae) 16 species in the region, Ips pini (Say) and Ips grandicollis (Eichhoff). Lower-stem flight traps were baited with 1:1 (þ)-a17 pinene:75% ethanol, and pitfall traps were baited with 1:1 ( )-a-pinene:75% ethanol. Healthy stands had higher populations 18 of predators, particularly Thanasimus dubius (F.) (Coleoptera: Cleridae), Platysoma cylindrica (Paykull) (Coleoptera: 19 Histeridae), and Platysoma parallelum Say than declining stands. Seasonal abundance patterns of predators and Ips also varied 20 between declining and healthy stands. Declining stands had higher numbers of Ips and lower numbers of predators early in the 21 season, whereas healthy stands had higher predator populations in the early season. Declining stands had more lower stem 22 infesting bark beetles Dendroctonus valens LeConte (Scolytidae) and weevils (Curculionidae) Pissodes spp. Surprisingly, 23 healthy stands had more root weevils, Hylobius pales (Herbst) and Hylobius radicis Buchanan, and root bark beetle Hylastes 24 porculus Erichson, over the entire season. However, spatial by temporal patterns again were important. Populations of root 25 colonizing insects were higher in healthy stands early in the season, but higher in declining stands throughout much of the 26 ovipositional period. These results suggest dispersal patterns and overwintering behaviors are important in the interactions 27 among herbivores, predators, and host plant condition in Red Pine Decline. The principal fungi isolated from roots were 28 Leptographium procerum (Kendr.) Wingfield and Leptographium terebrantis Barras & Perry. These were more prevalent in 29 declining than healthy stands. Staining fungi were more frequently isolated from roots of trees at the pocket margin than from 30 trees in the asymptomatic portion of declining stands. Heterobasidion annosum (Fr.) Bref. was not isolated from root samples or 31 stem disks, despite 40% recovery in positive controls using the latter method. Likewise, Armillaria spp. were not associated with 32 declining plantations. Our results further support the view that forest declines are due to complex interactions among multiple 33 biotic and abiotic stresses, and exhibit particular spatial and temporal patterns. # 2001 Published by Elsevier Science B.V. 34 35