Pre-release efficacy assessment of the leaf-mining moth Digitivalva delaireae (Lepidoptera: Glyphipterigidae), a potential biological control agent for Cape-ivy, Delairea odorata (Asteraceae), in western North America

Abstract

The leaf-mining moth Digitivalva delaireae Gaedike & Kruger (Lepidoptera: Glyphipterigidae) is a potential biological control agent for the invasive vine Cape-ivy, Delairea odorata Lemaire (Asteraceae), in western North America, where two morphological varieties (stipulate and exstipulate) of Cape-ivy occur. Two laboratory experiments were conducted to assess (1) the oviposition preference of D. delaireae for either of the two varieties and (2) its impact on plant performance using low and high densities of the moth on both varieties. There was no difference between the two varieties in the proportion of leaves oviposited on or damaged by D. delaireae. Similarly, the effect of D. delaireae herbivory on plant performance was not influenced by Cape-ivy variety. Independent of moth density treatment (low or high), herbivory by D. delaireae resulted in an overall reduction in plant growth and biomass accumulation, and Cape-ivy was unable to compensate for D. delaireae damage: mean relative growth rate, main stem length increment, dry shoot biomass, and leaf mass fraction were reduced 22%, 27%, 22%, and 17% in plants exposed to D. delaireae herbivory compared to unexposed plants. These results indicate that once released, D. delaireae has the potential to negatively affect stem growth, biomass accumulation and rate of stand expansion of Cape-ivy in the field.