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Grass Carp
Agasicles hygrophila- Alligatorweed flea beetle
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Last Updated: June 2005

Order: Coleoptera

Family: Chrysomelidae

The alligatorweed flea beetle is native to Argentina. It was the first biological control agent introduced into the United States as a result of the cooperative agreement between the US Army Corps of Engineers and the U.S. Department of Agriculture. The insect was first released in 1964 in California, and subsequently, in Alabama, Florida, Georgia, Louisiana, Mississippi, South Carolina, and Texas. It is very successful in controlling alligatorweed infestations.

Plant Host(s):

Alternanthera philoxeroides

Adult alligatorweed flea beetles are 5 to 7 mm long and about 2 mm wide. Adult flea beetles, like many terrestrial beetle species, have a waxy cuticle, imparting a shiny appearance to the animal. The head and thorax of the flea beetle are black, and the abdomen is covered by yellow and black stripes on the elytra (wing covers).Adult female flea beetles deposit an eggmass (12 - 54 eggs/mass) on the underside of the leaves of alligatorweed. The eggs are typically arranged in two parallel rows; -- each pair of eggs forming a "V," creating a "zigzag" pattern for the overall eggmass. Individual eggs are fairly large (1.25 mm x 0.38 mm) and are uniformly light cream at deposition, becoming pale orange-yellow. Eggs typically hatch within 4 days at temperatures between 20 and 30 C.Newly hatched larvae are somewhat nondescript. Pigmentation of the body is incomplete; head, legs, and body are pale gray. Within a few hours after hatching, the legs turn brown. Later instar larvae are typically pale gray with a brown head and brown legs. The third (final) instar larvae are very dark (almost black).Mature larvae burrow into the hollow stem of the aquatic form of alligatorweed to pupate. Adults emerge from holes within the stem.

Collection Techniques:
Adults can be collected by hand or swept from the plant material using a sweep net.

Feeding Damage:
Alligatorweed flea beetles may attack any exposed (above the waterline) portion of the plant. Both larvae and adult beetles feed primarily on the leaves. Younger larvae produce small, circular feeding scars on the undersides of leaves, while older larvae produce larger irregular feeding scars or pits. Larvae at all stages may also feed on the plant stem, producing small holes or pits. Adult beetles generally feed on the lower leaves of the plant.

Video of Agasicles feeding on an alligatorweed stem.

Video of Agasicles feeding on an alligatorweed leaf.

Plant Effects:
Alligatorweed flea beetles kill the plant by destroying the plant's stored food and interfering with the plant's ability to produce new food. Large populations of alligatorweed flea beetles can decimate alligatorweed, reducing the plant to bare stems in a short time.At a distance, an alligatorweed mat being attacked by large numbers of alligatorweed flea beetles appears yellow progressing to brown until finally the plants collapse. This insect is highly effective in reducing populations of alligatorweed, especially when present with the alligatorweed stem borer. Effect time can be as short as 3 months after its introduction.

Operational Status:
Alligatorweed flea beetles have proven to be very effective agents for the management of alligatorweed. Since their first release in the U.S. in the early 1960s only minimal use of herbicides has been required for the management of alligatorweed. In areas where the flea beetles are introduced, almost complete control is achieved in only a few months. It is unusual to find alligatorweed in the U.S. with no sign of the flea beetles. Population levels of the flea beetles are typically maintained at high enough levels to maintain complete control for many years after the original introductions. The only exception is in the more northern U.S. distribution of alligatorweed where the flea beetles cannot overwinter successfully. In these cases, frequent releases every growing season are needed to maintain population levels that are sufficient for control.

Contact Personel:
Angie Huebner
U.S. Army Engineer District, Jacksonville
701 San Marco Boulevard
Jacksonville, FL 32207
Phone: (904) 232-1067

Dr. Alfred Cofrancesco
U.S. Army Engineer Research and Development Center - CEERD-EM-W
3909 Halls Ferry Road
Vicksburg, MS 39180
Phone: (601) 634-3182

Dr. Michael Grodowitz
U.S. Army Engineer Research and Development Center -CEERD-EE-A
3909 Halls Ferry Road
Vicksburg, MS 39180
Phone: (601) 634-2972

Dr. Ted Center
USDA, ARS Invasive Plant Research Laboratory
3205 College Ave.
Ft. Lauderdale, FL 33314
Phone: (954) 475-0541 Ext. 103