Climate change: insect pests benefit

Bad news for Swiss agriculture: several species of insect pests will benefit from a warmer climate. This is one of the findings of geographer Léonard Schneider, a doctoral student at the joint chair of applied climatology at the University of Neuchâtel and the Swiss Federal Research Institute WSL.  His doctorate aims to model the impact of global warming in Switzerland on pests. He publicly defended his thesis on 12 May.
The pine processionary, which overwinters in the larval stage, could benefit from higher winter temperatures and thus extend its range. (Photo: Beat Wermlinger, WSL)

This is the first time that a study has used climate data, mainly temperature records, and linked them to the reproduction of insect pests in Switzerland. In this study, Léonard Schneider and his colleagues investigated whether changes in daily temperatures could favour the reproduction of certain pest species.

And this is indeed the case, driven by warmer winters overall, and longer, warmer development seasons. “This is particularly striking in the case of pests whose annual reproductive cycle comprises several generations, such as the box tree moth, the European grapevine moth, or the codling moth,” explains Léonard Schneider. “A warmer development season, for example, favours the emergence of an additional generation per year.”

To establish predictive models for this development, Léonard Schneider used the average daily temperature of the development season of these insects. These temperatures from April to September determine whether an additional generation will appear.

“To do this,” explains the researcher, “we collected average daily temperature data over the last 40 years (from 1980 to 2021) from 67 MeteoSwiss measuring stations located between 200 and 2300 metres above sea level. We then used two climate scenarios, predicting different increases in greenhouse gases in the atmosphere over the next few years, to infer the average daily temperatures from 2022 to 2099.

Both scenarios result in one or more additional generations of these insects per year, but the consequences will be much less severe with lower CO2 emissions.

Other species of pests could overwinter more easily, continues the researcher who worked under the supervision of climatology professor Martine Rebetez. These include the pine processionary (Thaumetopoea pityocampa) and the green spruce aphid (Elatobium abietinum), as well as certain crop pests, such as the southern green shield bug (Nezara viridula).

Models show that by the end of the 21st century, future temperature conditions favour certain crop pests, allowing them to overwinter more easily on the Swiss Plateau, as well as certain forest pests, which will probably reach higher altitudes.