Oxyops vitiosa Pascoe
Oxyops vitiosa and its host, Melaleuca quinquenervia, which is an invasive weedy tree, are native to Australia. The tree, known as melaleuca or the paperbark tree, was imported in 1906 and later planted extensively to drain the Everglades. Melaleuca is now considered to be destroying the Everglades, spreading to 50 additional acres of wetlands every day.
Adult melaleuca weevils are small, 6-9 mm long, and gray to brown. Eggs are covered with a secretion that dries chocolate to black in color and gives them a teardrop shape. Without this secretion, eggs are yellow, 1 mm long, and resemble a gelatin capsule. However, they are rarely found uncovered. Larvae range in size from less than 1 mm when newly emerged to 14 mm in the fourth instar. Newly hatched larvae are yellow but appear brown to black once feeding begins. They are usually covered with a sticky secretion or exudate, and, especially on older larvae, a long, thin coil of feces is prominent. The pupal stage takes place underground in pupal capsules formed from the soil.
Adults are inconspicuous on the leaves and stems of young seedlings and the young growth of saplings and older trees, and their presence can be determined most easily by scouting for adult feeding damage. This appears as holes 1-2 mm in diameter to elongate holes, 2-3 mm wide x 5-20 mm long. Occasionally, when feeding is superficial on leaves, trenches rather than holes are evident. On stems, feeding damage consists of trenches, short or long, and usually along one side. Sometimes when stem feeding occurs on very young growth, the stem is nearly excised causing the upper portion to fall over and hang down. Adults may feed superficially on buds, leaving holes in the outer portion, or may feed deeply, leaving pits.
When eggs are present, they are likely to be near or next to the feeding damage. Eggs usually will be layed singly or in small groups on the tips of young leaves and are sometimes also found on the upper and lower surfaces of leaves, leaf buds, and on tender stems.
Larval feeding damage differs from that of adults. Larvae eat through all layers of the leaf except the cuticle on the opposite side and produce paper-thin trenches in the leaves about the width of their bodies. This larval damage provides the most characteristic evidence of melaleuca weevil infestation.
Stands of Melaleuca quinquenervia, the paperbark tree, which is well established in central and south Florida.
Melaleuca quinquenervia, the paperbark tree which is in the family Myrtaceae. Testing in quarantine by G. Buckingham of over 100 plant species with adult O. vitiosa and of 30 species (including all native Florida Myrtaceae) with larvae and/or ovipositing females demonstrated that the weevil will establish populations only on melaleuca. Wandering adults and larvae might occasionally feed on young leaves of the native wax myrtle, Myrica cerifera and of some Myrtaceae (mostly imported bottlebrushes and eucalyptus), but feeding is transitory.
J. K. Balciunas conducted extensive field surveys in Australia prior to the Florida testing in quarantine. No more than 7 individuals, including all stages, were found in the field on non-host species (bottlebrush, eucalyptus, and other melaleucas) compared with more than 1000 on melaleuca. In Balciunas' laboratory tests, adults were produced only on melaleuca.
The family Myrtaceae includes 8 species native to Florida in the genera Eugenia, Psidium, Myrcianthes, and Calyptranthes. Many imported species are cultivated in Florida for the fruit (Eugenia, Myciaria, Psidium, and Syzygium) and for landscaping (Eucalyptus and the bottlebrushes, Callistemon).
Adults feed, mate, and lay eggs on the leaves and stems of young seedlings and the new growth of older plants. Newly hatched larvae begin feeding just outside the eggs. As they grow they disperse downward on plants, feeding as they go. Larval development takes about 28 days. When fourth instar larvae have finished feeding, they wander or drop to the ground where they locate a suitable site to go underground to pupate. They use the surrounding soil to form their pupal capsules, preferring drier areas with a high relative humidity. They are in capsules 11 days to 42 days, but this stage averages about 28 weeks at 77°F (25°C). Total time from egg to adult is about 48 days. A female lays about 470 eggs in her lifetime.
The melaleuca weevil is being evaluated as a biocontrol agent of melaleuca in Florida following a widely publicized release ceremony at Ft. Lauderdale, on April 26, 1997. It is not expected that the release of one species will control the paperbark tree but will more likely slow its spread.
Both adult and larval feeding interfere with normal plant processes. This feeding will slow plant growth and make plants more susceptible to other control measures. Seed production may be reduced as well. As many as 200 larvae, which consume ten times more than adults, have been found on one melaleuca tree in Australia - a good omen for Florida.
None. Dr. Ted Center maintains a research colony at the ARS/USDA Aquatic Plant Research Unit, Ft. Lauderdale, FL.
Thanks to Susan Wineriter and Gary Buckingham for supplying information and photographs for this page and for proofreading and offering suggestions, and to Philip Busey, also, for supplying information and a photograph.
Wineriter, Susan, and Buckingham, Gary. 1997. Love at first bite - Introducing the Australian melaleuca weevil. Aquatics 19:10-12.
Baker, Donald P. 1997 "USDA's latest weapon has a nose for noxious weeds," Washington Post, April 26, 1997.
Balciunas, J.K., D.W. Burrows, and M.F. Purcell. 1994. Field and laboratory host ranges of the Australian weevil, Oxyops vitiosa (Coleoptera: Curculionidae) a potential biological control agent for the paperbark tree, Melaleuca quinquenervia. Biol. Control. 4:351-360.
Purcell, M.F. and J.K. Balciunas. 1994. Life-history and distribution of the Australian weevil Oxyops vitiosa (Coleoptera: Curculionidae), a potential biological control agent for Melaleuca quinquenervia (Myrtaceae). Ann. Entomol. Soc. Am. 87:867-873.