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Intraspecific Competition among Bark Beetle Larvae (Coleoptera: Scolytidae)

R. A. Beaver
Journal of Animal Ecology
Vol. 43, No. 2 (Jun., 1974), pp. 455-467
DOI: 10.2307/3376
Stable URL: http://www.jstor.org/stable/3376
Page Count: 13
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Intraspecific Competition among Bark Beetle Larvae (Coleoptera: Scolytidae)
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Abstract

(1) The factors affecting the occurrence and intensity of competition for food among bark beetle larvae are discussed. The major effects of intraspecific competition among larvae of Scolytus scolytus, S. multistriatus and Tomicus piniperda are an increase in mortality and a decrease in mean adult weight. The relative importance of these effects differs in the three species. (2) At medium population densities (160-600 eggs hatching per 1000 cm2), the level of mortality is similar in the three species. Mortality is probably density-dependent in Scolytus scolytus and Tomicus piniperda, but apparently not in Scolytus multistriatus. It compensates for variations in initial density to a greater extent in Tomicus piniperda than Scolytus spp. At low population densities, mortality is probably due to intra-gallery competition: at higher densities, inter-gallery competition is more important. (3) The mean weight of all individuals emerging from a log is approximately constant at low population densities in S. scolytus, but decreases at higher densities. In S. multistriatus and Tomicus piniperda, the mean weight appears to decrease with increasing population density from the lowest densities observed. The variation in body weight is greater in Scolytus scolytus than the other species. (4) The emergence pattern of adults from a single log, based on either numbers or dry weights, usually shows a peak about a week after emergences start and a long `tail' extending over 5-7 weeks. The causes of this pattern are discussed. (5) The total biomass of adults emerging from a log increases at a lower rate than population density over the range of densities studied. At medium population densities, S. scolytus appears to be the most efficient converter of phloem into beetle tissue, followed by Tomicus piniperda. (6) In T. piniperda, the effects of poorer quality food are shown to be an increased level of mortality and a decreased mean individual weight. The rates of change of mortality and weight with population density do not change significantly with food quality. (7) Early-emerging adults have an advantage in access to fresh breeding material. Their offspring are subject to lower intensities of competition and are at a competitive advantage relative to later-hatching larvae. However, too short a development period produces smaller adults which probably have a lower fecundity. (8) The results are similar to those obtained with other insects whose larvae live in their food and compete mainly by exploitation of their food.

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