Environment

Alligator Weed Beetle. Biocontrol agent:
Alligator weed beetle

Scientific name:
Agasicles hygrophila

Target weed:
Alligator weed
Alternanthera philoxeroides

What do alligator weed beetles look like?

Adults are between 5.5mm and 7mm long with yellow and black stripes. Females are larger than males.

How would I find them?

You probably won’t see them in the winter as they hide low in plants and soil. Summer and autumn, however, they are out feeding on non-submerged parts of the alligator weed plants and their eggs may be seen in batches on the underside of the leaves. Large populations can completely destroy the plants down to water level.

What about their life-cycle?

The eggs are oval-shaped and start off white, turning pale yellowish-orange before hatching into black larvae. Egg laying begins in spring and hatching usually occurs within a week. Larvae hatch, feed and pupate within the plant stems.

Where are they established?

The beetles are widespread on weed in most lakes and waterways in the Dargaville area, the lake exit stream at Lake Omapere, the Kawakawa River at the three bridges, Mangamuka River at Mangamuka Bridge and the bridge over the Awanui River on Gill Rd, Awanui.

When and how can they be harvested for redistribution?

Collect at least 100 adults from alligator weed over water with a butterfly net in the warm summer months of January to March. Transfer them to new sites in ventilated containers with some of the host weed and damp tissue paper. Release them on to plants in relatively still water. Avoid using other control agents in areas where beetles are performing well.