Study site and trap configuration

This study was conducted at an apiary located near Palgongsan National Park in Daegu, South Korea (35°58’25.8”N, 128°39’48.2”E). The study area covered approximately 30 m². Five hornet attractant traps were deployed at 5-10 m intervals within the site (Kim et al., 2019). The attractant used in the traps was a mixture of plum extract and water at a 7:3 ratio. Given the relatively short distances between the traps and the wide foraging range of hornets, we assumed that the traps could potentially sample individuals from the same local population (Choi et al., 2012b). Therefore, the data from all traps were pooled for analysis.

Sampling schedule and frequency

For 2022, the survey focused on determining the emergence period of overwintered queens. Traps were installed on April 25 and collected seven times until July 30, when the queen activity ceased.

In 2024, to gain a more detailed understanding of species-specific queen emergence and seasonal dynamics of workers, traps were installed on April 7. Sampling was conducted 48 times between April 9 and October 22. During the expected emergence period of the new queens, traps were checked every 2-3 days to monitor the transition to the colony’s cooperative phase. After mid-July, when workers began to appear, the sampling intervals were extended to approximately two weeks (Table 1).

Species and caste identification

Among the insects collected from the traps, individuals belonging to the genus Vespa were isolated and their species and caste were identified. Identification was performed using the taxonomic key provided by Smith-Pardo et al. (2020).

Species composition and abundance of Vespa queens and workers over two years

Over the survey period, 748 individuals representing eight Vespa species were collected from the apiary. Among these, V. velutina (N=256, 34.2%) and Vespa crabro Linnaeus, 1758 (N=217, 29.0%) were the most frequently collected species, followed by Vespa ducalis Smith, 1852 (N=131, 17.5%), V. mandarinia (N=70, 9.36%), and Vespa analis Fabricius, 1775 (N=40, 5.4%). Vespa dybowskii André, 1884, Vespa simillima Smith, 1868, and Vespa binghami du Buysson, 1905 were collected in substantially lower numbers, generally fewer than 10 individuals each, and were thus considered minor components of the hornet community at the site (Fig. 1).

In 2022, 186 overwintered queens representing six species were collected. V. velutina was the dominant species (N=102, 54.8%), followed by V. crabro (N=29, 15.6%) and V. mandarinia (N=20, 10.8%; Figs. 1, 2).

In 2024, 562 individuals from eight species will be collected. The most frequently collected species was V. crabro (N=188, 33.7%), followed by V. velutina (N=154, 27.6%) and V. ducalis (N=113, 20.3%). Among these, 171 overwintered queens from eight species were identified, with V. velutina being the most dominant (N=51, 29.8%), followed by V. crabro (N=43, 25.1%) and V. mandarinia (N=37, 21.6%; Fig. 2).

In 2024, 391 workers from seven species were collected. V. crabro accounted for the highest proportion (N=145, 37.1%), followed by V. velutina (N=103, 26.3%) and V. ducalis (N=102, 26.1%; Fig. 3).

Emergence timing of overwintered queens

Emergence timing of workers

Vespa species observed in the apiary

Eight Vespa species were collected from the apiary during the study period. Among these, V. velutina was the most frequently collected species and was identified as the primary threat to apiaries. This species has now spread across South Korea and is the most prevalent hornet species near apiaries in most regions, contributing to widespread and significant damage (Choi & Kwon, 2015; Kim et al., 2025).

V. crabro and V. ducalis also appeared in relatively high numbers; however, these species tended to visit apiaries primarily to exploit floral resources rather than actively hunt honeybees. Consequently, their direct impact on apiculture is relatively minor (Matsuura & Yamane, 1990).

In contrast, although V. mandarinia was collected in smaller numbers, it poses a serious threat because of its tendency to engage in group attacks on beehives (Matsuura & Sakagami, 1973). Therefore, from a management perspective, V. velutina and V. mandarinia should be prioritized for control strategies in and around apiaries.

Emergence timing of overwintered queens

The sequences of overwintered queen emergence observed in the present study were V. mandarinia-V. velutina-V. crabro-V. analis-V. ducalis. V. mandarinia and V. velutina emerged the earliest in early April, followed by V. crabro and V. analis between late April and May. V. ducalis queens emerged in early June.

This emergence sequence closely aligns with previous observations in Japan by Matsuura (1984), who reported the queen emergence of V. mandarinia in April, V. analis and V. crabro in May, and Vespa tropica (Linnaeus, 1758), a species closely related to V. ducalis, between June 8 and 25.

Among the less frequently collected species, V. binghami, V. simillima, and V. dybowskii were primarily observed after late April. Notably, V. velutina exhibited an emergence pattern similar to that of V. mandarinia, with activity beginning in early April.

The overall advancement in emergence timing compared to earlier studies may be attributed to recent increases in average spring temperatures on the Korean Peninsula (An et al., 2011), which may accelerate the post-hibernation activity of overwintered queens (Spradbery, 1973).

Among all species, V. ducalis exhibited the latest colony initiation. This may reflect an adaptive strategy linked to its specialized ecological niche as a predator of paper wasps, with emergence timing synchronized with the development of its prey colonies (Archer, 1991; Matsuura, 1984; Starr, 1992).

From a methodological standpoint, the 2022 survey had wider intervals between site visits, limiting the precision of the emergence timing data. In contrast, the 2024 survey employed a shorter sampling interval, allowing for a more accurate tracking of emergence patterns.

Overall, most species ceased external activity from early to mid-June, after which queens were seldomly collected. This is likely due to the shift in colony dynamics around mid-June, when the first workers begin to emerge and the queens remain in the nest to focus on reproduction.

Seasonal emergence patterns of workers

This study examined the timing and abundance of hornet workers in an apiary. Most workers began to appear between early and mid-July, although in some species, the first individuals were not collected until mid-August. Worker abundance generally increased over time, peaking in August and September, followed by a sharp decline in October. This trend is consistent with previous reports on the life history of Vespa species, in which worker activity typically intensifies in mid-summer and lessens during autumn (Chang et al., 1993; Choi & Kwon, 2015; Matsuura & Yamane, 1990).

Interestingly, the current study showed a brief gap in worker collection between mid-June and early July. This may be attributed to the behavioral characteristics of early emerging workers, who are often smaller and less experienced in foraging. These individuals may avoid high-risk environments, such as apiaries, or escape from traps more easily because of their smaller size or less aggressive behavior (personal observation by Choi). Such traits could influence the frequency of their appearance at the apiary and the likelihood of their being collected by traps.

A particularly notable case was observed for V. velutina (Fig. 3). This species exhibited a sudden spike in worker abundance around July 10, with 30 individuals collected after a period of no capture. This sudden emergence coincided with approximately 250 mm of heavy rainfall recorded the day before and morning of sampling (KMA, 2024). It is likely that adverse weather conditions previously suppressed foraging activity, leading to delayed but concentrated post-rain emergence. Given the strong preference of V. velutina for honeybee predation (Norderud et al., 2021), such intensified activity near the apiary was expected.

However, these results were based on observations from a single apiary and may not reflect broader patterns of worker emergence across different landscapes. Factors such as topography, microclimate, vegetation, and local management practices also affect hornet activity. Thus, these findings should be interpreted with caution and should be supported by further studies across diverse geographical regions.

Implementation and effects of insecticide-based control

In this study, an insecticide-based control method targeting V. velutina was applied by the beekeeper at the apiary. The treatment was conducted beginning on July 25, using a method in which hornets were collected, treated with a neonicotinoid insecticide on the thorax and abdomen, and then released. The active ingredient used was clothianidin, a commercially available chloronicotinyl compound (International Organization for Standardization name: 3-[(2-chloro-1,3-thiazol-5-yl) methyl]-2-methyl-1-nitroguanidine; SG Hankooksamgong).

Immediately following the treatment, no sharp decline in trap collection was observed. According to previous studies, clothianidin, when applied at the recommended concentrations, can induce high mortality in adults within 6 hours and in larvae within 48 hours (Hong & Jung, 2024). Furthermore, this compound has been reported to spread throughout colonies within 24 hours, exerting a colony-wide effect (Kim et al., 2021). In theory, a noticeable population decline should have occurred within two days of application. However, as of August 7 sampling, 25 V. velutina workers were still being collected.

This delayed response may be due to the timing of the treatment, which coincides with the peak period of nest relocation in V. velutina (Diéguez-Antón et al., 2022). It is possible that newly arrived colonies that were not exposed to the insecticide subsequently established foraging routes for the apiaries. Hornet larvae are protected during pupation by cocoons, which form a sterile microenvironment that may prevent sufficient penetration by insecticides (Shabtai & Ishay, 1998). Given that pupation lasts approximately 16-19 days (Archer & Penney, 2012; Dong & Wang, 1989), and that clothianidin degrades naturally within approximately one week, it is plausible that newly emerged adults developed after the insecticide’s effective period had passed.

Despite these factors, the sustained application of the insecticide by the beekeeper likely contributed to the cumulative control effects over time. The number of V. velutina workers declined markedly from late August onward and did not recover until mid-October. These results suggested that the insecticide-based method had at least moderate efficacy in suppressing V. velutina activity.

Clothianidin, a neonicotinoid, is widely regarded by local beekeepers as an effective control agent for V. velutina (Hong & Jung, 2024). The findings of this study support the potential utility of such methods in mitigating hornet-related damage to apiaries. However, the repeated use of insecticides raises concerns about their unintended impacts on non-target organisms and residual contamination within apiaries. Therefore, future efforts should prioritize the development of more sustainable and ecologically responsible control strategies.