Native Pests in Fruit Production: The Codling Moth

The codling moth (Cydia pomonella) is considered to be one of the key pests in fruit production. The larva causes damage by boring into the apple (Fig. 1). Under current climatic conditions, one grub generation per year is observed in northern Switzerland. By contrast, two grub generations per year always appear in southern Switzerland. In warmer years, a second generation is possible in northern Switzerland, whilst a third grub generation may actually develop in southern Switzerland (Fig. 2).

A halved apple with a codling moth grub near the core. The grub has eaten its way through the apple from the side to the core. Isolated grub droppings can be seen in the feeding tunnel. — Figure 1. The grub of the codling moth feeds inside the fruit.
© Agroscope

Studies have shown that climate change will lead to an earlier start to the flight period of the overwintering generation, and to an even earlier occurrence of the subsequent stages of development (Stöckli et al., 2012). What’s more, data from warmer regions indicate that through natural adaptation to higher temperatures, the codling moth may go into the dormant stage later (Hirschi et al., 2012, Stoeckli et al., 2012). All this increases the likelihood that in future, the codling moth will more often develop two to three generations a year in northern Switzerland, and three generations a year in southern Switzerland (CH2014). This must be borne in mind when adapting control strategies (Stoeckli et al., 2012).

The regions in which, in the future, a third generation of grubs is likely to occur will enclose the Swiss Central Plateau, the Three-Lakes Region, the region around Lake Geneva, and the Rhine Valley, even under the assumption of a climate-stabilising emission scenario (RCP3PD; Fig. 2). With the assumption of emission scenarios that do not provide for any mitigating intervention, the potential distribution range of a third generation of grubs becomes significantly larger, encompassing the whole of Switzerland’s fruit-growing area (A1B and A2).

The graphics show maps of Switzerland that illustrate the probability of the occurrence of a third codling-moth grub generation. A total of ten maps are presented for different combinations of timescales (the present, 2035, 2060 and 2085) and emission scenarios (RCP3PD, A1B and A2). The current fruit-growing area is coloured grey. The likelihood of the occurrence of a third generation of grubs is shown by means of a three-level colour scale, ranging from light-yellow (low probability) to orange (moderate probability) to red (high probability). The map for the current climate shows a high probability of occurrence in the lower-lying valleys of Ticino, and a low probability in the canton of Geneva and along the Rhone. All three scenarios show a similar picture for 2035. In Ticino and in the canton of Geneva, along Lake Geneva, in the Rhone valley and in Basel, the probability of occurrence is high; but the Three Lakes Region, the Rhine Valley and Freiamt will also potentially be affected by a third generation of codling moth. Assuming the RCP3PD emission scenario, the areas with a high likelihood of occurrence for the 2060 and 2085 timescales increase slightly in size. If emission scenarios A1B and A2 are assumed, however, the extent of the areas with a high probability of occurrence is considerably larger. Around 2060, the areas include large parts of the Swiss Central Plateau and Rhone and Rhine Valleys as well as the canton of Jura, and by 2085 they completely encompass the current fruit-growing area. — Figure 2. Probability of the occurrence of a third generation of codling moth grubs for various timescales and emission scenarios. The grey-shaded area corresponds to the region in which fruits are grown under current climatic conditions. The CH2011 climate scenarios form the basis for the calculation of the maps.

Whether a third generation of codling moths can actually cause damage, however, depends on whether the grubs of this generation still find apples on the trees that they might attack. Ultimately, therefore, the phenological development of the host plant determines the effective risk of infestation; and this varies greatly depending on whether the apple varieties potentially affected are early- or late-ripening ones.

Results of more-recent analyses, for instance, show that nowadays in southern Switzerland, the likelihood of damage from a third generation of codling moth grubs exceeds 50% only in the case of the late-ripening variety Golden Delicious, whilst the probability for the earlier-ripening apple variety Gala stands at only around 10%. In future, the likelihood of an infestation by a third generation of grubs will increase for both apple varieties, but will remain lower for Gala than for Golden Delicious.

For the very-early-ripening Gravenstein variety, which nowadays is grown almost exclusively in northern Switzerland, the probability of damage by a third generation of codling moth grubs remains negligible, even up to the end of the current century. This underscores the future role of the variety selection and breeding to reduce the potential for damage by insects. Research aimed at this is carried out inter alia by Agroscope and the FiBL.

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References Cited in the text

Hirschi, M., Stoeckli, S., Dubrovsky, M., Spirig, C., Calanca, P., Rotach, M. W., Fischer, A. M., Duffy, B. and Samietz, J., 2012: Downscaling climate change scenarios for apple pest and disease modeling in Switzerland, Earth Syst. Dynam., 3(1), 33–47.

Stoeckli, S., Hirschi, M., Spirig, C., Calanca, P., Rotach, M. W. and Samietz, J. 2012: Impact of climate change on voltinism and prospective diapause induction of a global pest insect – Cydia pomonella (L.), PLoS ONE, 7(4), e35723.

Stöckli, S., Samietz, J., Hirschi, M., Spirig, C., Rotach, M. und Calanca, P., 2012: Einfluss der Klimaänderung auf den Apfelwickler, Schweizer Zeitschrift für Obst- und Weinbau, 19.

Additional reading

CH2014-Impacts, 2014: Towards quantitative scenarios of climate change impacts in Switzerland, herausgegeben von OCCR, FOEN, MeteoSwiss, C2SM, Agroscope und ProClim, Bern, Schweiz, 136 pp.

Felber, R., Stöckli, S., Calanca, P., 2018: Generic calibration of a simple model of diurnal temperature variations for spatial analysis of accumulated degree-days, Int. J. Biometeorol., 62, 621–630.

Harshman, J. M., Evans, K. M. and Hardner, C. M., 2016: Cost and accuracy of advanced breeding trial designs in apple, Hortic. Res., 3(1), 1–10.

Hirschi, M., Spirig, C., Weigel, A. P., Calanca, P., Samietz, J. and Rotach, M. W., 2012: Monthly weather forecasts in a pest forecasting context: Downscaling, recalibration, and skill improvement, J. Appl. Meteorol. Clim., 51(9), 1633–1638.

Samietz, J., Graf, B., Höhn, H., Schaub, L. and Höpli, H. U., 2008: Schädlingsprognose für den Obstbau, AGRARForschung, Forschungsanstalt Agroscope Changins-Wädenswil ACW, Wädenswil, Schweiz.

Samietz, J., Graf, B., Razavi, E., Höpli, H. U., Höhn, H. and Schaub, L., 2011: Web-based decision support for sustainable pest management in fruit orchards: Development of the Swiss system SOPRA, INTECH Open Access Publisher.

Samietz, J., Stoeckli, S., Hirschi, M., Spirig, C., Höhn, H., Calanca, P. and Rotach, M., 2015: Modelling the impact of climate change on sustainable management of the codling moth (Cydia pomonella) as key pest in apple, in Acta Horticulturae, pp. 35–42, International Society for Horticultural Science (ISHS), Leuven, Belgien.