Temperature-dependent phenology of Campaea margaritaria (L) (Lepidoptera: Geometridae) derived from field data

A new phenology model, using thermal sums of triangulated daily temperatures, was applied to the derivation and validation of lower temperature threshold limit and thermal constants of bivoltine Campaea margaritaria (L) from 70 observed flight peak days in The Netherlands (period of 1986-2020) and daily ambient air temperatures of 10 weather stations. Development was assumed to be controlled directly by temperature for the summer generation. During fall a diapause of young larvae was assumed and confirmed. A lower threshold limit of TL = 6.70 ± 0.06 °C was found and a mean thermal winter and summer generation constant of K_1,m = 838 ± 9 and K_2,m = 848 ± 6 °C.day, respectively, for the reference period of 1993-2013. Generation differences could not be explained with temperature-size rules in ectotherm organisms. Threshold limit and thermal constants depended slightly on the period of derivation indicating short-term plasticity. Flight peak days were calculated with root mean square errors of 2.2-3.0 days for both generations. Changing temperatures of the reference period led to temperature dependences of flight peak days of -6.4 and -8.7 day/°C of the winter and summer generation, respectively. Neglecting physiological changes a complete third generation would require an increase of 3.7 °C, a single generation a decrease of 4.1 °C.