Interaction Dynamics of Bark Beetle Aggregation and Conifer Defense Rates

Abstract

The requirement of host tree death for successful reproduction by some bark beetles (Coleoptera: Scolytidae) has placed strong selective pressures on conifers for rapidly induced, complex defensive systems. Conversely, the ability of bark beetles to engage in cooperative attacks mediated by aggregation pheromones and their associations with phytopathogenic fungi enable them to overcome these defenses under certain conditions. Although the outcome of colonization attempts is discrete, tree defensive capacities vary quantitatively within a population. There are multiple interactions among these features, and so the separate processes that govern coniferbark beetle systems have proven difficult to study or manipulate for improved forest protection. A model is developed which delineates the key parameters of colonization success or failure. The differential equations that structure the model are based entirely on validated assumptions from previous field and laboratory work. Using this model, various assumptions regarding the effects of such factors as environmental stress, underlying resistance, and beetle immigration can be evaluated for each coniferscolytid system. This model may also facilitate the development of comparative approaches for addressing coevolutionary interactions among bark beetles and their host plants.

Mixed messages across multiple trophic levels: the ecology of bark beetle chemical communication systems

“…4. Such models need to incorporate the conflicting rate dynamics of active herbivore and host processes (Raffa 1988(Raffa , 1991Berryman et al 1989). An example is provided in Fig.…”

Scots pine susceptibility to attack by Tomicus piniperda (L) as related to pruning date and attack density

“…but the 2 groups did not differ in tree characteristics (except Christiansen et al, 1987). Successful colonisation by bark beetles occurs when the beetles can exhaust the defence system of the host trees by massive synchronized attacks (Berryman et al, 1989; and references therein). Possession of aggregation pheromones as well as association with pathogenic blue-stain fungi seem to be typical features of tree-killing bark beetles (Christiansen et al, 1987; and references therein).…”

Animal’s Functional Role in the Landscape

“…and Europhium clavigerum , 'blue stain fungus') may get into the trees during bark beetle oviposition -probably as spores contained in the food. Expanding through the phloem and the water-conducting xylem, they impair sap fl ow in the pine stems and may also exhaust tree defenses (Berryman et al 1989 .…”