The relationship between bark peeling rate and the distribution and mortality of two epiphyte species

Tree bark characteristics influence epiphyte establishment and survival and consequently the way in which epiphytes are distributed on trees. Tree species with peeling bark have been reported as poor epiphyte hosts. We analyzed the distribution and seedling mortality of two Tillandsia species (Bromeliaceae) in relation to rate of bark peeling of Bursera fagaroides (Burseraceae). The highest peeling rate (0.12% per day) took place on the trunk and the lowest rate on twigs (0.04% per day; branches ≤2 cm in diameter). The highest proportion of Tillandsia plants appeared on twigs. The distributions of juvenile and adult plants on twigs were higher than those expected based on the distribution of first-year seedlings, suggesting that on twigs, survival could be greater than on trunks and branches, canopy areas where peeling is faster. On the trunk and branches, in contrast, the proportion of juveniles and adults were similar to or less than that expected for first-year seedlings. The main cause of mortality was peeling and the area of minor overall mortality was the trunk, suggesting that this area should be favored as the main distribution area for the Tillandsia species but is not. Our results show that the peeling rate of B. fagaroides depends on branch size and suggest that the Tillandsia distribution depends not only on peeling rate but also on seed dispersion. We suggest that to colonize B. fagaroides epiphytes would either have adaptations to counteract the peeling rate or should occur in the areas of lowest peeling rate located in the exterior crown of trees.     

Observations on the life cycle and establishment ofCochylis atricapitana (Lep: Cochylidae), a moth used for biological control ofSenecio jacobaea in Australia

Larvae of the mothCochylis atricapitana (Stephens) are monophagous leaf, crown, stem or bud borers of ragwort,Senecio jacobaea L. (Asteraceae). In the present investigation, aspects of the life cycle ofC. atricapitana were determined. Moths ofC. atricapitana lay an average of 158 eggs/female with as many as 355 eggs being laid by a single female. The majority of eggs are laid individually along the primary and secondary veins on the underside of ragwort leaves. Egg incubation ranges from 4.2 days at 30°C to 14.4 days at 15°C. At a constant 23°C under a 16 hour photoperiod,C. atricapitana takes approximately 40 days to complete a generation. Caterpillars make their way to young, actively growing ragwort shoots or buds, and begin mining into the plant tissue, boring into the leaf, crown, stem or bud.C. atricapitana has five larval instars and enters diapause as a final instar larva. In southern Victoria, moths ofC. atricapitana fly from late September through to the beginning of February. Adults emerge after overwintering towards the end of spring or beginning of summer.C. atricapitana has established at two sites while larvae, or signs of damage have been observed at approximately 52% of release sites.      

Choices and Consequences of Oviposition by Hylemya (Delia) Sp. (Diptera: Anthomyiidae)

Hylema sp. ⁵ females oviposit on the undersides of sepals of developing buds of both Ipomopsis aggregata and Polemonium foliosissimum. Eggs deposited on the latter are significantly more likely to be fully protected by the sepal than are eggs deposited on the former. Unexposed eggs have a significantly greater likelihood of successfully developing to the larval stage than do exposed eggs. The difference in frequency of egg exposure on the two plant species can be attributed to differences in sepal morphology: I. aggregata sepals are significantly narrower than those of P. foliosissimum. The hypothesis that females preferentially oviposit on larger flowers was unconfirmed by a manipulative choice experiment. Plants differing in the size of their flowers were potted together and presented to Hylemya in arrays in the field. Flowers of the larger-flowered pair were no more likely to be oviposited on than flowers of the smaller-flowered pair. However, there were significant negative correlations between the corolla length and the percentage of flowers laid on per day at each of two sites. There was also a significant positive correlation between the corolla width and the percentage of flowers laid on at one site. Thus females appear to be using some measure of flower morphology, or a correlated trait, in making oviposition decisions. The degree to which Hylemya is making suboptimal choices between host plant species is discussed and requires further examination.     

Oviposition choice by the Onopordum capitulum weevil Larinus latus (Coleoptera: Curculionidae) and its effect on the survival of immature stages

Female Larinus latus lay eggs into the capitula of their Onopordum spp. host plants from the onset of capitulum development until the completion of flowering. This tight linkage between insect life-history and plant development optimised larval survival, apart from some initial asynchrony between the readiness of the females to oviposit and the suitability of the very small capitula to physically support eggs. Eggs were laid on bracts and stems of capitula or directly in the florets, when these became available. Both the location of the egg and time of oviposition influenced mortality factors such as egg and larval parasitism, egg desiccation and larval establishment. Overall, survival of eggs laid later in the season into florets was higher, although the adults that emerged were smaller. The change in choice of oviposition site that occurs at the onset of flowering, not only favours survival, but ensures more efficient resource use by the larvae. This occurs because sequential flowering of Onopordum spp. drives a sequential oviposition pattern and spreads the egg load more evenly over the available capitula, reversing a trend earlier in the season to clump eggs that were laid directly on the bracts. Other potential constraints, such as capitulum size, absolute egg density and previous egg-laying do not play a major role in determining the oviposition pattern of L. latus. Larval survival was positively correlated with capitulum size and not strongly influenced by egg density. Competition for resources only appeared to play a role in smaller capitula, and manifested itself in a reduction in the size of emerging adults rather than the death of immatures. In the absence of strong interspecific competition, the oviposition behavior of L. latus has become geared to maximising resource use for larvae (i.e. its own potential competitiveness) rather than minimising interactions with other members of the capitulum endophage guild.     

Pollen beetle (Meligethes aeneus) oviposition and feeding preference on different host plant species

The oviposition and feeding preferences of the pollen beetle, Meligethes aeneus, were determined in choice and no-choice tests in field, semi-field and greenhouse trials. Plant species used were Brassica napus, B. campestris, B. juncea, B. nigra, B. carinata, Sinapis alba and Crambe abyssinica. With respect to number of eggs laid, S. alba and C. abyssinica were inferior to the other species. Pollen beetles laid fewer eggs on B. nigra than on the other Brassica spp. in no-choice tests, however this difference was partly due to fewer eggs laid per bud rather than fewer buds used for oviposition. Most eggs, for all plant species, were deposited in buds sized 2–3 mm. Feeding damage on all plant species was relatively similar. Pollen beetles seem to have a wider host range for feeding than for oviposition. There was good agreement in plant species ranking as oviposition hosts between the field, semi-field and greenhouse trials.     

Infection of Blissus antillus (Hemiptera: Lygaeidae) Eggs by the Entomopathogenic Fungi Metarhizium anisopliae and Beauveria bassiana

This study determined the pathogenicity and virulence of Beauveria bassiana and Metarhizium anisopliae to eggs of the chinch bug Blissus antillus (Hemiptera: Lygaeidae). Eggs were inoculated under laboratory conditions by immersion in concentrations of 1 × 10⁴ and 5 × 10⁶ conidia/ml. Inoculated eggs were kept under controlled conditions. Evaluations were carried out daily for 20 days. M. anisopliae isolates were highly virulent to eggs, even at 1 × 10⁴ conidia/ml. All B. bassiana isolates tested were considered to be of low virulence or avirulent. The most virulent isolate tested was ESALQ 818 (M. anisopliae), which caused 96.7% infection, when eggs were immersed in suspensions of 1 × 10⁴ conidia/ml. Conidial production on infected eggs was observed to be highest for M. anisopliae isolate CG144, with a mean value of 11.6 × 10⁵ conidia/ml/egg. Infection of Blissus eggs oviposited on plant stems was greater when M. anisopliae isolate CG144 was formulated in mineral oil (63.5% mortality) than when formulated in Tween 80 (27.1% mortality).     

Overwintering, phenology and fecundity of Harmonia axyridis in comparison with native coccinellid species in Italy

Classical biological control is generallyunderstood as an environmentally safe practiceof insect pest management. However, questionshave been raised about possible negativeeffects for native species. As part of a riskassessment study a semi-field trial was carriedout in northern Italy in order to compare theoverwintering of the native species Propylea quatuordecimpunctata (L.) and Adalia bipunctata (L.) (Coleoptera:Coccinellidae) with the exotic Harmoniaaxyridis (Pallas) (Coleoptera: Coccinellidae).All the experiments were carried out from April1998 to April 2001. Harmonia axyridis wasable to overwinter successfully in northernItaly. Fecundity, oviposition rate, longevityand rate of increase of overwintering femaleswere calculated and the phenology of the threespecies was studied. Harmonia axyridisoverwintering mortality (31.9%) was lower incomparison with mortality of native species(68.9% for P. quatuordecimpunctata and61.3% for A. bipunctata). As aconsequence, post-overwintering rate ofincrease of the exotic species was higher.Longevity of overwintered females was similaramong the species. Mean fecundity of H. axyridis (783.8 eggs per female) was slightlyhigher than A. bipunctata (720.2 eggs perfemale), and much higher than P. quatuordecimpunctata (193.7 eggs per female). H. axyridis and A. bipunctatacompleted four generations and P. quatuordecimpunctata three generations in a year. The results show that H. axyridisappears to posses a high potential for establishment in Italy.     

A role of the Dufour's gland in the dominance interactions of the paper wasp,Polistes fuscatus (Hymenoptera: Vespidae)

The Dufour's gland of the paper wasp, Polistes fuscatus,is a source of the cues used by dominant females to recognize the eggs laid by subordinates or nonnestmates on pre (worker)-emergence nests. When dominant wasps were presented with an egg covered with either (1) the Dufour's gland extract of a subordinate cofoundress, (2) the extract of an egg from the same subordinate, or (3) the solvent alone, the dominant female destroyed and replaced the eggs covered with the Dufour's extract significantly more frequently than the other eggs. Eggs with the extract of a nonnestmate's Dufour's gland were also eaten significantly more frequently than those with the solvent. Given similar choices, subordinates did not destroy any eggs. The Dufour's gland appears to have little or no role in communicating dominance directly among aggressively interacting cofoundresses.     

Embryopathic and embryocidal effects of purified fumonisin B1 orFusarium proliferatum culture material extract on chicken embryos

One hundred eight fertile eggs (Columbia × New Hampshire) were assigned to 10 groups of 10 eggs each (2 control groups had 14 eggs each). Five groups of eggs were inoculated on day 1 of incubation, while the other 5 groups were inoculated on day 10. The inoculum of the 4 treatment groups on both day 1 and 10 consisted of 1,10, or 100 µM purified fumonisin B₁ (FB₁) or a culture material extract (CME) ofFusarium proliferatum, having known amounts of FB₁, FB₂ and moniliformin (FB₁ 20 µM; FB₂ 4 µM and moniliformin 7 µM). Inoculum consisted of the respective toxin(s) dissolved in 100 µl double distilled, autoclaved water (diluent). Control eggs were inoculated with diluent only. Mortality was both dose- and time-responsive in all treatments. Eggs inoculated on day 1 with 1 µM FB₁ had 50% mortality; 10 µM FB₁ had 70% mortality; 100 µM FB₁ had 100% mortality; and CME had 100% mortality. Eggs inoculated on day 10 with 1,10 or 100 µM FB₁ or CME had 30, 60, 90 and 80% mortality, respectively. Normal chicks were hatched from all control eggs. The median death times (MDT₅₀) were inversely dose-responsive in all treatments, ranging from 3.0 to 7.4 days in embryos exposed on day 1 and from 3.2 to 9.0 days in those exposed on day 10. Early embryonic changes in exposed embryos included hydrocephalus, enlarged beaks and elongated necks. Pathologic changes were noted in liver, kidneys, heart, lungs, musculoskeletal system, intestines, testes and brain toxin-exposed embryos.     

Overwintering sites and winter mortality of Euseius finlandicus (Acari: Phytoseiidae) in a peach orchard in northern Greece

In peach orchards of northern Greece Euseius finlandicus Oudemans overwinters in various sites on the trees, usually in groups of 5–15 females. Overwintering females were mostly found in bark crevices near the hibernation cocoons of the peach moth Adoxophyes orana (Fischer von Rosslerstamm), and also in small crevices of the bark and in pedicels left after fruit harvesting. Empty scales of dead diaspidids and dead coccids, cocoons of lacewings and mummies of parasitized aphids sporadically found on trees, were less common overwintering sites for females of the mite. In two successive years, mortality of overwintering females was very low, approximately 4 and 4.5% which could be due to the mild climate of northern Greece and the high cold tolerance of the mite. This revised version was published online in July 2006 with corrections to the Cover Date.     

Biology of Lilioceris spp. (Coleoptera: Chrysomelidae) and their parasitoids in Europe

The biology and parasitoid complex of the lily leaf beetle (LLB), Lilioceris lilii Scopoli, and two congeneric species were investigated in Europe, as part of a biological control program against the LLB in North America. Eggs, larvae, and adults of L. lilii were collected in several countries in Europe, on both cultivated and wild Lilium spp., and reared in the laboratory and under natural conditions. Parasitoids were obtained and their biologies were studied. Similar investigations were made in Switzerland on two closely related species Lilioceris tibialis (Villa) found on wild Lilium spp., and Lilioceris merdigera (L.) on several other Liliaceae. The three species are strictly univoltine. Adults overwinter and lay eggs on leaves in early spring. The three beetle species have four instars, which were characterized by their head capsule width. Pupation occurs in a cocoon in the soil. Adults emerge in late summer and start feeding before reaching overwintering sites. Egg and larval parasitoids were obtained. Eggs of L. lilii and L. merdigera were parasitized by the mymarid Anaphes sp., a multivoltine species that needs alternate hosts for overwintering. Larvae were heavily attacked by several parasitoids, among which the most abundant were three ichneumonids, Lemophagus pulcher (Szepligeti), L. errabundus (Gravenhorst), and Diaparsis jucunda (Holmgren), and the eulophid Tetrastichus setifer Thomson. All four parasitoid species were found in the three beetles and in most European regions, but strong variations were observed in their relative abundance among hosts and geographic regions. Three of the four main larval parasitoids are strictly univoltine, whereas L. pulcher has a partial second generation. Lemophagus spp. are frequently parasitized by the ichneumonid hyperparasitoid Mesochorus lilioceriphilus Schwenke. Further details of the biology of the parasitoids are described, and their potential as biological control agents is discussed.     

Biology and population development ofAblattaria arenaria [Coleoptera: Silphidae], a snail predator

The biology ofAblattaria arenaria (Kraatz) was studied in the laboratory by using a helicid snail,Xeropicta derbentina (Kyrnicki) as prey. Population development ofA. arenaria in the field was studied in 1985 and 1986. The eggs ofA. arenaria were laid in the soil in lots of 5–45 at various intervals, and the total number of eggs per female varied from 144 to 193 during the oviposition period of 24–88 days.A. arenaria passed through the egg, 3 larval, prepupal, and pupal stages before reaching the adult stage. The mean duration of these stages was 9.8, 3.9, 2.5, 5.9, 3.8 and 5.7 days, respectively, with a total of 31.4 days. A. arenaria overwintered as an adult and became active and laid eggs during the spring. The start of spring activity seemed to be highly influenced by relative humidity. High humidity resulted in early emergence from overwintering sites. There was 1 generation in 1985, but 2 population peaks occurred in 1986. Immature stages of the 2nd generation became adult before the beginning of aestivation. Activity of the beetles was stopped by the beginning of hot weather in June, which synchronized well with the beginning of snail aestivation.      

Winter survival and oviposition before and after overwintering of a parasitoid wasp, Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae)

Winter survival and oviposition before and after overwintering in Ooencyrtus nezarae, an egg parasitoid of phytophagous heteropterans, were examined in Osaka, Japan. Eggs of Riptortus clavatus parasitized by O. nezarae were kept under natural photoperiod and temperature. When honey was supplied, some female adults emerging from early September to late November overwintered. The percentage of overwintering individuals increased as the date of adult emergence advanced. Most female adults supplied with honey and hosts oviposited soon after emergence, then stopped laying eggs. Female adults emerging in mid‐October and early November laid eggs and then overwintered. The induction of diapause in the field seems to vary greatly depending on host availability. Without honey, the survival time of female adults was very short, whether host eggs were supplied or not. After overwintering, most females began to lay eggs in early May if host eggs were supplied, and they produced both male and female progeny. In the study area, a legume field in Osaka, parasitization by O. nezarae was observed from early July to November.     

Selection of hibernation sites by Anthonomus pomorum: preferences and ecological consequences

The apple blossom weevil, Anthonomus pomorum (L.) (Coleoptera: Curculionidae), has a long period of aestivo-hibernation in the adult stage lasting from summer to early spring of the following year. Potential hibernation sites within an apple orchard consist of high-stem rough-bark trees or dwarf smooth-bark trees. Field release-recapture experiments in 2 consecutive years showed that 64 and 47% of the weevils remained in the vicinity of the release sites in an area of high-stem trees and dwarf trees, respectively. The dispersing weevils moved over an average distance of 5.5 m in the dwarf tree area, as compared to 3.8 m in the high-stem tree area. The prevalent direction of dispersal was along tree rows in both areas. Some weevils displayed, after release in mid-July, a directional dispersal to the adjacent forests. Others, released in the dwarf tree area, dispersed towards the area of high-stem rough-bark apple trees. Experiments simulating various hibernation sites demonstrated that the litter of dry leaves was the most preferred overwintering shelter, yielding a relatively high survival rate. Branches with rough bark ranked second, while branches with smooth bark, grass and pure soil were not favourable for overwintering. Flight tendency in newly emerged weevils of summer generation was significantly higher in June/July than in August/September. This corresponds to the dispersal behaviour in the field. The timing of spring colonisation of apple trees was similar for weevils overwintering within the orchard and for those from outside. These results suggest that modern, dwarf apple orchards offer unfavourable conditions for overwintering, but that the relatively small proportion of weevils which manage to reach the adjacent forests find optimal hibernation sites there.     

Morphometric and allometric studies on eggshells and embryos of free-living Canada geese (<Emphasis Type="Italic">Branta c. canadensis</Emphasis> Linnaeus, 1758)

A total of 289 eggs laid by free-living Canada geese (Branta canadensis canadensis Linnaeus, 1758) in the northwestern part of Germany were collected in spring 2002 and 2003 and examined for shell and embryo parameters. Mean egg mass was 160.88±19.68 g. Approximately 90% of all eggs had a mass between 140 and 185 g. About 90% of all clutches consisted of four to seven eggs. The form index of 90% of all eggs was in the range 62–74. The mean eggshell thickness on the blunt pole was 0.52±0.08 and 0.53±0.07 mm on the long axis. Embryo development follows a square function in the first half of development. Mean embryo length was correlated (P<0.01) with the mean body mass and shell thickness on the blunt pole and on the long axis of the eggs. No significant correlations were found between egg mass and form index and egg mass and shell thickness. Eggs with no visible fertilisation had a mean form index of 68.69±4.53 and fertile eggs had a mean form index of 68.50±3.73. Only 3 of 160 fertile eggs contained embryos with malformations of the beak, vertebral column, or leg. The question of regulating prevailing Canada goose populations is discussed.     

Diamondback moth egg susceptibility to rainfall: effects of host plant and oviposition behavior

Oviposition patterns of the diamondback moth (DBM), Plutella xylostella L. (Lepidoptera: Plutellidae), differ between common cabbage (Brassica oleracea L. var. capitata) and Chinese cabbage (Brassica rapa L. var. pekinensis) (Brassicaceae) host plants. This study shows that the moth prefers to oviposit on adaxial rather than abaxial leaf surfaces and petioles of both host plants. More eggs were laid in leaf veins than on leaf laminas of both host plants, especially in Chinese cabbage, where 94.6% of eggs were laid in veins. On Chinese cabbage, very few eggs were laid in clusters (≥2 eggs), whereas on common cabbage approximately 30% of eggs were laid in groups of 2 or more eggs. Removal of wax from common cabbage leaves dramatically increased the number of eggs laid singly on the leaf lamina of treated plants, suggesting that leaf waxes affect how eggs are distributed by ovipositing DBM. Eggs were most susceptible to removal by rainfall from the plant surface immediately (<1 h) after oviposition and when close to hatching (>72h old) whereas they were least susceptible 24 h after oviposition. Eggs laid on common cabbage plants were more susceptible to simulated rainfall than eggs laid on Chinese cabbage plants. On common cabbage plants, egg susceptibility to rainfall on different plant parts ranked adaxial leaf surfaces>petioles = abaxial leaf surfaces>stem, but there was no difference in egg susceptibility to rainfall on the various plant parts of Chinese cabbage. Furthermore, on common cabbage plants, eggs laid on both adaxial and abaxial leaf surfaces were afforded significant protection from the effects of rainfall by leaves higher in the plant canopy. On common cabbage plants, oviposition patterns reduce the potential impact of rainfall on eggs, possibly reducing the effect of this important abiotic mortality factor in the field.     

Life history of the Onopordum capitulum weevil Larinus latus (Coleoptera: Curculionidae)

The population structure and stage-specific survival of the capitulum weevil, Larinus latus, a potential control agent for weedy Onopordum thistles in Australia, was studied in its native range in Greece. Although fecundity of this univoltine insect was low (35.4 eggs/female), survival was relatively high, with 45% of eggs reaching adulthood when protected from predators and parasitoids, and 23% surviving when exposed to these natural enemies. Other mortality factors of importance for immature stages were a failure to establish, due largely to oviposition by females on inappropriate sites on the thistle capitula, and inter- and intraspecific competition for larval resources. Once emerged, adult losses due to overwintering mortality and net migration were estimated at a further 48%. Despite these losses there was a net doubling of the population at the study site between Onopordum flowering seasons. The data suggest that movement of adults occurs both within and between patches and that variability in population size relative to the resource base is low. Overall, L. latus may be considered a K-strategist which forms relatively stable populations over a fragmented habitat and which maintains its population integrity through a certain degree of annual redistribution. The implications of these data for the potential effectiveness of L. latus as a biological control agent of weedy Onopordum spp. are discussed.     

Effects of fenoxycarb on ovarian development, spring fecundity and longevity in winterform pear psylla

The insect growth regulator fenoxycarb prompts ovarian development in diapausing winterform pear psylla, Cacopsylla pyricola (Förster) (Homoptera: Psyllidae). We applied fenoxycarb to caged psylla in September, November, and December to test whether premature ovarian development reduced overwintering survival, spring fecundity, or spring longevity. Fenoxycarb prompted ovarian development in all treated psylla, with the largest effects occurring in the September-treated insects. Recovery of live psylla in spring was 46–95% in treated insects and 72–92% in controls; overwintered insects from the fenoxycarb treatment survived field temperatures below –20°C despite having had mature ovaries. Fecundity and longevity of psylla were the same in treated and untreated insects, indicating that overwintering with mature ovaries did not cause reduced spring egglaying capacity. Several treated insects each deposited over 1900 eggs and survived more than 120 days. Due to their more advanced development, treated insects had higher oviposition rates than controls during the first 5 days after removal from the field. The largest impact on spring fitness was due to the effects of fenoxycarb on egg hatch. Eggs deposited on clean foliage by September-treated females were less likely to hatch than eggs deposited by controls, suggesting that fenoxycarb affected developing eggs within the female. Prospects for using fenoxycarb in fall to control pear psylla appear to be limited.     

Temperature and host-plant effects on development and population growth of Mecinus janthinus (Coleoptera: Curculionidae), a biological control agent for invasive Linaria spp.

Mecinus janthinus Germar is a European stem-mining weevil that has been established in North America as a biological control agent against the invasive European weeds Linaria vulgaris P. Mill. and Linaria dalmatica (L.) P. Mill. (Scrophulariaceae). Establishment success and impact of the weevil have varied widely among sites. We investigated the hypothesis that some of this variation may be due to a lack of sufficient time for M. janthinus to develop to the adult (overwintering) stage in less favorable climates. Development time of M. janthinus was measured in L. vulgaris and L. dalmatica at four constant temperatures, and logistic regression was used to derive a model for the effect of temperature on development. Development rates were simulated using historic climate data for a site in central Alberta (where establishment was marginal on L. vulgaris) and one in southern British Columbia (where outbreaks occurred, resulting in heavy damage to L. dalmatica). The model showed that, on average, the British Columbia site had 50 more days available for the weevil to lay eggs that could reach the adult stage in time for overwintering than did the Alberta site. This may explain the more rapid population buildup at the British Columbia site. This model could be used to predict the climatic suitability of other areas for establishment of M. janthinus. An unexplained result was the very low survival rate of eggs laid in L. dalmatica under the same experimental conditions.     

Susceptibility of <Emphasis Type="Italic">Amblyomma variegatum</Emphasis> ticks to acaricides in Ghana

The susceptibility of unfed and fed stages of larvae, nymphs and adult females of Amblyomma variegatum ticks were tested using Shaws filter paper dip method against four acaricides; chlorfenvinphos and dioxathion, chlorfenvinphos, gamma benzene hexachloride and amitraz at four different concentrations including the recommended dose rates. Based on their lethal concentrations (LC₅₀ & LC₉₀) chlorfenvinphos and dioxathion combined and chlorfenvinphos alone placed first and second, respectively, in all stages except at the unfed nymphal stage where gamma benzene hexachloride topped with a LC₅₀ of 0.001629, while chlorfenvinphos and dioxathion combined and chlorfenvinphos alone had LC₅₀ of 0.001794 and 0.002258, respectively. Amitraz appeared to have a quick knock-down effect on larvae and nymphs but at the recommended dose rate, showed no mortality of the ticks at that stage. However, at a concentration of 0.040%, amitraz showed a 100% inhibition of oviposition and hatching of laid eggs. Gamma benzene hexachloride produced only 66% inhibition of oviposition while chlorfenvinphos and dioxathion combined and chlorfenvinphos alone produced 100% inhibition of oviposition at their recommended dose rates. Fed nymphs were more susceptible than the unfed nymphs. Eggs laid by engorged female ovipositing ticks, applied with gamma benzene hexachloride, hatched.This revised version was published online in May 2005 with a corrected cover date.