(1) Cerambycidae is one of the main saproxylic (dependent on dead wood) insect families. Two species, common in Sweden, Acanthocinus aedilis and Rhagium inquisitor, that colonize newly dead trees were studied in this experiment.
(2) In a two-way factorial experiment, pairs of beetles were released on caged bolts. Either two pairs of A. aedilis and two pairs of R. inquisitor, or four pairs of only one of the species were released on two occasions, with a 2-week delay between releases. The pairs released on the first occasion therefore had a 2-week priority over the pairs released on the second occasion.
(3) The hypothesis was that this 2-week priority would lead to a priority effect, manifested in offspring number and/or offspring quality.
(4) A priority effect was found in A. aedilis in offspring number and in R. inquisitor in offspring quality. Interspecific competition was asymmetrical with A. aedilis being the superior competitor. Exploitative resource competition rather than intra-guild predation was the most likely explanation.