Session 1 Pre-Release Testing of Weed Biological Control Agents 65 Preference and Damage by the Stem-Boring Moth, Digitivalva delaireae – a Potential Biological Control Agent of Cape-Ivy, Delairea odorata, on its Two Varieties in California, USA A. M. Reddy and C. N. Mehelis USDA-ARS-WRRC, Exotic and Invasive Weeds Research Unit, 800 Buchanan St., Albany CA, USA [email protected] Abstract Cape-ivy, Delairea odorata Lem. (Asterales: Asteraceae), is a perennial vine native to South Africa, and was introduced in the eastern United States (U.S.) in the 1850s as an ornamental. The plant is now well established in natural areas and has become a serious pest in coastal regions of California and upland Hawaii, as it is an aggressive climbing vine that can form solid covers which can block light and smother native vegetation. The U.S. Dept. of Agriculture, Area Research Service (USDA-ARS) has initiated a biological control project targeting Cape-ivy, and host-range testing of a potential agent - the stem- boring moth Digitivalva delaireae Gaedike & Krüger (Lepidoptera: Acrolepiidae), is nearly complete. In both South Africa and California, two morphological varieties (stipulate and astipulate) of Cape-ivy exist. The stipulate variety is most common in both South Africa and California, therefore host-range tests of Cape-ivy were conducted on plants of this variety. We are currently studying preference, as well as the effect of infestation by D. delaireae on the development of both Cape-ivy varieties found in California, and whether preference and damage inflicted on Cape-ivy by D. delaireae differs between varieties. Results of choice preference tests showed that D. delaireae infested 4% more leaves on the astipulate variety, though this difference is minimal, it is significant (P = 0.01). Tests assessing the effect of damage by D. delaireae on Cape-ivy development, on both varieties are on-going. XIII International Symposium on Biological Control of Weeds - 2011.