Efficacy of broadcast and perimeter applications of S-methoprene bait on the red imported fire ant in grazed pastures.

The red imported fire ant, Solenopsis invicta (Buren), is a major pest in the United States because of its painful sting. Toxic bait has been an important management tool against fire ants, but site registrations prohibit applications of most baits on grazed pastures. Extinguish, containing the insect growth regulator methoprene, was selected for this study because it has a broad site registration that includes grazed pastures. The primary objective of this research was to evaluate the efficacy for control of red imported fire ants by using broadcast applications of methoprene bait at a label rate of 1,121 g/ha versus applications around the perimeter of a target area at the reduced rate of 280 g/ha. Grazed pastures in Lee County, Alabama, and Chambers County, Alabama, were selected for this study, with broadcast treatments, perimeter treatments, and controls replicated three times at each site. All mounds were counted and rated using the USDA population index before applications and then at 8 and 16 wk posttreatment. Perimeter applications did not significantly reduce S. invicta mound abundance, but bait treatments significantly reduced mound abundance at 16 wk posttreatment at site 1 where applications were conducted in early evening. However, broadcast applications were not effective at site 2 where treatments were conducted in early morning with warmer temperatures. Emergence of winged alates was observed at 12 wk posttreatment, followed by a high density of incipient mounds that may have masked the full treatment effect of methoprene applications at site 2. Methoprene bait was effective in reducing abundance of S. invicta only when full label rates were applied.

Borrelia lonestari DNA in adult Amblyomma americanum ticks, Alabama.

Polymerase chain reaction analysis of 204 Amblyomma americanum and 28 A. maculatum ticks collected in August 1999 near the homes of patients with southern tick-associated rash illness and in control areas in Choctaw County, Alabama, showed Borrelia lonestari flagellin gene sequence from two adult A. americanum. The presence of B. lonestari in A. americanum ticks from Alabama suggests that this suspected pathogen may be widespread in the southeastern United States.

Seroprevalence of Borrelia burgdorferi in dogs in Alabama, USA.

A random sample of private small-animal practices in Alabama submitted sera from dogs with known tick contact. A total of 579 samples from the three geographic regions of the state were collected (58% of the targeted sample size). Sera were screened for antibodies to Borrelia burgdorferi using an indirect fluorescent antibody (IFA) test which had a sensitivity and specificity of greater than 90%. Anti-B burgdorferi titers of > or = 1:64 were considered to be positive, based on results from B. burgdorferi-inoculated dogs. Ten of the 579 samples (1.7%) were positive, and titers ranged from 1:64 to 1:512. Seropositive dogs were found throughbout the state, and there was no significant difference in seroprevalence by region (Mantel-Haenszel chi 2, P = 0.85). These results indicate that the seroprevalence for canine Lyme disease in Alabama is low and that use of the canine Lyme disease vaccine is not justified.

Monitoring of Culicoides spp. at a site enzootic for hemorrhagic disease in white-tailed deer in Georgia, USA.

Biting midges of the genus Culicoides (Diptera: Ceratopogonidae) were monitored at a Georgia (USA) site where epizootic hemorrhagic disease (EHD) and bluetongue (BT) viruses are enzootic among white-tailed deer (Odocoileus virginianus). Collections were made using a captive white-tailed deer and light traps from June 1993 through November 1994. We collected 210,482 females from the captive deer during morning and evening periods. Predominant species were C. lahillei (73%), C. stellifer (16%), C. biguttatus (6%), C. niger (3%), C. spinosus (2%), and C. paraensis (0.2%). Other species were C. venustus, C. obsoletus/sanguisuga, C. haematopotus, C. guttipennis, and C. arboricola, which together represented < 0.1% of the specimens collected. No C. variipennis, a known vector of EHD and BT viruses, were collected from the deer. An estimated 953,299 females were collected in 695 light-trap nights. The most common species in light-trap collections were C. spinosus (45%), C. biguttatus (27%) and C. stellifer (24%). Culicoides variipennis was rare in the light-trap samples, representing < 0.01% of the total collections. There was serological evidence from hunter-killed deer that local deer were infected with EHD and BT viruses during the study, particularly during 1994. A primary suspect vector was C. lahillei, which attacked the bait deer in large numbers during the summer and early fall of both 1993 and 1994. Based on their seasonality, relative abundance, and host-seeking activity, C. stellifer and C. spinosus also were considered as possible vectors. However, virus isolation attempts on 113,716 Culicoides, including 62,530 C. lahillei and 32,769 C. stellifer, were negative.

Borrelia sp. in ticks recovered from white-tailed deer in Alabama.

Six hundred sixty-five hunter-killed white-tailed deer (Odocoileus virginianus) from 18 counties in Alabama (USA) were examined for ticks. Most of the collections were made at state-operated wildlife management areas. Four species of ticks (n = 4,527) were recovered: the lone star tick Amblyomma americanum (n = 482); the Gulf Coast tick A. maculatum (n = 11); the winter tick Dermacentor albipictus (n = 1,242); and the black-legged tick Ixodes scapularis (n = 2,792). Fifty-six percent of the ticks (n = 2,555) were examined for Borrelia sp. spirochetes using an immunofluorescent, polyclonal antibody assay. Spirochetes were detected in I. scapularis (five females, seven males) from Barbour, Butler, Coosa, and Lee counties and A. americanum (four males, four nymphs) from Hale, Lee, and Wilcox counties. Area-specific prevalences in ticks were as high as 3.3% for I. scapularis and 3.8% for A. americanum.

Tick infestations of white-tailed deer in Alabama.

Four species of ticks were collected from 537 white-tailed deer (Odocoileus virginianus), examined during the hunting seasons (November to January) of 1988-89 and 1989-90 at selected locations in Alabama (USA). Ixodes scapularis was the most common tick recovered (2,060 specimens) and infested 54% of the deer. Dermacentor albipictus was the second most frequent tick (1,253 specimens) and infested 15% of the deer. Amblyomma americanum was the third most frequent tick (315 specimens) and infested 24% of the deer; this was the only species of tick collected from deer at all sampling locations. Amblyomma maculatum was an infrequent parasite (five specimens) and infested only 1% of the deer; this tick species was only recorded during the 1989-90 season. Year-to-year and geographical differences in tick infestation parameters were noted. The data are compared with those reported for previous surveys of ticks infesting white-tailed deer in Alabama and adjacent states.

Etiologic agent of Lyme disease, Borrelia burgdorferi, detected in ticks (Acari: Ixodidae) collected at a focus in Alabama.

The study was conducted at sites of known transmission of Borrelia burgdorferi in east central Alabama. The objectives were to determine species of ticks present at these sites, their host associations, and species of ticks and small mammals naturally infected with B. burgdorferi. A total of 451 hosts were examined for ticks, including cotton mice, Peromyscus gossypinus (Le Conte); cotton rats, Sigmodon hispidus Say & Ord; southern short-tailed shrews, Blarina carolinensis (Bachman); house mice, Mus musculus L.; golden mice, Ochrotomys nuttalli (Harlan); and white-tailed deer, Odocoileus virginianus (Zimmermann). Ticks were examined for B. burgdorferi using indirect and direct fluorescent antibody assays. Ear biopsy samples from rodents were cultured in modified Kelly's medium in attempts to isolate B. burgdorferi. A total of 859 Amblyomma americanum L., Dermacentor albipictus (Packard), D. variabilis (Say), Ixodes scapularis Say, and Rhipicephalus sanguineus (Latreille) were recovered from hosts and by dragging. A. americanum and I. scapularis accounted for 53.4% of all ticks collected. Nearly half of all ticks collected were examined for the agent. Spirochetes were detected in four nymphal and two adult A. americanum recovered from white-tailed deer and three larval I. scapularis recovered from cotton mice. No spirochetes were cultured from field-caught rodents.

Method for determining settling rates of Bacillus thuringiensis serotype H-14 formulations.

A water-column apparatus is described in which settling rates of Bacillus thuringiensis serotype H-14 [B.t. (H-14)] formulations can be indirectly quantified using mortality of mosquito larvae at restricted depths as an index of B.t. (H-14) activity. To illustrate the type of data provided by this method, commercial B.t. (H-14) products (Bactimos, Teknar, Vectobac) and experimental formulations were compared at the manufacturers' recommended rates for mosquito control. All evaluations utilized laboratory-reared, 4th-instar Aedes aegypti larvae. The procedure can be used to provide an index of suspension properties of different B.t. (H-14) formulations and to measure dispersion rates of granular formulations resting at the bottom of a water column. Standardization of the method provides a convenient and practical means of generating comparative data on the effectiveness of B.t. (H-14) and other mosquito larvicides against specific target species.

Potential vectors of bluetongue and epizootic hemorrhagic disease viruses of cattle and white-tailed deer in Alabama.

Fourteen Culicoides spp. were collected on Holstein cattle in Alabama: C. arboricola, C. bickleyi, C. biguttatus, C. debilipalpis, C. guttipennis, C. haematopotus, C. obsoletus, C. paraensis, C. piliferus, C. sanguisuga, C. spinosus, C. stellifer, C. variipennis and C. venustus. Six Culicoides spp. were collected directly from white-tailed deer (Odocoileus virginianus): C. debilipalpis, C. niger, C. obsoletus, C. paraensis, C. sanguisuga and C. stellifer. Based on their host-feeding behavior, abundance and seasonal occurrence, the following 4 species warrant particular attention as potential vectors of bluetongue (BT) and epizootic hemorrhagic disease (EHD) viruses in the southeastern US: C. debilipalpis, C. obsoletus, C. paraensis and C. stellifer.

Laboratory infections of Culicoides debilipalpis and C. stellifer (Diptera: Ceratopogonidae) with bluetongue virus.

Six species of field-collected Culicoides females were used in preliminary laboratory tests: C. biguttatus, C. debilipalpis, C. obsoletus, C. stellifer, C. variipennis and C. venustus. Tests were conducted to determine if females would take a blood meal through a membrane, if blood fed females could be maintained in the laboratory for up to 14 days and if they could support replication of bluetongue virus (BTV) serotype 11. One pool of C. stellifer (23 specimens) assayed positive for BTV 7 days following intrathoracic inoculation, which datum suggests that this species might be capable of harboring the virus. One of 52 individually assayed C. debilipalpis females in 2 trials was positive for BTV at 14 days after membrane feeding on a mixture of BTV and sheep blood (infection rate 1.9%), and 1 of 2 pools of C. debilipalpis (26 specimens) was positive 14 days after blood feeding. These data for C. debilipalpis showed that the species can pick up and harbor BTV through replication of the virus.

Field isolations of Dirofilaria from mosquitoes in Alabama.

Field collections of mosquitoes were made April-September 1977 and 1978 in the immediate vicinity of a hunting-dog kennel where the dogs had a chronic history of heartworm infection. Among 19 mosquito species taken in light-trap collections, only Aedes sticticus, Ae. vexans, and Anopheles punctipennis were found infected with what were presumed to be D. immitis larvae. Based on natural infection rates and the relative abundance of these three host species, An. punctipennis and Ae. sticticus appear to be among the most important vectors of dog heartworm at this site. Despite its greater abundance, Ae. vexans apparently plays a comparatively lesser role in D. immitis transmission owing to low natural infection rates and the development of only a few filariae per host. All Dirofilaria isolations were made in April, May, and June, suggesting that transmission may occur primarily during the spring and early summer in this area.