Infestation of Solanum carolinese Fruit by Frumenta nundinella: Are Larvae Affected by Interfruit Competition?

Abstract

I examined the interaction between Solanum carolinense L. and its hostspecific herbivore, Frumenta nundinella Zeller, for evidence of competition. Intraspecific competition could have occurred among fruit-infesting larvae or among seedcontaining fruits, and interkingdom competition could have occurred between the insect (infested fruits) and the plant (seed-containing fruits). The relationships among position (basal to distal) along the infructescence, fruit mass, infested fruit mass, pupa mass and pupa sex were determined by correlation. Mass of seed-containing fruits decreased significantly with position along the inflorescence in glasshouse and field plants, suggesting that fruits competed for resources. Mass of infested fruits also decreased significantly with position, but the relationship was not as strong. Pupa mass did not vary systematically with position, suggesting that distal pupae were not at a competitive disadvantage compared to basal pupae or fruits. Distal pupae gained their mass from smaller fruits than did basal pupae, so apparent pupa efficiency (pupa mass/fruit mass) increased significantly with position and decreased significantly with fruit mass. Overall, pupa mass and fruit mass were significantly and positively related. One hypothesis that may explain these results proposes that larvae are sinks that stimulate the plant to retain and provide for infested fruits, partly overcoming the usual resource gradient along the infructescence.