Work in Switzerland showed that winter eggs of rosy apple aphid hatch between 100 and 180 degree days, 50% emergence being reached at 130 degree-days above a thermal threshold of 4.5 °C.
- Temperature sums are started from 1 January. Rosy apple aphid eggs hatch a week or so after those of apple grass aphid.
- Rosy apple aphid begins to reproduce approximately 230 degree-days after emergence.
- This suggests that the optimum period for pre-bloom population monitoring for control measures extends from 180 (end of hatching) to 230 (beginning of reproduction) degree-days.
- These developments can be used for forecasting, but predictions have not been validated in the UK.