Pesticide risk reduction on crops in the Province of Ontario

We analyzed the changes in pesticide use and risk in the Province of Ontario, Canada, from 1973 to 1998 to monitor the success of Food Systems 2002, a program to reduce pesticide use by 50%. Pesticide risk was calculated by multiplying the amount of pesticide used (kilograms of active ingredient) by the Environmental Impact Quotient (EIQ), a score for the potential risk of pesticides to farmworkers, consumers, and the environment. Pesticide use increased by 46% from 1973 to 1983. From 1983, the baseline year for Food Systems 2002, to 1998, pesticide use decreased by 38.5% and risk declined 39.5%. The reductions in pesticide use and risk were primarily on corn (Zea mays L.) and tobacco (Nicotiana tabacum L.), the crops with the highest pesticide use in 1983. Total pesticide use on soybean [Glycine max (L.) Merr.] did not change, but the mean application rate (kg ha(-1)) decreased by 57%. Corn and soybean account for 65% of pesticide use, but have a relatively low pesticide use and risk per hectare and per tonne of production. Total pesticide use on tobacco, fruits, and vegetables was lower than on corn or soybean, but the pesticide use and risk per hectare were much higher. Small reductions in pesticide use on corn and soybean may allow a 50% reduction in pesticide use, but greater reductions in risk can be achieved by reducing the use of "high risk" pesticides on fruit and vegetables.

Microclimate and habitat in relation to Ixodes scapularis (Acari: Ixodidae) populations on Long Point, Ontario, Canada

The impact of microclimate and density of hosts for adult ticks on the density of Ixodes scapularis Say was evaluated within 4 habitats on Long Point, Ontario, from 1989-1992. During the period from May to September, mean weekly vapor pressure deficits were greater within the oak savannah and cottonwood dune habitats than at the maple forest and white pine habitats, which were similar. Vapor pressure deficit was likely the major factor affecting the survivorship of eggs and immature tricks in these habitats. Based on drag sampling, I. scapularis adults demonstrated peak activity in April and October of each year. The mean number of I. scapularis adults collected by dragging during the fall or in the spring did not differ significantly within each habitat. The mean number of adults collected also did not differ among tick cohorts within each habitat; however, significantly more adults were collected within the maple forest than in the white pine habitat. The mean number of I. scapularis adults per white-tailed deer, Odocoileus virginianus (Zimmerman), increased from 1989 to 1991 and then decreased in 1992. Significantly more adult I. scapularis infested deer were observed in 1990 than in 1989. Removal of deer in 1989 and 1990 resulted in a calculated decrease of > 100,000 fed female ticks. Although seasonal variation in microclimate within habitats was closely linked with tick survival and partly explains the differences in abundance of I. scapularis among habitats on Long Point, habitat utilization by deer was also a primary factor governing the local abundance of I. scapularis populations.

Abundance of Ixodes scapularis (Acari: Ixodidae) larvae and nymphs in relation to host density and habitat on Long Point, Ontario

Ixodes scapularis Say populations were evaluated within 4 habitats on Long Point, Ontario, from 1990 to 1992 to ascertain whether differences in density of mouse populations within and among habitats were correlated with that of immature I. scapularis populations. I. scapularis immatures were rarely collected by dragging within the cottonwood dune habitat. Significantly more larvae (P < or = 0.05) were collected by drag sampling within the maple forest habitat than in the oak savannah or white pine habitats for the 1989, 1990, and 1991 cohorts, whereas the size of the 1992 larval cohort did not differ significantly among these habitats. Significantly more nymphs were collected by dragging within the maple forest than in the other 2 habitats for all 4 cohorts. Nymphs from the 1989 and 1990 cohort were more abundant within the oak savannah than the white pine habitat, whereas the 1991 and 1992 cohorts were similar. With few exceptions, I. scapularis immatures were most prevalent on white-footed mice, Peromyscus leucopus (Rafinesque), captured within the maple forest > oak savannah > white pine > cottonwood dune, although differences were not significant in all years and in all habitats. The number of mice captured within the 4 habitats was not correlated with the number of I. scapularis larvae or nymphs infesting them. Likewise, the minimum number of mice alive was not significantly correlated with conversion indices of larvae to nymphs or nymphs to adults. Lack of association between mouse availability and relative size of subsequent cohorts of host-seeking ticks suggests that factors other than the size of the mouse populations were responsible for the observed differences in tick abundance among habitats.

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.

Duration of Borrelia burgdorferi infectivity in white-footed mice for the tick vector Ixodes scapularis under laboratory and field conditions in Ontario

The duration of Borrelia burgdorferi infectivity in white-footed mice (Peromyscus leucopus) experimentally inoculated or infested with infected Ixodes scapularis nymphs was evaluated. Infectivity was assessed by infesting these mice with unfed I. scapularis larvae at 7, 21, 35 and 49 days post-inoculation (DPI) or post-infestation (PI). At 7 DPI, B. burgdorferi was transmitted from 18 of 24 syringe-inoculated mice and all three tick-infected mice to I. scapularis larvae which fed upon them. However, at 21, 35 and 49 DPI, significantly fewer mice were infective. Borrelia burgdorferi was isolated from tissues of 14 of 22 syringe-inoculated mice about 56 DPI, and from all three tick-infected mice. However, the level of agreement between xenodiagnosis and bacterial culture was no greater than would be expected by chance alone. We also determined if B. burgdorferi infectivity of mice varied in relation to periods of tick feeding in the field. White-footed mice were trapped during April, July and August 1993 from two habitats on Long Point peninsula (Ontario, Canada), where B. burgdorferi is endemic. Mice from each habitat were infested with laboratory-reared I. scapularis larvae. Ticks from each mouse were subsequently examined by immunofluorescent assay for B. burgdorferi infection and mice were cultured for B. burgdorferi. None of 3577 I. scapularis larvae fed on 62 mice captured within the cottonwood dune habitat were infected with B. burgdorferi, although it was isolated from six of these mice. Within the maple forest habitat, 0/24, 8/21 (38%) and 1/21 (5%) mice transmitted B. burgdorferi to I. scapularis larvae during April, July and August, respectively. Most mice from the maple forest with B. burgdorferi-positive tissues (14/21) were collected during July, although the level of agreement between xenodiagnosis and tissue culture was poor. Because B. burgdorferi infectivity in mice appears to be of short duration, overwintered I. scapularis larvae and nymphs may have to feed upon infected hosts at the same time of year in order for a cycle of B. burgdorferi infection to be maintained on Long Point. Infected I. scapularis nymphs, rather than persistently infected vertebrate hosts, likely serve as the overwintering "reservoir" for B. burgdorferi on Long Point.

Evaluation of the efficacy of 3% citronella candles and 5% citronella incense for protection against field populations of Aedes mosquitoes

We assessed the efficacy of 3% citronella candles and 5% citronella incense in protecting subjects from bites of Aedes spp. under field conditions. The study was conducted in a deciduous woodlot in Guelph, Ontario, Canada from July 26 to August 10, 1995. Eight subjects, dressed identically, were assigned to one of 8 positions on a grid within the study area. Two citronella candles, 2 citronella incense, 2 plain unscented candles, or no candles (i.e., nontreated controls) were assigned to 2 positions on the grid each evening. Subjects conducted 5-min biting counts at each position and performed 16 biting counts per evening. On average, subjects received 6.2 +/- 0.4, 8.2 +/- 0.5, 8.2 +/- 0.4, and 10.8 +/- 0.5 bites/ 5 min at positions with citronella candles, citronella incense, plain candles, and no candles, respectively. Although significantly fewer bites were received by subjects at positions with citronella candles and incense than at nontreated locations, the overall reduction in bites provided by the citronella candles and incense was only 42.3 and 24.2%, respectively.

Essential oil analysis and field evaluation of the citrosa plant "Pelargonium citrosum" as a repellent against populations of Aedes mosquitoes

A plant recently introduced into North America as the citrosa, Pelargonium citrosum ('Van Leenii'), has been marketed as a biological repellent against mosquitoes. Citrosa is claimed to repel mosquitoes within a 10 ft.2 (0.93 m2) area due to a continuous fragrant release of citronella oil. The total essential oil yield was 0.2 +/- 0.1% from fresh plant material. Chemical analysis by the authors revealed that combined essential oils of fresh greenhouse- and field-grown citrosa have 35.4 +/- 6.2% geraniol, 10.4 +/- 1.6% citronellol, 8.9 +/- 2.0% isomenthone, and 6.8 +/- 3.8% linalool. Both the morphology and essential oil of citrosa fall within the Pelargonium x asperum hybrid complex and are similar to 'Rosé', the commercial rose geranium. No character of morphology or essential oil of a Cymbopogon species yielding commercial citronella oil could be detected in the citrosa. The effectiveness of the citrosa as a repellent against field populations of spring Aedes spp. mosquitoes was evaluated and compared with a 75% deet (N,N-diethyl-3-methylbenzamide) formulation. Deet provided > 90% reduction in mosquitoes biting subjects for up to 8 h post-treatment. There was no significant difference between citrosa-treated and nontreated subjects.

Permethrin as a tent treatment for protection against field populations of Aedes mosquitoes

A tent treated with an oil-based 1% permethrin formulation (0.936 g AI/m2) was evaluated for protection against Aedes spp. Mosquito biting assessment was conducted in the field using 8 human subjects positioned inside and outside tents. Subjects inside tents received 66.8% fewer bites than subjects outside tents prior to treatment. Following treatment, subjects inside the treated tent had significant (P < or = 0.05) protection (84-94% bite reduction) for 42 days. Subjects outside the treated tent experienced 43-82% fewer biting mosquitoes than subjects outside the untreated tent. The treated tent remained lethal > or = 42 days to mosquitoes exposed to the tent fabric in field bioassays.

Survival and development of Ixodes scapularis (Acari: Ixodidae) under various climatic conditions in Ontario, Canada

Distribution of the blacklegged tick, Ixodes scapularis Say, is poorly defined in Ontario. An endemic population is known on Long Point peninsula, Lake Erie, Ontario, but I. scapularis adults have also been collected from other localities within the province. To test the hypothesis that distribution of the blacklegged tick is limited by cold climatic extremes, 35 fed female, 70 unfed adult, and 70 unfed nymphal I. scapularis were held in containers within four natural habitats on Long Point (42 degrees 36' N; 80 degrees 5' W) and at northern localities near Ottawa (45 degrees 27' N; 75 degrees 42' W), Hearst (49 degrees 40' N; 83 degrees 41' W), and Kenora (49 degrees 47' N; 94 degrees 29' W), Ontario, from early December 1991 until May 1993. At the northern localities, 84.8 and 30.5% of fed females and unfed adults survived overwinter, respectively. On Long Point, 56.4% of fed females and 23.6% of unfed adults successfully overwintered. Longevity of fed females and unfed adults was increased by > 2 mo at the northern localities compared with Long Point, although survival rates for unfed nymphs at the northern sites and on Long Point were similar. Females within the four habitats on Long Point, and at Kenora and Ottawa, laid eggs from late April to mid-May, whereas eggs were deposited in late June at Hearst. Emergence of larvae from eggs began in late July or early August on Long Point and at Ottawa. Larvae were first observed in early October at Kenora, and no larvae emerged during 1992 at Hearst. Some eggs that overwintered during 1992-1993 at the northern sites were viable; however, hatching rate was < 10%. The minimum duration of the life cycle of I. scapularis is extended when ticks are introduced into regions of the province with seasonal degree-day accumulations lower than those observed on Long Point. Delays in deposition of eggs and emergence of larvae at Hearst and Kenora were likely a result of insufficient accumulation of degree-days above threshold temperatures for development in 1992. Though some eggs can overwinter successfully, suggesting that latitude-related reduction in seasonal temperature may not limit distribution of this tick in Ontario, hatchability was low. This factor, combined with innate incremental mortality at each instar, difficulty in finding a mate, and low density of medium to large mammal hosts for adults, may mitigate against establishment of I. scapularis by introduction of individual ticks into certain northern regions.

Response of the meadow vole (Microtus pennsylvanicus) to experimental inoculation with Borrelia burgdorferi

The response of the meadow vole (Microtus pennsylvanicus) to infection by experimental inoculation with Borrelia burgdorferi was evaluated. Forty-two adult voles were inoculated subcutaneously with 0.5 x 10(6) spirochetes. Sera taken during the 196 day trial were tested by indirect fluorescent antibody (IFA) assay for antibodies to B. burgdorferi. Tissues from animals which died during the trial, and from animals killed at 28, 112 and 196 days post-inoculation (DPI), respectively, were cultured in BSK-II medium for < or = 6 weeks. They also were examined histologically for lesions and the presence of spirochetes. All inoculated animals developed antibodies by 14 DPI and maintained titers > or = 1:10 for the duration of the trial. Spirochetes were isolated from ears, bladder, and spleen. Spirochetes also were identified by Bosma-Steiner silver stain or tissue IFA assay in sections of ears, bladder, kidney and heart. Infection as confirmed by re-isolation persisted for < or = 111 days. No lesions were identified in association with the presence of spirochetes. No increase in mortality was observed in inoculated animals compared with controls. Sensitivity of the IFA test at a cut-off titer of 1:10 was 100% from > or = 14 DPI, but at 1:20 reached a maximum of 97%. Specificity at 1:10 was 84% and at 1:20 was 97%. Use of antiserum to Microtus immunoglobulin (Ig) in a double-layered test provided no significant advantages over use of a commercial fluorescein-conjugated anti-mouse Ig in a single-layered IFA test.

The groundhog tick Ixodes cookei (Acari: ixodidae): a poor potential vector of Lyme borreliosis

Evidence for infection with the spirochete, Borrelia burgdorferi, was sought in Ixodes cookei and in groundhogs (Marmota monax) in southern Ontario, Canada, and ticks fed on experimentally inoculated hosts were examined for the spirochete. Borrelia burgdorferi was not detected by immunofluorescent examination of 110 larval, nymphal or adult I. cookei collected from the environment, or taken from humans and other animals. Three groundhogs inoculated with B. burgdorferi developed titers of 1:20 to 1:80 by the indirect immunofluorescent antibody test, but B. burgdorferi was not isolated from the spleens, kidneys, or urinary bladders of these animals. One of 30 wild groundhogs had an antibody titer of 1:20 to B. burgdorferi. Three (5%) of 59 I. cookei larvae fed on B. burgdorferi-infected hamsters became infected, in comparison with 23 (28%) of 82 I. dammini larvae fed on the same hosts. Borrelia burgdorferi was present in 5%, 16% and 4% of molted I. cookei nymphs fed on infected hamsters, rats or a groundhog, respectively; prevalences of infection in I. dammini fed on the same hosts were significantly (P < 0.05) higher (45%, 36%, and 23%, respectively), as was the intensity of infection. A naive groundhog on which I. cookei nymphs from an infected cohort fed did not become infected with B. burgdorferi, but it is uncertain whether an infected tick engorged on the experimental host. Ixodes cookei seems to be an inefficient vector of B. burgdorferi, and is unlikely to be significant in nature. Groundhogs are potential wildlife reservoirs of B. burgdorferi, based on their capacity to transmit infection to I. dammini.

The effect of lindane formulations on tissue residues in barrows and on stillbirths in sows

The potential effect of lindane and its formulations on stillbirths and abortion in pregnant sows was investigated. One of four formulations of lindane were applied at five times the registered dosage to each of ten sows within two weeks of farrowing. Each animal received 5 g of lindane. Formulations included: 1) a wettable powder diluted in water, 2) emulsifiable concentrate (EC) in xylene diluted with water, 3) an emulsifiable concentrate with heavy aromatic naptha diluted with mineral oil and 4) an emulsifiable concentrate ready-to-use mineral oil concentration. Number of stillbirths were not increased in the sows and signs of toxicity were not observed.Three barrows, for each formulation, were sprayed at three times the registered dosage (1.3 g/animal) and slaughtered 24 hours later to determine if increased absorption and residues of lindane were associated with different formulations. Residues of lindane in skin, fat, back meat, brain and liver were consistently higher in those animals sprayed with the water based formulations than with oil-based formulations.

Efficacy and dissipation of permethrin for the control of the northern fowl mite in hens

Laying hens were treated with permethrin at the rate of 20 mg per bird to determine efficacy against northern fowl mites Ornithonyssus sylviarum (Canestrini and Fanzago) and the dissipation of residues over a 42-day period. Permethrin provided greater than 99% control of mites for at least 42 days posttreatment as compared to malathion which did not substantially reduce mite infestations. Carbaryl and coumaphos treatment resulted in limited reductions with mite populations recovering by two to three weeks posttreatment. Maximum residues of permethrin in breast muscle, body fat and the uropidium occurred on day 1 posttreatment and were still present in fatty tissue in detectable quantities on day 42. Residues in egg yolk appeared on day 3 posttreatment and peaked on day 7 with trace quantities still present on day 21. Permethrin was not found in egg white. Low residues were found in the liver and gizzard from day 1 through to day 7.

Southern Ontario survey of eyeworms, Thelazia gulosa and Thelazia lacrymalis in cattle and larvae of Thelazia spp. in the face fly, Musca autumnalis

An eight month survey of bovine eyes from an abattoir in southern Ontario revealed the presence of the eyeworms Thelazia gulosa and T. lacrymalis in 32% of the cattle. In the same area, 3% of the natural population of face flies (Musca autumnalis) harbored larval eyeworms. A review of the literature is provided.