Changes in Functional and Numerical Responses of the Parasitoid Wasp Trichogramma brassicae (Hymenoptera: Trichogrammatidae) Over 45 Generations of Rearing on Ephestia kuehniella

Abstract

Abstract We assessed the functional and numerical responses of Trichogramma brassicae Bezdenko under long-term rearing (45 generations, G5-G45) on eggs of a common factitious host, Ephestia kuehniella Zeller (Lepidoptera: Pyralidae). Under such long-term mass rearing, the function response of this parasitoid shifted from Type III (from G5 to G20) to Type II (from G25 to G45). The maximum attack rate (T/Th) (33.62 hosts/day) and the shortest handling time (0.7138 ± 0.0272 h) were recorded in G5. Also, G45 had the lowest attack rate (21.67 hosts/day) and longest handling time (1.1076 ± 0.0689 h). The handling time increased gradually over the generations (P reg <0.01, R2 = 0.903). The number of eggs laid by the parasitoid increased significantly with increased host density, but reached a plateau at very high densities. While no significant differences in daily parasitism were observed over 45 generations at densities of 2, 4, 8, and 16 available host eggs per wasp, there were significant differences in parasitism at host densities of 32, 64, and 128 eggs per wasp. T. brassicae females were more active and foraged more frequently in earlier generations (G5 to G20), which allowed wasps to parasitize more E. kuehniella eggs compared to later generations. Also, continuous mass rearing of T. brassicae negatively affected foraging behavior and the quality of wasps after G20. However, rejuvenation of the colony by adding field-collected parasitoids or rearing wasps on more suitable factitious hosts is strongly recommended to lower the negative effects of long-term mass rearing on quality of this parasitoid.