Evaluation of Partially Submerged Sticky Traps On Lake Spillways For Adult Black Fly (Diptera: Simuliidae) Surveillance and Arbovirus Detection

ABSTRACT Sentinel surveillance systems demonstrate an improved ability to supplement monitoring data and anticipate arbovirus outbreaks (i.e., sentinel avian species). Management complications can arise during unpredictable or unseasonal disease detections, especially in rural areas where resident distribution is patchy. Using spillways near residential lake communities as static surveillance locations, we tested a novel partially submerged sticky trapping technique and screened wild populations of adult female black flies (Diptera: Simuliidae) for West Nile virus (WNV) and eastern equine encephalitis virus (EEEV). Trap site selection criteria considered the density of immature black fly colonization on spillway surfaces and the number of positive detections of arboviral targets in nearby Culex mosquito populations. On average (±standard error), sticky traps captured 134 (±33) adult black flies over a 24-h period, with 1 trap capturing as many as 735 individuals. Although we detected positive cases of WNV from 20 Culex mosquito trapping sites within 16 km (approx. flight radius) of the selected lake spillways, mixed pools of adult female Simulium vittatum complex and Simulium decorum were all negative for both arboviruses. This study yielded an application for partially submerged sticky traps to collect adult female black flies. Its potential uses for monitoring the infection rates of more well-documented Simulium parasites are discussed.

Phenotypic plasticity in the labral fan of simuliid larvae (Diptera): effect of seston load on primary-ray number

The number of primary rays in the labral fan of filter-feeding black fly (Diptera: Simuliidae) larvae has been used by some authors to aid in species identification. We examined the number of primary labral fan rays in field-collected last-instar larvae of Simulium rostratum and Simulium decorum. Significant inter- and intra-specific differences were found both spatially and temporally. Simulium rostratum and S. decorum larvae were also reared to last instar (from eggs or first- or second-instar larvae) under three feeding regimes to test the effect of seston load on the number of primary labral fan rays. In both species the fan-ray number decreased when the food supply was increased. We conclude that the primary fan ray number should be used cautiously in species diagnosis because it is a phenotypically plastic trait that varies with seston load. A potential feedback mechanism to explain the observed differences in fan-ray number is hypothesised.

Entomopathogenic fungi of the order Entomophthorales (Zygomycotina) in adult black fly populations (Diptera: Simuliidae) in Quebec

Infections by insect-pathogenic fungi of the order Entomophthorales in two adult black fly populations were studied in the Réserve Faunique du Saint-Maurice (Quebec). Entomophaga near limoniae infected Simulium verecundum/rostratum in June whereas Erynia curvispora predominantly parasitized Simulium decorum from the 2nd week of July to September and Erynia conica attacked the Simulium venustum complex, Simulium verecundum/rostratum, and the Simulium vittatum complex from May to September. The fungi did not infect the adult stage of Prosimulium species. Possible evidence of host specificity for Erynia conica is discussed.Key words: Entomophthorales, black fly, host specificity, Entomophaga, Erynia, Simulium.

Absence of population structure in black flies as revealed by enzyme electrophoresis

Analysis of allozyme variation by the FST-statistic in Simulium decorum and several other black fly species reveals very little genetic variation that could be attributed to genetic drift. This is consistent with what is known about the rates of migration of black flies and supports the idea that there is a lack of population subdivision in these insects. This picture of population structure is quite different from that presented by chromosome inversion polymorphisms. Chromosomal variation, however, can reasonably be attributed to selection and suggests that the role of inversions in black fly evolution is similar to population subdivision in the shifting balance process.Key words: black flies, allozymes, population structure, evolution.

Caloric reserves in natural populations of a blackfly, Simulium decorum (Diptera: Simuliidae), and a deerfly, Chrysops ater (Diptera: Tabanidae)

Simulium decorum and Chrysops ater immatures were collected in northern New Hampshire during 1982 and were reared to adults in the laboratory to describe follicular development, to quantify total available caloric reserves, and to determine longevity. Females of both species produced eggs without blood meals and sucrose solutions during the first ovarian cycle. Differences in mean fecundity (mean range, 152–215) were noted for the Chrysops obtained at three sites below a trout-rearing pond. A chemical test consisting of a sulfuric acid solution of sodium bichromate was used to quantify caloric reserves in the newly emerged blackflies and deerflies. Available reserves for S. decorum females, ≤4 h or 24 h after eclosion, were about sevenfold greater than those of the males. There were no significant differences in available reserves for adult deerflies. Although males and females of both species utilized stored reserves for survival during early adulthood, sugars greatly enhanced longevity.

Ecological characterization of two sibling species, IIIL-1 and IS-7, in the Simulium vittatum complex (Diptera: Simuliidae)

Larval polytene chromosomes provided the identification tool that enabled ecological characterization of two black fly sibling species, IIIL-1 and IS-7, in the Simulium vittatum complex. A 4-year study in the eastern United States demonstrated important differences between the two siblings, based primarily on differential occupancy of the stream continuum. Immatures of the IIIL-1 sibling predominated below nonspring-fed reservoirs, downstream of sewage effluent outflows, and in warm downstream areas. Immatures of the IS-7 sibling occurred, with IIIL-1, in cool well-oxygenated flows generally associated with groundwater discharge. These sibling–habitat relations produced sibling gradients along the stream continuum. Over their geographic ranges, the IIIL-1 sibling became increasingly abundant from north to south, relative to IS-7. At mixed-sibling sites, populations were asynchronous; IS-7 generally predominated in early spring and late fall. The major determinants of sibling distributions were those factors affecting respiration: temperature, oxygen, and current. Species such as the black fly Simulium decorum and the midge Chironomus riparius signalled essentially pure populations of IIIL-1. Preimaginal densities of Glossosoma spp. (Trichoptera) also indicated sibling proportions. IIIL-1 and IS-7 shared all pathogens. At mixed-sibling sites, proportionally more larvae of IIIL-1 occurred on rocks than on grasses. Regardless of sibling, larvae on rocks were darker than those on grasses, which suggested differences in the proportion of ingested materials.

Larval distribution and succession of outlet-breeding blackflies (Diptera: Simuliidae) in New Hampshire

Thirteen described species of outlet-breeding simuliids and five isomorphic sibling species of the Simulium venustum/verecundum complexes were collected in 1978 and 1979. Prosimulium fuscum, P. mixtum, Simulium aestivum, S. aureum, S. decorum; S. tuberosum, S. venustum (CC) and S. vernum were the most widely distributed species while S. aureum, S. decorum and S. venustum (CC) were the most abundant. Simulium decorum, S. tuberosum and S. venustum (AC(gB) and CC) were present at the same sites during both years while the remaining species varied in their occurrence at a specific site between the two years. Succession of Simulium spp. in late winter and spring was similar to that reported from other areas of northern North America. Most Simulium spp. studied were multivoltine while S. corbis, S. croxtoni and S. venustum (A/C) were univoltine. Simulium decorum had single or multiple generations, depending on the site. Larvae of S. venustum (A/C) and most species of the subgenus Eusimulium attached to trailing vegetation, while S. corbis, S. decorum, and S. tuberosum attached more frequently to submerged rocks and sticks. Prosimulium fontanum, S. gouldingi, S. venustum (CC and AC(gB)), and S. verecundum (A/C and ACD) did not demonstrate preference for a particular substrate. Reduction in stream flow affected the number of cohorts of S. aestivum and S. aureum and the number of generations per year of S. aureum and S. vernum.

Growth and development of geographic and crossbred strains of colonized Simulium decorum (Diptera: Simuliidae)

The developmental times from larval hatch to adult emergence were computed for strains of Simulium decorum from Warm Springs, Georgia (GA), and Dryden Lake, New York (DL). Rearings were conducted at several constant temperatures. Differences between geographic strains and between sexes within strains were significant in nearly every instance (P < 0.01). At cool temperatures (13 to 17 °C), the GA strain developed more quickly; however, this trend was reversed at intermediate temperatures (18 to 20 °C), and at 21 °C only GA males developed faster than DL males. With few exceptions, both sexes of the GA strain required more cumulative degree-days for development than their northern counterparts.The number of instars was determined for each strain by measuring the length of the postgena of head capsules collected during warm (21 °C) and cool (13 °C) rearings. Although both strains pass through seven stadia, differences between strains were noted in the size of middle instars. In all rearings sexual dimorphism was evident in the morphology of last-instar head capsules; in rearings conducted at cool temperatures (13 °C), sexes could also be separated by the size of last-instar head capsules.Strains were crossed and their progeny reared. High values for net reproductive rate (R0), fecundity, and adult survival suggest that heterosis resulted from crossbreeding the two geographic strains.