European Red Mite Research Articles

Overwintering Mite Diversity and Their Habitats in Apple and Pear Orchards of Korea with Emphasis on Phytoseiidae and Tetranychidae

Overwintering mite diversity and their habitats were studied in apple and pear orchards during 2002-2003 winter season. Twospotted spider mite was mostly found under the tree barks and fabric strips. European red mites were from crevices of twigs. Tydeid, tarsonemid and oribatid mites were mostly from soil and ground vegetation. Even in the protected overwintering habitat such as artificial fabric strip, twospotted spider mite suffered 81-91% mortality during winter. Predaceous phytoseiid mites found were Amblyseius womersleyi, A. makuwa, A. orientalis, A. rademacheri A. obtuserellus, and A. eharai. Amblyseius womersleyi was the most dominant species in both apple and pear orchards, followed by A. obtuserrellus in apple orchards and A. makuwa in pear orchards. Most phytoseiid mites were found on ground vegetation while their potential prey items were remained on the tree. Implication of the findings for conservation of beneficial mites and biological control of spider mite during season was further discussed.

Evaluation of Acaricides against the Two-spotted Spider Mite, Tetranychus urticae and the European Red Mite, Panonychus ulmi, from Apple Orchards in Aomori Prefecture

Evaluation of Acaricides against the Two-spotted Spider Mite, <I>Tetranychus urticae</I> and the European Red Mite, <I>Panonychus ulmi</I>, from Apple Orchards in Aomori Prefecture

Role of neonicotinyl insecticides in Washington apple integrated pest management. Part II. Nontarget effects on integrated mite control

The effect of neonicotinyl insecticides on integrated mite control in Washington apple was examined from 0 In a series of 20 field trials (54 treatments) designed primarily to look at efficacy against the codling moth, Cydia pomonella, nearly half of the treatments using four or more applications of acetamiprid had peak mite densities exceeding the economic threshold of 5 mites per leaf. Overall, acetamiprid treatments had 4.6-fold higher mite densities than the standard organophosphate insecticide treatment. Of the treatments with high mite populations, Panonychus ulmi, the European red mite, and Tetranychus urticae, the twospotted spider mite, were the dominant species in roughly equal numbers of cases. Only 11.1% of the thiacloprid treatments exceeded 5 mites per leaf; these experimental treatments included eight applications, whereas the current label restricts the number of applications at the rate for C. pomonella to two applications. One out of six clothianidin treatments caused a significantly higher mite density than the standard treatment; however, this material appeared to suppress predatory mites. Neonicotinyl insecticides did not eliminate predatory mites, but they inhibited their ability to respond normally to increasing prey populations. In field trials designed specifically to examine mite population densities where neonicotinyl insecticides were used, significantly higher levels of tetranychid mites occurred in one or more acetamiprid treatments (one, two or four applications) in five out of six trials. In the sixth trial (in a commercial orchard), only two acetamiprid applications were made, and mite populations were low in all treatments. While elevated mite densities were more likely to occur with four applications, in one case it occurred following a single application. The predominant tetranychid mite species (either P. ulmi or T. urticae) varied from trial to trial; however, there was no apparent bias regarding stimulation of the two species. Horticultural mineral oil was used with acetamiprid in some trials in an attempt to mitigate mite outbreaks. However, the addition of oil did not counteract the tendency of acetamiprid to increase tetranychid mite populations, and in one trial, had a negative effect on predatory mite densities. Seasonal tetranychid mite density was positively related to the total grams AI (or number of applications) of acetamiprid, thus reducing the number of applications per season should lower the probability of mite outbreaks.

Assessing dormant season organophosphate use in California almonds

Organophosphate (OP) pesticides were recommended during the dormant season to control overwintering insects such as peach twig borer, San Jose scale, European red mite, and brown mite in California almond and stone fruit orchards. However, since 1990, dormant OP use had fallen under increased scrutiny due to surface water contamination concerns. Studies have shown positive correlation between OP use and residue load in surface water. The purpose of this study is to assess the trends and regional patterns of OP use in almond orchards, and to identify factors that may have influenced those trends, including weather, pest pressure, and use of alternatives to OP such as pyrethroid, dormant oils, and Bacillus thuringiensis (Bt) for the assessment of the impacts to surface water quality. Pesticide use data from the California Department of Pesticide Regulation were analyzed. Regression analyses were used to assess trends from 1992 to 2000, and a geographic information system (GIS) was used to visualize the spatial variation in pesticide use. Results from this study indicated that, statewide, dormant OP use decreased while the use of some alternatives, such as dormant pyrethroid, no dormant insecticides, and in-season pyrethroid, oil alone, and Bt, increased in the last 9 years. The significant decreasing trend of OP use was observed for the measures of kilogram per hectare crop planted, percentage of total planted hectare treated, and numbers of growers who applied dormant OP. The reduction of dormant OP use appeared in all major almond-growing counties. Correlation analyses revealed that more rain was associated with less dormant OP use. A higher percent of almond damage, or rejects, was related to higher OP use in the following dormant season and in-season periods. However, the effects of weather and percent of nut rejects can only explain small portion of the variations in dormant OP use. Therefore, in addition to weather and pest pressures, economic pressures and various outreach and extension programs may also have played a role in encouraging farmers to reduce their use of dormant OP.

Seasonal population dynamics of Typhlodromus pyri Scheuten (Acari, Phytoseiidae) in apple orchards in the region Meckenheim

Typhlodromus pyri Scheuten (Acari, Phytoseiidae) has been reported as the most important predator of the European red mite, Panonychus ulmi (Koch) (Acari, Tetranychidae) in apple culture. However, biological data on T. pyri was insufficient on important parameters like seasonal population dynamics and within-tree and on-leaf distribution in apple orchards in the region of Meckenheim, Germany. The purpose of the present work was, therefore, to obtain experimental data on these parameters of T. pyri from 2000 to 2002 in the apple orchards in this region. The results showed that overwintered females of T. pyri reactivate and start laying eggs between late March and early April. The mean daily number of the different stages of T. pyri per leaf peaked in July each year, where it ranged between 0.92–1.68 eggs, 0.81–1.41 nymphs, 0.64–1.32 females and 0.37–0.52 males. A significantly higher number of T. pyri individuals congregated in the bottom layer of trees (0.34–0.64 individuals/leaf) than in the middle and top layers (0.23–0.38 and 0.12–0.23 individuals/leaf, respectively). We found that 91.4–94.1% of the total eggs, 89.6–91.7% larvae, 73.0–76.5% nymphs, 60.5–64.6% adult females and 52.6–55.9% adult males concentrated their activities in the inner area of the leaf surface. More than 50% of the predatory mites congregated in the bottom layer in winter. Mean total density of the overwintering females in December of 2000,2001 and 2002 ranged between 10.6–14.2 females/5 cm twig in the bottom, 7.3–10.4 in the middle and 4.1–6.9 in the top layers of the apple trees. Mean total fecundity recorded over the 3 years was lowest in the overwintering generation with 31.8–37.6 eggs/female, highest in the June generation with 45.9–53.7 eggs/female, and intermediate in the August generation with 41.5–46.1 eggs/female. The overwintering generation was composed entirely of females, while the female to male ratio in the June generation was 2:1, and in the August generation 3:1. T. pyri overwinters as adult females in rough structures, cracks and crevices of twigs.

An index for selective toxicity of miticides to phytophagous mites and their predators based on orchard trials.

Data from nine trials conducted from 1990 to 1998 in apple orchards in Nova Scotia and Quebec, Canada, were used to estimate the predator-prey selectivity of miticides and their potential compatibility with biological control of mites. The European red mite Panonychus ulmi (Koch) was the dominant and more harmful phytophagous species, followed by the apple rust mite, Aculus schlechtendali (Nalepa). Two predacious mites, the phytoseiid, Typhlodromus pyri Sheuten, and the stigmaeid, Zetzellia mali (Ewing), were often found in the orchards. We used one minus the ratio of mite-days in treated plots to those in the control plots as an index of population suppression and toxicity of the miticides. Miticides were then categorized into classes similar to those employed by the International Organization for Biological Control to rate pesticide toxicity to natural enemies of insect and mite pests. Selectivity of miticides was mostly based on toxicity to P ulmi, the major pest, versus toxicity to T pyri, the major predator, with some consideration of the two lesser species, A schlechtendali and Z mali. In most cases, our findings were in accord with other studies. Abamectin and clofentezine had favourable selectivity (more toxic to the two phytophagous mites than to T pyri). The higher recommended rate of pyridaben (450 g ha(-1)) and two rates of spirodiclofen (180 and 240 g ha(-1)) were neutral (equally toxic to pests and predators). The lower rate of pyridaben (216 g ha(-1)), dicofol, formetanate hydrochloride and propargite were unfavourably selective (more toxic to T pyri). A higher than recommended rate of pyridaben (2160 g ha(-1)) applied before bloom was disruptive--P ulmi-days after treatment were actually greater than with the untreated control. P ulmi resistance to dicofol and propargite were probable complicating factors in some of the orchard trials.

Resistance to fenazaquin and tebufenpyrad in Panonychus ulmi Koch (Acari: Tetranychidae) populations from South of France apple orchards

Following failures to control the European Red Mite ( Panonychus ulmi) using METI-acaricides in some apple orchards in the south of France, resistance to fenazaquin and tebufenpyrad was studied under laboratory conditions. Resistance ratios ranged from 19.8 to 28.8 and from 16.8 to 39.8, respectively, for fenazaquin and tebufenpyrad when compared to the most susceptible of the 2 reference populations. An examination of bioassays responses showed that resistance was higher with tebufenpyrad than with fenazaquin. The recommended field rates for these compounds corresponded only to the LC 95 for fenazaquin and the LC 70 for tebufenpyrad. These results confirm resistance development to METI-acaricides in ERM field populations and suggest it could be responsible for reduced persistence of mite control and in some cases for control failure in apple orchards.

Prey consumption during development as well as longevity and reproduction of Typhlodromus pyri Scheuten (Acari, Phytoseiidae) at higher temperatures in the laboratory

AbstractThe predatory mite Typhlodromus pyri Scheuten (Acari, Phytoseiidae) has been reported as an important predator of the European red mite, Panonychus ulmi (Koch) (Acari, Tetranychidae) in apple culture and vineyards at below 25 °C. However, sufficient biological data was lacking on its efficiency at temperatures above 25 °C. Therefore, the purpose of the present laboratory work was to obtain experimental data on prey consumption during development as well as longevity and reproduction of T. pyri on apple leaf discs and in Plexiglas cells at constant temperatures of 25 ± 2 °C and 30 ± 2 °C with P. ulmi as prey.The results showed that mean daily and total prey consumption by both the nymphs and adults of T. pyri decreased significantly on both the arenas as the temperature was increased from 25 °C to 30 °C, whereby adult prey consumption, both mean daily and total, was higher than that of nymphs. Prey consumption by both the nymphs and adults was significantly higher in the Plexiglas cells than on the leaf discs at both temperatures. Mean total prey consumption during nymphal development was 16.1 (♀♀) and 12.8 (♂♂) at 25 °C compared to 7.0 (♀♀) and 5.8 (♂♂) preys at 30 °C on the apple leaf discs and 46.0 (♀♀) and 38.5 (♂♂) at 25 °C compared to 25.2 (♀♀) and 20.3 (♂♂) preys at 30 °C in the Plexiglas cells. Mean duration of nymphal development was similar for the two sexes at the same temperature, but it was longer at 25 °C than at 30 °C. It was 6.0 and 4.0 days on the apple leaf discs while 7.0 and 6.0 days in the Plexiglas cells at 25 °C and 30 °C, respectively. Mean daily and total prey consumption by both male and female adults also decreased with the increasing temperature, whereby the females consumed more than double the mean total number of prey than the males on both the arenas of observation and at both temperatures: 355.4 versus 149.7 preys at 25 °C and 192.2 versus 85.6 preys at 30 °C on the leaf discs and 826.8 versus 374.5 preys at 25 °C and 488.9 versus 187.9 preys at 30 °C in the Plexiglas cells. Longevity of the females was longer than males on both arenas and at both temperatures and it was longer at 25 °C than at 30 °C. Mean total longevity on the apple leaf discs was 68.3 (♀♀) and 50.8 (♂♂) days at 25 °C compared to 52.5 (♀♀) and 36.8 (♂♂) days at 30 °C, while in the Plexiglas cells it was 91.0 (♀♀) and 65.8 (♂♂) days at 25 °C compared to 75.3 (♀♀) and 48.5 (♂♂) days at 30 °C. Reproduction in females also decreased significantly with increasing temperature. It decreased from 62.0 to 39.0 eggs/female on the leaf discs and 75.0 to 47.1 eggs/female in the Plexiglas cells. The females laid significantly higher numbers of eggs at both temperatures in the Plexiglas cells than on the leaf discs. Oviposition period in females was 30 days at 25 °C on both the arenas, while at 30 °C it was 26 days on the apple leaf discs and 27 days in the Plexiglas cells.

Soybean Oil as a Summer Spray for Apple: European Red Mite Control, Net CO2 Assimilation, and Phytotoxicity

Soybean [Glycine max (L.) Merrill] oil was applied to apple trees [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] as a summer spray in six studies to determine if it controls European red mites [Panonychus ulmi (Koch.)], how it affects net CO2 assimilation (A), and if it causes phytotoxicity. Sprays of 0.5%, 1.0%, and 1.5% soybean oil {TNsoy1 formulation [soybean oil premixed with Latron B-1956 (LAT) spreader-sticker at 10 oil: 1 LAT (v/v)]} reduced mite populations by 94%. Sprays of 1% and 2% soybean oil reduced mite populations to three and four mites per leaf, respectively, compared to 25 per leaf on water-sprayed plants. Soybean oil concentrations of 1.0% and 1.5% applied to whole trees reduced A for less than 7 days. Phytotoxicity did not occur when soybean oil was applied with an airblast sprayer at concentrations of 1.0% and 1.5% or with a mist bottle at 2%. Phytotoxicity occurred when soybean oil was applied with a mist bottle at 4% and 6%, which left soybean oil leaf residues of 0.22 to 0.50 mg·cm-2. No phytotoxicity occurred with 4% SunSpray, which resulted in a mean leaf residue of only 0.13 mg·cm-2. Spraying 1% soybean oil tended to give better mite control than 1% SunSpray Ultra-Fine oil, but caused greater oil residues and a greater reduction in A.

Behavioral and population consequences of acarodomatia in grapes on phytoseiid mites (Mesostigmata) and implications for plant breeding

AbstractWe examined the influence of acarodomatia in the riverbank grape Vitis riparia Michaux (Vitaceae) on the distribution and abundance of predatory mites (Phytoseiidae) and their interactions with herbivorous mites. Acarodomatia are tufts of nonglandular trichomes or pits located in major leaf vein axes of many species of woody perennial plants and are often occupied by predatory and mycophagous mites. In common garden plantings of different accessions of V. riparia we found a significant positive relationship between size of domatia and the abundance of naturally occurring predatory mites. Behavior of adult predatory mites may explain this positive association, in part. In separate laboratory experiments, gravid females of Typhlodromus pyri Scheuten and Amblyseius andersoni Chant spent more time and deposited more eggs on half of a V. riparia leaf with accessible domatia versus the other half in which access to domatia was blocked with pruning tar. Domatia also had population consequences. In an outdoor experiment using potted grapevines, population size of T. pyri and A. andersoni mites was greater on V. riparia with open domatia compared to V. riparia in which domatia were blocked with pruning tar. Population size of predatory mites was also greater on V. riparia with domatia than on Vitis vinifera L., whether their axils were blocked or not. Since V. vinifera have very small domatia, these results indicate that the presence of domatia is important, not just access to vein axils. Elevated predatory mite populations in response to domatia, however, did not translate into differences in the abundance of European red mite Panonychus ulmi (Koch), an important pest of grapes.Overall, these results indicate that domatia in uncultivated V. riparia promote higher densities of some species of generalist phytoseiid mites. However, domatia are small in most cultivated grapes. We crossed females and males of V. riparia that varied in domatia size and reared their offspring and found that average domatia size in the parents was highly correlated (r2= 0.77, slope = 0.55) with average domatia size in offspring (high narrow‐sense heritability). Given that V. riparia possesses many other desirable agronomic traits, this result suggests it should be practical to breed for well‐developed domatia in cultivated accessions.

Manejo integrado de pragas em macieira no Rio Grande do Sul II: uso de Neoseiulus californicus para o controle de Panonychus ulmi

Com o objetivo de implementar o controle biológico de ácaro-vermelho Panonychus ulmi em macieira foi proposta uma estratégia de controle baseada na criação de Neoseiulus californicus em estufa, em liberações inundativas e no uso de acaricidas, em um pomar comercial de macieira da Rincão das Flores Agropastoril (Agriflor), em Vacaria, Rio Grande do Sul, entre 1992 e 1996. A amostragem do ácaro-vermelho orientou as liberações e as transferências de ácaros predadores, das estufas de criação e dos ramos provenientes da poda verde, para parcelas de alta incidência de ácaro-vermelho. A eficiência da estratégia de controle do ácaro-vermelho foi avaliada com o levantamento de ovos de inverno. No primeiro ano, a associação de acaricidas com ácaros predadores permitiu um reduzido número de ovos de inverno do ácaro-vermelho, em torno de 1,3 ovo por unidade de amostragem contra 59,8 ovos na testemunha. No segundo ano, 58% das macieiras não foram pulverizadas com acaricidas. Nos dois anos subseqüentes, o controle do ácaro-vermelho foi realizado exclusivamente com ácaros predadores. N. californicus passou o inverno nas ervas daninhas do pomar e migrou espontaneamente para a copa das macieiras nos anos subseqüentes a sua introdução.

CARBON BALANCE MODELING APPROACHES TO INTEGRATING THE EFFECTS OF FOLIAR PESTS, ENVIRONMENT, AND CULTURAL PRACTICES IN APPLES

A basic tenet of integrated pest management (IPM) is that many crop plants can tolerate some threshold level of leaf injury from foliar pests before the crop is affected. In practice, foliar pests are monitored, and pesticides are used only when pests reach a density that is thought to cause too much damage. Sound monitoring methods for many pests have been developed, but our understanding of plant responses to pests is weak. A problem is that pest thresholds are usually used independently for each pest, and do not take into account other factors that affect the crop. We propose that in apple trees; (1) foliar pest injury primarily reduces leaf carbohydrate production and effects of multiple pests are additive, and (2) the effects of foliar pests and other factors on the crop can be integrated by the balance of the tree's carbohydrate supply from the leaves to the demands for crop and tree growth. A dry matter production model developed by Lakso and Johnson in 1990 and subsequently expanded was tested as an integrator of the effects of pests, environmental variations, and cultural practices (initially crop load adjustments) on fruit development. The model simulated the measured effects of European red mites (Panonychus ulmi Koch) on apple fruit growth at different crop levels. Simulations suggest that a threshold response of fruit growth to foliar pests occurs with light crop load, but may not at high crop loads. This is in agreement with empirical studies of pest stress interactions with tree crop load. The model provides a plant-based integration of multiple foliar pests, environment and cultural practices of apples.

Integrated apple pest management in New York State using predatory mites and selective pesticides

A 3-year demonstration study was conducted in four western New York apple orchards to evaluate current approaches of sustainable pest management in representative commercial orchards. Pests that could be tolerated were regulated by natural antagonists, including predatory mites that were introduced to supplement endemic populations, while those with lower tolerance levels were managed with a schedule of selective pesticides, e.g., insect growth regulators and horticultural mineral oil. Pesticide application decisions (timing and materials) were made on the basis of current state extension guidelines, which involved a combination of protectant and threshold-based sprays determined through timely scouting and sampling procedures. Only non-toxic or minimally toxic pesticides to the principal mite and aphid predators were applied in the orchards. By the third season, effective conservation biological control of European red mite was achieved in all orchards, and fruit quality at harvest was equal or superior to that in comparison blocks managed using the growers’ conventional practices.

Characterization of resistance to clofentezine in populations of European red mite from orchards in Ontario.

Resistance to clofentezine was identified in four populations of the European red mite, Panonychus ulmi (Koch), from apple orchards in Ontario after ca. 5 years use. Resistance was expressed at high levels (> 2000-fold at the LC 50) to clofentezine in a population selected in the laboratory. This population was resistant to hexythiazox and to the organotin compounds cyhexatin and fenbutatin-oxide. However, a population selected with fenbutatin-oxide did not show cross resistance to clofentezine. The clofentezine-resistant population was not resistant to pyridaben, propargite or dicofol. The synergists, piperonyl butoxide and DEF, were ineffective in overcoming the resistance. Resistance to clofentezine declined rapidly in a mixed population (most resistance was lost in fewer than three generations). There were several fitness factors (fewer eggs/female, longer egg stage, longer development time for males) associated with the resistant population which may have contributed to the loss of resistant phenotypes. However, in a second test in which selection was removed from a resistant population, resistance persisted for at least 10 generations. Observations on field populations indicated that resistance persisted for at least two seasons.

Acaricide toxicity and resistance in larvae of different strains of Tetranychus urticae and Panonychus ulmi (Acari: Tetranychidae).

The toxicities of eight structurally different acaricidal compounds to six-legged larvae (first motile stage) of three laboratory strains of the two-spotted spider mite, Tetranychus uritcae, and the European red mite, Panonychus ulmi, were evaluated following spray application. The larvae of five field-derived strains of T urticae originating from France, Italy, Brazil, California and Florida were also tested for their susceptibilities to discriminating concentrations of several acaricides resulting in 95% mortality when applied to the organophosphate-resistant laboratory reference strain WI. The spray bioassay used was robust and gave repeatable results with a wide range of acaricidal compounds, irrespective of their mode of action (ovo-larvicides or primarily acting on motile life stages). Compounds tested were abamectin, azocyclotin, chlorpyrifos, clofentezine, deltamethrin, fenpyroximate, hexythiazox and pyridaben. Larvae of one of the laboratory strains of T urticae, AK, originally collected in Japan in 1996 and maintained without further selection pressure, exhibited 2000- and > 4000-fold resistance to the mitochondrial electron transport inhibitors pyridaben and fenpyroximate, respectively. Another strain of T urticae, AU, obtained from Australia and maintained in the laboratory under selection with hexythiazox and clofentezine since 1987 showed > 770- and > 1000-fold resistance to clofentezine and hexythiazox, respectively. The same resistance pattern was observed against larvae of a laboratory strain of P ulmi, CE, also selected with hexythiazox. Larvae of one of the field-derived strains of T urticae, BR, showed a lower susceptibility to a number of compounds, whilst the others were susceptible to all compounds except the organophosphates.

Effects of Microbial, Botanical, and Synthetic Insecticides on `Red Delicious' Apple Arthropods in Arkansas

Insecticides were compared for control of codling moth (Cydia pomonella) and oriental fruit moth (Grapholita molesta), and effects on european red mites (Panonychus ulmi) and predatory mites (Neoseiulus fallacis) in `Red Delicious' apple trees (Malus ×domestica). Ten days after treatment with azinphosmethyl, celerylooper (Anagrapha falcifera) nuclear polyhedrosis virus, rotenone-pyrethrin, or codling moth granulosis virus, fruit damage by larval codling moth and oriental fruit moth was significantly less than trees treated with Bacillus thuringiensis var. kurstaki or water (control). Trees treated with azinphosmethyl or celery looper nuclear polyhedrosis virus had fewer damaged fruit where larvae exited than did other treatments. By 21 days after the last treatment, all treatments had significantly more wormy or damaged fruit than did azinphosmethyl. At 10 days after treatment, the two viruses were more deleterious to codling moth than to oriental fruit moth causing a &lt;1:3 ratio of these larvae compared to &gt;3:1 ratio for the other treatments. On 16 June, 100 predatory mites were released onto the trunk of each tree. The minimum ratio of predatory mites to european red mites (&gt;1:10) that favors biological control of european red mites occurred in all treatments by 14 July, except those treated with azinphosmethyl or rotenone-pyrethrin that had significantly more cumulative mite days of european red mites than the other treatments. The use of azinphosmethyl delayed biological control of the european red mites until 27 July whereas rotenone-pyrethrin treatment never attained biological control of the mites.

Evaluation of Acaricides against the European Red Mite, Panonychus ulmi, Collected from Apple Orchards in Aomori Prefecture

Evaluation of Acaricides against the European Red Mite, <I>Panonychus ulmi</I>, Collected from Apple Orchards in Aomori Prefecture

Sublethal effects of esfenvalerate residues on pyrethroid resistant Typhlodromus pyri (Acari: Phytoseiidae) and its prey Panonychus ulmi and Tetranychus urticae (Acari: Tetranychidae).

The effect of residues of esfenvalerate on oviposition of the resistant strain of the predatory mite Typhlodromus pyri and its main prey, European red mite Panonychus ulmi and two-spotted spider mite Tetranychus urticae, were investigated. T. pyri showed a significant linear reduction in oviposition after 24 h in the presence of increasing levels of esfenvalerate residue applied at the field rate. Furthermore, when given a choice, T. pyri preferred to lay eggs on residue-free surfaces. Of the two prey species, only P. ulmi showed significant avoidance of increasing levels of residues of the field rate concentration of esfenvalerate, as measured by runoff mortality, however both P. ulmi and T urticae, when given a choice, showed a preference for esfenvalerate-free surfaces. As with the predatory mite T. pyri, both prey species showed a significant linear reduction of oviposition with increasing esfenvalerate residues and a preference to lay eggs on esfenvalerate-free surfaces. Esfenvalerate residues as high as 15X field rate were not repellent to pyrethroid-resistant T. pyri. The possible effects of these sublethal effects on predator-prey dynamics and implications for integrated mite control programmes in apple orchards are discussed.

Threshold Temperature for Post-Diapause Development and Degree-Days to Hatching of Winter Eggs of the European Red Mite (Acari: Tetranychidae) in Northern Greece

The threshold temperature for postdiapause development in overwintering eggs of the European red mite, Panonychus ulmi (Koch), was determined after exposing the eggs to various constant temperatures (5, 10, 15, 20, and 258C) in the laboratory. The mean number of days to 50% hatch in each temperature was .120, 44.5, 22.0, 14.5, and 8.1 d, respectively. From the regression of postdiapause developmental rate to temperature, it was estimated that 50% of egg hatch coincides with the accumulation of 154.6 degree-days (DD) above the threshold of 7.48C. In the field (1991 and 1993—1996), 50% egg hatch occurred from the end of March to 20 April after the accumulation of a mean sum of 129.4 6 4.5 DD above the threshold of 7.48C from 10 February onward. The starting date of 10 February for heat accumulation was chosen because earlier experiments had shown that diapause is terminated in 50% of the eggs in the first half of February. Using the theoretical sum of 154.6 DD, the predicted dates for 50% egg hatch deviated from field observations by an average of 3.7 6 0.5 d over the 5 yr of experiments.

Supercooling Capacity and Survival of Low Temperatures by a Pyrethroid-Resistant Strain ofTyphlodromus pyri(Acari: Phytoseiidae)

An organophosphate/pyrethroid resistant strain of the phytoseiid mite Typhlodromus pyri Scheuten was imported from New Zealand in 1988 for use in biological control of European red mite, Panonychus ulmi (Koch), and apple rust mite, Aculus schlechtendali (Nalepa), in Nova Scotia. To better understand the overwintering strategy of T. pyri and the likelihood the New Zealand strain would withstand winter conditions in Canada, we measured supercooling points and mortality of diapausing females held at subzero temperatures. Mites in quartz crucibles were placed in the liquid nitrogen-cooled stage of a cryostage microscope, and temperature was lowered 1°C/min until the mites froze, as indicated by an instantaneous darkening of their body contents. Supercooling points of the New Zealand strain averaged −18.2°C for July to September, were −23.2°C in October, and averaged −28.2°C in the colder months from November to March. The mean supercooling points for December 1994 did not differ from the mean for the native Nova Scotian strain. However, the mean supercooling point of the New Zealand strain for March 1995 was higher than the means for the native strain and for a T. pyri strain that was imported from Geneva, NY. New Zealand strain T. pyri taken from cloth bands affixed to orchard trees were placed on apple leaves in plastic vials and exposed to low temperatures for various periods of exposure. At −5°C, mortality at 24 h was less for mites collected in February than for those collected in November (6% versus 44%) but at −10°C trends were similar, reaching 100% by 24 h in both trials. For the February trial, a logistic function with a coefficient for the product of time and temperature explained 61% of the variation in mortality. If these results are applied to populations in Nova Scotian orchards, where winter temperatures of −10°C are common, one would predict complete annihilation of the New Zealand strain. However, populations of the New Zealand strain, first released in orchards in 1988, have survived every winter since that date and have proven effective in biological control of European red mite and apple rust mite. Possible reasons for survival and increase of populations of this exotic strain of T. pyri, despite apparent susceptibility to cold-induced mortality, are discussed.