Effects of pyriproxyfen on off-host water-balance and survival of adult lone star ticks (Acari: Ixodidae)

Newly engorged nymphs of the lone star tick, Amblyoma americanum (L.), were continuously exposed to 4 microg/cm2 of pyriproxyfen residues in glass vials. Treatment of engorged nymphs (n = 285) resulted in significant molting inhibition, with more than one-fourth (26.7%, n = 76) of nymphs dying before or during ecdysis. Treatment effects were evident among ticks that molted to the adult stage, with 26.7% (n = 76) of females, and 17.9% (n = 51) of males exhibiting moribund physical characteristics (i.e., lethargy; dull, discolored and desiccated cuticles; lacking full locomotor competency). A few molted adult ticks (10 males, four females) were dead upon inspection. Only 11.2% of pyriproxyfen treated, emergent females (n = 32), and 11.5% of treated emergent males (n = 25) from 285 ticks treated as engorged nymphs, exhibited normal physical appearance and possessed a full range of locomotor activity. Treated adult ticks maintained within a desiccating environmental chamber at 0% RH and 23 degrees C, had significantly accelerated whole-body water loss rates in comparison to untreated males and females maintained under the same environmental conditions. Additionally, treated adult ticks maintained under optimal environmental conditions (23 degrees C and >95% RH) sustained 100% mortality within 32 d following assignment to these conditions (or 79 d posttreatment as engorged nymphs), whereas untreated ticks had 0% mortality for the same duration of time. Results demonstrate that continuous exposure of nymphs to pyriproxyfen disrupted molting, and accelerated both whole-body water loss and subsequent mortality among emergent adult ticks.     

Duration and regulation of the developmental cycle of Ixodes dammini (Acari: Ixodidae)

To determine how long the various developmental stages of the deer tick (Ixodes dammini Spielman, Clifford, Piesman & Corwin) survive in nature and to establish the interval between blood feeding and ecdysis or oviposition as well as subsequent larval eclosion, we observed ticks confined in the field. Unless adults feed during their first season (fall through spring) of activity, they die and do not survive the summer. Nonfed nymphs survive through two seasons (May through August) of feeding activity such that annual cohorts overlap. Nonfed larvae survive less than one year, and because they hatch toward the end of the summer, cohorts of this developmental stage do not overlap. Larvae that feed before September molt promptly and overwinter as nymphs; those that feed later overwinter engorged and ecdyse during the following spring. Fed nymphs fail to survive the winter, and thus must feed before late summer. They develop to the adult stage in the same year in which they feed. Regardless of time of feeding, females lay eggs in early summer, and the resulting larvae synchronously eclose late in that season. Although the cycle of this tick can be completed in nature in two years, it may extend to four years when hosts are relatively scarce. The seasonal inversion of larvae and nymphs appears to be regulated by physiological mechanisms and by host abundance.     

Fecundity of partially engorged female Dermacentor albipictus (Acari: Ixodidae) removed by cattle grooming

Eight Hereford heifer calves were infested 28 times over a 64-d period with approximately 49,560 Dermacentor albipictus (Packard) larvae per calf. The fecundity of partially engorged and small, fully engorged female ticks, prematurely removed by grooming behavior of the calves, were compared. A total of 3,532 females of various engorged weights was collected from all calves, resulting in a mean female tick yield of 1.78% based on the number of larvae used for all infestations. The ratio of partially to fully engorged females was 1:16. Female oviposition success was 96%. The mean (+/- SE) values for female weight, number of larvae, and percentage larval eclosion of 50 partially engorged females that ranged in weight from 54 to 397 mg was 174 +/- 99, 1,272 +/- 931 and 85 +/- 14, respectively. The correlation between preoviposition weight and number of larvae from partially engorged females was highly significant (r = 0.95, P less than 0.0001). A prediction model (Y = -354.6 + 9.07X) showed that the preoviposition weight of partially engorged females and larval fecundity from a separate study was highly correlated (r = 0.92, P less than 0.0001). There was no significant difference between mean values of larval numbers and percentage eclosion for partially engorged and small, fully engorged females of similar weight.     

Sublethal effects of Metarhizium anisopliae (Deuteromycetes) on engorged larval, nymphal, and adult Ixodes scapularis (Acari: Ixodidae)

Ixodes scapularis Say adults, nymphs, and larvae were treated with the entomopathogenic fungus Metarhizium anisopliae in a combination of field and laboratory experiments to assess sublethal effects of the fungus on I. scapularis fecundity and body mass. Postengorgement and egg mass weights were 33 and 50% lower, respectively, in adult females treated with M. ansiopliae in the field before engorging on laboratory rabbits. M. anisopliae did not significantly reduce egg mass weight, conversion efficiency, or oviposition period in I. scapularis females treated with the fungus after engorging on white-tailed deer, although only 33% of treated females oviposited. Engorged nymphs and larvae treated with M. anisopliae converted significantly lower percentages of their engorged weight to their molted adult and nymphal weights. This study indicates that M. anisopliae reduces fitness (fecundity and body mass) in all active I. scapularis stages and indicates that its impact as a biocontrol agent might be higher than that suggested by direct mortality alone.     

Larval behavioral diapause regulates life cycle of Amblyomma cajennense (Acari: Ixodidae) in Southeast Brazil

Previous studies have determined that Amblyomma cajennense (F.) produces one generation per year in Southeastern Brazil. Larvae predominate from April to July, nymphs from July to October, and adults from October to March. In the current study, we observed engorged females, their eggs, and respective larvae in the field. Engorged females were released in grass plots under natural conditions, at monthly intervals, from October 2000 to March 2001. Preoviposition periods lasted 1-2 wk, and mean egg incubation periods lasted 5-7 wk. Consequently, larvae hatched at different periods from early December 2000 to early April 2001. However, all hatched larvae stayed confined to the plot ground, under the vegetation, until late April or early May 2001, when some larvae were seen questing on top of vegetation for the first time. Thereafter, larvae were always seen on this questing position until August 2001, when all larvae had died on the plots. In addition, premolt period data of engorged larvae and nymphs held in laboratory at different temperatures were used to construct a premolt mathematical model, which was applied to reported seasonal dynamic data of A. cajennense in the field. The premolt model indicated that the field intervals between larvae and nymphs and between nymphs and adults are controlled solely by nondiapause events, such as ground temperature. We concluded that the 1-yr generation pattern of A. cajennense in Southeastern Brazil is primarily controlled by larval behavioral diapause, shown by larvae born during spring/summer months, before their activity period at next autumn.     

Seasonal distribution and abundance of ticks (Acari: ixodidae) in northwestern Florida

A 2-yr study was conducted in a northwestern Florida state park and recreation area to determine tick species composition, seasonal abundance, and spatial distribution. Risk of tick attachment to park visitors was also assessed relative to tick abundance from several habitats. Tick collections consisted of weekly cloth drag samples obtained from ground and emergent vegetation along a deer trail, a walking trail located in a 3-mo-old control burned area of forest, a nonburned walking trail, picnic area, and campsites. Sampling was conducted from February 1994 through February 1996. Ticks collected during the study were as follows in descending order of abundance: Ixodes scapularis Say, Amblyomma americanum (L.), A. maculatum Koch, and Dermacentor variabilis (Say). Significantly more (<0.05) adult ticks were recovered from vegetation compared with ground samples only for I. scapularis. Adult questing I. scapularis were collected from October through May (peak December). A. americanum adults were collected from March through August (peak May). Adult A. maculatum were collected during August and September and adult D. variabilis were collected July and August. Larval and nymphal stages of questing A. americanum were collected from June through November (peak July) and February through October (peak September), respectively. A. maculatum nymphs were collected from February through April, June, and September (peak March). No nymphs of I. scapularis were collected. Only four larvae of D. variabilis were collected during the study, all during February 1995. No I. scapularis or A. maculatum larvae were collected from vegetation or ground drags. The greatest risk for tick attachment was in campsites where approximately 60% of all adult and nymphal host-seeking ticks were collected. The next greatest risk area was the walking trail located in the control burned area where an additional 28% of ticks were obtained.     

Presence of Borrelia burgdorferi (Spirochaetales: Spirochaetaceae) in southern Kettle Moraine State Forest, Wisconsin, and characterization of strain W97F51

Lyme disease, caused by Borrelia burgdorferi Johnson, Schmidt, Hyde, Steigerwalt & Brenner; babesiosis, caused by Babesia microti Franca; and human granulocytic ehrlichiosis, caused by Anaplasma phagocytophilum Bakken & Dumler have been reported in Wisconsin, mainly in the endemic areas of the northwestern part of the state. People exposed to blacklegged ticks, Ixodes scapularis Say, from this region can potentially contract one or all of these diseases concurrently. Within the past several years, there have been cases of Lyme disease reported from southeastern Wisconsin, an area that contains deer, mice, and similar vegetation found at regions with high endemicity. However, past white-tailed deer surveys suggested no existence of I. scapularis in southeastern Wisconsin. However, in 1996, we identified questing adult I. scapularis in the southernmost part of the Southern Kettle Moraine State Forest, Walworth County. To determine whether an established population of I. scapularis exists in this region, we performed a detailed survey of the abundance of host-seeking I. scapularis adults and the presence and abundance of subadults feeding on white-footed mice, Peromyscus leucopus Rafinesque. We also tested for possible infections of B. burgdorferi, Ba. microti, and A. phagocytophilum in ticks and B. burgdorferi harbored by mice. In 1997 and 1998, a total of 249 P. leucopus mice and 118 questing adult I. scapularis ticks, in addition to 157 larvae and seven nymphs feeding on mice, were collected and their locations were recorded from the Nordic trails of the Southern Kettle Moraine State Forest. Only one P. leucopus and its attached engorged I. scapularis nymph were infected with B. burgdorferi, whereas none of the engorged larvae attached to mice were infected. However, 4.2% of questing adult I. scapularis were infected with B. burgdorferi. The abundance of questing adult I. scapularis was 1.6 ticks per hour. The prevalence of subadult ticks on mice was 27%, with a mean intensity on infested mice of 2.0. I. scapularis adults were not infected with either Ba. microti or A. phagocytophilum. A unique strain of B. burgdorferi s.l. (W97F51) was discovered, showing 33 nucleotide substitutions and one codon insertion in a 567-bp fragment of the OspB gene, compared with Borrelia bissettii (strain Ca389). The sequences of ospA, ospB, ospC,fla, and rrs genes and the rrf-rrl intergenic spacer region were compared between W97F51 and other B. burgdorferi s.l. species. Although W97F51 was most genetically related to B. bissettii, the genetic identity of W97F51 was less than that of B. bissettii conspecifics. This study documents the existence of an established population of I. scapularis and the presence of B. burgdorferi with a novel strain in southeastern Wisconsin.     

Laboratory studies on the life cycle of Amblyomma marmoreum (Acari: Ixodidae) on two different hosts.

A comparative study was made of the life cycle of the tortoise tick, Amblyomma marmoreum Koch, on tortoises and guinea pigs under laboratory conditions. At 25 degrees C and 85% RH with natural day length, duration of off-host stages (preoviposition, oviposition, incubation, and premolt) was similar for ticks fed on both hosts. Delay in preoviposition (up to 90 d) was observed in some gravid females. Larvae, nymphs, and adults had longer feeding periods on tortoises than on guinea pigs. Adult females fed on tortoises had greater engorgement wieght and ovipositional capacity than ticks fed on guinea pigs. It is suggested that the shortened feeding period of immature stages on mammalian hosts together with the occurrence of morphogenic diapause may be more important than previously recognized in determining whether the life cycle of A. marmoreum is completed in 1 or 2 yr under natural conditions.     

Borrelia burgdorferi s.l. in Ixodes ricinus (Acari: Ixodidae) ticks collected from vegetation and small rodents in recreational areas of the city of Poznań

During 1998-1999, Ixodes ricinus (L.) populations were investigated in three different biotopes (deciduous, mixed, coniferous forest) situated in popular recreational areas in Poznań, Poland. In total, 1,123 questing ticks (1,002 nymphs, 69 males, 52 females) were collected by flagging vegetation. Additionally, in 1998 between May and September small rodents were trapped and inspected for feeding ticks. Altogether, 213 rodents of three species: Apodemus agrarius Pall., A. flavicollis Melchior, Clethrionomys glareolus Schreber were captured. Of 323 engorged ticks, 304 were larvae and 19 nymphs. All ticks collected from vegetation, as well as from rodents were examined for the presence of Borrelia burgdorferi Johnson, Schmid, Hyde, Steigenwalt & Brenner s.l. spirochetes by indirect immunofluorescence assay (IFA) using PAB 1B29. The seasonal pattern of activity of questing I. ricinus was always bimodal (May/June and August/September). The most abundant tick population occurred in the deciduous forest. The total infection rate in questing ticks was 16.2%. Differences in mean infection prevalence of host-seeking ticks between three biotopes each year were not significant. On average more larvae parasitized on the genus of Apodemus than on C. glareolus. 17.8% of larvae and 31.6% of nymphs fed on rodents harbored spirochetes. The three rodent species contributed to a different degree in to transmission of the pathogen to subadult stages. Approximately 27% of larvae infested on A. agrarius, 22% on C. glareolus, and only 4.2% on A. flavicollis contained spirochetes. The results suggest that the prevalence of A. agrarius and C. glareolus in disturbed urban forests used for leisure activities seems to be crucial for the maintenance of B. burgdorferi s.l. in I. ricinus populations.     

Attempt to control ticks (Acari: Ixodidae) on deer on an isolated island using ivermectin-treated corn

We report an attempt by an offshore island community to control the vector tick of Lyme disease by providing ivermectin-treated corn to an isolated herd of free-ranging white-tailed deer, Odocoileus virginianus Zimmerman. Medicated corn was supplied in troughs within the island village and from automatic feeders at remote sites during 5 consecutive fall and spring adult tick questing seasons. Acaricide consumption was monitored by assaying its presence in fresh deer pellets and its concentration in deer sera. Its effectiveness was evaluated by recording the number of adult ticks collected from the hides of deer, the number of females becoming sufficiently engorged to oviposit, and the success of subsequent oviposition and eclosion. Entomologic risk was monitored by collecting immature ticks from hosts and adult ticks from vegetation. Estimates based on a subsequent deer reduction program indicated that up to twice as many deer had been present during the project as originally presumed. For this and other reasons related to deer behavior, target levels of serum ivermectin were achieved in a minority of deer. Nevertheless, > 90% control of female tick infestation, subsequent oviposition, and larval eclosion was obtained in those 8 of 16 sampled deer with serum ivermectin levels of > or = 15 ng/ml. In addition, the ratio of females to males, the numbers of females engorging > 10 mg body weight, and the numbers of those eventually hatching, were all significantly less among ticks from island deer in comparison with ticks from untreated deer. No consistent changes in the numbers of ticks found on immature-stage hosts or removed from vegetation were noted within 3 yr of the cessation of treatment.     

Experimental infection of Hyalomma marginatum ticks with West Nile virus

To define the possible role of Hyalomma marginatum ticks in the transmission of West Nile virus (WNV) in Portugal an experimental infection was established. Ticks were fed on viremic rabbits previously infected with WNV. In different developmental stage of H. marginatum virus isolation and detection of viral antigen and viral RNA were attempted. The oral infection rates were 3%, 33% and 75% for engorged larvae, nymphs and females after oviposition, respectively. Transstadial transmission rates for nymphs exposed to virus as larvae, for adults exposed as larvae, and for adults exposed as nymphs were 33%, 11% and 46%, respectively. No evidence of transovarial transmission was obtained. Ticks in the stages of nymphs and adults were able to transmit the infection to uninfected hosts. This study demonstrated that H. marginatum could be involved in the natural circulation of WNV in Portugal.     

Effects of selected meterological factors on diurnal questing of Ixodes scapularis and Amblyomma Americanum (Acari: Ixodidade)

The diurnal questing behavior of adult Ixodes scapularis Say and Amblyomma americanum (L.) were monitored in the field to determine whether ticks would be collected with greater frequency during certain times of the day and under certain ambient meteorological conditions. Temperature and relative humidity explained a significant amount of the total variation in tick collections. Although both species were collected during every period, I. scapularis adults tended to quest earlier and later in the day when temperatures were lower and relative humidity higher, whereas A. americanum were collected with greater frequency in late morning and early afternoon during periods of higher temperatures and lower humidity. Questing of I. scapularis adults was observed at temperatures as low as -0.6 degrees C, whereas no adult A. americanum were collected below 4.4 degrees C. The questing temperature threshold for I. scapularis adults observed in this study was below that reported previously. The implications of these temporal activity patterns on the assessment of disease transmission risk and sampling bias are also discussed.     

Ixodes scapularis ticks (Acari: Ixodidae) from Louisiana are competent to transmit Borrelia burgdorferi, the agent of Lyme borreliosis

The principal vector of Borrelia burgdorferi, the Lyme borreliosis spirochete, in the Northeast and Midwestern regions of the United States is the blacklegged tick Ixodes scapularis. Because of a favorable environment, I. scapularis is also plentiful in the South; however, a correlation with Lyme borreliosis cases does not exist in this region of the United States. Concern existed that something intrinsic to ticks found in Louisiana could mitigate their ability to transmit B. burgdorferi. Therefore, we set out to assess the ability of I. scapularis ticks from Louisiana to become infected with and transmit B. burgdorferi using mice as hosts. In the laboratory, mating adult female ticks collected in southeastern Louisiana were fed on the ears of rabbits. After oviposition and egg hatching, the resulting larvae were fed on mice that had been needle-inoculated with two different strains of B. burgdorferi sensu stricto, B31 and JD1. Larvae were found to be positive for spirochetes. Additional fed larvae were allowed to molt into the nymphal stage. Flat nymphs remained infected with B. burgdorferi. Infected nymphs were allowed to feed on na?ve mice, all of which became infected as shown by culture of ear biopsy specimens. Na?ve larvae were then fed on these same mice to assess transmissibility. The resulting engorged larvae harbored spirochetes. We have demonstrated that the I. scapularis ticks found in Louisiana are fully competent to carry and transmit B. burgdorferi infection.     

Feeding efficiency of larval Hyalomma truncatum (Acari: Ixodidae) on hosts previously exposed to ticks.

The effect of guinea pig response to feeding larval Hyalomma truncatum Koch ticks was studied by measuring the percentage of ticks engorging and molting, their engorged weight, and hemoglobin content. Four guinea pigs were infested with 100, 200, 400, and 1,000 larvae, respectively, on three occasions at 21-d intervals, followed by a fourth infestation with 500 larvae. During the second, third, and fourth infestations, significantly fewer ticks engorged on each guinea pig than during the first infestation. The greatest reduction in percentage molting occurred during the fourth infestation on the animal with successive exposure to 400 larvae; only 24% of the ticks that fed molted. Ticks with the lowest mean weight and hemoglobin content also engorged on this animal during the fourth infestation. Guinea pigs exposed to 200 and 400 H. truncatum larvae elicited the greatest change in feeding efficiency during the fourth infestation. However, these hosts had no effect on a single subsequent fifth infestation with Amblyomma cajennense (F.) nymphs, as greater than 95% successfully engorged.     

African swine fever virus infection in the Iberian soft tick, Ornithodoros (Pavlovskyella) marocanus (Acari: Argasidae).

One thousand six hundred Ornithodoros (Pavlovskyella) marocanus Velu larvae were fed on a pig infected with African swine fever virus (titer: 10(7.4) HAd50/ml), and 1,600 larvae were fed on an uninfected pig. Ticks in each group were compared for mortality rates, mean time to death for ticks that died, mean time from feeding to either molting or eclosion, percentage of ticks that eclosed or molted, and the number of blood meals per nymph or instar. Cumulative virus-induced mortality for all immature stages (larvae to adult) of O. marocanus that had been fed as larvae on a pig infected with African swine fever was ca. 73% over a 390-d period. In contrast, less than 9% mortality was observed among ticks fed on uninfected pigs. Mean time to death for infected ticks was 15-87 d versus 10-17 d for uninfected ticks. Differences in the premolt period (number of days from blood meal to molt) between infected and control ticks were not observed. Mean premolt periods for larvae and first-, second-, third-, fourth-, and fifth-instar nymphs fed on pigs were 7, 9, 15, 11, 15, and 15 d, respectively. The majority of infected and all uninfected ticks required only one blood meal from pigs to molt. Mean weights for unfed second-, third-, and fourth-instar nymphs and males and females were 0.50, 0.67, 3.07, 3.63, and 5.91 mg, respectively.     

The luxS gene is not required for Borrelia burgdorferi tick colonization, transmission to a mammalian host, or induction of disease

luxS mutants of Borrelia burgdorferi strain 297 naturally colonized their arthropod (Ixodes scapularis) vector, were maintained in ticks throughout the molting process (larvae to nymphs), were tick transmitted to uninfected mice, and elicited histopathology in mice indistinguishable from that induced by wild-type B. burgdorferi.     

Meteorologically mediated diurnal questing of Ixodes scapularis and Amblyomma americanum (Acari: Ixodidae) nymphs

Questing Ixodes scapularis Say and Amblyomma americanum (L.) nymphs were collected in the field by drag sampling to determine whether ticks would be collected in greater numbers during certain times of the day and under certain ambient meteorological conditions. Ticks were collected hourly for 16 h on 4 d and counts were contrasted with simultaneous measurements of ambient temperature and relative humidity, and with similar measurements made within the leaf litter. Peak numbers of questing I. scapularis and A. americanum nymphs were collected at distinctly different times of day, suggesting that the two species were responding to different environmental conditions. Both species demonstrated responses to diel changes in local meteorological conditions. Numbers of ticks were correlated with ambient temperature and humidity and with conditions recorded in the leaf litter that appeared to play a significant role in mediating questing behavior of both species. The time of day when tick sampling is conducted might significantly bias population estimates for sympatric species and the assessment of tick-borne disease transmission risk.     

Evaluation of transovarial transmission and transmissibility of Ehrlichia chaffeensis (Rickettsiales: Anaplasmataceae) in Amblyomma americanum (Acari: Ixodidae)

It has long been assumed that Ehrlichia chaffeensis (Anderson, Dawson & Wilson), is not transmitted transovarially in the lone star tick vector Amblyomma americanum (L.). To test this hypothesis, three beagle dogs, Canis familiaris (L.) (Carnivora: Canidae), were subcutaneously infected with E. chaffeensis (Arkansas strain). Uninfected nymphal lone star ticks were placed on the infected dogs and allowed to feed to repletion. These nymphal ticks were allowed to molt, and five of five adult female ticks sampled were confirmed to be infected by polymerase chain reaction (PCR). Forty infected adult ticks, the majority of which were female with several males included to stimulate feeding, were then placed on two uninfected dogs. Fourteen females were removed early and the rest were allowed to feed to repletion. After feeding to repletion, the six remaining females detached and two of these females were tested preoviposition, whereas the remaining four were allowed to lay eggs. All six of these fully engorged females tested negative by PCR. The egg clutches laid by four engorged adult females, and the larvae that hatched from these eggs along with larvae from a previously untested egg clutch, were shown to be uninfected by PCR. This seems to support the long-held assumption of lack of transovarial transmission. Also of interest, we found that these PCR-confirmed infected adult ticks reared in the laboratory did not transmit E. chaffeensis to uninfected dogs.     

Effect of ambient temperature on competence of deer ticks as hosts for Lyme disease spirochetes.

We determined whether the temperature of extrinsic incubation affects the competence of vector ticks as hosts for Lyme disease spirochetes (Borrelia burgdorferi). Larval Ixodes dammini ticks that had engorged on spirochete-infected C3H mice were incubated continuously at various temperatures, and the gut contents of the resulting nymphs were examined for spirochetes by direct immunofluorescence microscopy. Spirochetes were present in virtually all nymphs kept at 27 degrees C or less for 6 months, in only 10% of those kept at 33 degrees C, and in none kept at 37 degrees C. Spirochetes became undetectable within 8 weeks when nymphs were warmed from 27 to 33 degrees C beginning at the time of molting. Nymphs became virtually noninfective for mice after incubation at temperatures higher than 27 degrees C for 2 weeks or longer. We conclude that ambient temperatures in excess of 27 degrees C are not permissive for transmission of the agent of Lyme disease.     

Immune response of lizards and rodents to larval Ixodes scapularis (Acari: Ixodidae).

The house mouse (laboratory strain), Mus musculus (L.), the cotton mouse, Peromyscus gossypinus (LeConte), the broad-headed skink, Eumeces laticeps (Schneider), and the guinea pig, Cavia porcellus (L.), were successively infested five times with larvae of the blacklegged tick, Ixodes scapularis Say. Tick feeding success, engorgement weight, and subsequent molting success were measured after each infestation. A greater percentage of ticks (P less than 0.05) fed on M. musculus and E. laticeps than on P. gossypinus or C. porcellus. P. gossypinus expressed a transitory partial resistance, measured in percentage of ticks feeding, during the third infestation but showed increased tolerance during the fourth and fifth infestations. Ticks fed on E. laticeps were heavier than those fed on any other host (P less than 0.05). Those fed on M. musculus were heavier than those fed on P. gossypinus, but the difference was not statistically significant. On C. porcellus, only 1.6% of larvae from the third infestation and none thereafter engorged; weights of larvae from first and second infestations were higher (P less than 0.05) than those fed on M. musculus and P. gossypinus and lower (P less than 0.05) than those fed on E. laticeps. A greater percentage of larvae from E. latticeps and M. musculus (P less than 0.05) molted to nymphs compared with those from P. gossypinus and C. porcellus. Molting success was the same for ticks fed on P. gossypinus and on C. porcellus during the first and second infestations. M. musculus, P. gossypinus, and E. laticeps expressed no resistance (measured as percentage feeding, engorgement weight, and molting) to feeding by I. scapularis larvae after five infestations. Host serum was tested using an ELISA for detection of antibodies against I. scapularis salivary gland antigens before and after each infestation. Antibodies were detected after the second infestation and thereafter in C. porcellus, the only species to show antibodies or to express and maintain an acquired resistance to tick feeding throughout five infestations.