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PubMed2003

Variation in abundance and feeding impact of tarnished plant bug (Hemiptera: Miridae) for different cultivars of strawberry: role of flowering phenology and yield attributes.

The current study evaluated whether flowering phenology and yield attributes of different strawberry cultivars affect the abundance and feeding impact of tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), as well as behavioral decisions made by feeding nymphs and ovipositing adults. The distribution of emerged nymphs in cage experiments involving nine different cultivars of June-bearing strawberry cultivars suggests that females lay more eggs on plants with numerous flower receptacles, while cultivar per se did not influence their oviposition behavior. A large number of nymphs emerged from receptacles of strawberry plants, while the distribution of emerged nymphs among receptacles, petioles, leaves, and stems varied for different cultivars. These results suggest that the relative intensity of damage caused by ovipositing females may vary for different cultivars. Foraging nymphs did not exhibit a preference for any strawberry cultivar per se, although the abundance of nymphs increased with the weight of receptacles, especially for late instars. Evaluating the density and feeding impact of L. lineolaris for different cultivars under field conditions revealed that some host plant attributes affect the abundance of plant bugs, such as early flowering season and high productivity. Decreasing number of emerged nymphs per flower per plant with increasing density of receptacles per plant suggests that females lay relatively more eggs per receptacle on plants with few receptacles; this pattern of oviposition may explain, in part, why patches with low density of plants typically have high incidence of damage. Planting a high yielding early season cultivar such as 'Cavendish' may contribute to reduce the incidence of damage by L. lineolaris.

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PubMed2003

Irradiation of Maconellicoccus hirsutus (Homoptera: Pseudococcidae) for phytosanitation of agricultural commodities.

Studies on the tolerance of pink hibiscus mealybug, Maconellicoccus hirsutus (Green), to ionizing irradiation were undertaken to determine the dose needed to disinfest commodities of this pest. Overall, radiotolerance of M. hirsutus was found to increase with maturity. Target doses of 50 Gy reduced eclosion of eggs to <50%, but doses as great as 750 Gy did not eliminate hatching during the study. At 100 Gy, M. hirsutus eggs, crawlers, and nymphs were controlled, because progeny were not produced despite crawlers and nymphs living for much longer periods than unexposed individuals. Fecundity of treated crawlers and nymphs was greatly impacted by treatment of 100 Gy; crawlers developing into adults produced no eggs, and 10 adults of 3,983 treated nymphs (0.25%) produced 309 eggs. Few adult females exposed as nymphs deposited eggs because male nymphs died during development, which left the females unfertilized. By comparison, 89% of female nymphs treated at 100 Gy and mated as adults with nonirradiated males produced a total of 1,447 eggs (19 eggs per female). Evidence from this study suggests M. hirsutus reproduces sexually, not parthenogenetically. Adults, the most resistant stage, exposed to target doses of 100 Gy produced eggs that were 1.2% viable, from which a small portion of individuals successfully completed development and produced progeny. A target dose of 250 Gy was sufficient to control adult M. hirsutus because, at that dose, none of the eggs produced by 3,093 irradiated adults eclosed. The minimum dose needed to ensure quarantine security is between 100 and 250 Gy.

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PubMed1993

Spatial and temporal patterns of Ixodes scapularis (Acari: Ixodidae) in southeastern Connecticut.

The spatial distribution and abundance of host-seeking Ixodes scapularis Say (formerly I. dammini) were studied in 10 residential sites in woodlands during 1989-1991. In total, 7,385 larval, 2,202 nymphal, 164 female, and 248 male I. scapularis were collected in Old Lyme, Lyme, East Haddam, and Chester, CT. The majority of host-seeking I. scapularis larvae (84.2%) and nymphs (73.5%) were collected within the woodland plots, whereas a large proportion of the adults were recovered from lawn (36.4%) and transitional areas between lawns and forest (20.9%). The majority (71.1% of 1,244) of all stages of I. scapularis on the lawn were recovered within 1 m of the lawn edge, particularly along woods and stone walls. In contrast, most of the I. scapularis (60.0% of 3,065) collected in the woods were > 3 m from any defined edge and ticks were recovered throughout the forested plots. The abundance of nymphs on the lawns (1.0-29.4 nymphs per ha per sample) and in the woods (17.3-271.5 nymphs per ha per sample) varied significantly among the 10 residences during June and July. The average rate of infection by Borrelia burgdorferi, the causal agent of Lyme disease, in the nymphs was 14.2, 14.1, and 15.5% for 1989, 1990, and 1991, respectively. The abundance of I. scapularis nymphs in the forest was significantly higher in June 1991, than in 1989 or 1990. The risk of exposure to infected nymphs of I. scapularis varied spatially with the landscape and individual residence, and temporally.

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PubMed1996

Survival of Ixodes scapularis (Acari: Ixodidae) exposed to cold.

The cold hardiness of Ixodes scapularis Say unengorged larvae, engorged larvae, unengorged nymphs, engorged nymphs, and unengorged adults was evaluated. Ticks were exposed to cold for 2 or 8 h at a range of temperatures. Likelihood ratio tests and LT50 estimates were used to evaluate cold hardiness. Likelihood ratio tests indicated that stage and engorgement effects were significant with the exception of the stage effect between engorged larvae and engorged nymphs. LT50 estimates indicated that unengorged nymphs were the most cold-hardy, followed by engorged nymphs, unengorged adults, and both unengorged and engorged larvae. Sex of adult ticks had no statistically significant effect on cold hardiness. Unengorged larvae and unengorged nymphs were tested for evidence of a cold-hardening response. No larvae or nymphs exposed to a cold pretreatment and subsequent cold treatment displayed rapid cold-hardening.

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PubMed1996

Relationship between Ixodes ricinus density and prevalence of infection with Borrelia-like spirochetes and density of infected ticks.

During 1994-1995 we examined the density of questing Ixodes ricinus (L.) nymphs and their prevalence of infection with Borrelia-like spirochetes at 43 localities in south-central Sweden with median nymphal densities ranging from 0.1 to > 50/100 m2. The general pattern was that the infection prevalence in nymphs increased with nymphal density at < 10 nymphs per 100 m2, peaked (20-30%) at 10-20 nymphs per 100 m2, and decreased at higher nymphal densities. A low infection prevalence (7-10%) in nymphs at 4 of the 5 localities with the highest nymphal densities (> 35 nymphs per 100 m2) at the small island of Bedarön was most likely related to the presence of large numbers of fallow deer, Dama dama (L.), which are reservoir-incompetent for Borrelia burgdorferi s.l. Johnson, Schmid, Hyde, Steigerwalt & Brenner. However, because the increase in nymphal density at Bedarön was greater than the decrease in infection prevalence, 5 of the 6 highest densities of infected nymphs occurred in the 5 localities at Bedarön. We suggest that reservoir-incompetent cervids, being more important hosts for adult 1. ricinus than for the larvae, indirectly increase the density of infected nymphal ticks by feeding large numbers of adult ticks, thereby increasing the number of larvae feeding on reservoir-competent shrews, rodents, and hares.

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PubMed2004

Acarologic risk of exposure to Borrelia burgdorferi spirochaetes: long-term evaluations in north-western California, with implications for Lyme borreliosis risk-assessment models.

Over a 5-year period (1997-2001) the population densities of Ixodes pacificus Cooley & Kohls (Acari: Ixodidae) nymphs infected with spirochaetes of Borrelia burgdorferi sensu lato (s.l.) were evaluated in areas of 2000 ha at two localities (CHR, nine sites; HREC, seven sites) 25 km apart in Mendocino County, north-western California. The 5-year median density of infected nymphs was significantly higher at CHR than at HREC (0.51 vs. 0.09 per 100 m(2) and site-specific yearly densities exceeding one infected nymph per 100 m2 were 10-fold more likely to occur at CHR than at HREC. The importance of long-term data in acarologic risk assessment was demonstrated by significantly higher median yearly densities of infected nymphs at CHR from 1997 to 1999, whereas both areas had similar densities during 2000-2001. Overall, the causative agent of Lyme borreliosis in North America, B. burgdorferi Johnson et al. sensu stricto (s.s.) accounted for 76% of 46 genetically characterized B. burgdorferi s.l. infections from I. pacificus nymphs. Tremendous variability in acarologic risk was recorded within both areas: yearly densities of infected nymphs varied 11-97-fold between sites at CHR and 8-30-fold at HREC. Part of this variation could be explained by environmental traits, most notably deer usage. However, correlations between environmental factors and density of infected nymphs (for CHR and HREC combined) did not necessarily apply when these areas were considered separately. Thus, a Lyme borreliosis ecology model developed in one of these areas needs testing in the other area.

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PubMed2002

Ecology and economic impact of two plant bugs (Hemiptera: Miridae) in commercial vineyards.

The current study investigated the seasonal phenology, spatial distribution, feeding damage and economic impact of two plant bugs, Lygocoris inconspicuous Knight and Taedia scrupeus Say, in commercial vineyards. For both plant bugs, densities of nymphs were higher on vines located near the edge of woodlots rather than in the interior of vineyards, which may be attributed to the presence of wild vines and other alternate host-plants in wooded areas. Nymphs of both species fed on apical leaves and developing fruit clusters of vine shoots, initiating development after swelling of buds in the spring and reaching the adult stage when vines were in bloom. Confining high densities of L. inconspicuous (10 nymphs) on individual shoots early in the season resulted in significant reduction of the number of fruit clusters per shoot, even when feeding was restricted to short (7 d) duration; the average weight of fruit clusters, in contrast, was not affected to a large extent by feeding activity of nymphs. An experiment evaluating the impact of low density of L. inconspicuous (0-0.3 nymphs per shoot) indicated a marginally significant negative relationship between density of nymphs and average weight of fruit clusters. Control measures may be economically justified when population density exceeds a combined threshold of one nymph of either L. inconspicuous or T. scrupeus per 10 shoots of vines.

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PubMed2002

Comparative behavior of different life-cycle stages of Ixodes ricinus (Acari: Ixodidae) to human-produced stimuli.

Nymphs of Ixodes ricinus (Linnaeus, 1758), I. scapularis Say, 1821, and I. pacificus Cooley & Kohls, 1943 are epidemiologically the most dangerous stage for transmission of Lyme disease to humans. Many factors play a role in the epidemiological significance of the nymphs. In this study, we address the question of whether nymphs show a greater tendency than adults to accept humans as their host. To evaluate this, we have compared the host acceptance behavior of nymphs and adults (males and females) with respect to a human in Rambouillet forest, a focus of Lyme disease. Individual ticks (nymph, male or female) located on a herbaceous stem were exposed to different stimuli (e.g., approach, stem movement, breathing), and the response of each individual to these stimuli was noted. Tick responses were categorised into classes (from 0 to 3) according to their intensity. Statistical analysis carried out on 22 ticks allowed us to compare the behavior of the nymph stage with respect to males and females. Despite the small sample sizes, it appears that nymphs are more responsive to a human than are the adults.

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PubMed2003

Vector competence of Ixodes pacificus and I. spinipalpis (Acari: Ixodidae), and reservoir competence of the dusky-footed woodrat (Neotoma fuscipes) and the deer mouse (Peromyscus maniculatus), for Borrelia bissettii.

We investigated the experimental vector competence of Ixodes pacificus Cooley and Kohls and Ixodes spinipalpis Hadwen and Nuttall, and the reservoir competence of the dusky-footed woodrat (Neotoma fuscipes Baird) and the deer mouse (Peromyscus maniculatus [Wagner]), for Borrelia bissettii Postic, Marti Ras, Lane, Hendson, and Baranton. Both rodent species are capable reservoirs for B. bissettii; infection rates for I. pacificus or I. spinipalpis nymphs fed as larvae on infected animals ranged from 50 to 57%. Moreover, both I. pacificus and I. spinipalpis are efficient vectors of B. bissettii. Viable infections were recorded from all rodents known to be exposed to one or more infected nymphs of I. spinipalpis (seven deer mice, two white mice) or I. pacificus (seven deer mice). In contrast, none of four New Zealand white rabbits fed upon by 90 I. pacificus nymphs with a probable B. bissettii infection rate of >50% became infected or seroconverted. The attachment and feeding success of laboratory-reared nymphs similarly confined with deer mice in muslin-covered wire-mesh cages for 24 h ranged from 0% for I. pacificus to 17-73% for I. spinipalpis. Notably, the I. pacificus nymphs were physiologically capable of feeding; nymphs failing to attach to rodents fed readily when placed in feeding capsules upon rabbits. We conclude that the dusky-footed woodrat and the deer mouse are capable experimental reservoir hosts of B. bissettii, and that both I. spinipalpis and I. pacificus are efficient experimental vectors of B. bissettii. However, the reluctance of I. pacificus nymphs to feed on certain rodents may limit its importance as an enzootic vector of B. burgdorferi sensu lato spirochetes.

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PubMedDate not supplied

[A laboratory model of the parasitic system of Lyme disease].

A laboratory model of the parasitic system of Lyme borreliosis (LB) with Ixodes persulcatus and Borrelia burgdorferi s.s. underwent 5 epizootic cycles (Cycle I transition of Borreliae by the scheme a tick-->a mouse-->a tick corresponds to the seasonal cycle). A group of 5-6 mice was inoculated with the suspension of infected nymphs by the intracutaneously route and 35-45 days later intact tick larvae or nymphs were fed on them. In the first three cycles, 40-100% of mice in a group (a total of 33 of 59) were susceptible, but 3 of 11 groups of mice were not inoculated. 20-50% of larvae and 75-92% of nymphs were susceptible on the infected mice. The mean geometric abundance of borreliae was 2.8-6.3 cells per 100 fields of vision in the nymphs infected in the larval phase and 16.1-29.5 cells in the image phase. In cycle IV, 2 of 6 groups of mice were unsusceptible to borreliae and 5 of the 17 mice from 4 groups got infected. One mouse died from Lyme borreliosis when larvae were fed on it. The nymphs remolted from underfed larvae were infected in 62.2% of cases, the mean geometric abundance in these nymphs was 5.7% per 100 fields of vision. A total of 3.2-14.7% of the ticks fed on the remaining 4 mice were infected and the abundance of boreliae was 1-2 per 100 fields of vision. In cycle V, one of 12 mice got infected, the infection rate in nymphs was 9.1%, the abundance of borreliae was 1 per 100 fields of vision. Thus, as the number of epizootic cycles increases, the proportion of infected mice, that of ticks infected on these mice on feeding, and the abundance of borreliae in the infected ticks decrease. Moreover, there was a reduction in the length of borreliae reduced from 17-18 mm to 10-11 mm and in the duration of multiplication and preservation of borreliae in the infected ticks and there was concurrently an increase in the duration of development of an infectious process in mice. It is suggested that the population of borreliae consists of 2 morphophysiological groups or more. During cultivation of the laboratory model of the parasitic system of Lyme borreliosis, a group of borrelia that are short and slightly pathogenic for mice had got many points in its favour. A five-fold procedure of artificial election of precisely defining this group set the model on the verge of disappearance. The capacity of the populations of borreliae to alter their properties rapidly and fundamentally suggests that there might be violent annual fluctuations in human morbidity.

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PubMed2003

Triacylglycerol and phospholipid fatty acids of the silverleaf whitefly: composition and biosynthesis.

The identification and composition of the fatty acids of the major lipid classes (triacylglycerols and phospholipids) within Bemisia argentifolii Bellows and Perring (Homoptera: Aleyrodidae) nymphs were determined. Comparisons were made to fatty acids from the internal lipids of B. argentifolii adults. The fatty acids, as ester derivatives, were analyzed by capillary gas chromatography (CGC) and CGC-mass spectrometry (MS). All lipid classes contained variable distributions of eight fatty acids: the saturated fatty acids, myristic acid (14:0), palmitic acid (16:0), stearic acid (18:0), arachidic acid (20:0); the monounsaturated fatty acids, palmitoleic acid (16:1), oleic acid (18:1); the polyunsaturated fatty acids, linoleic acid (18:2), linolenic acid (18:3). Fourth instar nymphs had 5-10 times the quantities of fatty acids as compared to third instar nymphs and 1-3 times the quantities from adults. The fatty acid quantity differences between fourth and third instar nymphs were related to their size and weight differences. The percentage compositions for fatty acids from each lipid class were the same for the pooled groups of third and fourth instar nymphs. For nymphs and adults, triacylglycerols were the major source of fatty acids, with 18:1 and 16:0 acids as major components and the majority of the polyunsaturated fatty acids, 18:2 and 18:3 were present in the two phospholipid fractions, phosphatidylethanolamine and phosphatidylcholine. Evidence was obtained that whiteflies indeed synthesize linoleic acid and linolenic acid de novo: radiolabel from [2-(14)C] acetate was incorporated into 18:2 and 18:3 fatty acids of B. argentifolii adults and CGC-MS of pyrrolidide derivatives established double bonds in the Delta(9,12) and Delta(9,12,15) positions, respectively.

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PubMed1991

Acaricide susceptibility of Amblyomma variegatum (Acari:Ixodidae) from Puerto Rico and Guadeloupe.

Base-line data on acaricide susceptibility of larvae and of larvae and nymphs of the tropical bont tick, Amblyomma variegatum (Fabricius), from Puerto Rico and Guadeloupe were collected on 14 and six compounds, respectively. Nymphs 7-8 weeks old from Puerto Rico and Guadeloupe, and larvae 3-4 weeks old from Guadeloupe, were exposed for 24 or 48 h to residues of acetone dilutions of technical-grade or commercial formulations of acaricides on disposable glass pipettes. Effectiveness of the acaricides in killing nymphs (LC50) from Guadeloupe and Puerto Rico ranged from 0.0001% for deltamethrin2 to 0.269% for malathion. For Puerto Rico, the susceptibility to toxaphene and amitraz, but not to dioxathion, increased with increasing age of nymphs. Nymphs from Guadeloupe were 9.5 times more susceptible to chlorpyrifos than nymphs from Puerto Rico. The susceptibility of larvae from Guadeloupe to acaricides tested ranged from LC50 0.000012% for deltamethrin to 0.0141% for ethion. There was no evidence of development of acaricide resistance in ticks from Guadeloupe or Puerto Rico.

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PubMed1991

Morphology and structural organization of Haller's organ during postembryonic development of Argas (Persicargas) walkerae (Ixodoidea: Argasidae).

Scanning-electron-microscopic investigations of Haller's organ in larvae, nymphs I, II, III and IV, and male and female adult Argas (Persicargas) walkerae ticks showed that morphology and structural organization change during postembryonic development. Stage-dependent differences existed regarding setal numbers of the anterior pit as well as formation and reticulation of cuticular projections in the capsule cavity. The anterior pit increased in size in the course of postembryonic development. It contained only seven setae in larvae, one conical, setiform and grooved seta each as well as two porose and fine setae. Nymphs I, II, III and IV adult ticks had equal numbers of setae; however, one additional unilaterally serrate and grooved seta each were present. Setal length increased continuously during postembryonic development and attained maximum values in adult ticks. The capsule consisted of roof and cavity and was located distinctly lateral in larvae, slightly lateral in nymphs I and II, and in all other stages directly on the longitudinal axis of tarsus. The capsule roof showed a reticular structure. The slit-like main aperture was located peripherally and arranged transversally to the longitudinal axis of tarsus I in larvae. Nymphs and adult ticks had a central, circular main aperture. Stage-dependent cuticular projections of varying form protruded into the capsule cavity. Larvae had only single, free-standing projections which ramified slightly and communicated with each other. Projections were more heavily reticulated in nymphs I and II. In nymphs III and IV as well as male and female adult ticks, a long centrally situated tube of reticular appearance was seen, which was supported by a large number of radially organized and interlocking pillars and communicated with the capsule roof. In all tick stages there were always four porose setae present, arranged on the capsule floor.

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PubMed2006

Induction of egg hatching by high humidity in the cicada Cryptotympana facialis.

The timing of egg hatching in Cryptotympana facialis was examined in relation to short-term weather conditions. The brief underwater submergence, once a week, of dead twigs bearing cicada egg nests resulted in high hatching rates both at 25 degrees C and under outdoor conditions protected from rainfall. Under outdoor conditions with natural rainfall, most eggs hatched on rainy days. There was a significant positive correlation between the number of hatching eggs and daily relative humidity (RH). When eggs picked from twigs were exposed to various humidity levels, many eggs hatched quickly at higher humidity without direct contact with liquid water. Newly hatched nymphs showed a low tolerance to desiccation; at 81% RH at 25 degrees C, most of them died within 6 h. Under outdoor conditions, most nymphs died within 2 h on sunny days, whereas nymphs survived longer on rainy days. When newly hatched nymphs were released on dry ground, only 24% of them succeeded in burrowing into the soil, and many were killed by ants or desiccation. However, 92% of nymphs released onto wet ground successfully burrowed into it. The direct induction of hatching by high humidity ensures the survival and establishment in the soil of newly hatched nymphs in this species.

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PubMed1989

Habitat distribution of Ixodes dammini (Acari: Ixodidae) an Lyme disease spirochetes on Fire Island, New York.

The distributions of Ixodes dammini Spielman, Clifford, Piesman, and Corwin and Lyme disease spirochetes were studied on Fire Island, N.Y. Adult ticks were more common in high-shrub habitats (shrubby vegetation greater than or equal to 1 m high) than in grassy and lowshrub habitats (vegetation less than 1 m) in spring and fall. In the fall, adults were also common in the woods. Adults were more abundant on narrow trails than in nearby vegetation. During the summer, questing nymphs and larvae were far more common in the woods (primarily in leaf litter) than in open grass-shrub habitats. In contrast, the number of nymphs and larvae per white-footed mouse did not differ among habitats, suggesting that mice play a role in tick dispersal. CO2 trap captures of nymphs on trails were not significantly greater than off trails. Most collections of larvae and nymphs had more than one tick, whereas most samples of adults had only one individual. Borrelia burgdorferi infection rates in free-living ticks were 38% (n = 12) to 50% (n = 32) in adults, 32% in nymphs (n = 184), and 0% in larvae (n = 15). The proportion of ticks infected did not differ significantly among habitats. Therefore, during the spring and fall, activities that take place in high-shrub areas or in the woods (e.g., landscaping, trail or brush clearing) involve a high risk of exposure to adult ticks infected with Lyme disease. In late spring to early summer, any activity involving close contact with leaf litter (e.g., playing in the leaves, gathering leaves for camp bedding) results in a high risk of exposure to infected nymphs.

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PubMed1993

Efficient transmission of tick-borne encephalitis virus between cofeeding ticks.

Most of the data on oral infections of ticks with tick-borne encephalitis virus have been derived from experiments using animals infected by syringe inoculation. To mimic the natural conditions of virus transmission, tick-borne encephalitis virus-infected Ixodes ricinus (Linnaeus) or Rhipicephalus appendiculatus Neumann adults (donors) were cofed with uninfected nymphs (recipients) of either tick species on uninfected guinea pigs. Two tick-retaining cells were attached to each guinea pig: cell 1 contained uninfected nymphs and virus-infected adults, and cell 2 contained uninfected nymphs. Following engorgement, 55% of I. ricinus nymphs and 65% of R. appendiculatus nymphs were shown to have acquired the virus while cofeeding with I. ricinus donor ticks. Similarly, 66% of R. appendiculatus recipient nymphs that cofed with R. appendiculatus virus-infected adults were infected. Some of the guinea pigs on which the ticks cofed were apparently nonviremic. The results indicate that efficient transmission of tick-borne encephalitis virus can occur between cofeeding ticks even when the host on which they feed does not develop a detectable viremia.

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PubMed1993

Reduced abundance of Ixodes scapularis (Acari: Ixodidae) with exclusion of deer by electric fencing.

To assess the effect of deer exclusion on populations of Ixodes scapularis Say (formerly I. dammini Spielman, Clifford, Piesman & Corwin) in the northeastern United States, host-seeking ticks and ticks on white-footed mice, Peromyscus leucopus (Rafinesque), were monitored inside and outside a wooded, residential deer exclosure (approximately 3.5 ha) in Lyme, CT, in 1991 and 1992. Another deer exclosure was added in Lyme (approximately 7.4 ha) during 1992. Additional sample sites at other residences served as secondary controls. A seven-wire, slanted, high-tensile electric deer fence was used at both areas. Larvae of I. scapularis were 81.5% (1991) and 97.8% (1992) less abundant within the exclosure than immediately outside the deer exclosures. Nymphs of I. scapularis were 47.4% (1991) and 55.8% (1992) less abundant within the deer fence. The effect on adult ticks was mixed. No difference in tick abundance was seen at the 3.5-ha site. However, larvae, nymphs, and adults were 100, 83.8, and 74.1% less abundant, respectively, in plots at the 7.4-ha exclosure > or = 70 m from the deer fence and isolated from woodlands outside the fence by lawns, driveways, and buildings. The recovery of larvae and nymphs of I. scapularis from mice captured within the deer exclosures indicates that infestations of nymphs and adults are probably, at least in part, a result of the movement of these rodents. Based upon the number of nymphs per 100 m2 infected with Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner, the causal agent of Lyme disease, there were 73 and 82% fewer infected nymphs within the deer exclosures in 1992 in comparison with the number of infected ticks outside the fence and at the secondary control sites, respectively. The exclusion of deer in conjunction with other tick control strategies in large areas could substantially reduce populations of I. scapularis and the risk of acquiring Lyme disease.

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PubMed1998

Survival and development of the different life stages of Ixodes scapularis (Acari: Ixodidae) held within four habitats on Long Point, Ontario, Canada.

From November 1989 to April 1993, blood-fed females and unfed adults and nymphs of lxodes scapularis Say were maintained in housings within 4 different habitats on Long Point, Ontario, Canada, to evaluate the effects of habitat on tick development. More fed females survived the winter within the maple forest (75.6%) than the cottonwood dune (36.1%), whereas 52.8-62.0% survived the winter within the 2 remaining habitats. The proportions of females that laid eggs within the maple forest (90.3%), oak savannah (83.9%), and white pine habitats (78.4%) were similar and greater than in the cottonwood dune (53.8%). In each habitat and all years, females began laying eggs during late April or early May. The time of egg deposition was consistent whether females fed in November and overwintered, or fed during April of the subsequent year. Significantly more eggs hatched within the maple forest (96.4%) and white pine (79.3%) than in the oak savannah (3.8%) or cottonwood dune habitats (0.0%). Hatch occurred in mid- to late July each year. The proportion of unfed I. scapularis adults that survived the winter was not significantly different among the 4 habitats. Unfed adults held in the oak savannah and cottonwood dune habitats died by early June, whereas ticks survived until late June or early July within the maple forest and white pine habitats. Unfed nymphs survived an average of 3.4 mo (range, 0.5-5.5) longer than unfed adults. Fed larvae placed in the field from 22 April to 3 July 1992 molted or died that year. In contrast, 66.7 and 100% of fed larvae placed in the field between 15 and 28 July, and after 28 July, respectively, overwintered before molting. More larvae successfully molted before overwintering (46.9%) than did those that overwintered (17.9%). The proportion of larvae that successfully molted was greatest within the maple forest and least within the cottonwood dune. Fed nymphs placed in the field from 22 April to 4 June molted or died in 1992, whereas 53.6 and 99.2% of fed nymphs placed in the field between 17 June and 28 July, and later than 28 July, respectively, overwintered before molting. Over all habitats, the proportion of nymphs that molted successfully was similar for those that overwintered (43.5%) and those that did not (36.0%). The proportion of nymphs that molted successfully was greatest in the maple forest (60.6%) and least within the cottonwood dune (13.3%). Differences in seasonal extremes of vapor pressure deficits among habitat types were likely responsible for habitat-specific differences in survival of I. scapularis. Based on observations on captive I. scapularis, the life cycle of this tick on Long Point is completed in 3 or 4 yr.

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