Black-margined Loosestrife Beetle

Appearance

The black-margined loosestrife beetle is cylindrical in shape, mid brown, three to six millimetres long and half that width. When seen from above it often has two blackish lateral lines down either side. The eggs are spherical, white and usually topped with frass. The larvae are yellow speckled with black and resemble small caterpillars.

Behavior

Adults overwinter in leaf litter near purple loosestrife plants. They emerge in the spring and start to feed on the young growth. They cause damage to the leaves characterised by neat rounded shot holes between the veins. The females lay up to 500 eggs from May to July in small batches on leaves and stems. On hatching, the first instar larvae feed on growing shoot tips and may kill them. Later instars feed on stems and leaves leaving the upper cuticle of the leaf intact. When the density of the larvae is high enough, the plant can be completely defoliated. After feeding for about three weeks and undergoing further moults, the larvae move down the plant to pupate in the soil or leaf litter. If the water level is high, larvae sometimes pupate in the hollow aerenchyma tissue in the plant stems. Both adults and larvae can float and may be wafted by water currents or wind to new host plants.