Interactions among intraspecific competition, emergence patterns, and host selection behaviour in Ips pini (Coleoptera: Scolytinae)

1. Variations in developmental conditions of bark beetles, particularly intraspecific competition, can induce morphological and physiological modifications in the offspring. It is hypothesised that intraspecific competition could also affect host selection behaviour. Such behavioural changes might be manifested in response to host (alpha-pinene) or beetle (verbenone) compounds. 2. Ips pini were bred at different densities. The offspring were measured for size, weight, and lipid concentration, and then subjected to tunnelling bioassays in agar media amended with varying amounts of alpha-pinene or verbenone. 3. High parental colonisation densities reduced emergence time of parents and offspring. Increasing colonisation density and emergence time had a negative influence on offspring vigour, resulting in a reduction of the distance tunnelled by the beetles. 4. Both alpha-pinene and verbenone were repellent. Surprisingly, verbenone was also toxic at high concentrations, with its effect being greater on beetles arising from high densities. The repellent effect of these compounds did not vary according to colonisation density, but for both compounds, at a 1.5 mg g(-1) concentration, it increased with emergence time. 5. The consequences of varying vigour and behaviour in relation to developmental conditions and emergence patterns on population dynamics of I. pini are discussed.