A dome-shaped relationship between host plant allelochemical concentration and insect size

A dome-shaped relationship was found between the concentration of resin acids in larval food and the weight of female pine sawfly (Neodiprion sertifer) cocoons. Sawflies feeding on pine needles with low to intermediate resin acid concentrations attained a higher weight than sawflies feeding on needles with resin acid levels in the lower or upper part of the concentration range; cocoon weight reached its maximum at approximately 0.4% d.w. Cocoons were obtained by rearing larvae enclosed in sleeve cages in the field on two species of pine, Pinus contorta and P. sylvestris (n=15 trees with two cages per tree per pine species). The discussion addresses the question of whether the relationship is continuous and dome-shaped or consists of one positive and one negative relationship at low and high concentrations, respectively. (C) 1997 Published by Elsevier Science Ltd.