Abstract: Tetrastichus hagenowii （Ratzeburg） adults are minute endoparasitoids that attack only insect eggs, mainly those of Blattaria. Laboratory studies were conducted to determine the reproductive biology of the parasitoid for its potential as a biological control agent of cockroaches. The results showed that T. hagenowii employed parthenogenesis and sexual reproduction. The sexual reproduction produced 46.02% female progeny, but the parthenogenesis produced only male progeny. The female T. hagenowii has a pair of ovaries, each consisting of 8 to 12 of ovarioles. One ovariole has 1 to 6 eggs. The number of eggs in the ovaries for 1-d-old female was 45.2, while for 2-d-old female 80.1. The oviposition period ranged from 4 to 11 d. The average fecundity per female per day was 0.86-7.57 within 11 d after emergence. A female wasp parasitized one ootheca on average during her lifetime. The parasitism was affected by the ratio of wasps to host oothecae. The parasitism increased with increasing of the ratio of wasps to host oothecae within 1∶5-3∶1, but the number of parasitized oothecae per female declined.

Key words: Tetrastichus hagenowii, reproductive biology, number of eggs in an ovary, oviposition, biological control