The role of endogenous and exogenous factors in regulation of synchronous emergence of Trichogramma embryophagum Hartig and T. principium Sug. et Sor. (Hymenoptera, Trichogrammatidae)

Arrhythmic adult ecdysis but rhythmic emergence from the host chorion in Trichogramma embryophagum (Hymenoptera: Trichogrammatidae)

“…The above results strongly suggest that the observed rhythm of Trichogramma adult emergence (Dahiya et al, 1993;Corrigan et al, 1995;Pompanon et al, 1995;Zaslavski et al, 1995Zaslavski et al, , 1999Karpova & Reznik, 2002;Doyon & Boivin, 2005;Karpova, 2006) is based exclusively (or at least mostly) on the rhythmic egression from the host egg chorion, not on the rhythmic pupal-adult ecdysis, although these two steps were not distinguished in the previous studies. Noteworthy, in most of the other studied insect taxa, adult ecdysis shows a robust circadian rhythm, although this rhythmicity could be based not only on the entrained circadian rhythm, but also on exogenous "masking" effects (Saunders, 2002).…”

“…The timing of the next step, i.e., of the emergence from the host chorion is much more important. Synchronous eclosion of Trichogramma during the morning hours apparently minimizes the risk of desiccation and optimizes the reproductive activity of these parasitoids (Zaslavski et al, 1995(Zaslavski et al, , 1999Karpova & Reznik, 2002;Karpova, 2006). Interestingly, a similar distinct rhythm of emergence from the host was also observed in the braconid wasp Cotesia congregata (Say) that parasitizes larvae of the tobacco hornworm, Manduca sexta L. (Beckage et al, 2002).…”

“…Therefore, the method used in the earlier studies (Zaslavski et al, 1995(Zaslavski et al, , 1999Karpova & Reznik, 2002;Karpova, 2006), i.e., periodic counting of emerged individuals, was no longer feasible. Thus, a new method was elaborated to monitor the temporal patterns of the processes under study: at regular intervals, one card was randomly selected from the cohort and immediately placed in a freezer (-18°C).…”

“…It was repeatedly demonstrated that Trichogramma species possess circadian rhythms of adult emergence which could be synchronized with photo-or thermoperiod (Corrigan et al, 1995;Pompanon et al, 1995;Zaslavski et al, 1995;Zinovjeva et al, 1996;Doyon & Boivin, 2005). The rhythms persisted with a period close to 24 h after transfer to aperiodic conditions (constant darkness and constant temperature), suggesting they were under the control of endogenous circadian oscillators (Dahiya et al, 1993;Karpova, 2006). However, direct influence of a light-on and/or a temperature step-up can induce emergence of a considerable fraction of adults almost at any moment of the circadian time, suggesting a strong exogenous (masking) effect (Zaslavski et al, 1999;Karpova & Reznik, 2002;Karpova, 2006).…”

“…The rhythms persisted with a period close to 24 h after transfer to aperiodic conditions (constant darkness and constant temperature), suggesting they were under the control of endogenous circadian oscillators (Dahiya et al, 1993;Karpova, 2006). However, direct influence of a light-on and/or a temperature step-up can induce emergence of a considerable fraction of adults almost at any moment of the circadian time, suggesting a strong exogenous (masking) effect (Zaslavski et al, 1999;Karpova & Reznik, 2002;Karpova, 2006). Similar results were obtained for other egg parasitoids (Fantinou et al, 1998).…”