Two species of Trichogramma wasps were assessed for their effectiveness against yellow stem borer Scirpophaga incertulas. A laboratory cage test with T. japonicum and T. chilonis showed that both species parasitized yellow stem borer egg masses at 60.0% ± 9.13% and 40.7% ± 7.11%, respectively, with egg parasitism rates of 15.8% ± 22.2% for T. japonicum and 2.8% ± 5.0% for T. chilonis. Once the host eggs were parasitized, emergence rates were high for both species (95.7% ± 0.12% for T. japonicum and 100% for T. chilonis). In paddy field trials, the two Trichogramma species were released at three densities (50,000/ha, 100,000/ha and 200,000/ha) in Southwestern China. Egg mass parasitism was 9% ± 7.7% for T. japonicum and 15% ± 14.1% for T. chilonis, and again only a relatively small fraction of eggs was successfully parasitized. No clear conclusion could be drawn on the most efficient release rate as no significant differences were found among the three release rates. A comparison of field-collected T. japonicum with T. japonicum and T. chilonis mass reared on Corcyra cephalonica showed significantly larger body size and ovipositor length in field-collected wasps, suggesting potentially higher effectiveness on yellow stem borer eggs after at least one generation on the target host. Factors contributing to the low field parasitism rates are discussed.

Trichogramma wasps were collected from the parasitized eggs of lepidopteran pests from 21 sampling sites in East Asia and South-East Asia. Six Trichogramma species were identified based on the molecular identificationmethod using the internal transcribed spacer 2 (ITS2) region of the rDNAof Trichogramma chilonis, T. evanescens, T. ostriniae, T. embryophagum, T. dendrolimi and T. japonicum. The results of molecular identification were confirmed by morphological identification. Additionally, natural populations were screened for the prevalence of Wolbachia. Five out of 21 populations were infected by the same Wolbachia strain, which was identified by using Wolbachia wsp gene and multilocus sequencing approach. The phylogenetic analysis of Wolbachia wsp sequences revealed that the Wolbachia strain was classified in the strain wEvaA in the group of EvA of the supergroup A.