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Some aspects of the population dynamics of the mountain pine beetle, Dendroctonus ponderosae in lodgepole pine forests of British Columbia Peterman, Randall Martin


Outbreaks of mountain pine beetle (Dendrcctonus ronderosae Hopk.) are common in lodgepole pine forests cf western North America. Characteristics of both the tark beetle and its host tree were compared using field replicates cf epidemic and endemic areas to test for any possible intrinsic differences between populations cf trees cr insects in these two different states. laboratory studies were conducted on beetle dispersal characteristics and cn effects of attack density and female parent size on beetle reproductive success and offspring size. Results are as follows: Trees in outbreak areas are older than in endemic regions, and trees of a given size and beetle attack density are more likely to be overcome and to permit successful beetle reproduction in epidemic than in endemic areas. However, tree spatial distributions, average attack densities and proportions of trees unsuccessfully attacked by beetles dc net differ consistently between epidemic and endemic areas. A method (in which blue-staining fungi were inoculated into trees) of measuring potential of trees tc resist mountain pine beetle was tested and found to be inadequate. Epidemic and endemic bark beetles did not differ consistently in dispersal, size, cr reproductive characteristics. However, early emerging beetles were larger than late emergers and females had a larger coefficient of variation in size than males. Field and laboratory data shew that the number of offspring emerging per parent decreases with increasing attack density. Breeding experiments further indicated that, 1) small female parents produce fewer and smaller offspring than large females, 2) small female parents produce female offspring with more strongly bimcdal size distributions than large females, and 3) high parental attack densities result in smaller offspring. Dispersal studies on the insect using chemical extracts of lodgepole pine bark showed that early emerging beetles are more likely to respond positively to tree chemicals than late emergers with the same flight history. Increasing lengths of flight increase female but not male responses to these chemicals. Evidence from a simulation model is presented tc support the hypothesis that the age at which lodgepcle pine normally becomes susceptible to mountain pine beetle attack is clcse to the age at which certain tree fitness measures are maximized.

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