Development time plasticity of the pine processionary moth (Thaumetopoea pityocampa) populations under laboratory conditions

The pine processionary moth Thaumetopoea pityocampa (Lepidoptera, Notodontidae) is a univoltine defoliator that is active over a wide range of latitudes and elevations, being largely influenced by temperature variations, especially during larval development across the winter. This work compares field development time with that observed in the laboratory rearing under controlled conditions, in four Th. pityocampa populations characterized by different life history phenology: two populations from the Italian Alps characterized by early and late adult emergence, and two populations from Portugal, the first characterized by winter feeding and late adult emergence, the second by a switch of the larval feeding from winter to summer. The rearing started from the egg stage and was maintained in the laboratory at 20-25°C under natural light in transparent boxes. In spite of the different geographic origins and asynchrony of the period of larval development, all populations maintained an annual life cycle under laboratory conditions, as well as a phenology similar to that of the field populations. Such an outcome was possible due to a trade-off in the duration of the larval and pupal stages, the latter being identified as the phase of development when an efficient regulatory mechanism is acting to maintain the univoltine life cycle.