[4] The black-margined loosestrife beetle is cylindrical in shape, mid brown, three to six millimetres long and half that width.

After feeding for about three weeks and undergoing further moults, the larvae move down the plant to pupate in the soil or leaf litter.

[5] Larval damage to buds and shoots reduces the growth of the purple loosestrife plant and its ability to flower and produce seed.

Damage to the leaves reduces their photosynthetic capability and means there is less starch stored in the roots which may cause plant death in adverse winter conditions.

It is now found in large stands throughout the northeastern United States, southeastern Canada and the American Midwest where it crowds out other species and is a threat to biodiversity.

They show great ability to find new stands of the host plant and can locate patches of purple loosestrife a kilometre away within a few days of emergence.