INTRODUCTION
Adult horse and deer flies, or tabanids (Diptera: Tabanidae), blood feed on wild/domestic animals and humans. They are serious pests wherever they occur, resulting in economic losses in the dairy and beef industries due to reduced milk and meat production. Tabanids pose a threat to animal health and hygiene because of their ability to transmit numerous bloodborne pathogens by mechanical transmission (e.g., equine infectious anemia, bovine leukosis, vesicular stomatitis, hog cholera, bacteria of anthrax and tularemia, and trypanosomes that cause surra) [
1,
2]. They also act as biological or mechanical vectors of helminth and bacterial infections among humans (e.g., African eye worm and tularemia), which are life-threating/damaging without treatment [
3].
In the Republic of Korea (ROK), many systematic studies of the family Tabanidae have been recorded, but there are few observations on their seasonal activity. Kim et al. [
4] reported data on the seasonal abundance of female tabanids in Jeollabuk-do, and listed 20 species with
Tabanus pallidiventris and
Tabanus amaenus being the most frequently collected. Hyun and Shin [
5] investigated the seasonal population dynamics of tabanid flies in Jeongeup-si, Jeollabuk-do, using emergence and Manitoba or cow bait traps, and reported 17 species, of which
T. amaenus and
T. pallidiventris were the most frequently collected. A survey using both New Jersey light traps and Mosquito Magnet traps in the northern part of Gyeonggi-do resulted in high numbers of
Chrysops mlokosiewiczi (as
C. vanderwulpi) and Haematopota sinensis during late June [
6].
The purpose of this survey was to identify the seasonal and population distributions of members of the family Tabanidae collected at United States (US) and ROK Army military installations/training sites and nearby villages in/near the demilitarized zone (DMZ) in the ROK.
RESULTS
A total of 2,999 specimens belonging to the Family Tabanidae, 2 subfamilies, Chrysopsinae (deer flies) and Tabaninae (horse flies), 5 genera, and 20 species were collected from 2010-2013 (
Table 2).
C. mlokosiewiczi (=
C. vanderwulpi) (90.93%) was the most frequently collected, followed by
Haematopota koryoensis (4.83%) and
Chrysops suavis (1.03%). The remaining 17 species comprised only 3.3% of all species collected. The annual mean numbers of tabanids collected/site during 2010 (35.0), 2011 (167.3), 2012 (372.8), and 2013 (153.8) from late-April to mid-October were variable. The mean numbers of tabanids collected during 2012 were 2.2, and 2.4 fold greater than the mean numbers collected during 2011 and 2013, respectively (
Table 2).
C. mlokosiewiczi accounted for 75.0-96.8% of all tabanids collected for each of the 5 survey sites (
Table 3). Compared to the annual numbers collected at the same survey sites during 2010-2013, abundance (catches) was more influenced by the previous winter temperatures (December-February) when compared to the spring (March-May) or summer season (June-August) temperatures, with a tendency to be affected by low mean temperatures (
P=0.054) and precipitation (
P=0.071) (
Table 4;
Fig. 2). Populations of
C. mlokosiewiczi and
H. koryoensis peaked from mid-June to early August, while others (e.g.,
Chrysops japonicus,
Hybomitra astur,
Hybomitra bimaculata and
Hybomitra brevis) peaked during May (
Table 5;
Fig. 3).
Chrysops mlokosiewiczi populations demonstrated bimodal peaks with the first peak occurring in late June (25.7%) and the second peak in early August (17.3%), whereas
H. koryoensis populations represented a unimodal peak in late July (58.6%).
Atylotus horvathi populations peaked in early August (42.9%) and was the most frequently collected species during August.
The numbers of tabanids collected for the different sites were variable (
Table 3). Survey sites were divided into 3 groups by their property characteristics: NNSC and Camp Bonifas (adjacent to a low lying area and intermittent stream bordered by young mixed forests), Daeseong-dong and Warrior Base (bordered by rice paddies), and Tongilchon (adjacent to a cow shed and bordered by rice paddies and dry land agriculture on 2 sides and residences on the other 2 sides). Overall, the highest numbers (53.2%) of tabanids were collected from the NNSC camp, while the lowest numbers (0.7%) were collected at a beef farm in Tongilchon (
Table 3). Overall, tabanids were found to be the most abundant during all years for habitats consisting of low lying areas with intermittent streams bordered by forests (
Fig. 4).
DISCUSSION
Adult deer and horse flies oviposit on vegetation in damp environments, e.g., wetland agriculture, low lying areas that periodically flood, borders of intermittent streams, and forested areas, where the larvae emerge and feed on small insects. Mature larvae pupate in damp soil at the edge of water sources where they remain until adults emerge. Adult deer flies are medium sized flies that belong to the genus Chrysops, while horse flies are generally much larger. Females of both groups are vicious biters, cutting the dermis with “knife-like” mandibles that make a cross-shaped incision and then using other mouth parts to ingest the blood, while the males feed on pollen. The adults readily attach domestic livestock and wildlife, as well as humans, and are regarded as pests due to their bites. Horse and deer fly bites can be extremely painful, while their saliva can result in mild to severe allergic reactions that result in itching, discomfort, and other health issues. In addition, they are known to vector pathogenic bacteria, viruses, and helminths through mechanical transmission and pose disease threats to wildlife, domestic livestock, and local human and military populations that work or conduct operations in open sunlit areas where the adults are found.
Only 6 species,
C. mlokosiewiczi,
C. suavis,
H. koryoensis,
H. sinensis,
H. astur, and
T. trigeminus, were collected in sufficient numbers for analysis of seasonal abundance. In the southern part of Korea (Jeollabuk-do), Kim et al. [
4] collected 20 species of deer and horse flies belonging to 4 genera, with
T. griseinus (26.7%) and
T. amaenus (22.3%) as the most frequently collected. Hyun and Shin [
5] also found
T. amaenus (33.9%) and
T. griseinus (21.8%) as the most frequently collected species at Jeongeup-si, Jeollabuk-do. In a survey of tabanids of northern ROK, Suh et al. [
6] identified 14 species of tabanids belonging to 5 genera.
Chrysops mlokosiewiczi (57.3%) was the most frequently collected, followed by
H. sinensis (29.1%),
H. koryoensis (4.4%) and
T. mandarinus (2.3%). The most common tabanid species in northern ROK was
C. mlokosiewiczi, which accounted for 7.4% and 9.1% of the total collections for 2 survey sites in Jeollabuk-do [
4,
5]. Overall for years 2010-2013,
C. mlokosiewiczi accounted for 90.93% (range 87.1-96.82%) of all tabanids collected by Mosquito Magnets, compared to 57.3% in previous surveys using NJ light traps and Mosquito Magnet traps [
6]. Additional surveys and studies are required to determine reasons for the very high abundance of
C. mlokosiewiczi near the DMZ. Comparison of the annual numbers collected at the 4 survey sites during 2011-2013, abundance (catches) were more influenced by previous winter temperatures when compared to the spring or summer season temperatures, with a tendency to be affected by low mean temperatures (
P=0.054) and precipitation (
P=0.071). Krcmar [
12] reported that the seasonal meteorological variability significantly influenced the abundance of adult tabanids at low spring (May) temperatures. However, while the data is suggestive that low mean temperatures and precipitation during December-February result in fewer adults collected during the summer months, there was no significant difference between the mean numbers collected based on annual temperatures and precipitation variations from March to August.
In this study, populations of adult tabanids of some species (e.g.,
C. mlokosiewiczi and
H. koryoensis) peaked from mid-June to early August, while other species (e.g.,
C. japonicas,
H. astur,
H. bimaculata, and
H. brevis) demonstrated population peaks during May. Surveys in the southern part of the ROK (Jeollabuk-do) showed that populations of many of the species peaked from the end of June to early July [
4,
5], and early and mid-July [
6].
The surveyed areas were divided into 3 groups by their property characteristics: NNSC and Camp Bonifas (adjacent to a low lying and frequently flooded area and intermittent stream bordered by a forested area), Daeseong-dong and Warrior Base (bordered by rice paddies), and Tongilchon (adjacent to a cow shed). Kim et al. [
4] and Hyun and Shin [
5] reported that the association of hills and mountains resulted in increased numbers and diversity of tabanids collected. Although not all sites were collected over the 4-year period, the highest numbers of tabanids were collected from low lying areas often associated with water and intermittent streams that were bordered by forests, followed by sites surrounded by rice paddies, and lastly, the beef farm. The low numbers of tabanids collected at Tongilchon (beef farm) may in part be due to competition of beef cattle due to the close proximity (<5 m) from the Mosquito Magnet.
Haematopota koryoensis (97.2%) was more frequently collected in the forest areas, while the other Haematopota spp. were collected mostly from areas associated with rice paddies. Few
H. sinensis were collected, which are reported to be associated with mountain habitats [
4].
Chrysops japonicas (100%),
C. suavis (80.6%),
H. astur (77.8%) and
T. trigeminus (100%) were collected more frequently in forested areas, while
A. horvathi (100%) and
C. mlokosiewiczi (99.4%) were collected more frequently in both forest and rice paddy habitats. While Inaoka [
13] indicated that
C. suavis and
T. trigeminus were eurytopic or uniformly distributed over various habitats, all T. trigeminus and most
C. suavis (80.6%) were collected near forest habitats.
C. mlokosiewiczi was collected near forest habitats and rice paddies, unlike previous reports that indicated it was collected more frequently in pastures and open land habitats [
13].
In conclusion, C. mlokosiewiczi and H. koryoensis were the 2 most commonly collected tabanids collected from various habitats near and inside the southern boundary of the DMZ, with peak populations observed from mid-June to early August. Adult populations were more influenced by low winter temperatures and precipitation rather than high temperatures during throughout the adult stage. Habitat differences accounted for differences in relative abundance and diversity of tabanids collected. Tabanids are pestiferous and vicious biters, affecting wildlife and domestic animals and local and military populations during farming/military activities. In addition, they vector viruses, bacteria, and helminths that pose medical and veterinary threats.