Effects of host-egg ages on host selection and suitability of four Chinese Trichogramma species, egg parasitoids of the rice striped stem borer, Chilo suppressalis

The striped stem borer, Chilo suppressalis (Walker), is one of the most economically important rice pests worldwide. However, biological control of this pest using natural-enemy insects has been rarely documented to date. With the objective of screening suitable candidate species for controlling the striped stem borer, we investigated the effect of the age of host eggs on the host selection and suitability by four indigenous Trichogramma species on their native host, C. suppressalis. The results indicated that the differently aged eggs of C. suppressalis were all accepted by T. japonicum, T. dendrolimi and T. chilonis, and there was a clear tendency to parasitize older eggs less under no-choice and choice conditions. The number of parasitized host eggs by T. ostriniae also decreased with the increasing host age in the no-choice test, but more 2-day-old host eggs were parasitized in the choice test. When 0-, 2-day-old eggs were offered, T. dendrolimi, T. japonicum and T. chilonis exhibited similar parasitism ability, whereas T. ostriniae appeared to have a stronger ability to attack the older host eggs (4-day-old). Trichogramma japonicum developed and emerged on parasitized C. suppressalis eggs of all ages tested, while showing a better adaptation to younger host eggs with significantly faster developmental time, higher survival and more female progeny on 0-day-old eggs. No adults for each of the other three Trichogramma species emerged from parasitized 4-day-old host eggs, and they had similar developmental time, survival and female progeny on parasitized 0-, 2-day-old host eggs with an exception of female progeny for T. chilonis. On 0-day-old host eggs, T. japonicum developed faster and T. ostriniae had lower progeny survival than the other three Trichogramma species evaluated, respectively. The current study provides useful information to select suitable Trichogramma species for controlling the striped stem borer, C. suppressalis.