Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/2015
Publication Date: 7/13/2015
Citation: Reddy, A.M., Mehelis, C.N. 2015. 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. Biological Control. 90:67-74.
Interpretive Summary: Cape-ivy (Delairea odorata) is a non-native vine found in western North America where it exists as two morphological varieties. Once established in a new habitat, Cape-ivy is highly invasive and outcompetes native vegetation by smothering it. Cape-ivy is a successful invader partly because there are no insect natural enemies (biological control agents) in North America that can feed on the plant and control its spread. A biological control program to target Cape-ivy was initiated in Albany, by the USDA-ARS, Exotic and Invasive Weeds Research Unit, and the leaf-mining moth (Digitivalva delaireae) has been identified as a potential agent. Thus, two greenhouse experiments were conducted to assess 1) whether the moth prefers one plant variety over the other and 2) moth damage on Cape-ivy using low and high densities of the moth on both varieties. Results showed that the moth did not distinguished between the two plant varieties when selecting leaves to lay eggs. Similarly, feeding damage by moth on Cape-ivy did not differ between plant varieties. Feeding damage by the moth, however, resulted in a significant reduction in plant growth compared to plants that were not exposed to moth feeding. If permission is given to release the moth against Cape-ivy into North America, this study shows that the moth is an effective candidate because of its potential to reduce Cape-ivy growth in the field.
Technical 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.