The effect of host plant intraspecific genetic variation on the fitness of a monophagous biological control agent

Variation in insect life-history traits when developing on different host plant genotypes with known genetic relationships was tested using the monophagous biological control agent Phenrica guérini Bechyné (Chrysomelidae) and its host plant, Pereskia aculeata Miller (Cactaceae). Differences in insect fitness among tested host plant genotypes were expected because of geographic isolation and large genetic distances between plant genotypes, and because P. guérini has been associated with some of the plant accessions in the field while others have never been exposed to herbivory by the insect. There was little variation in insect life-history traits among plant genotypes and no differences in the insect's ability to utilise different plant genotypes. The results of the study suggest that, in some cases, biological control agents collected from the native genotype most closely related to the target weed population will not always be more effective than those collected from more distantly related genotypes.