Evaluation of permethrin-impregnated cotton balls as potential nesting material to control ectoparasites of woodrats in California.

The dusky-footed woodrat, Neotoma fuscipes Baird is a natural reservoir of the Lyme disease spirochete, Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner, in California. To investigate the potential of host-targeted insecticide to control the tick vectors of B. burgdorferi, permethrin-impregnated or untreated cotton balls were distributed in metal cylinders as potential nesting material adjacent to 95 woodrat houses in chaparral-covered rangeland. Laboratory experiments demonstrated that adult woodrats would enter the cylinders and construct nests from permethrin-treated or untreated cotton. The residual concentration of permethrin did not vary significantly during an 11-mo period and remained > 60% of the registered insecticidal formulation (7.5% [AI] by cotton weight). The abundance of 4 species of ticks (Ixodes neotomae Cooley; the western blacklegged tick I. pacificus Cooley & Kohls; I. woodi Bishopp; and the Pacific Coast tick, Dermacentor occidentalis Marx) infesting woodrats was similar in the treatment and control areas. Although > 90% of the cotton disappeared from the metal cylinders in both areas, examination of 8 active woodrat houses revealed that small amounts of cotton had been incorporated into the nest cups of only 25%. In contrast, the abundance of the flea Orchopeas sexdentatus (Baker) decreased significantly in the treatment area only. Spirochetes were not detected in 168 adult O. sexdentatus fleas that had fed on spirochetemic woodrats, which demonstrates that this flea is an inefficient host of B. burgdorferi. We conclude that the use of permethrin-impregnated cotton as potential nesting material is ineffective for controlling ticks associated with the dusky-footed woodrat in brushlands, but this methodology may be useful for reducing populations of sylvatic fleas.

Responses of horse flies (Diptera: Tabanidae) to Jersey bullocks and canopy traps baited with ammonia, octenol, and carbon dioxide.

The attraction of females of six species of tabanids to stanchioned Jersey bullocks, unbaited canopy traps, and canopy traps baited with either octenol (1-octen-3-ol), ammonia (NH4OH), a combination of ammonia and octenol, or 5 kg of dry ice (CO2) was studied. A randomized Latin square design (treatments x sites x days) was used. Species diversity and number of flies captured in canopy traps unbaited or baited with octenol, ammonia, or the combination of octenol and ammonia did not differ significantly. Females of Tabanus americanus Forster, T. fuscicostatus Hine, and T. lineola F. were captured more frequently in CO2-baited canopy traps than on Jersey bullocks, but the reverse was observed for females of Leucotabanus annulatus (Say). The number of females of T. pallidescens Philip and T. wilsoni Pechuman collected from CO2-baited canopy traps and bullocks did not differ significantly.

Insect blood meal studies using radiosodium 24Na and 22Na.

Rabbits were infused with 3.7 GBq (100 mCi) of [24Na]Na ion in a 100-ml sodium carbonate solution. Beta particles were detected using a Tennelec Counting System; background counts were 1.6 +/- 1 counts per minute (cpm). Counts for one nanoliter of blood ranged from 22 to 30 cpm. Blood volumes on the mouthparts of tabanids following a 15-sec interrupted feeding were estimated to be 12.5 nl for Tabanus fuscicostatus, 10.8 nl for T. nigrovittatus and 6.12 nl for Chrysops fuliginosus. Estimates of the quantity of blood adhering to 22-gauge needles and insect pins (size 2) following a percutaneous intramuscular needle-stick were 8.8 +/- 1.0 nl and 5.7 +/- 1.8 nl, respectively. Mosquitoes, Aedes aegypti females, were fed to repletion with a 22Na-artificial diet, and radioactivity was measured using a Packard Autogamma 5650. The estimated average blood meal size was 2.80 +/- 0.94 microliters.

Relationships among body size, blood meal size, egg volume, and egg production of Tabanus fuscicostatus (Diptera: Tabanidae).

Number of ovarioles, egg production, and weight of unfed and bloodfed Tabanus fuscicostatus Hine females were related linearly to wing length. Wing length did not change whether flies were freshly thawed, preserved in formalin solution, or oven dried. Left and right wings were similar in length. The length from the costa to the anterior cross vein or to the intersection of R4 and R5 veins was associated linearly to wing length. The number of eggs produced by flies bloodfed on one or two bovine hosts was similar when adjusted by wing length. The average number of ovarioles per female was 277 +/- 50 (+/- SD), and eggs developed in only 63% of the ovarioles after a bloodmeal. An estimated 3.1 eggs were produced for each milligram of blood ingested by a fly, and the average bloodmeal size was 110% of the unfed weight of the flies (49.7 mg). Egg volume was unrelated to body size, but was associated inversely with the number of eggs produced per female.

Relative susceptibility of beef and dairy calves to infection by bovine leukemia virus via tabanid (Diptera: Tabanidae) feeding.

Differences in susceptibility of beef (mixed breeds) and dairy (Holstein) calves to infection by bovine leukemia virus (BLV) were compared. Transmission was accomplished by interrupted feeding of horse flies, Tabanus fuscicostatus Hine, on a donor cow exhibiting persistent lymphocytosis. Flies were transferred individually from the donor cow to each of 11 beef and 10 dairy calves. Transmission of BLV was accomplished with groups of 50 and 250 flies for beef calves and 75 and 250 for dairy calves. These findings indicate that susceptibility of beef and dairy calves to transmission of BLV by tabanids is equivalent and that BLV prevalence differences previously observed among cattle breeds may be caused by management practices.

Similar reproductive status and body size of horse flies (Diptera: Tabanidae) attracted to carbon dioxide-baited canopy traps and a Jersey bullock.

The reproductive status and body size of four Tabanus species collected from canopy traps baited with carbon dioxide and from a Jersey bullock were compared. Parity rates, sperm prevalence, stage of follicular development in terminal follicles of parous females, prevalence of females retaining eggs, average number of eggs retained in parous flies, and the body size of parous females did not differ significantly between sampling methods. Based on the presence of nulliparous host-seeking flies, Tabanus pallidescens Philip and T. wilsoni Pechuman can be added to the list of tabanids found to be anautogenous.

Single-step technique for staining Anaplasma marginale in bovine blood smears.

Three available differential stains, Camco-Quik, Diff-Quik, and Wright-Giesma were compared for detection of intraerythrocytic Anaplasma marginale in bovine blood smears. In samples where < 1% to more than 51% of the RBC were infected, statistical analysis of the data indicated no significant difference in the detection of A marginale with Camco-Quik or Diff-Quik stains. However, a significantly lower percentage of infected RBC were detected when blood smears were stained with the Wright-Giemsa stain, compared with the other 2 methods.

Ammonia as an attractant for adult Hybomitra lasiophthalma (Diptera: Tabanidae).

Ammonia and carbon dioxide were evaluated as attractants in canopy traps for Hybomitra lasiophthalma (Macquart). Ammonia-baited traps collected 2.5 times as many flies as did unbaited traps (33.27 versus 12.93 per trap per day). Over 45 times as many flies were captured in carbon dioxide-baited traps as in unbaited traps (1,630.64 versus 35.82 per trap per day). Both ammonia and carbon dioxide are effective attractants for H. lasiophthalma.

Design for a canopy trap for collecting horse flies (Diptera: Tabanidae).

A design for a canopy trap for collecting horse flies is described. The collecting heads can easily be changed since the collar is fixed in place and supports the trap. The collar allows an unobstructed pathway to the collecting head. The center pole has a sliding steel rod that allows adjustment of canopy height upon installation in one operation.

Increasing horse fly (Diptera: Tabanidae) catch in canopy traps by reducing ultraviolet light reflectance.

Application of UV Killer, a commercially available product which reduced ultraviolet reflectance from cloth fabrics, increased the catch of tabanids in canopy traps by 24% and in CO2-baited traps by 30%. Catch decreased as ultraviolet reflectance increased during the experiment.

Survival and dispersal of horse flies (Diptera: Tabanidae) feeding on cattle sprayed with a sublethal dose of fenvalerate.

A mark-recapture study was undertaken to determine the fate of tabanids feeding on cattle sprayed with a sublethal dose of fenvalerate. A total of 15,465 tabanids belonging to at least 17 species and five genera were marked individually; flies were divided equally between control and fenvalerate-sprayed bullocks. Data were summarized for the four most abundant species: Tabanus fuscicostatus Hine, T. lineola F., T. pallidescens Philip, and T. wilsoni Pechuman. The recapture rate of tabanids was 6.6% for the control and 3.4% for the fenvalerate treatment. When the proportion of flies predicted to die or be unaffected after feeding on the sprayed bullocks was considered, an estimated 75% of the flies exposed to a sublethal knockdown dose survived and attempted to seek a subsequent host. Dispersal of tabanids was not affected by treatment. The recapture data after the first day of marking was significantly delayed for tabanids that fed on fenvalerate-sprayed bullocks.

Transmission of bovine leukemia virus by Tabanus fuscicostatus.

Bovine leukemia virus (BLV) was transmitted by horse flies, Tabanus fuscicostatus, from a cow with a lymphocyte count of 31,500/mm3 to goats and dairy calves. As few as 10 and 20 flies transmitted BLV to goats and calves respectively, but the minimal number of flies required to transmit the infection was not established. Groups of 150 and 100 T fuscicostatus transmitted BLV to beef calves from a cow with a lymphocyte count of 14,600/mm3. These results support a role for horse flies in the horizontal transmission of BLV.

Gonotrophic status, sperm presence and sugar feeding patterns in southwestern Quebec tabanid (Diptera) populations.

Parity, stage of follicular development, sperm and fructose presence were determined for 6 tabanid species from southwestern Quebec during 2 consecutive years. Females were collected in canopy traps baited with or without carbon dioxide. Based on the presence or absence of host-seeking nulliparous flies (nullipars), Hybomitra epistates, H. nitidifrons nuda, H. sodalis, Tabanus lineola and T. similis were classified as being anautogenous. Hybomitra frontalis was classified as autogenous for its first ovarian cycle. Sperm was found in 88% and fructose was detected in 84% of the 700 specimens dissected. In anautogenous species, sperm and fructose prevalence was higher in pars than in nullipars.

Changes in the parity rate of Tabanus fuscicostatus (Diptera: Tabanidae) populations associated with controlling available hosts.

The parity rates of Tabanus fuscicostatus Hine populations were monitored at two areas of a wildlife management complex for 24 d using canopy traps baited with dry ice. Overall, 1,235 flies were dissected. Three cows placed in Area T were sprayed with 0.05% fenvalerate, and three cows placed in Area U were not sprayed. The parity rate in Area T decreased from 43.6 to 31.2% following the introduction of cattle. Conversely, the parity rate in Area U increased from 30.3 to 43.7% following the introduction of cattle. These results indicate that a segment of T. fuscicostatus populations returns to the previous location for a subsequent blood meal.