Effects of host-egg age on the parasitism by Trichogramma chilonis Ishii (Hymenoptera : Trichogrammatidae), an egg parasitoid of the diamondback moth

Eggs of Plutella xylostella (DBM), 0, 1, 2, 2.5 and 3 days old, were offered to female Trichogramma chilonis in a laboratory experiment. Females oviposited on host eggs of all ages tested. However, the percentage of oviposition was highest on the l-day-old host eggs, and decreased as the host egg became younger or older than the 1-day-old host. Parasitized host eggs did not hatch. The emergence rate was high on the 1-day-old eggs but did not differ among other host ages, except the 3-day-old host. A T. chilonis progeny failed to complete development on the 3-day-old DBM eggs. Hind tibia length of the emerging parasitoid female progeny also tended to decrease as the host egg became older than 2 days. Host age had no significant effect on development time. A method of utilization of the parasitoid in a biological control program against DBM is also discussed based on the effect of DBM egg age on the parasitism of the parasitoid.