Weather Sensitivity of Sugar Bait Trapping of Nocturnal Moths: A Case Study from Northern Europe

SIMPLE SUMMARY: Sugar baits are not only used to attract butterflies; they are also used to attract nocturnal moths. Similarly to most sampling techniques, the results of bait trapping are influenced by ambient conditions. In order to understand how bait trap catches depend on weather parameters, we performed a study in the north European forest zone using portable weather stations placed next to the traps. We found that the number of moths caught was strongly positively dependent on temperature and negatively dependent on air humidity. Diversity showed a similar dependence on temperature and humidity but was also negatively affected by air pressure and positively affected by the change of pressure during the night. Our findings help to interpret the results of quantitative insect trapping projects as they allow one to properly account for variability in weather conditions. ABSTRACT: Assemblages of insects need to be quantitatively sampled in the context of various research questions. Light trapping is the most widely used method for sampling nocturnal Lepidoptera. Attracting moths to sugar baits offers a viable alternative. However, this method is rarely used in professional research despite its popularity among amateur lepidopterists. As the activity of insects is strongly dependent on ambient conditions, the sensitivity of any trapping method to weather parameters needs to be known for the quantitative interpretation of trapping results. In the present paper, we report data on the weather dependence of moth catches obtained by automatic bait traps. The study was performed in Estonia, representing the European hemiboreal forest zone. Portable weather stations set up next to each of the traps were used for collecting weather data. Both abundance and diversity of the moths in the catches depended strongly positively on temperature and negatively on air humidity. Diversity was also negatively correlated with air pressure and positively with the change in pressure during the night. The results show that in situ recording of weather parameters in connection to insect trapping provides useful insights for the study of insect behaviour and the interpretation of the results of monitoring projects.