Stythe joins southern team-mates Kate and Georgia Heffernan and Kimiora Poi in the 14-strong squad.
Shooters Martina Salmon, Filda Vui and defender Catherine Hall will also pull on the black dress for the first time.
Grace Nweke spearheads a young shooting circle and Mila Reulu-Buchanan and Parris Mason return from injury.
A game-day squad of 12 players will be named 24 hours before each test and a game-day captain, and vice-captain, will be selected from that squad.
Interim coach Yvette McCausland-Durie, who has stepped up in place of Noeline Taurua who has been stood down by Netball New Zealand for the series, looked forward to seeing the depth of the squad.
"We’ve selected a group that brings both proven international experience and fresh energy," McCausland-Durie said.
"It’s a great chance for some of our newer players to step up on the international stage, while our established athletes will play a key role in leading the way."
Shooter Amelia Walmsley, who is captaining New Zealand at the Netball Youth World Cup, Saviour Tui, Tayla Earle and Kate Burley have not been selected from the wider squad.
The Silver Ferns meet South Africa in Auckland on Sunday.
They will then play a second test in Napier (September 24) and wrap up the series in Invercargill (September 28).
