|Mehelis, Christopher - Chris|
|BALCIUNAS, JOSEPH - Retired ARS Employee|
|VAN DER WESTHUIZEN, LIAME - Agricultural Research Council Of South Africa|
|NESER, STEFAN - Agricultural Research Council Of South Africa|
Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2014
Publication Date: 4/15/2015
Citation: Mehelis, C.N., Balciunas, J., Reddy, A.M., Van Der Westhuizen, L., Neser, S., Moran, P.J. 2015. Biology and host range of Digitivalva delaireae (Lepidoptera: Glyphipterigidae), a candidate agent for biological control of Cape-ivy (Delairea odorata) in California and Oregon. Environmental Entomology. 44(2):260-276. doi: 10.1093/ee/nvu030.
Interpretive Summary: Cape-ivy is a non-native, invasive vine along the California and southern Oregon coast, where it grows most robustly in moist soil near creeks and rivers, but is also found in grassland and scrub habitats on coastal cliffs.Cape-ivy smothers native plants, some of which are rare, threatened, or endangered under Federal or state guidelines, and its vines can cover small trees. Cape-ivy is native to the eastern coast of South Africa, where it is attacked by numerous insects that cause damage to leaves and stems. One of the insects found to be widespread and damaging is a leaf-mining and stem-boring moth, Digitivalva delaireae, which was described as a new species in 2002. Past studies showed that the moth can substantially reduce plant size and growth. In the present study, the biological life cycle of the moth was determined to take about 42 days from egg to adult under constant temperature conditions (25 Celsius, about room temperature, 77 F) and 54-60 days under greenhouse conditions varying from 15- 30 C (59-86 F), with about two weeks required for eggs to hatch, one month for larvae to complete feeding, and two weeks for pupae to complete development to adult. Laboratory tests with 100 plant species conducted by the USDA-ARS in Albany, CA, and the South African Agricultural Research Council-Plant Protection Research Institute (ARC-PPRI) in Pretoria, South Africa, found that exposing potted plants to adults of the Cape-ivy moth led to leaf-mining/stem-boring damage by larvae, and production of a new generation of pupae, only on Cape-ivy . The plants were tested in groups of four species per cage, and 98 of the 100 plant species were tested in at least five cages. The plants tested included 37 species from the same 'subtribe' as Cape-ivy, considered its closest relatives, a total of 42 species from the same 'tribe', and 78 species from the same plant family (Asteraceae, the daisy/sunflower family). Seventy of the 100 plant species tested grow in the same coastal habitats in California as Cape-ivy, of which 39 are native to the U.S., and 34 native to California; 26 non-native, beneficial crops and ornamental plants (20 of which grow with or near Cape-ivy in California) were tested, as were 15 non-native weeds (11 of which grow with Cape-ivy in California). We even tested 16 plants native to South Africa that do not occur in the U.S., to verify that the Cape-ivy moth larvae feed only on Cape-ivy, even when its closest plant relatives, that it encounters every day in South Africa, are present. The Cape-ivy moth poses no risk of damage to native plants or beneficial non-native plants in California and Oregon, and is expected to complete multiple generations per year in the field. This moth has been recommended for field release by the USDA-APHIS Technical Advisory Group on Biological Control of Weeds, and a field release permit application is currently under review.
Technical Abstract: Cape-ivy (Delairea odorata Lamaire) is an ornamental vine, native to eastern South Africa, that has escaped into natural areas in coastal California and Oregon, as well as in Hawaii and several other countries, displacing native vegetation. Extensive surveys in South Africa led to the discovery of the leaf- and stem-mining moth Digitivalva delaireae Gaedike and Kruger (Lepidoptera: Glyphipterigidae: Acrolepiinae), a recently-described species, as one of several common and damaging native herbivores on Cape-ivy. In life cycle studies under greenhouse conditions, adult female lifespan averaged 16 days (46 days maximum). Most (72%) mated females began laying eggs within 72 h of emergence. Females had an average lifetime fecundity of 52 eggs, with over 70% laid on leaf laminae, and 89% of eggs were laid by the 15th day post-emergence. Lifetime fertility (adult production) averaged three to four offspring per female. At 25 °C, egg hatch required 10 days, pupal formation 26 days, and adult emergence 41 days, while under variable greenhouse and laboratory conditions development to adult required 54–60 days. In laboratory host range choice tests, among 100 plant species other than Cape-ivy, including 11 genera and 38 species in the Family Asteraceae, subtribe Senecioninae from both the native and invaded ranges, D. delaireae inflicted damage and produced pupae only on Cape-ivy. The moth D. delaireae is expected to be monophagous and multivoltine on Cape-ivy in North America, posing no risk of causing feeding damage to native plants or beneficial non-native plants.