N. D. Voinovich, T. Ya. Umarova, T. S. Kats, and S. Ya. Reznik

Variation of the Photoperiodic Reaction in Trichogramma embryophagum Htg. (Hymenoptera, Trichogrammatidae)

Entomological Review, Vol. 83, No. 7, 2003, pp. 779–782. 

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A laboratory study of photoperiodic control of diapause in the egg parasitoid Trichogramma embryophagum Htg was carried out. Experiments conducted at 20°C and eight photoperiods (day-lengths of 3, 6, 9, 12, 15, 18, 21 and 24 h) revealed the long-day type response based on the maternal influence on prepupal diapause in progeny at 15°C. The maximum rate of diapause in progeny was recorded at day-lengths of 12–15 h, the estimated threshold photophases were between 6–9 h (left threshold) and 16–17 h (right threshold). A comparative analysis of photoperiodic responses in seven laboratory generations reared under constant conditions revealed endogenous variability of the tendency toward diapause. The left threshold day-length was highly variable, whereas the right threshold day-length remained relatively constant. The possible reason is that the right threshold is subject to stabilizing selection in the natural conditions, whereas the left threshold zone is a selectively neutral character revealed only in laboratory experiments.