Genome resequencing reveals population divergence and local adaptation of blacklegged ticks in the United States.

Tick vectors and tick-borne disease are increasingly impacting human populations globally. An important challenge is to understand tick movement patterns, as this information can be used to improve management and predictive modelling of tick population dynamics. Evolutionary analysis of genetic divergence, gene flow and local adaptation provides insight on movement patterns at large spatiotemporal scales. We develop low coverage, whole genome resequencing data for 92 blacklegged ticks, Ixodes scapularis, representing range-wide variation across the United States. Through analysis of population genomic data, we find that tick populations are structured geographically, with gradual isolation by distance separating three population clusters in the northern United States, southeastern United States and a unique cluster represented by a sample from Tennessee. Populations in the northern United States underwent population contractions during the last glacial period and diverged from southern populations at least 50 thousand years ago. Genome scans of selection provide strong evidence of local adaptation at genes responding to host defences, blood-feeding and environmental variation. In addition, we explore the potential of low coverage genome sequencing of whole-tick samples for documenting the diversity of microbial pathogens and recover important tick-borne pathogens such as Borrelia burgdorferi. The combination of isolation by distance and local adaptation in blacklegged ticks demonstrates that gene flow, including recent expansion, is limited to geographical scales of a few hundred kilometres.

Why Lyme disease is common in the northern US, but rare in the south: The roles of host choice, host-seeking behavior, and tick density.

Lyme disease is common in the northeastern United States, but rare in the southeast, even though the tick vector is found in both regions. Infection prevalence of Lyme spirochetes in host-seeking ticks, an important component to the risk of Lyme disease, is also high in the northeast and northern midwest, but declines sharply in the south. As ticks must acquire Lyme spirochetes from infected vertebrate hosts, the role of wildlife species composition on Lyme disease risk has been a topic of lively academic discussion. We compared tick-vertebrate host interactions using standardized sampling methods among 8 sites scattered throughout the eastern US. Geographical trends in diversity of tick hosts are gradual and do not match the sharp decline in prevalence at southern sites, but tick-host associations show a clear shift from mammals in the north to reptiles in the south. Tick infection prevalence declines north to south largely because of high tick infestation of efficient spirochete reservoir hosts (rodents and shrews) in the north but not in the south. Minimal infestation of small mammals in the south results from strong selective attachment to lizards such as skinks (which are inefficient reservoirs for Lyme spirochetes) in the southern states. Selective host choice, along with latitudinal differences in tick host-seeking behavior and variations in tick densities, explains the geographic pattern of Lyme disease in the eastern US.

Correction: Why Lyme disease is common in the northern US, but rare in the south: The roles of host choice, host-seeking behavior, and tick density.

[This corrects the article DOI: 10.1371/journal.pbio.3001066.].

Modeling of historical and current distributions of lone star tick, Amblyomma americanum (Acari: Ixodidae), is consistent with ancestral range recovery.

The lone star tick, Amblyomma americanum L., is a three-host hard tick notorious for aggressive feeding behavior. In the early to mid-20th century, this species' range was mostly limited to the southern USA. Since the 1950s, A. americanum has been detected in many new localities in the western, northcentral, and northeastern regions of the country. To examine the influence of climate on this apparent expansion, we used historical (1748-1950) lone star locations from the literature and museum records to model areas suitable for this species based on past environmental conditions in the late 1800s - early 1900s. We then projected this model forward using present (2011-2020) climatic conditions and compared the two for evidence of climate-associated distributional shifts. A maximum entropy distribution or Maxent model was generated by using a priori selected climatic variables including temperature, precipitation, and vapor pressure deficit. Temperature and vapor pressure deficit were selected as the most important factors in creating a sensitive and specific model (success rate = 82.6 ± 6.1%) that had a good fit to the existing data and was significantly better than a random model [partial ROC (receiver operating characteristic) to AUC (area under the ROC curve) ratio = 1.97 ± 0.07, P < 0.001]. The present projected model was tested with an independent dataset of curated museum records (1952-2020) and found to be 95.6% accurate. Comparison of past and present models revealed > 98% A. americanum niche overlap. The model suggests that some areas along the western fringe are becoming less suitable for A. americanum, whereas areas in some Great Lakes and coastal northeastern regions are becoming more suitable, results that are compatible with possible effects of climate change. However, these changes are minor, and overall climate in North America does not appear to have changed in ways significant to A. americanum's distribution. These findings are consistent with an alternative hypothesis that recent changes in A. americanum's distribution are a result of this species re-occupying its historical range, driven predominantly by factors other than climate, such as shifts in land use and population densities of major hosts.

Nonlinearities in transmission dynamics and efficient management of vector-borne pathogens.

Integrated Pest Management (IPM) is an approach to minimizing economic and environmental harm caused by pests, and Integrated Vector Management (IVM) uses similar methods to minimize pathogen transmission by vectors. The risk of acquiring a vector-borne infection is often quantified using the density of infected vectors. The relationship between vector numbers and risk of human infection is more or less linear when both vector numbers and pathogen prevalence in vectors are low, but the relationship is nonlinear when vector density and/or infection prevalence are high. Therefore, the density of infected vectors often does not accurately predict risk of human exposure to pathogens, and traditional estimates of the percent control often overestimate the level of protection from infection resulting from management programs. We suggest a modified estimator, percent protection, which more accurately quantifies protection against human infection resulting from a management intervention. Cost-effectiveness of a management program is critical to protection of both public health and the environment, because the more efficiently available resources and funding are used, the fewer people get sick, and well-targeted efficient management programs minimize the need for poorly targeted, expensive environmental interventions (e.g., broadscale pesticide applications) that tend to damage nontarget organisms and natural systems. Design of an efficient, cost-effective IVM program requires knowledge of the cost-effectiveness functions (the effectiveness of control methods at lowering vector bites and/or infection prevalence with different levels of application) of the various control methods to be applied. Alternative programs can be designed that optimize percent protection by integrating different control methods at different levels of investment, and environmental effects of these alternatives can be compared, allowing environmental considerations to be included explicitly in the decision process. IPM, IVM, and Adaptive Management share the characteristic that management decisions must be made with incomplete knowledge of the functioning of natural systems or the efficacies of interventions. IVM surveillance programs that assess the effects of individual control methods and of combinations of control methods on the numbers of vector bites and on infection prevalence in vectors can increase knowledge of pathogen transmission dynamics and provide information to improve program effectiveness in subsequent applications.

A Dynamic Population Model to Investigate Effects of Climate and Climate-Independent Factors on the Lifecycle of Amblyomma americanum (Acari: Ixodidae).

The lone star tick, Amblyomma americanum, is a disease vector of significance for human and animal health throughout much of the eastern United States. To model the potential effects of climate change on this tick, a better understanding is needed of the relative roles of temperature-dependent and temperature-independent (day-length-dependent behavioral or morphogenetic diapause) processes acting on the tick lifecycle. In this study, we explored the roles of these processes by simulating seasonal activity patterns using models with site-specific temperature and day-length-dependent processes. We first modeled the transitions from engorged larvae to feeding nymphs, engorged nymphs to feeding adults, and engorged adult females to feeding larvae. The simulated seasonal patterns were compared against field observations at three locations in United States. Simulations suggested that 1) during the larva-to-nymph transition, some larvae undergo no diapause while others undergo morphogenetic diapause of engorged larvae; 2) molted adults undergo behavioral diapause during the transition from nymph-to-adult; and 3) there is no diapause during the adult-to-larva transition. A model constructed to simulate the full lifecycle of A. americanum successfully predicted observed tick activity at the three U.S. study locations. Some differences between observed and simulated seasonality patterns were observed, however, identifying the need for research to refine some model parameters. In simulations run using temperature data for Montreal, deterministic die-out of A. americanum populations did not occur, suggesting the possibility that current climate in parts of southern Canada is suitable for survival and reproduction of this tick.

Effect of Temperature on Feeding Period of Larval Blacklegged Ticks (Acari: Ixodidae) on Eastern Fence Lizards.

Ambient temperature can influence tick development time, and can potentially affect tick interactions with pathogens and with vertebrate hosts. We studied the effect of ambient temperature on duration of attachment of larval blacklegged ticks, Ixodes scapularis Say, to eastern fence lizards, Sceloporus undulatus (Bosc & Daudin). Feeding periods of larvae that attached to lizards under preferred temperature conditions for the lizards (WARM treatment: temperatures averaged 36.6°C at the top of the cage and 25.8°C at the bottom, allowing behavioral thermoregulation) were shorter than for larvae on lizards held under cool conditions (COOL treatment temperatures averaged 28.4°C at top of cage and 24.9°C at the bottom). The lizards were infested with larvae four times at roughly monthly intervals. Larval numbers successfully engorging and dropping declined and feeding period was longer after the first infestation.

Deer management generally reduces densities of nymphal Ixodes scapularis, but not prevalence of infection with Borrelia burgdorferi sensu stricto.

Human Lyme disease-primarily caused by the bacterium Borrelia burgdorferi sensu stricto (s.s.) in North America-is the most common vector-borne disease in the United States. Research on risk mitigation strategies during the last three decades has emphasized methods to reduce densities of the primary vector in eastern North America, the blacklegged tick (Ixodes scapularis). Controlling white-tailed deer populations has been considered a potential method for reducing tick densities, as white-tailed deer are important hosts for blacklegged tick reproduction. However, the feasibility and efficacy of white-tailed deer management to impact acarological risk of encountering infected ticks (namely, density of host-seeking infected nymphs; DIN) is unclear. We investigated the effect of white-tailed deer density and management on the density of host-seeking nymphs and B. burgdorferi s.s. infection prevalence using surveillance data from eight national parks and park regions in the eastern United States from 2014-2022. We found that deer density was significantly positively correlated with the density of nymphs (nymph density increased by 49% with a 1 standard deviation increase in deer density) but was not strongly correlated with the prevalence of B. burgdorferi s.s. infection in nymphal ticks. Further, while white-tailed deer reduction efforts were followed by a decrease in the density of I. scapularis nymphs in parks, deer removal had variable effects on B. burgdorferi s.s. infection prevalence, with some parks experiencing slight declines and others slight increases in prevalence. Our findings suggest that managing white-tailed deer densities alone may not be effective in reducing DIN in all situations but may be a useful tool when implemented in integrated management regimes.

Selective Host Attachment by Ixodes scapularis (Acari: Ixodidae): Tick-Lizard Associations in the Southeastern United States.

Questing behavior and host associations of immature blacklegged ticks, Ixodes scapularis Say, from the southeastern United States are known to differ from those in the north. To elucidate these relationships we describe host associations of larval and nymphal I. scapularis from 8 lizard species sampled from 5 sites in the southeastern U.S. Larvae and nymphs attached in greater numbers to larger lizards than to smaller lizards, with differential levels of attachment to different lizard species. Blacklegged ticks are generally attached to skinks of the genus Plestiodon in greater numbers per unit lizard weight than to anoles (Anolis) or fence lizards (Sceloporus). The broad-headed skink, Plestiodon laticeps (Schneider), was a particularly important host for immature I. scapularis in our study and in several previous studies of tick-host associations in the southeast. Blacklegged ticks show selective attachment to Plestiodon lizard hosts in the southeast, but whether this results from behavioral host preferences or from ecological factors such as timing or microhabitat distributions of tick questing and host activity remains to be determined.

Using Surrogate Insects in Acid Bioassays for Development of New Controls for Varroa destructor (Arachnida: Varroidae).

Resistance to traditional synthetic compounds by Varroa destructor Anderson and Trueman and shortcomings of the organic acid class of acaracides commonly used in varroa management requires continual development of new controls. V. destructor, however, are difficult to obtain for use in control bioassays because they are obligate parasites that cannot be easily reared outside of a honey bee colony. We conducted bioassays using other, more easily obtainable species to find organisms that could be used as surrogates for V. destructor when testing new potential controls. We compared the toxicities of acetic acid, lactic acid, formic acid, and oxalic acid at 0.005%, 0.05%, 0.5%, 5%, and 50% (20% oxalic acid only) concentrations based on natural volatility (nonheated) for the control of two beetle species, Oryzaephilus surinamensis L. and Alphitobius diaperinus Panzer, greater wax moth larvae, Galleria mellonella L., and V. destructor. The assay results were consistent across all species with formic acid and acetic acid showing 100% mortality of all four test species at 50% concentration. The assays also provided insight into the method of application (vaporization or contact) needed to cause mortality. Our results show that other organisms can be used in place of V. destructor for initial testing of acids and possibly other chemicals for control of the ectoparasite.

Potential Effects of Climate Change on Tick-borne Diseases in Rhode Island.

Human cases of tick-borne diseases have been increasing in the United States. In particular, the incidence of Lyme disease, the major vector-borne disease in Rhode Island, has risen, along with cases of babesiosis and anaplasmosis, all vectored by the blacklegged tick. These increases might relate, in part, to climate change, although other environmental changes in the northeastern U.S. (land use as it relates to habitat; vertebrate host populations for tick reproduction and enzootic cycling) also contribute. Lone star ticks, formerly southern in distribution, have been spreading northward, including expanded distributions in Rhode Island. Illnesses associated with this species include ehrlichiosis and alpha-gal syndrome, which are expected to increase. Ranges of other tick species have also been expanding in southern New England, including the Gulf Coast tick and the introduced Asian longhorned tick. These ticks can carry human pathogens, but the implications for human disease in Rhode Island are unclear.

Possible Effects of Climate Change on Ixodid Ticks and the Pathogens They Transmit: Predictions and Observations.

The global climate has been changing over the last century due to greenhouse gas emissions and will continue to change over this century, accelerating without effective global efforts to reduce emissions. Ticks and tick-borne diseases (TTBDs) are inherently climate-sensitive due to the sensitivity of tick lifecycles to climate. Key direct climate and weather sensitivities include survival of individual ticks, and the duration of development and host-seeking activity of ticks. These sensitivities mean that in some regions a warming climate may increase tick survival, shorten life-cycles and lengthen the duration of tick activity seasons. Indirect effects of climate change on host communities may, with changes in tick abundance, facilitate enhanced transmission of tick-borne pathogens. High temperatures, and extreme weather events (heat, cold, and flooding) are anticipated with climate change, and these may reduce tick survival and pathogen transmission in some locations. Studies of the possible effects of climate change on TTBDs to date generally project poleward range expansion of geographical ranges (with possible contraction of ranges away from the increasingly hot tropics), upslope elevational range spread in mountainous regions, and increased abundance of ticks in many current endemic regions. However, relatively few studies, using long-term (multi-decade) observations, provide evidence of recent range changes of tick populations that could be attributed to recent climate change. Further integrated 'One Health' observational and modeling studies are needed to detect changes in TTBD occurrence, attribute them to climate change, and to develop predictive models of public- and animal-health needs to plan for TTBD emergence.

Seasonality of acarological risk of exposure to Borrelia miyamotoi from questing life stages of Ixodes scapularis collected from Wisconsin and Massachusetts, USA.

Measures of acarological risk of exposure to Ixodes scapularis-borne disease agents typically focus on nymphs; however, the relapsing fever group spirochete Borrelia miyamotoi can be passed transovarially, and I. scapularis larvae are capable of transmitting B. miyamotoi to their hosts. To quantify the larval contribution to acarological risk, relative to nymphs and adults, we collected questing I. scapularis for 3 yr at Fort McCoy, Wisconsin (WI, n = 23,367 ticks), and Cape Cod, Massachusetts (MA, n = 4190) in the United States. Borrelia miyamotoi infection prevalence was estimated for I. scapularis larvae, nymphs, females, and males, respectively, as 0.88, 2.05, 0.63, and 1.22 % from the WI site and 0.33, 2.32, 2.83, and 2.11 % from the MA site. Densities of B. miyamotoi-infected ticks (DIT, per 1000 m2) were estimated for larvae, nymphs, females, and males, respectively, as 0.36, 0.14, 0.01, and 0.03 from the WI site and 0.05, 0.06, 0.03, and 0.02 from the MA site. Thus, although larval infection prevalence with B. miyamotoi was significantly lower than that of nymphs and similar to that of adults, because of their higher abundance, the larval contribution to the overall DIT was similar to that of nymphs and trended towards a greater contribution than adults. Assuming homogenous contact rates with humans, these results suggest that eco-epidemiological investigations of B. miyamotoi disease in North America should include larvae. A fuller appreciation of the epidemiological implications of these results, therefore, requires an examination of the heterogeneity in contact rates with humans among life stages.

Prioritizing Water Security in the Management of Vector-Borne Diseases: Lessons From Oaxaca, Mexico.

Changes in human water use, along with temperature and rainfall patterns, are facilitating habitat spread and distribution of Aedes aegypti and Aedes albopictus mosquitoes, the primary vectors for the transmission of Dengue, Chikungunya, and Zika viruses in the Americas. Artificial containers and wet spots provide major sources of mosquito larval habitat in residential areas. Mosquito abatement and control strategies remain the most effective public health interventions for minimizing the impact of these vector-borne diseases. Understanding how water insecurity is conducive to the establishment and elimination of endemic mosquito populations, particularly in arid or semiarid regions, is a vital component in shaping these intervention strategies.

Spatiotemporal modeling of dengue fever risk in Puerto Rico.

Dengue Fever (DF) is a mosquito vector transmitted flavivirus and a reemerging global public health threat. Although several studies have addressed the relation between climatic and environmental factors and the epidemiology of DF, or looked at purely spatial or time series analysis, this article presents a joint spatio-temporal epidemiological analysis. Our approach accounts for both temporal and spatial autocorrelation in DF incidence and the effect of temperatures and precipitation by using a hierarchical Bayesian approach. We fitted several space-time areal models to predict relative risk at the municipality level and for each month from 1990 to 2014. Model selection was performed according to several criteria: the preferred models detected significant effects for temperature at time lags of up to four months and for precipitation up to three months. A boundary detection analysis is incorporated in the modeling approach, and it was successful in detecting municipalities with historically anomalous risk.

Biological control of Aedes mosquito larvae with carnivorous aquatic plant, Utricularia macrorhiza.

BACKGROUND: Biological controls with predators of larval mosquito vectors have historically focused almost exclusively on insectivorous animals, with few studies examining predatory plants as potential larvacidal agents. In this study, we experimentally evaluate a generalist plant predator of North America, Utricularia macrorhiza, the common bladderwort, and evaluate its larvacidal efficiency for the mosquito vectors Aedes aegypti and Aedes albopictus in no-choice, laboratory experiments. We sought to determine first, whether U. macrorhiza is a competent predator of container-breeding mosquitoes, and secondly, its predation efficiency for early and late instar larvae of each mosquito species. METHODS: Newly hatched, first-instar Ae. albopictus and Ae. aegypti larvae were separately exposed in cohorts of 10 to field-collected U. macrorhiza cuttings. Data on development time and larval survival were collected on a daily basis to ascertain the effectiveness of U. macrorhiza as a larval predator. Survival models were used to assess differences in larval survival between cohorts that were exposed to U. macrorhiza and those that were not. A permutation analysis was used to investigate whether storing U. macrorhiza in laboratory conditions for extended periods of time (1 month vs 6 months) affected its predation efficiency. RESULTS: Our results indicated a 100% and 95% reduction of survival of Ae. aegypti and Ae. albopictus larvae, respectively, in the presence of U. macrorhiza relative to controls within five days, with peak larvacidal efficiency in plant cuttings from ponds collected in August. Utricularia macrorhiza cuttings, which were prey-deprived, and maintained in laboratory conditions for 6 months were more effective larval predators than cuttings, which were maintained prey-free for 1 month. CONCLUSIONS: Due to the combination of high predation efficiency and the unique biological feature of facultative predation, we suggest that U. macrorhiza warrants further development as a method for larval mosquito control.

Local abundance of Ixodes scapularis in forests: Effects of environmental moisture, vegetation characteristics, and host abundance.

Ixodes scapularis is the primary vector of Lyme disease spirochetes in eastern and central North America, and local densities of this tick can affect human disease risk. We sampled larvae and nymphs from sites in Massachusetts and Wisconsin, USA, using flag/drag devices and by collecting ticks from hosts, and measured environmental variables to evaluate the environmental factors that affect local distribution and abundance of I. scapularis. Our sites were all forested areas with known I. scapularis populations. Environmental variables included those associated with weather (e.g., temperature and relative humidity), vegetation characteristics (at canopy, shrub, and ground levels), and host abundance (small and medium-sized mammals and reptiles). The numbers of larvae on animals at a given site and season showed a logarithmic relationship to the numbers in flag/drag samples, suggesting limitation in the numbers on host animals. The numbers of nymphs on animals showed no relationship to the numbers in flag/drag samples. These results suggest that only a small proportion of larvae and nymphs found hosts because in neither stage did the numbers of host-seeking ticks decline with increased numbers on hosts. Canopy cover was predictive of larval and nymphal numbers in flag/drag samples, but not of numbers on hosts. Numbers of small and medium-sized mammal hosts the previous year were generally not predictive of the current year's tick numbers, except that mouse abundance predicted log numbers of nymphs on all hosts the following year. Some measures of larval abundance were predictive of nymphal numbers the following year. The mean number of larvae per mouse was well predicted by measures of overall larval abundance (based on flag/drag samples and samples from all hosts), and some environmental factors contributed significantly to the model. In contrast, the mean numbers of nymphs per mouse were not well predicted by environmental variables, only by overall nymphal abundance on hosts. Therefore, larvae respond differently than nymphs to environmental factors. Furthermore, flag/drag samples provide different information about nymphal numbers than do samples from hosts. Flag/drag samples can provide information about human risk of acquiring nymph-borne pathogens because they provide information on the densities of ticks that might encounter humans, but to understand the epizootiology of tick-borne agents both flag/drag and host infestation data are needed.

Effects of open marsh water management on numbers of larval salt marsh mosquitoes.

Open marsh water management (OMWM) is a commonly used approach to manage salt marsh mosquitoes than can obviate the need for pesticide application and at the same time, partially restore natural functions of grid-ditched marshes. OMWM includes a variety of hydrologic manipulations, often tailored to the specific conditions on individual marshes, so the overall effectiveness of this approach is difficult to assess. Here, we report the results of controlled field trials to assess the effects of two approaches to OMWM on larval mosquito production at National Wildlife Refuges (NWR). A traditional OMWM approach, using pond construction and radial ditches was used at Edwin B. Forsythe NWR in New Jersey, and a ditch-plugging approach was used at Parker River NWR in Massachusetts. Mosquito larvae were sampled from randomly placed stations on paired treatment and control marshes at each refuge. The proportion of sampling stations that were wet declined after OMWM at the Forsythe site, but not at the Parker River site. The proportion of samples with larvae present and mean larval densities, declined significantly at the treatment sites on both refuges relative to the control marshes. Percentage of control for the 2 yr posttreatment, compared with the 2 yr pretreatment, was >90% at both treatment sites.

Eastern Carpenter Bee (Hymenoptera: Apidae): Nest Structure, Nest Cell Provisions, and Trap Nest Acceptance in Rhode Island.

Analysis of pollen provisions in Xylocopa virginica (L.) nests in southern Rhode Island showed that this species produced pollen loaves from 21 different genera of plants in 2016, 19 in 2017, and 39 in 2018. Antirrhinium majus L. (garden snapdragon) pollen was the most common type collected in all three years (21.4%). Overall, wind-pollinated tree pollen comprised 22.1% of all pollen loaves. Blueberry pollen was a minor component of pollen loaves (0.1%), despite abundant blueberry plants nearby. Mean values of X. virginica nest measurements (tunnel length 15.4 ± 1.2 cm, width 15.0 ± 0.5 mm, and cell length 17.7 ± 0.3 mm) were similar to those reported in previous studies. Only 2 of the 216 trap nests deployed in 2017 were occupied by 11 X. virginica bees (9 females and 2 males). However, 17 nests contained 230 Osmia taurus Smith, 6 nests contained 73 O. cornifrons (Radoszkowski), and 1 nest contained 8 O. lignaria Say. Thirty-four nests (15.7%) were occupied by 151 grass-carrying wasps, Isodontia sp. and 6 vespid wasps occupied three nests (1.4%) in 2017. In 2018, 4 of 96 trap nests were occupied by carpenter bees. Understanding the nesting and foraging habits of X. virginica will help us to manage natural populations for pollination services.

Effect of Corolla Slitting and Nectar Robbery by the Eastern Carpenter Bee (Hymenoptera: Apidae) on Fruit Quality of Vaccinium corymbosum L. (Ericales: Ericaceae).

Eastern carpenter bees, Xylocopa virginica (L.) (Hymenoptera: Apidae), are among the most abundant native bee visitors to highbush blueberry, Vaccinium corymbosum L., flowers in the northeastern United States, and they sometimes display corolla-slitting behavior to rob nectar. We studied foraging behavior of X. virginica on 14 blueberry cultivars in an experimental planting in Rhode Island, and assessed factors related to slitting frequency, and the effects of slitting on fruit set and blueberry quality. Among 14 cultivars in bloom, an average of 35% (range 16-67%) of flowers were slit in 2017, and 39% (range 20-62%) in 2018. Factors that affected the proportion of corollas slit included cultivar, anther length, flower volume, and number of days in bloom at or above 15°C. Corolla slitting did not affect fruit set. Average weight and percent soluble solids of fruit resulting from slit and non-slit corollas did not differ significantly in two early- ('Bluehaven', 'Earliblue'), two mid- ('Collins', 'Bluecrop'), and two late-season ('Herbert', 'Lateblue') ripening cultivars in 2017. In 2018, average fruit weight and percent soluble solids resulting from slit and non-slit flowers did not differ significantly in most cultivars, but slit corollas resulted in berries with greater mass in two cultivars, 'Bluehaven' and 'Collins'. 'Collins' fruit from non-slit corollas had a significantly higher percentage of soluble solids at maturity than fruit from slit corollas in 2018. Corolla slitting and nectar robbery by X. virginica did not have a significant negative effect on fruit quality under the described growing conditions and pollinator community.