I'm guessing this is Trichogramma semblidis
. More photos and info here
Comment from John D. Pinto: "It is not possible to give a definite ID to this wasp. T. semblidis
- as suggested - may be correct since that species has been previously taken from Sialis
eggs. However, we have minimal knowledge of host range for many species of Trichogramma
- and there are others besides semblidis
occurring in aquatic habitats. One requires slide-mounted males to be sure of species."