A review of semiochemicals associated with bark beetle (Coleoptera: Curculionidae: Scolytinae) pests of coniferous trees: A focus on beetle interactions with other pests and their associates

Bark beetles (Curculionidae) have assumed increasing prominence as pests of coniferous trees and wood products. Some species of Ips and Dendroctonus introduce blue stain fungi that cause damage to trees and downgrading of wood products. In forest ecosystems, bark beetles respond to fire, frost, drought, lightening or windstorms, all of which can initiate tree stress. Silvicultural practices that improve tree vigour are widely used to manage these pests. Pruning, disposing of infested limbs and salvage logging following storm damage are also frequently employed. Systemic insecticide applications can be used to protect trees from beetle attack for several months to a year. Insecticides are also frequently used to protect trees of high value in landscape settings, seedlings in nurseries and can be used as bole sprays where trees may be treated during outbreaks Insecticides are, however, often uneconomical in natural and commercial forests, particularly in broad acre landscapes. Options for better management could involve the wider use of semiochemicals (pheromones and kairomones) that influence beetle behaviour such as feeding, mating and oviposition. Currently, semiochemicals are used extensively for monitoring bark beetle populations and for optimising timing of silviculture treatments. Semiochemical use for protecting trees using 'push-pull' strategies are promising and, in some cases, effective strategies for control of scolytines. Recent research shows that volatiles from unsuitable and non-host tree species could impede bark beetle attack on conifer trees. Applications of bark beetle pheromone components, such as verbenone, when used as a blend with non-host volatiles can deter scolytine bark beetles from trees.The use of semiochemicals and non-host volatiles in the management of bark beetles is, however, complicated when other insect pests and their associates are present together with bark beetles. Effective, management of bark beetles under these circumstances will depend on a better understanding of the key chemical ecology stimuli of relevance to each pest. We review semiochemicals of bark beetles and their use as interruptants or inhibitors when used together with non-host- volatiles. Implications of using semiochemicals when scolytine bark beetles attack trees together with other tree pests is discussed with an example of interactions between a wood wasp and an Ips species presented.