SEASONAL OCCURRENCE OF EGG PARASITOIDS AND PARASITISM OF OOENCYRTUS SP. ON RIPTORTUS PEDESTRIS (HEMIPTERA: ALYDIDAE) EGGS

Abstract

Riptortus pedestris (Hemiptera: Alydidae) is one of the most important pests of various crop plants in Korea and Japan and a newly introduced pest of various leguminous crops in Bangladesh. In this study, the seasonal abundance of R. pedestris and its egg parasitoids were observed in three different locations in Dinajpur and biological attributes of Ooencyrtus sp. (Hymenoptera: Encyrtidae) were studied in laboratory condition. Eggs, nymphs and adults of R. pedestris were observed in three different study locations. R. pedestris were captured by aggregation pheromone traps during the study period. Gregarious parasitoids, Ooencyrtus sp. and solitary Gryon nigricorne (Hymenoptera: Scelionidae) emerged from natural eggs. Ooencyrtus sp. and G. nigricornewere observed during the whole study time. Ooencyrtus sp. displayed drumming, drilling, feeding and oviposition behaviors and increased time spent in newly emerged fresh host eggs and decreased when the host eggs age was increased. Ooencyrtus sp. can successfully parasitize fresh host eggs and up to 48 hours and produced 22 parasitoids /female within 24 hours. The fresh host eggs of 96-hour, parasitism decreased by approximately 29% compared to the control. Emergence rate and sex ratio were not affected by the age of fresh host eggs. No eggs were hatched after 30 days of refrigeration. In addition, none of the attributes of Ooencyrtus sp. was negatively affected by host eggs refrigerated up to 30 days. Refrigeration of host eggs was not affected in emergence rate and sex ratio of this gregarious egg parasitoid. Therefore, fresh and refrigerated eggs of R. pedestris can be successfully parasitized by Ooencyrtus sp. and refrigeration of host eggs can be a good alternative for the mass rearing of Ooencyrtus sp.