Plants vs. Caterpillars- Is Trypsin Inhibitor a Plant Defense Against the Larvae of the Forest Tent Caterpillar (Malacosoma disstria)?

Forest tent caterpillars (Malacosoma disstria) are ubiquitous defo­liating insects in North America. In Canada trembling aspen is their favourite host tree which can produce an inducible protein trypsin inhibitor (TI) to inhibit trypsin a major proteolytic enzyme in cater­pillars' midguts.To determine the digestion-inhibiting effect of TI on M. disstria this study focused on the performance of second instar larvae with different levels of TI on both balanced and low protein diets. Both protein deficiency and higher levels of TI impaired the growth of caterpillars but the impairing effect of TI only appeared on the caterpillars fed on balanced diet. This study confirmed the digestion-inhibiting function of TI as a defense of aspen against forest tent caterpillars. Also it suggested that caterpillars were able to regulate their growth under severe protein deficiency possibly as an adap­tation to this defense.