The role of lignin as a physical defence against Dendroctonus micans was investigated in laboratory feeding experiments. The effect of lignin is dose-dependent, reducing larval survival, growth rate, and weight, as well as affecting gallery construction. Adults lay fewer eggs in lignified bark and also tend to construct abnormal galleries. The distribution of lignin in trees suggests a role in defence against bark beetles that feed in the thicker bark on the lower bole.

1. Within a seed orchard in southern England, beech trees (Fagus sylvatica L.) belonging to three clones were artificially infested by introducing beech scale larvae (Cryptococcus fagisuga Lind. Hornoptera: Coccidae) into small cages attached t o the bark.2. Some larvae developed t o fecund adults on trees of two susceptible clones but all failed t o develop on a third, resistant clone.3. Within susceptible clones, survival of larvae on individual trees was positively related t o their degree of natural infestation.4. Larvae deriving from several separate trees differed significantly in their ability to survive when inoculated onto trees of susceptible clones. 5. Five forest trees which acted as both donors of larvae and as hosts for artificial inoculation were each inoculated with larvae from all five trees.6. There was significant variation in survival of inoculated larvae both between the host trees and between sources of larvae on each host. 7. Survival of larvae reinoculated onto their original host was significantly higher than that of larvae originating from other trees.8. Fecundity of adults on the forest trees was positively correlated with the probability of inoculated larvae surviving to the adult stage.

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A lure based on the proportional composition of monoterpenes inD. micans larval frass and deployed in Theysohn slot traps was highly attractive toR. grandis released in the field. The relative response to frass and lure was consistent over a range of doses, and behavior close to traps baited with either lure or frass appeared to be similar. The monoterpenes, formulated with antioxidant, appear to be stable over several weeks when released from proprietary reservoir and wick "air fresheners." The lure may be of value in monitoring predator populations.

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