Abstract: The effect of Ostrinia f urnacalis eggs age on parasitism by Trichogramma ostriniae and their respective development after parasitism were observed in the laboratory. Under 25 ±1 ℃, 15L∶9D andRH 70 % , O. f urnacalis eggs started to hatch from 96 h onwards. The proportion of wasps that successfully parasitized host eggs decreased with increase of age of host eggs , but the decrease was not linear ,and no successful parasitization occurred when eggs were 84 h old. When provided with 0 - 12 h old host eggs , female wasps parasitized the most number of host eggs , and the parasitized hose eggs yielded the most number of offspring wasps and female wasps , which were 14. 9 , 20. 0 and 17. 4 , respectively , and were significantly higher than those when host eggs of older ages were provided. The total number of
progeny eventually produced from parasitization per female within 6 h was significantly influenced by host age. The highest total number of progeny , 25. 6 , was produced when host age was 0 - 12 h and the least number of total progeny , 7. 6 , was produced when host age was 72 - 84 h. The number of parasitoid progeny died inside host eggs were 5. 6 , 6. 7 , and 5. 7 , respectively , when host age was 0 - 12 h , 12 -24 h and 60 - 72 h , and were significantly higher than that when eggs of other age groups were provided as hosts. In some host eggs all parasitoids died inside , and the number of parasitoids that died in this way was significantly higher when host eggs of 0 - 12 h and 60 - 72 h old were provided than when host eggs of other age groups were provided. As the age of host eggs increased from 12 h onwards , the number of host embryos that developed into larvae but failed to hatch increased , and reached 21. 2 when the host age was 72 - 84 h. In all the host age groups from 0 - 84 h , the following three types of outcome occurred : one O. furnacalis larva , one or two parasitoid wasps , neither wasp nor host larva. The total number of hosts that failed to result in either parasitoid wasp or host larva increased with age of host eggs.These results suggest that there were attack-defense interactions between the developing parasitoid and host embryo inside host eggs.