Risk assessment: progress of quarantine biocontrol research on Chinese Tallow, Melaleuca, and Downy Rose Myrtle

Authors: Wright, Susan; Wheeler, Gregory; PURCELL, MATTHEW - Commonwealth Scientific And Industrial Research Organisation (CSIRO); Pratt, Paul; Center, Ted

Submitted to: Florida Exotic Pest Plant Council
Publication Type: Other
Publication Acceptance Date: 12/21/2009
Publication Date: N/A
Citation: N/A

Interpretive Summary: During 2009 and continuing into 2010, risk assessments, or tests to demonstrate whether nonnative plant feeding insects would be safe to release in the continental USA to control nonnative invasive plants, were conducted by USDA scientists located at a state operated quarantine facility in Gainesville, Florida. Three invasive plants are being targeted, Chinese tallow, Downy rose myrtle, and Melaleuca. Chinese tallow. The first two candidates for biocontrol of Chinese tallow, an invasive tree species in the southern USA were studied. Tests showed one of these beetles was not safe to release as it had a broad feeding range, and although it only reproduced on tallow, it laid eggs on a Florida endangered species. The other beetle species, a flea beetle, is still under assessment. Its juvenile stage or larvae, in large numbers, appear to significantly damage and even kill small tallow plants. Melaleuca. A species of beetle from Queensland, Australia is undergoing assessment as the seventh candidate for biocontrol of melaleuca, an invasive tree species in south Florida, USA, and where its control is especially problematic in natural areas such as the Everglades. This beetle or weevil damages the tips of young shoots of melaleuca altering growth and reproduction. More than fifty percent of the tests on this weevil are completed. Numbers of adults available fluctuates throughout the year slowing the assessment process. In late April or May 2010, colonization and assessment of an eighth species, a fly or cecid that galls and damages melaleuca leaves and plant vigor, will begin. High numbers of cecids can be reared year round and tests are expected to progress at a steady rate. Downy rose myrtle. In late April 2010, colonization and assessment of a moth species from Bangkok, Thailand will begin. This moth species, the first to be assessed, targets the plant species, Downy rose myrtle, an invasive shrub species in south Florida. The red and white striped larvae tunnel in flower buds and fruit altering reproduction of this plant.

Technical Abstract: Risk assessments of two biocontrol candidates for Chinese tallow, Triadica sebifera (Euphoriales: Euphorbiaceae), and one for Melaleuca, Melaleuca quinquenervia (Myrtales: Myrtaceae), were conducted during 2009 and continuing into 2010 by USDA scientists located at the Florida Department of Agriculture and Consumer Services, Division of Plant Industry quarantine facility in Gainesville, FL, USA. Preparations for the receipt of the first candidate for Downy Rose Myrtle (Myrtales: Myrtaceae), in late April 2010 have been made as well. The risk assessment of the first Chinese tallow candidate, Heterapoderopsis bicallosicollis (Coleoptera: Attelabidae), a primitive beetle was completed in February 2010. Adults feed on tallow leaves, skeletonizing them. Females oviposit one to four eggs in undamaged leaves, and roll them into nidi, burrito like structures that hang from the petiole. While this species completed development only on tallow, it fed on and made nidi on a Florida endangered euphorb species, Heterosavia bahamensis, Bahama maidenbush. It also fed on several species outside the euphorb family. These data indicate this species is not safe to release as a biocontrol agent and no further tests will be conducted. No-choice tests of the second candidate for Chinese tallow have recently begun. Adults of Bikasha collaris (Coleoptera: Chrysomelidae), a flea beetle, feed on the leaves of tallow, also skeletonizing them, but more delicately than H. bicallosicollis. Females oviposit eggs on the soil surface, larvae migrate downward through the soil and feed on young roots. Large numbers of larvae appear to dramatically affect plant condition, causing leaf droop, color change, and drop. Small plants are killed. Plant stability in the soil, ability to absorb water and minerals, and capacity to store carbohydrates is reduced. The risk assessment of the seventh melaleuca candidate, Haplonyx multicolor (Coleoptera: Curculionidae) is more than half completed. Fluctuations in numbers reared, possibly due to seasonal changes in melaleuca plants, have slowed testing. Adult weevils feed on new growth of melaleuca causing minor damage. Females oviposit eggs downward through feeding holes in buds, one egg/bud, then cover the distal portion of the eggs with tightly packed melaleuca hairs, forming protective covers over the eggs. Hair plugs can be seen through the feeding holes and usually indicate the presence of an eggs. After oviposition, females partially sever stems 1-2 cm beneath the oviposition sites killing the plant tissue above. Larvae feed and complete development on the dead plant bud. Thus far, the laboratory host range of this insect is limited to Melaleuca spp. with low numbers developing on congeneric species other than M. quinquenervia. It is likely tests will be completed this year and a determination will be made of whether this weevil will enhance biocontrol efforts. While the assessment of H. multicolor is being completed, importation, colonization, and assessment of an eighth candidate, a cecid, Lophodiplosis indentata, will begin in late April or May 2010. Larvae of this species severely damage melaleuca plants by causing pea-like galls on young leaves. This insect requires little rearing effort. Tests protocols similar to those for L. trifida, assessed previously, will be followed. These factors should move its assessment forward at a steady rate. Preparations for a new quarantine project on Downy Rose Myrtle, Rhodomyrtus tomentosa (Myrtales: Myrtaceae), were initiated in 2009. This species is native to Asia but is problematic in Florida, displacing native vegetation. Shrubs grow to 6 feet though plants can be up to 12 feet tall. After being introduced as an ornamental it has spread into native areas, particularly in the understory of pine forests and sloughs. Infestations occur in cent