Leafroller tachinid

Description:

A small black and white banded fly about 10mm long; wings clear and longer than body. Strong erect discal setae on abdomen.

Habitat:

On lakeside rushes in nature reserve.

Notes:

Reference link contains the only visual confirmation I could find that the abdominal banding doesn't always continue underneath. Interestingly it was introduced to NZ deliberately in the 1960's. This is parasitising fly laying a single egg onto a larva.