Avian hosts of Ixodes pacificus (Acari: Ixodidae) and the detection of Borrelia burgdorferi in larvae feeding on the Oregon junco.

Larval and nymphal western blacklegged tick, Ixodes pacificus Cooley & Kohls (Acari: Ixodidae), were collected from birds, rodents, and lizards at Quail Ridge Reserve located in Napa County in northwestern California. Species from three vertebrate classes were sampled simultaneously from two transects during two consecutive spring seasons. Feeding larval and nymphal ticks were removed and preserved for counting, examination and testing for the presence of Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner. Mean infestations with I. pacificus subadults on lizards were 10.0, on birds 2.9, and on rodents 1.3. I. pacificus larvae (204) collected from 10 avian species and (215) collected from two rodent species were tested for the presence of B. burgdorferi s.s. via real-time polymerase chain reaction. Three B. burgdorferi-infected larvae were taken from two Junco hyemalis and two infected larvae from one Neotoma fuscipes Baird. This is the detection of B. burgdorferi ss in an Ixodes pacificus larvae feeding on a Junco hyemalis L., [corrected] in western North America.

A survey of hantavirus antibody in small-mammal populations in selected United States National Parks.

Hantavirus activity in 39 National Parks in the eastern and central United States was surveyed by testing 1,815 small mammals of 38 species for antibody reactive to Sin Nombre virus. Antibody-positive rodents were found throughout the area sampled, and in most biotic communities. Antibody was detected in 7% of 647 deer mice (Peromyscus maniculatus), 2% of 590 white-footed mice (P. leucopus), 17% of 12 rice rats (Oryzomys palustris), 3% of 31 cotton rats (Sigmodon hispidus), and 33% of 18 western harvest mice (Reithrodontomys megalotis). Antibody was also found in three of six species of voles, and in one of 33 chipmunks (Tamias minimus). Prevalence among Peromyscus was highest in the northeast. Although few cases of hantavirus pulmonary syndrome have been identified from the eastern and central regions, widespread infection in reservoir populations indicates that potential exists for human infection throughout much of the United States.

5-hydroxytryptamine in the salivary glands of adult female Aedes aegypti and its role in regulation of salivation.

A dense plexus of axons, immunoreactive to antisera against 5-hydroxytryptamine (5-HT, serotonin) and surrounding the proximal medial lobe of the salivary gland of adult female Aedes aegypti mosquitoes, was demonstrated by means of whole-mount fluorescence immunocytochemistry. This innervation originates in the stomatogastric nervous system. 5-HT-immunoreactive innervation is absent in male salivary glands, suggesting that 5-HT is involved in blood-feeding. Furthermore, female mosquitoes treated with the 5-HT-depleting agent alpha-methyltryptophan (AMTP) and then allowed to feed on a rat exhibited a significantly longer mean probing period and a lower blood-feeding success rate than did control mosquitoes. When female mosquitoes were experimentally induced to salivate into mineral oil, AMTP-treated individuals secreted significantly less saliva than did control mosquitoes. These samples of saliva also contained significantly lower concentrations of apyrase, an enzyme important in blood-feeding. Injection of 5-HT into both AMTP-treated and control mosquitoes elicited significant increases in the volume of secreted saliva and/or its apyrase content. We conclude that 5-HT plays an important role in the control of salivation in adult female A. aegypti.

Serotonin depletion affects blood-feeding but not host-seeking ability in Aedes triseriatus (Diptera: Culicidae).

The host-seeking and blood-feeding abilities of Aedes triseriatus (Say) were evaluated after treatment with the amine depleting drugs alpha-methyl-tyrosine (AMT) and alpha-methyl-tryptophan (AMTP). High-performance liquid chromatography with electrochemical detection (HPLCED) was used to demonstrate that AMTP depleted serotonin levels, whereas AMT reduced dopamine levels. The host-seeking ability (evaluated with an olfactometer) of Ae. triseriatus was not altered by treatment with either AMT or AMTP. Blood-feeding success was reduced significantly by either oral administration or injection of AMTP. Mosquitoes treated with AMTP responded positively when placed in close proximity to a host (rabbit), but fewer treated than untreated mosquitoes fed to repletion or fed at all. Those feeding to repletion took longer to do so. No differences in feeding ability were observed between control and AMT-treated mosquitoes. These observations indicate that serotonin plays a role in modulating blood-feeding activities of Ae. triseriatus.

Studies on the biology of Ixodes dammini in the upper midwest of the United States.

The seasonal activity pattern of Ixodes dammini was monitored in south-central Wisconsin in 1989 and 1990. Immature tick activity and abundance were assessed by small mammal trapping (732 Peromyscus leucopus examined) and supplemented with flagging. Tick survival and molting times were evaluated by maintaining ticks in environmental chambers at field sites. Results indicate the biology of I. dammini in the upper midwest is similar to that previously reported from the eastern United States. One notable difference was that seasonal larval activity appeared broader (late April through October) and peaked earlier (on 9 July 1989 mean was 7.7 larvae/mouse; on 9 June 1990 mean was 7.3 larvae/mouse). Nymphal activity on P. leucopus peaked in May of both years (mean = 2.5 in 1989; mean = 1.8 in 1990). Bloodfed females placed in the field in early May 1990 oviposited in early June, and larvae emerged by early August. All bloodfed stages successfully overwintered at field sites.

Rates of Borrelia burgdorferi infection in Ixodes dammini (Acari: Ixodidae) in southwestern Wisconsin.

Ixodes dammini Spielman, Clifford, Piesman & Corwin collected from a study site in southwestern Wisconsin were examined for Borrelia burgdorferi infection. Adult spirochete infection rates varied seasonally (38.1%, spring 1990; 60.3%, fall 1990; 41.2%, spring 1991) and were similar to or higher than rates reported in various studies from the northeastern United States. Statistical comparison of seasonal infection rates indicated a significant difference between the fall 1990 adult population and the subsequent overwintered population of the same cohort (spring 1991). Additionally, a significant decrease in the intensity of spirochete infection was observed in the overwintered adult sample.

Comparison of four membranes for artificially bloodfeeding mosquitoes.

Four species of mosquitoes, Aedes aegypti, Ae. triseriatus, Culex pipiens and Cx. tarsalis, were allowed access to defibrinated rabbit blood via 4 different membranes and a standard membrane feeder. Natural animal skins (mouse or quail) were the most effective. More than 50% of the Aedes mosquitoes fed within 5 min and approximately 90% fed within 20 min on either mouse or quail skin. Culex species fed best on quail skin, but the difference in feeding on quail skin and sheep intestine was not significant at 10 or 20 min. In general Culex mosquitoes fed less readily on natural animal skins than Aedes.

Efficacy of Bacillus sphaericus and Bacillus thuringiensis var. israelensis for control of Culex pipiens and floodwater Aedes larvae in Iowa.

Granular and flowable concentrate formulations of Bacillus thuringiensis var. israelensis provided a 90-100% reduction in Aedes vexans and Culex spp. larvae in natural larval habitats. A briquet formulation of B. thuringiensis was less effective, providing a 12-76% reduction. No residual activity occurred in sites treated with B. thuringiensis. Granular formulations of Bacillus sphaericus (2.78-8.42 kg/ha) caused a 100% reduction in Culex pipiens larvae in natural sites and artificial pools. Bacillus sphaericus also controlled (84-98% reduction) a mixed population of Aedes trivittatus and Cx. pipiens in subplots of a retention pond. In field sites, B. sphaericus continued to control Cx. pipiens larvae for 96 hr.