2012 Annual Report
1a.Objectives (from AD-416):
Preliminary assessment of the host specificity of two potential biological control agents, the galling flies, Ophiomyia alternantherae and Ophiomyia buskii.
1b.Approach (from AD-416):
USDA-ARS-SABCL will assist the CSIRO with a preliminary assessment of the host specificity of two potential biological control agents, the galling flies, Ophiomyia alternantherae and Ophiomyia buskii. A SABCL scientist will collect populations of the two flies and maintain colonies on alligator weed (Alternanthera philoxeroides) at the SABCL. The scientist will also collect and maintain healthy plants for host range testing, including 3 species in the Alternanthera genus and 6 species in the Amaranthaceae family (but not in the Alternanthera genus). These species will be nominated based on availability and relatedness to alligator weed, and then approved by the CSIRO technical contact. Using standard procedures, SABCL will then conduct a series of no-choice tests to determine the host range of the two flies. There will be a minimum of 4 replicate tests for each species and the number of galls and subsequent adult flies produced will be recorded for each test. A final report will be submitted to CSIRO with the dates of tests and a comparison of galls and adults produced on all test plants, including a control using alligator weed.
Biological control and ecology of alligator weed: preliminary host range testing of two galling flies. Field trip to search for the alligator weed pathogen. Alligator weed is an amphibian plant native to South America. It has become a serious exotic weed in more than 30 countries, including Australia.
Three exploratory surveys were conducted in northern Argentina to search for plants of alligator weed infected with the rust pathogen and damaged by miner flies. Alligator weed was found in 17 out of 24 sites, the rust was not found, and the fly was found in three sites. A total of 200 stems of alligator weed were transplanted from the field into tubes, covered with plastic bags and transported to the laboratory for cultivation. Stems and leaves with mines were checked for insects and reared in chambers. Biological observations were recorded. From the 200 stems, 150 had galleries of the fly, and 56 pupae were obtained in the laboratory from which 35 adults of the fly (19 males, 16 females) and 6 parasiotid wasps (17.14 %) emerged. Preliminary host specificity tests of the fly revealed a high degree of specificity. Galleries, pupae and adults were only recorded on alligator weed stems. A different fly was found in 5 out of 17 alligator weed sites. Host specificity tests are needed.
For populations with unknown cytogenetical characterizations, pieces of stems were taken to the laboratory and then encouraged to root in a fertilized watery solution or sand-peat mix substrate (70:30). Once roots were ready they were treated following standard cytogenetical procedures to count chromosomes. Preliminary results showed that alligator weed from one site in NW Argentina is a tetraploid (2x= ca. 66), but more studies are needed since samples studied showed diffuse chromosomes. If tetraploidy is confirmed, it would be the first record of this cytotype in such latitudes. Further analyses for the remaining sites are still pending because roots obtained were too tiny and no chromosomes were detected yet.