Tabanid Populations Research Articles

Richness, Endemism and Seasonality of Horseflies (Diptera: Tabanidae) in Forests of the Equatorial Pacific Region of Ecuador.

The Equatorial Pacific Region (EPR) in Ecuador is characterized by high rates of vegetation diversity, and rapid loss of vegetation cover due to anthropogenic pressures. In this study, general ecological aspects of the Tabanidae family, including richness, endemism, and seasonality, were evaluated. Analyses reveal that approximately 42% of the species recorded for Ecuador are present in the EPR, and out of the 84 species cataloged in the EPR, 6 are endemic, representing an endemism of 7.14%. Furthermore, it was established that tabanid populations in a coastal dry forest significantly increased their population density during the dry season, while decreasing during the wet season.

Horse Flies (Diptera: Tabanidae) in Mangrove Forests and Estuarine Floodplains on Marajó Island, Brazil.

Tabanids constitute an important group of hematophagous insects that can transmit zoonoses, but with studies on the ecological distribution of species still neglected in the Amazon. We evaluated the role of mangrove forests and estuarine floodplains located inside and outside a conservation unit (UC) on the coast of Marajó Island, Amazon River estuary, on the diversity and distribution of tabanids. Specifically, we studied whether the community of mangrove and estuarine floodplain tabanids located inside and outside the UC differ in abundance, richness, and species composition. We collected tabanids using a Malaise trap at 40 sampling points, resulting in 637 specimens distributed in 13 species and one morphotype, representing approximately 37% of the tabanid fauna ever recorded for the Marajó Island. There was no significant difference in the richness and composition of tabanids between the phytophysiognomies, but the abundance was significantly different, with greater abundance in the mangrove. The areas inside and around the UC had an influence on the tabanids, with the areas inside the UC having the highest number of specimens and species, also influencing the species composition. Two species are new records for the Marajó Island, bringing the number of species recorded to 38. Our results suggest that, along the Amazonian coast, mangroves and estuarine floodplains maintain part of the diversity of tabanids known for the Brazilian Amazon. Our data also indicate that the region's UC provides potentially important habitats for the maintenance of local tabanid populations.

Was the decline of saltmarsh tabanid populations after the 2010 oil spill associated with change in the larval food web?

AbstractHorse flies of the species Tabanus nigrovittatus and Tabanus acutus are native to coastal marshlands. Their larvae are apex invertebrate predators, and their development is dependent on the food web in the marsh sediment. Surveillance of T. nigrovittatus after the 2010 Deepwater Horizon Oil Spill in the Gulf of Mexico showed population crashes of adult flies in southeast Louisiana marshes near oil landfall, but not in southwest Louisiana where oil did not reach. Sediment collection in 2011 from Louisiana marshes showed a near‐complete absence of larvae in the southeast yet high numbers in the southwest. We hypothesized that oil contamination destroyed critical components of the larval food web and/or residual toxicity led to larval death. We used 18S rRNA gene metagenomics to identify components of the food web in larval guts and sediment from southeast and southwest Louisiana marshes. Sediment oil contamination, biochemistry, and toxicity could not explain the lack of larvae in the southeast, because oiling at our high‐tide mark sites was low at the time of the study and toxicity was independent of sediment biochemistry. Hexapods were the main food web components in tabanid larval guts. Abundance of stink bug, vinegar fly, and mosquito species in the sediment was positively associated with the presence of larvae. However, these taxa were enriched in southeastern (near oil) versus southwestern (unoiled reference) sediment, and thus, lack of major food web components due to oiling could not explain lack of larva in the east. We conclude that the immediate crash in adult populations in oiled regions was the main cause for the absence of larvae the following year. While most saltmarsh arthropod groups had rebounded within a year after the oil spill, recovery of saltmarsh horse flies was ongoing for 5 years.

Diversity and abundance of tabanids in Northern Spain

Tabanids (Diptera: Tabanidae) are large haematophagous flies that cause both direct (by biting nuisance) and indirect (primarily by mechanical transmission of diseases) damage to host species. Research studies on this family have received little attention in some parts of Europe. Our aims were to characterise the species richness, abundance, and peak of activity of tabanid fly species in a region of Northern Spain. Home-made canopy traps, sweep nets, and Malaise traps were employed for the collection of tabanids across four cattle farms, two equestrian centres, and two golf courses during a 3-month period in the summer of 2020. A total of 300 specimens of 27 tabanid species belonging to eight genera were identified. The most prevalent species were Haematopota pluvialis (23.3%), Tabanus eggeri (20.0%), and Tabanus bromius (8.0%). The former species was recorded biting humans and therefore should be considered of relevance to public health. Tabanids were more diverse and abundant in scrubland and grazing pastures [relative abundance (RA) = > 10%; species richness (S) = 8-12; Shannon-Index (H´) = 1.5 - 2.1] compared to crop landscapes (RA = < 1%; S = 0-1; H´ = 0) according to canopy traps. The tabanid population dynamics was determined to be short, with the greatest abundance and diversity concentrated in mid-late July. This study updates the checklist of this Diptera group in the Northern Spain from nine known extant species to 31 species, providing the first data on the summer peaks of activity of tabanids for this region.

Insect (Hexapoda) diversity in the Oceanic Archipelago of Fernando de Noronha, Brazil: Seasonality and Populational Density of Tabanidae (Diptera)

Abstract: The seasonal population density is informed for two epidemiologically important species of bloodsucking Tabanidae, Tabanus occidentalis Linnaeus and T. pungens Wiedemann, recorded at the Fernando de Noronha archipelago that was never connected to the continent. The two species are widespread in the Neotropical Region, have not been recorded from any other oceanic island, and have most likely been introduced accidentally in the archipelago. Tabanus occidentalis dominated the samples, encompassing 99.6% of the specimens collected in the two local seasons, rainy and dry. Tabanus pungens was rarer, encompassing 0.4% of the specimens collected mainly in the dry season. The tabanids of Fernando de Noronha are able to transmit blood pathogens, bringing risks to the health of the livestock. They also pester the tourists, which brings losses to the local tourist industry. Larvae of both species were already collected in the water lettuce Pistia stratiotes Linnaeus and it is highly recommend that this introduced aquatic plant be removed from the ponds of Fernando de Noronha to control tabanid populations.

Evaluation of the relative roles of the Tabanidae and Glossinidae in the transmission of trypanosomosis in drug resistance hotspots in Mozambique

BackgroundTsetse flies (Diptera: Glossinidae) and tabanids (Diptera: Tabanidae) are haematophagous insects of medical and veterinary importance due to their respective role in the biological and mechanical transmission of trypanosomes. Few studies on the distribution and relative abundance of both families have been conducted in Mozambique since the country’s independence. Despite Nicoadala, Mozambique, being a multiple trypanocidal drug resistance hotspot no information regarding the distribution, seasonality or infection rates of fly-vectors are available. This is, however, crucial to understanding the epidemiology of trypanosomosis and to refine vector management.MethodsFor 365 days, 55 traps (20 NGU traps, 20 horizontal traps and 15 Epsilon traps) were deployed in three grazing areas of Nicoadala District: Namitangurine (25 traps); Zalala (15 traps); and Botao (15 traps). Flies were collected weekly and preserved in 70% ethanol. Identification using morphological keys was followed by molecular confirmation using cytochrome c oxidase subunit 1 gene. Trap efficiency, species distribution and seasonal abundance were also assessed. To determine trypanosome infection rates, DNA was extracted from the captured flies, and submitted to 18S PCR-RFLP screening for the detection of Trypanosoma.ResultsIn total, 4379 tabanids (of 10 species) and 24 tsetse flies (of 3 species), were caught. NGU traps were more effective in capturing both the Tabanidae and Glossinidae. Higher abundance and species diversity were observed in Namitangurine followed by Zalala and Botao. Tabanid abundance was approximately double during the rainy season compared to the dry season. Trypanosoma congolense and T. theileri were detected in the flies with overall infection rates of 75% for tsetse flies and 13% for tabanids. Atylotus agrestis had the highest infection rate of the tabanid species. The only pathogenic trypanosome detected was T. congolense.ConclusionsDespite the low numbers of tsetse flies captured, it can be assumed that they are still the cyclical vectors of trypanosomosis in the area. However, the high numbers of tabanids captured, associated to their demonstrated capacity of transmitting trypanosomes mechanically, suggest an important role in the epidemiology of trypanosomosis in the Nicoadala district. These results on the composition of tsetse and tabanid populations as well as the observed infection rates, should be considered when defining strategies to control the disease.

Diversity and population dynamic of Tabanidae (Diptera) in the cerrado-pantanal ecotone

Tabanid (Diptera) species are associated with the mechanical transmission of several pathogens to both domestic and wild animals around the world. The aim of this study was to evaluate the diversity, abundance, and seasonal dynamic of tabanids in the Cerrado-Pantanal ecotone in Miranda, state of Mato Grosso do Sul, Brazil. Tabanids were collected once a month, from June 2001 to May 2003, for seven consecutive days per collection, using canopy and nzi type traps baited with a chemical attractant (1-octen-3-ol). A total of 6,492 individuals from 39 species and 18 genera was collected, which increases from 25 to 34 the number of tabanid species reported for the studied region. Tabanus occidentalis Linnaeus, 1758 (62.21%) was the most abundant species throughout the collection period, followed by Lepiselaga crassipes (Fabricius, 1805) (7.19%) and Tabanus sorbillans Wiedemann, 1828 (5.68%). The peak of the tabanid population was reached during the rainy season, which is the period of the highest potential risk of mechanical transmission of pathogens by these insects in the studied region.

Seasonal succession of tabanid species in equine infectious anaemia endemic areas of Italy.

Equine infectious anaemia (EIA) is a disease with an almost worldwide distribution, with several outbreaks having been reported recently in European countries. In Italy, two regions, Lazio and Abruzzo, are considered as endemic areas for this disease. In nature, the EIA virus is mechanically transmitted by biting flies such as tabanids (Diptera: Tabanidae), although few studies have investigated the epidemiological implications. In the present study, several sites characterized by different levels of EIA prevalence were sampled. In sites with high tabanid populations, a seasonal succession of tabanid species with a dual-peak corresponding to early active species (i.e. in June to July) and late active species (i.e. in August to September) was clearly observed. Moreover, a positive correlation was found between EIA prevalence and tabanid abundance and species richness, suggesting that tabanid diversity might extend the duration of the seasonal transmission period of EIA. Further observations are required to better assess how vector diversity influence EIA transmission.

Impact of the 2010 Deepwater Horizon oil spill on population size and genetic structure of horse flies in Louisiana marshes.

The greenhead horse fly, Tabanus nigrovittatus Macquart, is frequently found in coastal marshes of the Eastern United States. The greenhead horse fly larvae are top predators in the marsh and thus vulnerable to changes in the environment, and the adults potentially are attracted to polarized surfaces like oil. Therefore, horse fly populations could serve as bioindicators of marsh health and toxic effects of oil intrusion. In this study, we describe the impact of the April 2010 Deep Water Horizon oil spill in the Gulf of Mexico on tabanid population abundance and genetics as well as mating structure. Horse fly populations were sampled biweekly from oiled and unaffected locations immediately after the oil spill in June 2010 until October 2011. Horse fly abundance estimates showed severe crashes of tabanid populations in oiled areas. Microsatellite genotyping of six pristine and seven oiled populations at ten polymorphic loci detected genetic bottlenecks in six of the oiled populations in association with fewer breeding parents, reduced effective population size, lower number of family clusters and fewer migrants among populations. This is the first study assessing the impact of oil contamination at the level of a top arthropod predator of the invertebrate community in salt marshes.

Tabanids: Neglected subjects of research, but important vectors of disease agents!

Tabanids are nuisance pests for people and livestock because of their painful and irritating bite, persistent biting behavior, and blood ingestion. About 4400 tabanid species have been described; they are seasonally present in all kinds of landscapes, latitudes, and altitudes. High populations have a significant economic impact on outdoor activities, tourism, and livestock production. Tabanids are also vectors of animal disease agents, including viruses, bacteria and parasites. However, tabanids have received little attention in comparison with other hematophagous Diptera. Here, we highlight the many direct and indirect impacts of tabanids and provide a brief summary of tabanid morphology, biology, and life cycle. Impacts include pathogen transmission, parasite transportation (Dermatobia hominis), biological transmission (Loa loa), and mechanical transmission of viruses, such as equine infectious anemia virus, protozoa, such as Trypanosoma evansi and Besnotia besnoiti, and bacteria, such as Bacillus anthracis and Anaplasma marginale. We discuss parameters of mechanical transmission and its mathematical modeling. Control methods for tabanid populations are also summarized; these include trapping, the use of insecticides, repellents, and livestock protection. Lastly recommendations are provided for the direction of future research.

Trypanosoma vivax infection dynamics in a cattle herd maintained in a transition area between Pantanal lowlands and highlands of Mato Grosso do Sul, Brazil

Trypanosoma vivax outbreaks in beef cattle in the Pantanal region of Mato Grosso do Sul state, Brazil, causes relevant economical impact due to weight loss, abortion and mortality. Cattle moved from the Pantanal to adjacent areas of this ecosystem for breeding and fattening is a common feature. Therefore an epidemiological study on breeding cows in the transition area between Pantanal lowland and adjacent highlands of Mato Grosso do Sul was performed to determine the T. vivax infection dynamics and outbreak risk. Three experimental groups were formed: Group 1 consisted of cows parasitologically negative by the Woo test and in the enzyme-linked immunosorbent assay for T. vivax antibody detection (Tv-ELISA-Ab); Group 2 parasitologically negative and positive in the Tv-ELISA-Ab; and in Group 3 cows were parasitologically positive and with positive reactions in the Tv-ELISA-Ab. During 24 months, the cows' dislodgment between the above established groups was monitored by Woo test and Tv-ELISA-Ab exams. The tabanid population was also monitored and the highest number occurred during the rainy season. Although parasitemias were detected only in the first four samplings of the experimental period, the cows could be considered as trypanotolerant, because no clinical signs were observed. Despite the higher T. vivax incidence during the dry season, no disease symptoms were seen. Even though T. vivax epidemiological situation in the herd was characterized as endemic with seasonal variation, the probability of outbreaks was null within the conditions of the study.

Biology and control of tabanids, stable flies and horn flies.

Tabanids are among the most free-living adult flies which play a role as livestock pests. A single blood meal is used as a source of energy for egg production (100-1,000 eggs per meal), and females of certain species can oviposit before a blood meal is obtained (autogeny). Therefore, the maintenance of annual populations requires successful oviposition by only 2% of females. Wild animal blood sources are usually available to maintain annual tabanid populations. Larval habitats are also independent of domestic livestock. Thus, the use of repellents or partial repellents is the only effective chemical strategy to reduce the incidence of tabanids on livestock. Permanent traps (and possibly treated silhouette traps) can be employed to intercept flies. Selective grazing or confinement can also reduce the impact of tabanids. Stable fly adults are dependent on vertebrate blood for survival and reproduction, but the amount of time spent in contact with the host is relatively small. Stable fly larvae develop in manure, spilled feed and decaying vegetation. Management of larval habitats by sanitation is the key to stable fly control. Treatment of animals with residual insecticides can aid in control; thorough application to the lower body parts of livestock is important. Proper use of modified traps, using either treated targets or solar-powered electrocution grids, can be effective in reducing stable fly populations. Adult horn flies spend the major part of their time on the host, and the larvae are confined to bovid manure. Therefore, almost any form of topical insecticide application for livestock is effective against horn flies, in the absence of insecticide resistance. Treatments should be applied when economic benefit is possible; economic gains are associated with increased weaning weights and weight gains of yearling and growing cattle. Oral chemical treatments (insect growth regulators or insecticides) administered at appropriate rates via bolus, water, food or mineral mixtures can inhibit horn fly larval development. However, adult horn fly movement among cattle herds limits the use of larval control for horn fly population management. The augmentation of native parasites, predators and competitors has been attempted and even promoted for horn fly and stable fly control, but evidence for the success of such programmes is equivocal.

Biting flies of the eastern maritime provinces of Canada. I. Tabanidae.

Fifty-seven species of Tabanidae are recorded from maritime Canada. Thirty-one species have been collected during the period 1973–1976 in the Maritime Provinces, particularly in the Nova Scotia–New Brunswick border region. Larval and pupal habitats were not determined. Feeding habits of 20 species of tabanids were determined; 15 species were collected feeding on man, and 9 species feeding on cattle. Chrysops mitis was the most abundant deer fly and accounted for 14.5% of the tabanid population, 37.1% of the deer flies collected, and 52.6% of the deer flies feeding on man. Hybomitra epistates was the most abundant tabanid; it comprised 19.7% of the tabanids collected and 32.6% of the Hybomitra population. Hybomitra frontalis was the most abundant horse fly feeding on man, and comprised 74.2% of this group. Chrysops frigidus accounted for 42.9% of the deer flies feeding on cattle, while H. typhus Form A accounted for 50% of the horse flies feeding on cattle. Hybomitra illota was the most abundant tabanid collected in tabanid traps. Generally, species of Chrysops were more annoying to man while species of Hybomitra were more of a pest of cattle. Specimens of Tabanus were uncommon.

Extracting Larvae of Chrysops hirsuticallus (Diptera: Tabanidae) from Soil: Efficiencyof Two Methods

A comparison of the efficiency of Tullgren funnels vs. a wire sieve for extracting known numbers of late instar Chrysops hirsuticalhis Philip from soil samples ca. 5.1 cm thick by 0.093 m2 revealed that the sieve was more efficient when both high (20) and low (10) larval densities were used. The differences between replicates during funnel extraction were significant at high larval density (chi-square test, p=.034), which raises doubts about the reliability of this method for quantitative studies of larval tabanid populations.

Growth, Abundance and Distribution of Larval Tabanids in Experimentally Fertilized Plots on a Massachusetts Salt Marsh

The coastal salt marshes of the eastern United States provide breeding habitats for several species of biting flies of the family Tabanidae. The larvae are found in the sod of the marsh where they spend a year or more before pupating and emerging as adults in the summer months. Many investigators have studied the distribution and density of larval tabanids in salt marshes but few have provided quantitative data on the seasonal abundance and distribution of larval horseflies. No one has evaluated the effect on them of the contamination of coastal marshes with nutrient-rich waste water. In the present investigation small areas were sampled intensively to estimate the abundance and distribution of tabanid larvae on a salt marsh, and to study the effect of experimental nutrient enrichment simulating eutrophication on larval tabanid populations. In addition, the feeding preferences of the larvae of Tabanus nigrovittatus Macquart, the major horsefly in Massachusetts marshes, and the role that cannibalism may play in regulating larval numbers and distribution were investigated.

Tabanidae: Use of a Self-marking Device to Determine Populations in the Mississippi-Yazoo River Delta 12

Fluorescent pigment in a self-marking device on a Malaise trap baited with CO2 (released at rates of 100 or 500 ml/min) was used to estimate the size of the tabanid population in the Delta Experimental Forest, Stoneville, MS. The estimated daily average for the 1st test from August 1–25, 1974, was 989,195 ♀ tabanids in the 4-mile2 (10.4 km2) area. The estimated daily average for a 2nd test from Sept. 10 to Oct. 7, 1974 was 275,497 ♀ tabanids in the same area.

Physiological age structure of adult tabanid populations (Diptera: Tabanidae) in Alberta, Canada.

The seasonal distributions of age classes of Atylotus incisuralis and 11 species of Hybomitra (frontalis, itasca, liorhina, rhombica osburni, rupestris, affinis, arpadi, lasiophthalma, lurida, nuda, typhus) collected in Manitoba fly traps were determined. The first 6 species were autogenous. In these species maximum numbers occurred after mid-July. In the anautogenous species maximum numbers were trapped before mid-July. In the anautogenous species, survival of nullipars to the beginning of the 2nd gonotrophic cycle ranged between 19% and 51% and survival of unipars to the beginning of the 3rd cycle ranged between 31% and 63%. In the autogenous species few biparous flies were trapped, survival of unipars ranging between 1% and 15%. It is probable that some anautogenous species had individuals completing 3 gonotrophic cycles. More uniparous than biparous flies retained eggs after oviposition. Anautogenous and autogenous species retained eggs to the same extent.

Reduction of Tabanid Populations on Cattle with Sticky Traps Baited with Dry Ice

Horse fly populations on cattle were reduced by operation of sticky traps baited with dry ice situated around the periphery of a pasture in which the animals were confined. Fly populations remained relatively low on cattle while traps were in operation, but increased within a few days after trapping was discontinued. Large numbers of flies were collected during the brief trapping periods.

Predation on Horse Flies by Two Bembicine Wasp Species in Certain Areas of Southern Louisiana1

The effect of two wasp species. Stictia carolina (F.) and Bembix texana Cresson, predators of horse flies in some areas of Louisiana, on tabanid populations in South Louisiana was studied in 1965. Weekly counts of fly and wasp populations on and around cattle, respectively. indicated that population densities of 2 or more wasps per animal noticeably reduced the tabanid population. During 3 consecutive days in July 9 S. carolina females carried an average of 3.1 tabanids daily to their burrows. No other prey was captured by this species during the study period. Seven B. texana females carried an average of 3.9 flies per day to their burrows during 2 consecutive days in August, however 92.3% of the flies was composed of species of Sarcophagidae, Stratiomyidae, and Syrphidae.

Abundance and Survival of Tabanid Larvae in Effluent from a Dairy Barn

The effluent of fecal debris from a dairy barn collected in a dry creek bed and provided a habitat for large numbers of tabanid larvae. The total tabanid population was estimated to be about 1200 larvae when samples were taken from a 250-ft2 section of the debris. Large numbers of other immature invertebrates in the area were believed to sustain the high density of tabanids by serving as a food source.