Seasonal and diel activity of Ixodes ricinus (Acari: Ixodidae) subpopulations in Denmark. Aspects of size, physiological age, and malate dehydrogenase genotype in a forest site without any undergrowth

The underlying population dynamics and the behavioural patterns of the vectors are key issues in understanding the transmission of vector borne pathogens. For the tick Ixodes ricinus both seasonal and diel activity have been described as bimodal patterns, which in seasonal aspect has been interpreted as representing two cohorts. However, recent studies have shown that this interpretation may be incorrect. The aim of this study was to obtain more detailed information on nymph host seeking by studying subpopulations of ticks during the day and season. The study was designed to allow for comparisons of the diel variation and seasonal variation in their dependency in a number of tick characteristics. The study took place in a forest with planted beech trees without any undergrowth. Ticks were collected by flagging the dead leaves on the forest floor. For each nymph, a number of visual observations were made. The size and physiological age was observed and the nymphs were genotyped in the malate dehydrogenase locus (MDH, E.C. 1.1.1.37). Briefly the main results can be given as: (i) There were significant differences in the composition of size classes during the season, but only limited trends in time. (ii) The proportion of the small nymphs was highly variable, with a variation from 3% to 24% in October and September, respectively. (iii) The diel variation in MDH genotypes was significant in May and August. (iv) Nymph size classes and physiological age appeared to interact. The non-random interaction was caused by a relatively even distribution of small nymphs in all four age classes, while large nymphs tended to fall into age class 2 and 3. The length by age interaction for the individual months was noted to be significant in May, July, August and September, but not in June. Similarly the interaction was significant in the morning and afternoon, but not at midday. The overall results describe the seasonal and diel activity patterns as changing systematically for several characteristics under the influence of weather condition and population dynamics. In conclusion: The observations are best interpreted as being produced of a single cohort of ticks, but the revealed complexity of the host seeking activity suggest that measures of activity x abundance should be interpreted very cautiously in relation to population dynamics.     

Activity periods and questing behavior of the seabird tick Ixodes uriae (Acari: Ixodidae) on Gull Island, Newfoundland: the role of puffin chicks

Questing behavior of Ixodes uriae and their associated seasonal, host-feeding patterns are crucial to our understanding of tick life history strategies and the ecology of diseases that they transmit. Consequently, we quantified questing behavior of nymphs and adult female I. uriae ticks at Gull Island, a seabird colony in Newfoundland, Canada, to examine seasonal variation of off-host and on-host tick activity. We sampled a total of 133 adult Atlantic puffins (Fratercula arctica), 152 puffin chicks, and 145 herring gull (Larus argentatus) chicks for ticks during the breeding seasons of 2004 and 2005. Questing ticks were sampled by dragging a white flannel cloth across the grassy breeding areas during the mo of May, June, July, and August. Nymph questing activity reached a peak during mid-July (79 and 110 individuals/hr in 2004 and 2005, respectively). The prevalence of nymphs and adult female ticks on different seabird hosts varied between years and during the seasons. Puffin chicks had the highest prevalence (above 70% in July) of nymphs in both years and this was correlated with questing activity. Female ticks rarely fed on puffin chicks, but were prevalent on adult puffins and gulls, although prevalence and questing of ticks were not correlated in these hosts. These patterns of off-host and on-host tick activity suggests that I. uriae ticks likely use a combination of questing and passive waiting, e.g., in puffin burrows, to detect hosts, depending on the tick stage and the host species.     

Temporal Distribution of the Annual Nymphal Stock of Ixodes Ricinus Ticks

The human risk of contracting Lyme disease or other tick borne diseases transmitted by the tick species Ixodes ricinus is broadly linked to the tick nymph density. The study was performed in Rambouillet forest (Yvelines, France), a known focus of Lyme borreliosis, from January 1997 to December 1999. We used a nymph sampling methodology which permitted us to obtain a monthly nymph density index (from 0 to 5). Studying the seasonal nymph and larval activity patterns and estimating the larval developmental duration, we demonstrate the existence of an annual nymphal stock. Secondly, we elucidate how this stock is distributed throughout the year, month by month. Its distribution is principally dependent on two factors: the monthly mean ambient temperature and the proportion of active nymphs which find a host each month. Expected monthly nymph densities derived from a theoretical model describing the temperature-dependent stock distribution gave a good fit to the observed densities, accounting for between 76–86% of the monthly variation in observed nymph densities. Predicting the temporal distribution of nymph activity within a stable Lyme borreliosis focus enables more precise identification of risk periods.     

Modelling the effect of temperature variation on the seasonal dynamics of Ixodes ricinus tick populations

Seasonal variation in temperature is known to drive annual patterns of tick activity and can influence the dynamics of tick-borne diseases. An age-structured model of the dynamics of Ixodes ricinus populations was developed to explore how changes in average temperature and different levels of temperature variability affect seasonal patterns of tick activity and the transmission of tick-borne diseases. The model produced seasonal patterns of tick emergence that are consistent with those observed throughout Great Britain. Varying average temperature across a continuous spectrum produced a systematic pattern in the times of peak emergence of questing ticks which depends on cumulative temperature over the year. Examination of the effects of between-year stochastic temperature variation on this pattern indicated that peak emergence times are more strongly affected by temperature stochasticity at certain levels of average temperature. Finally the model was extended to give a simple representation of the dynamics of a tick-borne disease. A threshold level of annual cumulative temperature was identified at which disease persistence is sensitive to stochastic temperature variation. In conclusion, the effect of changing patterns of temperature variation on the dynamics of I. ricinus ticks and the diseases they transmit may depend on the cumulative temperature over the year and will therefore vary across different locations. The results also indicate that diapause mechanisms have an important influence on seasonal patterns of tick activity and require further study.     

An empirical quantitative framework for the seasonal population dynamics of the tick Ixodes ricinus

The wide geographic and climatic range of the tick Ixodes ricinus, and the consequent marked variation in its seasonal population dynamics, have a direct impact on the transmission dynamics of the many pathogens vectored by this tick species. We use long-term observations on the seasonal abundance and fat contents (a marker of physiological ageing) of ticks, and contemporaneous microclimate at three field sites in the UK, to establish a simple quantitative framework for the phenology (i.e. seasonal cycle of development) of I. ricinus as a foundation for a generic population model. An hour-degree tick inter-stadial development model, driven by soil temperature and including diapause, predicts the recruitment (i.e. emergence from the previous stage) of a single cohort of each stage of ticks each year in the autumn. The timing of predicted emergence coincides exactly with the new appearance of high-fat nymphs and adults in the autumn. Thereafter, fat contents declined steadily until unfed ticks with very low energy reserves disappeared from the questing population within about 1 year from their recruitment. Very few newly emerged ticks were counted on the vegetation in the autumn, but they appeared in increasing numbers through the following spring. Larger ticks became active and subsequently left the questing population before smaller ones. Questing tick population dynamics are determined by seasonal patterns of tick behaviour, host-contact rates and mortality rates, superimposed on a basal phenology that is much less complex than has hitherto been portrayed.     

Monitoring the diel activity of Ixodes ricinus ticks in Hungary over three seasons

Ixodes ricinus is the most common tick species in Europe and vector of many diseases of humans. The risk of contracting such a disease is influenced by many factors, but one of the crucial points is questing activity of unfed ticks. In order to supplement the few literature data on patterns of diel activity of this tick species and to examine the correlations between data on diel activity of ticks and their small mammal hosts and some meteorological variables, a survey was performed. Diel activity of questing I. ricinus and small rodents was studied in a known natural tick-borne encephalitis virus focus over 7 months at one sampling day monthly. 1,063 I. ricinus ticks and 25 rodents were sampled. Air temperature and humidity data were also recorded in the 24 study plots at time of sampling. From April to October questing activity of nymphs increased in the 3-h-period after sunrise, comparing to activity of the 3 h before sunrise. Proportion of nymphs sampled 3 h after sunset compared to total sampled nymphs 3 h before and 3 h after sunset showed correlation to activity of rodents. In the period of April–July both nymphs and larvae showed stronger activity from sunrise to sunset, this turned to dominant nighttime activity in August–September, whereas activity changed to equal in day and night in October. Our results indicate that natural light and rodent population have positive effect on questing activity of I. ricinus.     

Simulation of climate‐tick‐host‐landscape interactions: Effects of shifts in the seasonality of host population fluctuations on tick densities

Tick vector systems are comprised of complex climate‐tick‐host‐landscape interactions that are difficult to identify and estimate from empirical observations alone. We developed a spatially‐explicit, individual‐based model, parameterized to represent ecological conditions typical of the south‐central United States, to examine effects of shifts in the seasonal occurrence of fluctuations of host densities on tick densities. Simulated shifts in the seasonal occurrence of periods of high and low host densities affected both the magnitude of unfed tick densities and the seasonality of tick development. When shifting the seasonal densities of all size classes of hosts (small, medium, and large) synchronously, densities of nymphs were affected more by smaller shifts away from the baseline host seasonality than were densities of larval and adult life stages. When shifting the seasonal densities of only a single size‐class of hosts while holding other size classes at their baseline levels, densities of larval, nymph, and adult life stages responded differently. Shifting seasonal densities of any single host‐class earlier resulted in a greater increase in adult tick density than when seasonal densities of all host classes were shifted earlier simultaneously. The mean densities of tick life stages associated with shifts in host densities resulted from system‐level interactions of host availability with tick phenology. For example, shifting the seasonality of all hosts ten weeks earlier resulted in an approximately 30% increase in the relative degree of temporal co‐occurrence of actively host‐seeking ticks and hosts compared to baseline, whereas shifting the seasonality of all hosts ten weeks later resulted in an approximately 70% decrease compared to baseline. Differences among scenarios in the overall presence of active host‐seeking ticks in the system were due primarily to the degree of co‐occurrence of periods of high densities of unfed ticks and periods of high densities of hosts.     

Vertical vs. horizontal transmission of the microbiome in a key disease vector,Ixodes pacificus

Vector‐borne pathogens are increasingly found to interact with the vector's microbiome, influencing disease transmission dynamics. However, the processes that regulate the formation and development of the microbiome are largely unexplored for most tick species, an emerging group of disease vectors. It is not known how much of the tick microbiome is acquired through vertical transmission vs. horizontally from the environment or interactions with bloodmeal sources. Using 16S rRNA sequencing, we examined the microbiome of Ixodes pacificus, the vector of Lyme disease in the western USA, across life stages and infection status. We also characterized microbiome diversity in field and laboratory‐collected nymphal ticks to determine how the surrounding environment affects microbiome diversity. We found a decrease in both species richness and evenness as the tick matures from larva to adult. When the dominant Rickettsial endosymbiont was computationally removed from the tick microbial community, we found that infected nymphs had lower species evenness than uninfected ticks, suggesting that lower microbiome diversity is associated with pathogen transmission in wild‐type ticks. Furthermore, laboratory‐reared nymph microbiome diversity was found to be compositionally distinct and significantly depauperate relative to field‐collected nymphs. These results highlight unique patterns in the microbial community of I. pacificus that is distinct from other tick species. We provide strong evidence that ticks acquire a significant portion of their microbiome through exposure to their environment despite a loss of overall diversity through life stages. We provide evidence that loss of microbial diversity is at least in part due to elimination of microbial diversity with bloodmeal feeding but other factors may also play a role.     

Tritrophic interactions between a fungal pathogen,a spider predator,and the blacklegged tick

The blacklegged tick Ixodes scapularis is the primary vector for the bacterium causing Lyme disease in eastern North America and for other medically important pathogens. This species is vulnerable to attack by fungal pathogens and arthropod predators, but the impacts of interactions between biocontrol agents have not been examined. The biocontrol agent Met52^®, containing the entomopathogenic fungus Metarhizium brunneum (=M. anisopliae), controls blacklegged ticks with efficacy comparable to chemical acaricides. The brush‐legged wolf spider Schizocosa ocreata is a predator of I. scapularis that reduces their survival under field conditions. We conducted a field microcosm experiment to assess the compatibility of Met52 and S. ocreata as tick biocontrol agents. We compared the fits of alternative models in predicting survival of unfed (flat) and blood‐fed (engorged) nymphs. We found the strongest support for a model that included negative effects of Met52 and S. ocreata on flat nymph survival. We found evidence for interference between biocontrol agents, with Met52 reducing spider survival, but we did not find a significant interaction effect between the two agents on nymph survival. For engorged nymphs, low recovery rates resulted in low statistical power to detect possible effects of biocontrol agents. We found that nymph questing activity was lower when the spider was active above the leaf litter than when the spider was unobserved. This provides the first evidence that predation cues might affect behavior important for tick fitness and pathogen transmission. This study presents field microcosm evidence that the biopesticide Met52 and spider Schizocosa ocreata each reduced survival of blacklegged ticks Ixodes scapularis. Met52 reduced spider survival. Potential interference between Met52 and the spider should be examined at larger scales, where overlap patterns may differ. Ticks were more likely to quest when the spider was inactive, suggesting the ticks changed their behavior to reduce danger.     

Introduced Siberian chipmunks are more heavily infested by ixodid ticks than are native bank voles in a suburban forest in France

By serving as hosts for native vectors, introduced species can surpass native hosts in their role as major reservoirs of local pathogens. During a 4-year longitudinal study, we investigated factors that affected infestation by ixodid ticks on both introduced Siberian chipmunks Tamias sibiricus barberi and native bank voles Myodes glareolus in a suburban forest (Forêt de Sénart, Ile-de-France). Ticks were counted on adult bank voles and on adult and young chipmunks using regular monthly trapping sessions, and questing ticks were quantified by dragging. At the summer peak of questing Ixodes ricinus availability, the average tick load was 27-69 times greater on adult chipmunks than on adult voles, while average biomass per hectare of chipmunks and voles were similar. In adult chipmunks, individual effects significantly explained 31% and 24% of the total variance of tick larvae and nymph burdens, respectively. Male adult chipmunks harboured significantly more larvae and nymphs than adult females, and than juveniles born in spring and in summer. The higher tick loads, and more specifically the ratio of nymphs over larvae, observed in chipmunks may be caused by a higher predisposition - both in terms of susceptibility and exposure - to questing ticks. Tick burdens were also related to habitat and seasonal variation in age- and sex-related space use by both rodents. Introduced chipmunks may thus have an important role in the dynamics of local vector-borne pathogens compared with native reservoir hosts such as bank voles.     

Attachment site selection of ticks on roe deer, <Emphasis Type="Italic">Capreolus capreolus</Emphasis>

The spatio-temporal attachment site patterns of ticks feeding on their hosts can be of significance if co-feeding transmission (i.e. from tick to tick without a systemic infection of the host) of pathogens affects the persistence of a given disease. Using tick infestation data on roe deer, we analysed preferred attachment sites and niche width of Ixodes ticks (larvae, nymphs, males, females) and investigated the degree of inter- and intrastadial aggregation. The different development stages showed rather consistent attachment site patterns and relative narrow feeding site niches. Larvae were mostly found on the head and on the front legs of roe deer, nymphs reached highest densities on the head and highest adult densities were found on the neck of roe deer. The tick stages feeding (larvae, nymphs, females) on roe deer showed high degrees of intrastadial spatial aggregation, whereas males did not. Male ticks showed large feeding site overlap with female ticks. Feeding site overlap between larval-female and larval-nymphal ticks did occur especially during the months May–August on the head and front legs of roe deer and might allow pathogen transmission via co-feeding. Tick density, niche width and niche overlap on roe deer are mainly affected by seasonality, reflecting seasonal activity and abundance patterns of ticks. Since different tick development stages occur spatially and temporally clustered on roe deer, transmission experiments of tick-borne pathogens are urgently needed.     

Risk factors associated with ixodid tick species distributions in the Basque region in Spain

Ixodid tick abundance was investigated in the Basque region in Spain in two 1-year longitudinal studies, in 1992-1993 and 2003-2004. Forty zones were visited monthly and 162 672 ticks (87% larvae, 12% nymphs and 1% adults) were collected by blanket dragging. Eleven tick species belonging to the genera Ixodes, Haemaphysalis, Rhipicephalus and Dermacentor were identified including Haemaphysalis concinna Koch, which had not previously been reported in Spain. Tick species abundance differed between zones, studies and seasons. In 1992-1993, Haemaphysalis punctata Canestrini & Fanzago was the predominant species and distinct spring-summer and autumn-early winter peaks of activity were observed. In 2003-2004, Ixodes ricinus (Linneaus) was the most common species and was active throughout the winter. Larval and nymph seasonal activity patterns coincided in both 1993 and 2003 and this could facilitate co-feeding transmission of pathogens. Higher tick abundance was associated with increased livestock abundance in 1992-1993 and milder winter temperatures in 2003-2004. Tick collection rates in areas with moderate and high tick density were positively associated with the interaction between ambient temperature at sampling and rainfall 7 days prior to sampling. Collection rates were also significantly higher at medium rather than higher altitude, in forested areas than in open grasslands and lower in recreational areas frequented by people and with wet vegetation at sampling.     

Drop off rhythm and survival periods of <Emphasis Type="Italic">Amblyomma lepidum</Emphasis> (Acari: Ixodidae) under field conditions

In this study, engorged Amblyomma lepidum ticks were found to drop off in two peaks, one in the morning and one in the evening. Most larvae and females engorged during the morning hours between 06.00 h and 10.00 h with a peak around 08.00 h, whereas the majority of the nymphs dropped in the evening between 18.00 h and 24.00 h with the peak around 22.00 h. Although the effect of time on drop-off patterns of the ticks was statistically significant (p≤ 0.001), there were no significant seasonal influences. Survival of unfed stages of A. lepidum was also studied and was found to increase from larvae to adult ticks. The longest survival periods of 10, 11 and 14 weeks were recorded during the wet season for larvae, nymphs and adults, respectively. It is concluded that environmental conditions required for survival of A. lepidum are optimal only during the wet season and that during other seasons the tick depends primarily on prevailing micro-climatic conditions for its survival.     

Tick burden on European roe deer (<Emphasis Type="Italic">Capreolus capreolus</Emphasis>)

In our study we assessed the tick burden on roe deer (Capreolus capreolus L.) in relation to age, physical condition, sex, deer density and season. The main objective was to find predictive parameters for tick burden. In September 2007, May, July, and September 2008, and in May and July 2009 we collected ticks on 142 culled roe deer from nine forest departments in Southern Hesse, Germany. To correlate tick burden and deer density we estimated deer density using line transect sampling that accounts for different detectability in March 2008 and 2009, respectively. We collected more than 8,600 ticks from roe deer heads and necks, 92.6% of which were Ixodes spp., 7.4% Dermacentor spp. Among Ixodes, 3.3% were larvae, 50.5% nymphs, 34.8% females and 11.4% males, with significant seasonal deviation. Total tick infestation was high, with considerable individual variation (from 0 to 270 ticks/deer). Adult tick burden was positively correlated with roe deer body indices (body mass, age, hind foot length). Significantly more nymphs were found on deer from forest departments with high roe deer density indices, indicating a positive correlation with deer abundance. Overall, tick burden was highly variable. Seasonality and large scale spatial characteristics appeared to be the most important factors affecting tick burden on roe deer.     

Diel activity of Ixodes ricinus Acari: Ixodidae at two locations near Stockholm, Sweden

The diel ‘activity’, i.e. availability, of Ixodes ricinus larvae, nymphs and adults was investigated in a meadow and a forest habitat near Stockholm during 1991–1993. Generally, the immature ticks were more prevalent in the forest than in the meadow. In the meadow, the mean larval and adult numbers varied significantly between 4 h time intervals with the peak activity from 2300 to 0300 h. In the forest, the tick numbers did not differ significantly between the time intervals. The association of the tick activity with certain meteorological variables was strongest in the meadow, where the mean numbers of all tick stages were negatively correlated with the temperature. The relative humidity was positively correlated only with the mean numbers of larvae. In contrast, the larval activity in the forest was positively and negatively correlated with the temperature and relative humidity, respectively, while the nymphal and adult activity showed no association with these climatic variables. The impact of the host activity on the tick diel activity is also discussed.     

Ticks on reptiles and amphibians in Central Amazonia,with notes on rickettsial infections

Reptiles and amphibians are exceptional hosts for different ectoparasites, including mites and ticks. In this study, we investigated tick infestations on reptiles and amphibians trapped in Central Amazonia, and also assessed the presence of rickettsial infections in the collected ticks. From September 2016 to September 2019, 385 reptiles (350 lizards, 20 snakes, 12 tortoises, and three caimans) and 120 amphibians (119 anurans and one caecilian) were captured and examined for ectoparasites. Overall, 35 (10%) lizards, three (25%) tortoises and one (0.8%) toad were parasitized by ticks (124 larvae, 32 nymphs, and 22 adults). In lizards, tick infestation varied significantly according to landscape category and age group. Based on combined morphological and molecular analyses, these ticks were identified as Amblyomma humerale (14 larvae, 12 nymphs, 19 males, and one female), Amblyomma nodosum (three larvae, one nymph, and one female), and Amblyomma rotundatum (four larvae, three nymphs, and one female), and Amblyomma spp. (103 larvae and 16 nymphs). Our study presents the first records of A. nodosum in the Amazonas state and suggests that teiid lizards are important hosts for larvae and nymphs of A. humerale in Central Amazonia. Moreover, a nymph of A. humerale collected from a common tegu (Tupinambis teguixin) was found positive for Rickettsia amblyommatis, which agrees with previous reports, suggesting that the A. humerale-R. amblyommatis relationship may be more common than currently recognized.

     

Nymphal survival and habitat distribution of Ixodes scapularis and Amblyomma americanum ticks (Acari: Ixodidae) on Fire Island, New York, USA

The distribution and survival of Ixodes scapularis and Amblyomma americanum were studied in deciduous and coniferous wooded habitats and in open habitats on Fire Island, New York, USA. The survival of nymphal I. scapularis in field enclosures was greater in forests than in open habitats, suggesting that greater survival contributes to the higher tick population in the woods. The nymphs of each species were more common in deciduous thickets (predominantly Aronia arbutifolia and Vaccinium corynbosum) than in coniferous woods (mostly Pinus rigida) in most but not all years. Larval I. scapularis were more common in coniferous sites in 1994, while the same ticks, as nymphs, were more common in deciduous sites in 1995. The survival of the nymphs was not consistently greater in either the deciduous or coniferous woods. Therefore, factors other than nymphal survival (e.g. larval overwintering survival and tick movement on hosts) probably influenced the relative nymph abundance in different forest types. Overall, the survival of A. americanum was far higher than that of I. scapularis.     

Seasonal patterns of abundance and host relationships of the Australian paralysis tick,Ixodes holocyclus Neumann (Acarina: Ixodidae), in southeastern Queensland

Estimates of seasonal abundance of larvae, nymphs and females of the paralysis tick, Ixodes holocyclus, were obtained by collecting ticks that engorged on small mammals and birds trapped in two localities in southeastern Queensland: Brisbane (wet sclerophyll forest) and Tamborine Mountain (cleared rain forest). The long-tailed short-nosed bandicoot, Isoodon macrourus, was the most common mammal trapped but small numbers of other marsupials, rodents and ground frequenting birds were also captured. Small numbers of five other tick species were also collected. In both habitats there was clearly one dominant generation of I. holocyclus;7er year, although the presence of all stages at most times of the year indicated overlapping of smaller cohorts. Females were most abundant in spring and early summer, larvae in summer-autumn, and nymphs in autumn-winter. I. holocyclus was abundant on I. macrourus and rare on most other mammals and birds captured. At the peak of abundance of each instar, each bandicoot dropped from 500 to 2000 engorged larvae, 100 to 200 engorged nymphs, and four to six engorged females. Life tables were compiled for the tick in both habitats and these indicate that there was relatively high survival from engorged larva to engorged nymph and thence to engorged female and that most mortality occurred between detaching of the engorged female and the detaching of the engorged larva. The tick was more abundant on bandicoots from cleared rain forest and rain forest edge, than on those from sclerophyll woodland. The survival of engorged larvae and nymphs of I. holocyclus and the larval productivity of engorged females were examined in a warm moist climate where the tick was abundant (Tamborine Mountain) and in a hotter dryer climate where the tick was rare or absent (Amberley). In both localities engorged larvae and nymphs survived to the next instar in all seasons of the year. On most occasions engorged females produced eggs which hatched. Mature bandicoots from tick infested areas showed little or no resistance to infestation with larvae or nymphs of I. holocyclus, whereas other small mammals from the same area showed an appreciable degree of resistance to the immature stages of the tick. Feeding larvae and nymphs exposed to normal light-dark cycles in the laboratory detached during the afternoon and early evening. This behaviour and host resistance are discussed in relation to the daily activity cycles of host species, their habitat preferences, and their role as hosts for I. holocyclus.     

Accelerated phenology of blacklegged ticks under climate warming

The phenology of tick emergence has important implications for the transmission of tick-borne pathogens. A long lag between the emergence of tick nymphs in spring and larvae in summer should increase transmission of persistent pathogens by allowing infected nymphs to inoculate the population of naive hosts that can subsequently transmit the pathogen to larvae to complete the transmission cycle. In contrast, greater synchrony between nymphs and larvae should facilitate transmission of pathogens that do not produce long-lasting infections in hosts. Here, we use 19 years of data on blacklegged ticks attached to small-mammal hosts to quantify the relationship between climate warming and tick phenology. Warmer years through May and August were associated with a nearly three-week advance in the phenology of nymphal and larval ticks relative to colder years, with little evidence of increased synchrony. Warmer Octobers were associated with fewer larvae feeding concurrently with nymphs during the following spring. Projected warming by the 2050s is expected to advance the timing of average nymph and larva activity by 8–11 and 10–14 days, respectively. If these trends continue, climate warming should maintain or increase transmission of persistent pathogens, while it might inhibit pathogens that do not produce long-lasting infections.