Reznik S.Ya., Vaghina N.P. 2007. Effect of photoperiod on parasitization by Trichogramma principium (Hymenoptera: Trichogrammatidae). European Journal of Entomology 104 (4): 705-713.

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The effect of photoperiod on parasitization of the eggs of the Angoumois grain moth, Sitotroga cerealella (Olivier, 1789) by Trichogramma principium Sugonyaev & Sorokina, 1976 was investigated under several photoperiodic regimes of L : D = 3 : 21, 6 : 18, 9 : 15, 12 : 12, 15 : 9, 18 : 6 and 21 : 3. In all regimes, certain wasps delayed ovipositing in this non-preferred host. Potential fecundity of T. principium females (the number of mature ovarial eggs at emergence) and subsequent oogenesis (estimated by the number of mature ovarial eggs in non-ovipositing females) was independent of photoperiod. However, the percentage of females that oviposited was higher for females that developed and were kept under 6–12 h long photophase than for those that developed and were kept under ultra short (3L : 21D) and under long (18L : 6D and 21L : 3D) photophases. The average duration of the preoviposition (egg retention) period showed the opposite pattern to the photoperiodic response. A possible explanation of this reaction is that the delay in oviposition is adaptive if the probability of finding a better host is high. In autumn, when the last Trichogramma females are still active but their lepidopteran hosts are already much less abundant, then parasitization of any suitable host is the best strategy.

Key words. Photoperiod, egg parasitoids, Trichogramma, oviposition, pre-oviposition period, oogenesis, egg retention, fecundity