Codling moth (Cydia pomonella)

The usual tools for making codling moth control decisions, such as pheromone traps and temperature summations to predict key events, have proven to be unreliable in the field. The first eggs are laid days or weeks after the first male moths are caught in the traps, and peaks in male catches in the traps do not coincide with peaks in egg deposition by females. The temperature sums roughly indicate the first moths, the first hatching of eggs, the first moths of the second generation and so on. However, we are not interested in these ‘first events’ to make our decisions. We need to know when the bulk of the larvae hatch and when the next batch is expected, in order to plan our treatments.

 

The model

The model follows the development of a codling moth population in the orchard from the end of winter and throughout the production season. Climate and geographical location determine whether the moth multiplies in one or several generations. The end of diapause depends on temperature and day length.

The graph below shows the active flight of the female moth. The flight of the female moth depends on twilight air temperatures. Methods leading to sexual confusion of the moths must be installed in the orchard before the start of the flight.

The central graph shows daily egg laying (yellow). Female flight during warm afternoons leads to abundant egg-laying. During cooler or rainy afternoons, fewer eggs are laid. The graph below shows a decrease in egg laying around 15 May due to unfavourable weather conditions. Insecticides with ovicidal activity should be applied just before heavy egg laying is expected.

The graph above shows the number of hatched eggs in black (and the dotted line for the cumulative number) as well as the number of young larvae from newly hatched eggs. Larval development is temperature-dependent. These larvae are sensitive to insecticides with larval activity, including granulosis virus.

Fully developed codling moth larvae that leave the fruit may pupate and contribute to the next generation in the same year, or they may enter diapause to survive the winter and pupate the next spring. The potential size of the second generation of carpocapsa is therefore determined by the number of larvae that complete larval development before mid-July (February in the southern hemisphere). However, the actual magnitude of the second generation in each orchard depends to a large extent on the successful management of the first generation.

 

Special attention must be paid to the accuracy of temperature measurements, as most of the processes in the model are temperature-dependent. As processes are simulated over a longer period of time, errors in the measurements accumulate.