Intraspecific competition in the southern pine sawyer, Monochamus titillator (Fabricius): Effects of oviposition density and phloem thickness

Two species of pine sawyer, Monochamus titillator and M. carolinensis, have overlapping ranges and both appear to utilize pine phloem from the same host trees.  We examine intraspecific competition in M. titillator to establish the role of oviposition niche density and phloem thickness on survivorship and fitness.  We hypothesize that intraspecific competition among larvae of Monochamus spp. for the limited phloem resource is strongly density dependent.  This hypothesis was tested by collecting adult beetles from pine forest in Arkansas using baited panel traps.  The insects were placed in cages containing fresh pine bolts and foliage where they were allowed to mate, construct niches and oviposit.  All bolts had the same surface area, but differed in the average phloem thickness.  Bolts with low and high phloem thickness were paired and each pair was assigned an oviposition density of one, two four, eight, or 16.  From each treatment, we counted the number of adults that emerged.  We measured the size and weight of each adult to determine how each treatment impacts overall fitness of the offspring.  We predict that survivorship is density dependent and decreases with decreasing phloem availability.  Through our research we will better understand how niche density relates to emergence patterns and trap catches observed in the field.