Variation in Herbivore Infestation: Historical vs. Genetic Factors

Variation in insect infestation levels among plants is a result of both genetic variation in susceptibility and variation in previous insect attack. A plant's history of insect attack can either increase or decrease susceptibility and can also influence the number of potential colonizers. Experiments were conducted to determine whether infestation levels of Eurosta solidaginis, the goldenrod ball gallmaker, on Solidago altissima were a result of genetic variation among plant clones (i.e., resistance) or previous attack levels. Results indicated that current infestation levels are primarily due to genetic variation in the plant's resistance. Plant clones were found to differ in the percentage of ramets in which oviposition was attempted by Eurosta, the percentage of ramets galled, and in the percentage of ramets with Eurosta oviposition punctures that were galled. Field resistance or susceptibility was maintained in plant clones grown in a common garden.