Outbreak year, season, and time
Shizuoka University, encountered outbreaks of H. breviantenna aproximately 2004 (Tagami 2011). Many individuals in were trapped in 2007 but not in 2008 (Fig. 11). We did not record any individuals after 2009, and there were no outbreaks in the university. Additionally, the abundance of this species gradually decreased until 2010 and became stable at a low density (Tagami, personal observation). No significant differences in precipitation and temperature could be detected between 2006 and 2007 (Japan Meteorological Agency 2023). We began our investigations on this species in Tajimi City in 2020, as outbreaks have been reported since 2010. In the city, outbreaks have occurred during the rainy season, similar to Shizuoka University (Figs. 15–18: Tagami, personal observation). The seasonal abundance in Tajimi city must be similar to that in Shizuoka, but annual differences in the outbreaks between the two distant localities remain unclear.
When we investigated the occurrence time of H. breviantenna at one day in 2007 at Shizuoka University, all case outbreaks occurred in the morning, especially from 9 to 10 AM (Fig. 13: Tagami 2011, 2014). In Tajimi City, we collected samples until 10:00 AM because the adults almost disappeared after that time. We usually could observe many individuals until 10:00 AM and it became difficult to observe any adults flying after that. Mayflies are well-known insects that experience mass swarming in the evening (Allan and Flecker 1989). In the case of mayflies, they practice mass -swarming as a mate -seeking behavior (Kondoh and Ide 2003). Compared to this example, however, the H. breviantenna adults that appeared were almost only females, and it was difficult to find males (Figs. 11 and 14). Thus, the outbreaks of this species cannot be sex -seeking behavior, as males were collected at only some limited numbers of the traps set at the forest edge (Figs. 15–17) but these males did not disperse. Future research is need to determine why males occurs and disperses in the morning.
Distribution
We confirmed that H. breviantenna adults emerged from the forest floor (Fig. 14) and especially inhabited the forest edge (Figs. 15 and 16). It is possible that the females oviposited at the forest edges, and then flew to open areas. This could be one of the reasons why we found a vast number of adults outside the forests such as at houses and buildings.
Outbreaks of H. breviantenna sometimes occur in urban area (Fig. 18). Both females and males were collected, indicating that they may also be reproductive in this area. We performed this investigation in 2022, and there were no outbreaks during this year (Tagami personal observation).
Outbreaks of H. breviantenna have been reported in Honshu, Shikoku, and Kusyu, Japan (Sueyoshi 2023). The adults appeared only in the rainy season and died immediately after emerging. It appears difficult for the species to spread over distant areas in nature, and it remains unclear why it spread over a broad area of Japan. Hyperlasion wasmanni has been found in many regions of the world (Hardy 1956; Mohring et al. 2019) and occurs in various habitats (Menzel et al. 2006). Many agricultural pest insects enter Japan from other countries with crops (Abe 2017; Fujiwara et al. 2015). Furthermore, H. breviantenna is found in Australia (Sueyoshi et al. 2022), though the relationship between these two populations remains unclear.
Reproduction mode and male appearance
Sexual organisms oviposit on both females and males. Two modes of sex determination were found in Sciaridae: monogenic and digenic (Nigro et al. 2007). A monogenic female oviposits either only females or males, and a digenic female oviposits both females and males (Nigro et al. 2007). Moreover, Sciara ocellaris changes the sex of progeny depending on temperature (Nigro et al. 2007).
In this study, outbreaks of H. breviantenna occurred in different habitats in the same season, and only females were found in these habitats at Shizuoka University, investigated in 2008, by yellow sticky traps (Fig. 13) and IES was instigated in 2020 by emergence traps (Fig. 14). In 2021 and 2022, however, we collected many males from forests using hyaline sticky traps (SMP, IES, and urban area of Tajimi city: Fig. 16–18). Sueyoshi et al. (2022) confirmed that H. breviantenna males have intact wings. We collected males using many hyaline sticky traps 30 cm above the ground (Figs. 16 and 17). Sciarid species need males to reproduce offspring (Nigro et al. 2007). Although some traps collected more males than females in our results (Fig. 17), the sex ratio biased females in total. Hyperlasion wasmanni was also observed to have a female-biased sex ratio (Heller et al. 2009, Mohrig et al. 2019, Nielsen and Nielsen 2016). It remains unclear what kinds of environmental factors affect its reproduction. We did not observe whether the females collected were already copulated. Further investigations are needed to confirm monogenic or digenic changes in sex depending on temperature.
Factors of outbreak and habitats
We need to review the reasons for outbreaks of H. breviantenna from various perspective. Some factors stimulate outbreaks of several insects (Maron et al. 2001), such as changes in food quality (Mattson and Hack 1987; Rossiter 1992; Schultz and Baldwin 1982; White 1984), suitable weather (Martinat 1987), and decreases in natural enemies or diseases (Price 1987; Strong et l. 1984). Some pest insects, such as Lymantria dispar, periodically experience outbreaks (Williams and Liebhold 1995). There are two rainy seasons in Japan, south of Honshu. The first is from the end of May to mid-July and the second is from the end of August to October. In addition to the H. breviantenna outbreaks during the first rainy season in 2007, some individuals appeared in the second rainy season (Fig. 11). Our results suggested that humidity may affect the emergence of adults. To test this hypothesis, we need to research its annual occurrence successively in multiple outbreak areas in Japan.
The outbreaks of H. breviantenna occurred in the open area of Shizuoka University and the urban area of Tajimi City (Figs. 11, 13, and 18). It occurs and reproduces in urban areas, however, it may be difficult to obtain sufficient reasons why outbreaks occur in urban areas.
Control
The outbreak of H. breviantenna induces nuisance and sanitation problems not only to the human but also commercial buildings. From this study, outbreaks occur from not only forest edges but also from urban areas with small gardens, woodlands, and parks. It is possible for humans to spray themselves with a repellent, but it is difficult to spray chemical pesticides on all personal and commercial gardens and forest edges. Spraying insecticides in the field has a poor effect on protecting the natural environment. In Japan, many houses use mesh screens at the windows from the rainy season to summer for ventilation and mosquito avoidance, as shown in Fig. 1. We preliminarily tested mosquito screens (the smallest aperture was 0.76 mm) for preventing invasion. Most individuals could enter homes through mesh screens (Tagami, personal observation). Fortunately, the adults disappear after noon. In houses, closing doors until noon is the best way to avoid invasion, but large dead bodies of H. breviantenna must be disposed of. Wearing face masks and glasses is important to protect the eyes and noses from this species when outside. As mentioned above, this species is distributed widely in Japan. Thus, we need to develop effective control measures when this species is broadly distributed.