The Collaborative International Dictionary of English v.0.48:

Thelytokous \The*lyt"o*kous\ (th[-e]*l[i^]t"[-o]*k[u^]s), a.
   [Gr. qh^lys female + to`kos a bringing forth.] (Zool.)
   Producing females only; -- said of certain female insects.
   [1913 Webster]