Coinciding development of winter wheat and leaf beetles along an Alpine transect

The degree of temporal coincidence in the development of winter wheat (Triticum aestivum L.) and the cereal leaf beetles Oulema melanopus (L.) and Oulema duftschmidi (Redtenbacher, 1874) was studied by means of explanatory phenology models. Temperature and photoperiod control crop development, whereas oviposition and development of eggs and larvae of the two beetles depend on temperature and crop phases. The models parametrized with literature data satisfactorily represented crop and prepupal insect development at several Swiss and Italian locations. The successfully validated models were used for representing multiannual crop and insect development at seven locations on a European transect between the Danube river in the North and the Po River in the South. Depending on temperature and photoperiod, the crop phases occurred at different time periods but were generally of similar durations. The shifting of the crop phases exposed the cereal leaf beetles to environmental conditions which were similar during oviposition and slightly different as the growing season progressed. The simulated oviposition and prepupal survivorship was much higher for O. melanopus than for O. duftschmidi but did not differ between the locations. The crop phase-dependent mortality (Mc) was consistently higher for O. duftschmidi than for O. melanopus, whose Mc increased with increasing altitude. The extent of coinciding development was investigated by means of the summed larval development rates divided by the summed wheat development rate. During the oviposition period the insect development was coincident with wheat development. With time progression, however, the temperature difference between the locations increased causing an incomplete coincidence in the development of wheat and cereal leaf beetles. These results support the hypothesis that the extent of coinciding development of the three species is largely controlled by temperature and photoperiodic conditions.