The existing information on arthropods as predators of ticks is based mainly on sporadic observations and their role in reducing tick populations and in most cases is still not clear. Some reports suggest that in certain ecological habitats arthropods play an important role in the control of the tick population. This publication reports on some 100 relevant publications that appeared between 1906 and 1999. Ants, beetles, and spiders seem to be the major arthropods preying on ticks. In general, engorged ticks are more often preyed upon by arthropods than are unfed or feeding ticks.

The epidemiology of the visceral leishmaniasis in the Americas is associated with both a natural and a domestic cycle. The existence of reproductively isolated populations of Lutzomyia longipalpis (Lutz & Neiva), and the scarcity of records of this species from natural habitats in areas where it has been associated with domestic habitats indicated that natural populations could be genetically distinct from domestic ones. Therefore, we compared the genetic structure and estimated the gene flow between L. longipalpis from domestic and peridomestic habitat and from an adjacent undisturbed natural environment along a 1.2-km transect. The analyses were performed on electrophoretic data from eight isozyme loci. The absence of fixed differences in the diagnostic loci Ak and Hk indicated that all specimens belonged to one of the two cryptic species identified in Venezuela. The average number of alleles per locus ranged from 2.0 to 2.9 and the average heterozygosity ranged from 7.8 to 13.4%. No differences were detected in the genetic structure of this species from domestic or peridomestic habitats and those trapped as far as 1.2 km from human dwellings. Nm, estimated from Wright’s F_st, indicated that at least 208 individuals per generation migrated between the peridomestic habitat and a 1.2-km distant point to maintain the observed similarities in allelic frequencies. This high rate of gene flow indicated that this species has high migration rates between domestic and natural environments, and has the potential to transport for Leishmania from natural to domestic environments.

Vertical transmission of Orientia tsutsugamushi (Hayashi), the etiologic agent for scrub typhus, was studied in two lines of naturally infected Leptotrombidium deliense Walch. In one line of mites originating from a single adult (V3M), the rate of filial transmission was 100% for the first two laboratory generations, but declined to 86.6% in the third laboratory generation. The vertical infection rate in this line of mites was 100% for the parental generation, but declined to 95.6% for the F1 generation and 88.6% for F2. The transmission of O. tsutsugamushi in another line of L. deliense (V3F) was less efficient than mites originating from V3M. In the initial laboratory generation of V3F a filial transmission rate of 100% was recorded. However, none of the F2 generation of this line transmitted rickettsiae to mice (Mus musculus L.), resulting in a filial transmission rate of 0%. Transmission of O. tsutsugamushi to mice by progeny from cohort larvae originally from the same adult (V3F) was also studied in the laboratory and these were found to be relatively poor transmitters of rickettsiae. The filial infection rate of F2 larvae was 60%, F3 was 88.8%, and F4 was 55.9%. The biology of infected L. deliense was studied and compared with uninfected mites reared under the same laboratory conditions. The results showed that infected female L. deliense laid approximately the same or more eggs as uninfected adults. The rate of development of the progeny of infected L. deliense was not significantly different from uninfected mites.

Although females of most mosquito species are known to use sugar as a necessary source of energy, female Anopheles gambiae Giles sensu stricto are thought to use it facultatively or not at all. However, field evidence of sugar-free living is inconclusive, and the implications for reproductive fitness and vectorial capacity are unknown. To evaluate the role that sugar may play in the ecology of these mosquitoes, mated female An. gambiae in the laboratory were given access to either no food (water only), 10% sucrose, human blood, or human blood 10% sucrose, and comparisons of daily mortality, fecundity, and biting frequency were made. The effect of sugar availability on vectorial capacity and the intrinsic rate of increase, a measure of fitness, then were determined. Females (pooled and individual) given blood sugar lived significantly longer than did those on the other diets. Daily fecundity was higher for females given blood alone than for those fed blood sugar (13 versus 9 eggs per female daily). However, total fecundity and intrinsic rate of increase were not affected by sugar availability. Biting frequency was significantly higher (0.41 versus 0.26 bites per female per day) for females given blood alone. Despite the reduced survivorship, exclusive blood-feeding led to a theoretically higher vectorial capacity for Plasmodium falciparum at 27°C. These data indicate that female An. gambiae could replace sugar with increased blood feeding without suppressing reproductive fitness. Increased blood feeding could, in turn, increase the rate of malaria transmission and may explain the unusual efficiency of this vector.

The location of midgut bacteria relative to meconial peritrophic membranes (MPMs) and changes in bacterial numbers during midgut metamorphosis were studied in Anopheles punctipennis (Say), Culex pipiens (L.), and Aedes aegypti (L.) pupae and newly emerged adults. After adult emergence in Aedes, Anopheles, and most Culex, there were few to no bacteria in the midgut. In most newly emerged adult mosquitoes, few bacteria were found in either the lumen or within the MPMs/meconia. In a few Culex specimens, high numbers of bacteria were found in the MPMs/meconia and low numbers in the lumen. In all three species bacterial counts were high in fourth instars, decreased after final larval defecation, increased in young pupae, and increased further in old pupae. A very effective gut sterilization mechanism is operating during mosquito metamorphosis and adult emergence. This mechanism appears to involve the sequestration of remaining larval gut bacteria within the confines of the meconium and one or two MPMs and the possible bactericidal effect of the exuvial (molting) fluid, which is ingested during the process of adult emergence.

Four state parks located in Lyme disease endemic regions of Wisconsin were surveyed for the presence of Ixodes scapularis Say during May and June of 1998 by drag sampling along hiking trails. Nymphal abundance varied between parks, with the average number of nymphs encountered in 1 h ranging from 6.2 ± 3.8-47.1 ± 36.3 (mean ± SD). Questing nymphs were tested for the presence of Borrelia burgdorferi by culture in BSK medium and 7-12% was found to be infected. The average risk of encountering an infected nymph (entomologic risk index) ranged from 0.5 to 5.2 infected nymphs per hour. The highest entomological risk index was recorded from a small island park in northwestern Wisconsin during the last week in May (8.0 infected nymphs per hour). These results indicate a lower risk for human Lyme disease exposure in Wisconsin state parks in comparison with highly endemic areas of the northeastern United States.

In this work we have used for the first time green fluorescent protein (GFP) tagged cells of the human parasite Leishmania donovani to observe its development in the gut of phlebotomine sand flies. Low numbers of GFP-tagged L. donovani were more easily detected than nontagged Leishmania, suggesting that GFP-tagged Leishmania could be used to efficiently study the biology of Leishmania in their vectors, and open the possibility of using nonaxenic flies. Using this method, we found that GFP-tagged L. donovani, the ethiological agent of Old World Kala-azar, were able to establish an infection within the gut of Lutzomyia species, which are vectors of New World Leishmania. The GFP-tagged parasites divide successfully in the gut of colonized and in wild caught Lu. longipalpis (Lutz & Neiva, 1912), Lu. ovallesis (Ortiz, 1952), and Lu. youngi (Feliciangeli & Murillo, 1985). In the case of Lulongipalpis the labeled parasite exhibited a normal anterior development as the one observed in its natural vector.

A polymerase chain reaction-based assay was developed to detect the presence of a pyrethroid resistance-associated amino acid substitution in Boophilus microplus (Canestrini). The assay uses a simple method for the extraction of genomic DNA from individual larvae and genotypes individuals for the presence of a Phe → Ile amino acid substitution in the S6 transmembrane segment of domain III of the para-like sodium channel, clearly distinguishing heterozygotes from homozygotes. High frequencies for this amino acid substitution were found in the Corrales and San Felipe strains, which have target site insensitivity mechanisms for pyrethroid resistance. The Caporal resistant strain contained lower yet substantial numbers of amino acid-substituted alleles. Low amino acid substitution frequencies were found in the susceptible reference Gonzales strain and the Coatzacoalcos strain, which has metabolic esterase-mediated pyrethroid resistance. The amino acid substitution was not found in six other strains that were susceptible to pyrethroids.

The attraction of Aedes albopictus (Skuse) to hands and forearms of human subjects treated with several concentrations of L-LA solution were studied in a test chamber containing proboscis-amputated mosquitoes. Fewer mosquitoes alighted on L-LA treated human skin than on water-treated control skin. Similar results were found using normal mosquitoes following L-LA and water treatment of mouse skin. The relative repellent effects of L-LA varied with concentration. The minimum repellent concentration was lower than previously reported for human skin. The number of alightments decreased at increasing concentrations of L-LA, demonstrating the absolute repellency of L-LA. Unlike previous reports suggesting that L-LA attracted mosquitoes, our studies using human and mouse skin showed that L-LA exhibited both relative and absolute repellency.

The successful long-term storage of insects that are used for research purposes can eliminate the need for ongoing colony maintenance on a large scale. In addition, rare and valuable genotypes of insects can be preserved. This study was conducted to determine whether cryopreservation is a suitable means of storing embryos of Culicoides sonorensis Wirth & Jones, an important vector of animal pathogens. We determined that eggs of C. sonorensis can withstand vigorous treatments of dechorionation, permeabilization, and loading with the cryoprotectant, elthylene glycol. Although their viability was reduced, an average of 80.3% of the embryos developed into larvae. Dehydration in vitrification solution caused a much greater reduction in egg viability (42.7% survival), and freezing in liquid propane further reduced the number of eggs that developed into larvae (40.1%), pupae (22.9%) and adults (18.8%). This work demonstrated that this procedure may prove useful for the cryopreservation of standard laboratory colonies and genetic lines of C. sonorensis.

To determine whether Culiseta melanura (Coquillett) mosquitoes tend to take multiple blood meals when birds of certain species serve as hosts, we compared the frequencies with which such mosquitoes fed upon caged starlings and robins and determined whether similar volumes of blood were imbibed from each. The blood of robins (Turdus migratorius) and European starlings (Sturnus vulgaris) was marked contrastingly by injecting birds with rubidium or cesium salts. Caged birds were placed together in a natural wetland setting overnight. Mosquitoes captured nearby on the following morning were analyzed for each of the elemental markers. Where marked robins and starlings were equally abundant, 43% of freshly engorged Cs. melanura fed on more than or equal to two hosts. More Cs. melanura fed on robins than on starlings. Individual mosquitoes tended to contain far more robin- than starling-associated marker, indicating that mosquitoes “feasted” on robins but only “nibbled” on starlings. Mosquitoes marked with both elements apparently fed meagerly on the starlings then abundantly on the robins. Our estimates of bloodmeal volume indicate that 85% of mosquitoes that fed on marked starlings obtained <0.5 μl of blood from them. We suggest that defensive behavior by starlings interrupts mosquito blood-feeding and that, in a communal roost of starlings, each mosquito will tend to feed on more than one bird, thereby promoting rapid transmission of such ornithonotic arboviruses as eastern equine encephalomyelitis virus and West Nile virus.

In 1997, ticks removed from humans and received alive by the Tick-Borne Disease Laboratory of the U.S. Army Center for Health Promotion and Preventive Medicine (USACHPPM) were tested for pathogens by polymerase chain reaction (PCR). Thirty-three of 222 (15%) Amblyomma americanum (L.) DNAs produced amplicons of the expected size of Ehrlichia chaffeensis Anderson, Dawson & Wilson and 26/222 (12%) produced amplicons indicating Borrelia burgdorferi Johnson, Schmid, Hyde, Steigalt & Brenner. Five (2%) appeared to be co-infected with both organisms. Thirteen of 308 (4%) Dermacentor variabilis (Say) were PCR-positive for spotted fever group rickettsiae. Restriction fragment-length polymorphism analysis indicated all were Rickettsia montana. One hundred twenty-seven D. variabilis from Monroe County, WI, were tested for B. burgdorferi and 14 (11%) were positive. Five of 24 (21%) Ixodes scapularis Say were positive for B. burgdorferi and one (2%) was positive for the agent of human granulocytic ehrlichiosis. Different species of ticks transmit different pathogens, and most tick-borne diseases have similar early symptoms, therefore knowing the species and infection status of the tick enhances the physician’s ability to consider tick-borne agents as a potential cause of disease and recommend appropriate therapy. Ongoing surveillance of the vector species of human diseases provides an additional estimate of human encounters with infected ticks, and testing ticks removed from humans may increase our knowledge of the vector status of tick species for transmitting tick-borne pathogens.

An orally delivered arthropod development-inhibitor (fluazuron) was evaluated for its potential to reduce the number of flea and tick vectors found on the dusky-footed woodrat Neotoma fuscipes Baird, a reservoir host important in disease enzootiology in northern California. Pigmented bait cubes containing fluazuron were distributed monthly to woodrat nests in a chaparral habitat for 1 yr. When compared with control woodrats, the numbers of fleas [primarily Orchopeas sexdentatus (Baker)] on treated woodrats were significantly reduced 3–4 mo after initial application, and remained so for the duration of the application period. By contrast, tick numbers were not significantly reduced on treated woodrats. After the cessation of treatments, flea indices remained lower on treated animals for up to 2 mo after application. Approximately 93% of woodrats captured in the treatment area excreted pigmented feces and 93% of distributed bait cubes were removed by woodrats, which indicates that the bait cube formulation and delivery system were highly effective. Bait cubes also were attractive to small rodents and ground-frequenting birds. The results of this study suggest that a monthly application program of fluazuron delivered by bait cube is effective in reducing woodrat flea-burdens, but is not effective, at least in the short-term, in controlling ticks.

Juvenile hormone III plays a major role in regulating feeding and reproduction in the adult cat flea, Ctenocephalides felis (Bouché). Both blood consumption and egg production increased in a dose-dependent manner up to a maximum at 1,250 ppm when fleas were continuously exposed to concentrations up to 12,500 ppm juvenile hormone. Histological studies demonstrated that juvenile hormone III also stimulated cellular differentiation of salivary gland epithelia, midgut epithelia, and fat body cells, enhancing the ability of the adult flea to digest blood and synthesize vitellogenins for the maturing oocytes. In unfed fleas, exposure of adults to concentrations of ≥1,000 ppm juvenile hormone III applied to filter paper resulted in membrane lysis and destruction of salivary gland and midgut epithelial cells, fat body cells, and ovarian tissue. Unlike juvenile hormone mimics, which have potent ovicidal effects in fleas, juvenile hormone had little effect in preventing egg hatch; 58% of the eggs laid by fleas treated with 12,500 ppm juvenile hormone III hatched, and a concentration of 30,000 ppm was required to reduce hatch to 2% in untreated eggs exposed to treated filter paper for 2 h. Compared with the juvenile homone mimic pyriproxyfen, juvenile hormone III was less toxic to fed adult fleas. However, at a concentration of 12,500 ppm, juvenile hormone killed ≈45% of the adults and caused autolysis and yolk resorption in the developing oocytes. Thus, at high concentrations, juvenile hormone appears to have a pharmacological effect on fleas, which is highly unusual in insects.

A mark-release-recapture experiment was conducted in a small isolated village on Hainan Island, China, to examine the dispersal and movement of adult Aedes aegypti (L.). Two cohorts of mosquitoes marked with uniquely colored fluorescent dye were released at two different sites and recaptured for 6 d at every house in the village using human bait collections. The distribution pattern of houses around release site affected dispersal. The recapture rate of females released at the center of the village was higher (3.49%) than females released at the edge of the village (2.47%). The average day of recapture differed significantly between sexes, but not cohorts. The average day of recapture of females and males released at the center was 2.5 and 1.54 d, respectively. The total number of mosquitoes recaptured was the greatest at premises near the release site, and decreased at a constant rate of 0.43–0.48 with increasing distance from the release site. The proportion of nulliparous females decreased during the first 4 d and proportion of females with developing or mature ovaries increased during the latter half of the experiment. The daily survival rate for females and males released at the center of the village was estimated by log-regression to be 0.763 and 0.52, respectively.

The blacklegged tick, Ixodes scapularis Say, transmits the Lyme disease spirochete Borrelia burgdorferi, whereas the American dog tick, Dermacentor variabilis (Say), is unable to transmit the bacterium. We compared the innate immune response of these ticks against spirochetes directly inoculated into the hemocoel cavity of ticks. In I. scapularis, some Borrelia were found associated with hemocytes, while numerous other spiral-shaped, intact bacteria remained free in the hemolymph. In contrast, in D. variabilis only remnants of the bacteria were evident in the hemolymph, indicating lysis; intact spirochetes were rare. Spirochetes were observed bound to or within the organs of both tick species, although many more spirochetes were found associated with the I. scapularis organs. The few spirochetes observed with the D. variabilis organs appeared to be dead because D. variabilis tissues rarely contained culturable bacteria, unlike I. scapularis tissues. When spirochetes were incubated with I. scapularis hemolymph plasma in vitro, bacterial survival and motility were not reduced. In contrast, incubation of spirochetes with D. variabilis hemolymph plasma resulted in >50% of the spirochetes becoming nonmotile by 45 min. The differences in the responses of the two different tick species indicate that I. scapularis is immunotolerant when challenged with B. burgdorferi and dependent on a slow phagocytic response to clear Borrelia from the hemolymph. In contrast, D. variabilis is highly immunocompetent (i.e., innate immunity), using plasma borreliacidal factors and a rapid increase in phagocytic cells to clear the infection and limit tissue invasion.

Eggs from seven colony lines of the chigger mite Leptotrombidium imphalum (Vercammen-Grandjean & Langston) were examined for infection with Orientia tsutsugamushi (Hyashi), the etiologic agent of scrub typhus. The polymerase chain reaction (PCR) using primers OtP 56.809 and OtM 56.1221, which amplify a 291 bp region of the P56 gene of O. tsutsugamushi, was used to detect scrub typhus within single eggs. All seven chigger mite lines produced infected eggs with varying rates of infection (Li1 = 8.1%, n = 124; Li2 = 45.6%, n = 90; Li3 = 30.1%, n = 144; Li4 = 31.7%, n = 145; Li5 = 21.3%, n = 136; Li6 = 41.6% n = 77; Li7 = 22.5%, n = 110). The 3 wk with the highest infection rates for each line using Fourier analysis were as follows: Li1 = 2, 7, 14; Li2 = 4, 6, 12; Li 3 = 3, 6, 12; Li4 = 4, 6, 12; Li5 = 5, 7, 14; Li7 = 4, 6, 12. Li6 only had nine measurements over time; therefore, Li6 was excluded from individual analysis. Infection rates of scrub typhus in eggs occurred in a 2-wk 2-d cycle, using Fourier analysis of combined data. Not only did infection rates vary among the progeny of females, but temporal variation also occurred.

The seasonal occurrence of Ctenocephalides felis felis (Bouché) and Ctenocephalides canis (Curtis) infestation on dogs and cats in Cuernavaca City in Mexico, was determined by examining 1,803 dogs and 517 cats at two veterinary clinics during 1995–1997. The overall flea infestation was 30.3 and 30.1% for dogs and cats, respectively. There were no significant differences (P > 0.05) in percentage of infestation among years for both hosts. The infestation was somewhat higher in spring, summer, and autumn than in winter, but no statistical differences was found among seasons (P > 0.05) for both pets. No relationship existed between percentage of flea infestation and temperature or rainfall among seasons. On dogs, 81.1% were infested with only C. felis felis, 16.8% with C. canis, and 2% had both flea species; whereas 92.3% of the cats were infested with C. felis felis and 7.7% with C. felis felis and C. canis. The cat flea was the most prevalent flea species found other than C. canis; no other species were found on the dogs and cats. It appeared that flea life cycle development continued throughout the year.

Host-seeking male and female blacklegged ticks, Ixodes scapularis Say, exhibited an arrestant response when contacting substances from front and rear interdigital glands of male and female white-tailed deer, Odocoileus virginianus (Zimmermann). Female I. scapularis responded positively to substances from interdigital glands on the fore legs and hind legs of female deer, whereas male I. scapularis responded only to samples from the fore legs of does. These results showed that previously reported responses of I. scapularis to residues from interdigital glands of hind legs of deer were independent of tarsal gland substances, which may contaminate interdigital gland substances on hind legs. Nymphs of I. scapularis and female lone star ticks, Amblyomma americanum (L.), did not show an arrestant response to substances from hind legs of does, but male A. americanum did.

During the spring and fall turkey hunting seasons of 1999, hunters and Kansas Department of Wildlife and Parks field personnel examined wild turkeys, Meleagris gallopavo L., for ticks and submitted them to us for identification. From springtime hunting, we received 113 ticks from 12 turkeys killed in nine counties, all in the eastern one-third of Kansas. Collectors reported examining three additional wild turkeys on which no ticks were found. All ticks were nymphal lone star ticks, Amblyomma americanum (L.). Of 11 wild turkeys examined in seven counties during October, one was parasitized by 30 A. americanum larvae. Data from this study and accounts from the published literature suggest that parasitism of wild turkeys by immature lone star ticks is commonplace wherever this host and ectoparasite are sympatric. Our study suggests that M. gallopavo may be an important host that supports lone star tick populations.

The host source and human blood index (HBI) of an exophilic population of the “forest” cytoform of Anopheles gambiae Giles sensu stricto, from a peri-urban area of the island of São Tomé, were assessed. Blood meals of 434 An. gambiae females from all-night indoor light-trap collections, 193 from indoor and 422 from outdoor resting collections, were determined by ELISA. Significant differences were found in the HBI estimates from insects collected indoors (0.93) and outdoors (0.27). Blood-fed insects collected resting outdoors provided the most representative sample for host determination. Dogs were the predominant hosts, followed by humans and pigs. Of all human feeds, it was estimated that 81.5% were taken inside houses. The low HBI of 0.27 for the An. gambiae population explains the low sporozoite rate and the meso-endemicity of malaria in the island.