Vespula vulgaris, (Linnaeus, 1758) (Linnaeus, 1758)

Komonen, Atte, Järvinen, Essi & Lindell, Kristiina, 2022, All-day activity of a Vespula vulgaris (Linnaeus, 1758) (Hymenoptera, Vespidae) colony in Central Finland, Norwegian Journal of Entomology 69, pp. 1-7 : 4-6

Results

The flight started 59 minutes before sunrise and ended 39 minutes after sunset. During the full-day monitoring we observed 8801 wasps entering the nest between sunrise and sunset (9408 wasps during the entire day, including the August 20 morning). The sunrise to sunset traffic rate varied from 0 to 23 min-1 (mean = 9.26, SD = 3.50; CV% = 38), i.e. the mean time between wasps entered the nest was 7 seconds. Traffic rate varied throughout the day overall and from one 5-min period to another ( Figure 3 ); the peak was between 7:00 to 10:00 in the morning. The lows of the 5-min periods were 31% and the lows for 35-min moving average were 42% of the peak ( Figure 3 ). The activity was modelled best by a simple seasonal time series model (stationary r 2 = 0.76, Ljung-Box Q = 19.9, df = 16, p = 0.27). Because temperature was not included in the final model, this suggests no relationship between traffic rate and ambient temperature (see also Figure 3 ). There was also irregular cyclicity at the scale of minutes ( Figure 4 ).

Discussion

Colony activity varied over day. Wasps were active about an hour before sunrise and 40 minutes after sunset, which is typical for vespids ( Gaul 1952, Potter 1964, Archer 2004, Kasper et al. 2008, Heinrich 1984, Komonen & Torniainen 2022). Overall, there was a small early morning (5:00) activity peak, followed by decline and then the daily peak at 7:00. After 8:30 activity decreased until the evening peak at 19:30. Early morning and evening peaks have been repeatedly observed for Vespula ( Potter 1964, Heinrich 1984, Archer 2004), but they are not a universal pattern ( Kasper et al. 2008). It has been suggested that between- and within-days variation in activity is linked to different activities carried out by the workers ( Archer 2000), yet some research indicates that this variation is caused by weather ( Potter 1964, Kasper et al. 2008).

Traffic rate showed cycles over a few minutes. This pattern is not idiosyncratic for the studied colony, since similar cyclicity was documented for all the studied colonies of Dolichovespula saxonica (Fabricius, 1793) ( Komonen & Torniainen 2022) . For a particular colony, the foraging and pulp collecting trip times, as well as the in-nest times, are typically rather constant, even for individuals carrying out different activities ( Archer 2012). The reason might be that wasps tend to revisit good foraging sites and might be capable of information sharing (Santoro et al. 2015), or local enhancement (D’Adamo et al. 2000), regarding food sources. This could maintain similar trip times for workers of a particular colony and enhance cyclicity in activities. Among colonies, constancy in trip times would indicate that the availability of food and pulp sources do not vary markedly. This is a reasonable expectation, since vespids are generalist foragers.

Colony activity was not related to ambient temperature. This was not surprising, since monitoring was done during good weather: wind was calm, the sky clear or half cloudy, and the temperature outside the nest over +6.3 oC, which is clearly more than the threshold for vespid activity ( Blackith 1958, Potter 1964). Many older studies have not accounted for autocorrelation in the activity time series. Because ambient temperature increases in the morning and decreases in the evening, simple regression of activity against temperature does not indicate causal relationships. Furthermore, discontinuous monitoring is not optimal for detecting the effect of temperature on activity, and do not allow detailed time series analyses of activity. Our results also show that ambient temperature cannot explain the observed fine-scale, minute-to-minute variation in activity, since ambient temperature was rather constant during the day and changed gradually (see also Komonen & Torniainen 2022).

The large within-day variation in activity has implications for monitoring Vespula colonies. In order to estimate worker numbers, Malham et al. (1991) suggested a 10-min count, which seems to work well for invasive, perennial Vespula colonies. The desired precision and accuracy of the estimate depends on the purpose, but our study suggests that even a half-an-hour monitoring may produce biased estimates (see also Komonen & Torniainen 2022). Thus, we encourage longer monitoring times (at least an hour) divided in (at least) two discrete time periods, one before noon and one afternoon.

Our study provides novel, fine-scale information about the flight activity of a natural colony of Vespula vulgaris in the native range of the species in the boreal biome. Many important and interesting questions about wasps’ activity patterns can only be answered with such continuous and high-resolution data. Our study is the first to demonstrate the irregular fine-scale cyclicity in the all-day activity of Vespula . This fine scale pattern and the underlying causal factors needs further verification with more nests, and in different geographical locations.

Figures

FIGURE 3. Observed number of Vespula vulgaris individuals entering the nest per 5 minute, the 35-min centered moving average and ambient temperature (oC) starting from 04:00 and ending at 22:30 on 18 August 2020 (04:00–05:30 is from the morning of 20 August). Note the small break in temperature recordings.

FIGURE 4. Minute-to-minute variation in the observed number of Vespula vulgaris individuals entering the nest per minute, starting from 04:00 and ending at 22:30 (the last individual entered the nest 21:54) on 18August 2020 (04:00–05:30 is from the morning of 20 August). Sunrise was at 5:32 and sunset at 21:15.