Effect of hibernation length on termination of diapause in European Tettigoniidae (Insecta: Orthoptera)

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Abstract
The effect of the length of cold treatment on development time of embryos of eight Central European tettigoniid species was investigated in laboratory experiments, using chilling periods of 3, 4, 5, 6, 9, and 12 months. Two different types of response were observed: (1) The hatching date was not influenced by hibernation length (Conocephalus) or only after the 3-month cold treatment (Phaneroptera, Platycleis), or (2) The time required for post-diapause development was significantly reduced by each 1-month increase in the length of cold treatment up to 6 months (Meconema, Metrioptera, Tettigonia). Thus, the correct timing of hatching is achieved by one of two different strategies. In lat-hatching species, the influence of hibernation length is small. Premature appearance is prevented by a high thermal threshold. In early-hatching species, the embryos are obviously able to measure the length of the chilling period. Thus, they gradually change their physiological state so that the potential speed of postdiapause development increases as the ‘winter’ is prolonged. This strategy can be understood as an adaptation to the necessity of hatching at low or moderate temperatures. Field experiments with two Tettigonia species confirm the laboratory data.