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. This revised version was published online in July 2006 with corrections to the Cover Date.     

Clofentezine and hexythiazox resistance in Tetranychus urticae Koch in Australia

Clofentezine resistance in T. urticae was first confirmed in Australia in 1987 after Queensland glasshouse roses had been exposed to 40 applications of clofentezine over a 10 month period. Clofentezine resistance in this strain was extremely high (>2.500x) and conferred high level cross-resistance to the chemically unrelated compound hexythiazox. Clofentezine resistance in T. urticae was detected in pome fruit orchards in the Goulburn Valley, Victoria in 1988 and caused field control failure after 5–6 sprays. Resistance was subsequently detected in Adelaide during 1988 and the Bathurst Orange region, NSW in 1989. Clofentezine and hexythiazox resistance appears particularly stable making it difficult to manage.This work contributes in part for the fulfilment of the requirements of the degree of PhD. at the University of Sydney.     

Baseline Susceptibility and Cross Resistances of Some New Acaricides in the European Red Mite, Panonychus ulmi*

We have developed baseline susceptibility values for four new acaricides: bifenazate, acequinocyl, spirodiclofen and etoxazole for eggs or adult females of a susceptible laboratory population of Panonychus ulmi (Koch) (Acari: Tetranychidae). Further, we have tested diagnostic concentrations of each acaricide against populations resistant to organochlorine, organotin or IGR-type acaricides. Resistance to etoxazole (ca. 4-fold) was identified in populations resistant to the IGRs clofentezine and hexythiazox. *The Canadian Crown’s right to retain a non-exclusive, royalty-free licence in and to any copyright is acknowledged.     

Clofentezine and fenbutatin oxide resistance in the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) from deciduous fruit tree orchards in Western Australia

The resistance status of Tetranychus urticae Koch to the miticides clofentezine and fenbutatin oxide was investigated in deciduous fruit tree orchards in Western Australia. Mites were collected from 30 orchards across three fruit growing regions and subjected to discriminating–dose assays. There was a significant relationship between clofentezine (=;0.64) and fenbutatin oxide (V=;0.44) use and the proportion of resistant mites in each sample. Improved clofentezine models were obtained when the Perth Hills region (V=;0.90) was modelled separately from Donnybrook and Manjimup (V=;0.80). Clofentezine could be expected to fail in the latter regions after four sprays and in the former region after only one spray. The relatively low pest status of T. urticae in Western Australia did not delay the clofentezine resistance. For any given number of spray applications the response of T. urticae to fenbutatin oxide was more variable than it was to clofentezine.     

Biological activity of clofentezine against egg and motile stages of tetranychid mites

The activity of clofentezine (3,6-bis(2-chlorophenyl)-1,2,4,5-tetrazine) against eggs, immature and adult stages of tetranychid mites has been examined under laboratory and field conditions. The compound has been shown to be active against the eggs and immature stages but does not kill the adults. Eggs become less susceptible to the compound as they mature, and this has been demonstrated both on laboratory cultures ofTetranychus and on the overwintering eggs ofPanonychus ulmi. Control of infestations ofP. ulmi on deciduous fruit is the combined result of direct ovicidal activity and residual activity against the early motile stages.     

Integrated control of apple pests in New Zealand 8. Commercial assessment of an integrated control programme against European red mite using an insecticide-resistant predator

Abstract

An integrated control programme against Panonychus ulmi (Koch) is described which uses a phytoseiid predator, Typhlodromus pyri Scheuten, known to be common in commercial orchards and to be highly resistant to azinphos-methyl. The programme was tested in commercial export orchards in Nelson in the 1975–76 and 1976–77 seasons. By regular monitoring of the levels and ratios of T. pyri and P. ulmi the application of miticides was confined to occasions when specified population thresholds were exceeded. At these times a selective miticide, cyhexatin, was applied to improve predator: prey ratios. No other changes were made to normal commercial spray practices for pest and disease control in the monitored orchards. The integrated mite control programme saved an average of N.Z.$75–80/ha in spray materials each season. No fruits were rejected from export grade because of contamination with mite eggs. Procedures for the wider implementation of integrated mite control in commercial orchards are described and the response of growers is noted. The role of selective miticides in the integrated control of P. ulmi is discussed.     

Codling moth granulosis virus: effects of its use on some other orchard arthropods

In four field trials from 1978 to 1980, sprays of codling moth granulosis virus (CpGV) plus 1·0% skimmed milk powder did not significantly affect damage to fruit by leaf rollers (tortrix moths). In laboratory tests, survival of larvae of the leaf roller Archips podana fed on leaves sprayed with CpGV plus milk was unaffected and they grew faster than on unsprayed leaves, because of the milk deposits. This might increase damage by A. podana if CpGV plus milk were applied during the feeding period of this species. In one field trial an unusual infestation of fruit by larvae of pith moth Blastodacna atra was not affected by CpGV. Azinphos-methyl significantly reduced damage by B. atru and, in one field trial where sprays were correctly timed, that by leaf rollers. CpGV had no consistently significant effects on numbers of fruit tree red spider mite Panonychus ulmi or its predators, whereas azinphos-methyl induced outbreaks of P. ulmi by killing its predators.     

Feeding preference of Zetzellia mali: does absolute or relative abundance of prey matter more?

The importance of the acarine predator, Zetzellia mali, in the control of phytophagous mites in apple orchards is not well understood. Zetzellia mali tends to prefer the eriophyid, Aculus schlechtendali, over the economically more significant tetranychid, Panonychus ulmi, but quite a wide range of preference values have been reported in the literature. In sets of laboratory choice trials, we determined that prey preference of this predator varies with the relative but not absolute density of its prey. We attempt to explain these results in terms of behavioural mechanisms and discuss the potential implications of our results for the effectiveness of Z. mali in the biological control of phytophagous mites in apple orchards.     

Variation in the intensity of diapause in winter eggs of fruit tree red spider mite, Panonychus ultni

Winter eggs of Panonychus ulmi from six orchards in Kent showed a range of 3 weeks in the dates of 50 % hatch at field temperatures. From the effects of the duration and temperature of chilling, and the temperature of incubation, it was concluded that samples varied in their chilling requirement, and not in threshold temperatures for development. Diapause was terminated most effectively by chilling initially at o ^oC (for late-hatching strains) or 5 followed by 9 for the last month or two. Heritable variation in diapause intensity is discussed in relation to heat sums and the forecasting of hatch, and to phenology.     

High resolution genetic mapping uncovers chitin synthase-1 as the target-site of the structurally diverse mite growth inhibitors clofentezine,hexythiazox and etoxazole in Tetranychus urticae

The acaricides clofentezine, hexythiazox and etoxazole are commonly referred to as ‘mite growth inhibitors’, and clofentezine and hexythiazox have been used successfully for the integrated control of plant mite pests for decades. Although they are still important today, their mode of action has remained elusive. Recently, a mutation in chitin synthase 1 (CHS1) was linked to etoxazole resistance. In this study, we identified and investigated a Tetranychus urticae strain (HexR) harboring recessive, monogenic resistance to each of hexythiazox, clofentezine, and etoxazole. To elucidate if there is a common genetic basis for the observed cross-resistance, we adapted a previously developed bulk segregant analysis method to map with high resolution a single, shared resistance locus for all three compounds. This finding indicates that the underlying molecular basis for resistance to all three compounds is identical. This locus is centered on the CHS1 gene, and as supported by additional genetic and biochemical studies, a non-synonymous variant (I1017F) in CHS1 associates with resistance to each of the tested acaricides in HexR. Our findings thus demonstrate a shared molecular mode of action for the chemically diverse mite growth inhibitors clofentezine, hexythiazox and etoxazole as inhibitors of an essential, non-catalytic activity of CHS1. Given the previously documented cross-resistance between clofentezine, hexythiazox and the benzyolphenylurea (BPU) compounds flufenoxuron and cycloxuron, CHS1 should be also considered as a potential target-site of insecticidal BPUs.     

Aerial dispersal of European red mites (Acari: Tetranychidae) in commercial apple orchards

Aerial dispersal of European red mite, Panonychus ulmi (Koch), in commercial apple orchards was estimated by trapping windborne mites. Studies were conducted at four orchards in eastern New York during 1989 and 1990 and at three orchards in western New York during 1989. In each orchard mites were trapped in three locations; the interior of the orchard, at the border of the orchard and in a field or woodlot beyond the orchard. Large numbers of mites were captured, even when the numbers of mites on apple foliage were well below levels where mite injury to leaves was visible (less than five per leaf). The log numbers of mites trapped were linearly related to the log density of mites on leaves and this relationship was consistent for each year and region the study was conducted. The trap captures among the three locations in and outside an orchard were highly correlated. The implications these findings may have on metapopulation dynamics and resistance to acaricide dynamics are discussed.     

Historical tests of the toxicity of pesticides to Typhlodromus pyri (Acari: Phytoseiidae) and their relevance to current pest management in New Zealand apple orchards 2. Short-term field tests

A two-part review is presented relating historical tests of the toxicity of pesticides to Typhlodromus pyri and their relevance to modern pest management in New Zealand pome-fruit orchards. Over the past 30 years, the initial need for T. pyri to be resistant to broad-spectrum pesticides has substantially declined as a growing array of new selective chemicals have come into use. In Part 2, a short-term field test is described for determining the toxicity of single applications of pesticides at recommended rates to European red mite (ERM), Panonychus ulmi, and its predator, an organophosphate (OP)-resistant strain of T. pyri on apples in New Zealand. For each pesticide, changes in mite density were measured from pre-treatment to 2, 7 and up to 25 days post-treatment compared with a water-sprayed control. Density was recorded and analysed for live adult and immature ERM, and live and dead eggs, larvae, nymphs and adults of T. pyri. Fifteen acaricides, 17 fungicides and 17 insecticides were evaluated. Chemicals more toxic to T. pyri than ERM were aminocarb, amitraz, binapacryl, chlordimeform, etrimphos, fenvalerate + azinphos-methyl, mancozeb + dinocap, methidathion, methiocarb, omethoate, oxamyl, pirimiphos-methyl and pyrazophos. Chemicals equally or less toxic to T. pyri than to ERM were acequinocyl, azocyclotin, benzoximate, bromopropylate, chlorpyrifos, clofentezine, cycloprate, cyhexatin, dinocap, mineral oil, propargite, triazophos and vamidothion. The remaining 23 chemicals (primarily fungicides and OP insecticides) had slight or no toxicity to ERM and T.pyri. The short-term field tests provided a useful guide to the long-term effects on ERM and T. pyri populations of almost all the pesticides. However, the potential disruptive effect of pyrazophos was not found in long-term field trials, and conversely, the apparently harmless dithiocarbamate fungicides were later shown to be highly disruptive when repeatedly sprayed, as in commercial practice. Most of the chemicals tested are no longer used in commercial pome-fruit orchards in New Zealand, all of which now practise integrated fruit production or organic fruit production based on selective pest management methods. The tested pesticides of continuing importance are identified and discussed with special emphasis on the current need to retest for dithiocarbamate resistance in T. pyri, some populations of which have been exposed to these compounds for up to 40 years. This and the changes in pesticide use in New Zealand are paralleled by similar developments in most pome-fruit growing areas of the world.     

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 24h 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.     

Assessment of Amblyseius fallacis (Acari: Phytoseiidae) for biological control of tetranychid mites in an Ontario peach orchard

We introduced a mass-reared pyrethroid-resistant strain of the predatory phytoseiid mite Amblyseius fallacis (Garman) into an Ontario peach orchard in an attempt to control populations of the phytophagous mites Panonychus ulmi Koch and Tetranychus urticae Koch (Acari: Tetranychidae). Releases of 1,000 and 2,000 mites per tree were made, at three different times. The release of 2,000 mites per tree in June and in July resulted in significantly higher phytoseiid densities than was observed on control trees. However, densities of P. ulmi or T. urticae were not significantly affected by any release rate or by timing. The release of 1,000 A. fallacis per tree, or of any density in August, did not significantly increase phytoseiid abundance. In the following year, population dynamics of both phytoseiid and phytophagous mites were not significantly affected by the previous year's release. Amblyseius fallacis can be a useful predator in some fruit orchards. However, further research is necessary into the timing and rate of release, modified spray programmes, and with different crops, in order to clarify the role of this species for biological control in Ontario peach orchards.     

Influence of prey on developmental performance, reproduction and prey consumption of Neoseiulus californicus (Acari: Phytoseiidae)

The Spical strain of the predatory mite Neoseiulus californicus (McGregor) is used as a biological control agent, but little is known about its preferred prey and host plants in Japan. Here we studied the development, reproduction and prey consumption of the Spical strain when fed on eggs of five different spider mite species deposited on both their laboratory-rearing plant and cherry, on which all five spider mite species developed well. The developmental periods of immature N. californicus females and males were significantly affected by the prey species they fed on, but not by the plants. No difference was found between males and females. The developmental period was shorter on eggs of two Tetranychus species than on eggs of Panonychus ulmi. Immature females had a higher predation rate than immature males. Preoviposition period, oviposition period and the number of eggs laid per female were not significantly affected by either the plants or the type of prey eggs. The postoviposition period and total adult longevity were shorter on eggs of P. ulmi than of the other four prey species, but there was no effect of plant substrate. The postoviposition period of the Spical strain was much longer than that of other N. californicus strains or other predatory mite species: the postoviposition period of the Spical strain was more than three times longer than the oviposition period, accounting for more than 75% of the total adult longevity. This suggests that the females need multiple mating to reach full egg load, but this remains to be tested. Total consumption by N. californicus adults was lower for eggs of P. ulmi than for eggs of the other four species, apparently because of the shorter postoviposition period when fed on eggs of P. ulmi. The intrinsic rates of natural increase (r _m) on the rearing plant did not differ among prey species, whereas those on cherry were significantly different: the value was higher on Tetranychus urticae eggs than on eggs of other species. Only when N. californicus fed on T. urticae eggs, the r _m-values were significantly different between the rearing plant and cherry (higher on cherry). Thus, the Spical strain of N. californicus could feed on eggs of all five spider mite species, deposited on a variety of plants with similar r _m-values, suggesting that it could be successfully used to control spider mites in orchards and various crop fields of Japan.     

Analysis of prey preference in phytoseiid mites by using an olfactometer,predation models and electrophoresis

Prey preference of three phytoseiid species,Typhlodromus pyri Scheuten,Amblyseius potentillae (Garman) andA. finlandicus (Oudemans) which occur in Dutch orchards, was analysed with respect to two economically important phytophagous mites, the European red spider mitePanonychus ulmi (Koch), and the apple rust miteAculus schlechtendali (Nalepa). Two types of laboratory experiments were carried out: (1) olfactometer tests to study the response when volatile kairomones of both prey species were offered simultaneously; and (2) predation tests in mixtures of the two prey species and comparison with calculated predation rates, using a model provided with parameters estimated from experiments with each prey species alone. In addition, the diet of field-collected predators was analysed using electrophoresis. For each predator species the results of the different tests were consistent, in thatT. pyri andA. potentillae preferredP. ulmi overA. schlechtendali, whereasA. finlandicus preferredA. schlechtendali overP. ulmi.     

Distribution of Streptomycin Resistant Strains of Erwinia amylovora in Egypt during 1988

A survey of the occurrence of strains of Erwinia amylovora resistant to streptomycin in certain Egyptian pear orchards was earned out during April and May 1988. Twenty-two isolates out of 604 isolates collected from 11 orchards showed resistance to streptomycin. All the streptomycin resistant (Str^r) strains isolated in the present work were resistant to high levels of streptomycin with minimal inhibitory concentrations ranging from 1000 to 3000 μg/ml. The occurrence of Str^r strains in Egypt is still limited and the population of resistant strains was at relatively low level. However, such occurrence of E. amylovora with resistance to streptomycin is a potentially serious situation.     

Developmental success and reproductive incompatibility among populations of the European red mite,Panonychus ulmi (Acari: Tetranychidae)

Developmental success on 47 species of plant and reproductive compatibility were studied for four strains of the European red mite,Panonychus ulmi (Koch), collected from dwarf bamboo, elm and apple trees. The host range was variable in those strains and there was no plant species on which all four strains were able to reach maturity.Intra-populational crosses in the dwarf-bamboo strain and the two apple strains of mites, as well as crosses between the two apple strains, gave both female and male progeny. Inter-populational crosses between the dwarf-bamboo and apple strains produced only male progeny, as in the case where females of each strain were kept virgin, indicating that these two were reproductively incompatible and had an arrhenotokous reproductive system. When females of the elm strain were crossed with males of the elm, dwarf-bamboo or apple strain, no males were produced, as in the case for virgin females of the elm strain which had a thelytokous reproductive system. It is thus concluded that the strains derived from different host species were reproductively incompatible with one another.     

Hatching of the winter eggs of the fruit-tree red spider mite (Panonychus ulmi (Koch))

Observations on the hatching of winter eggs of Panonychus ulmi (Koch) from apple orchards in England over the 5 years 1962-6 are described. Differences of 2–3 weeks between orchards in the date at which 50% hatch was reached were quite common and this was out of step with petal fall in the majority of orchards. There was a continuous range between early and late hatching populations and a tendency for the populations to hatch in the same order every year. In 1966 populations on Cox's Orange Pippin hatched earlier than those on Worcester Pearmain but the difference was unlikely to be of practical importance. Neither recording accumulated day degrees for populations hatched out-of-doors nor hatching in an incubator after chilling was considered to give a sufficiently reliable forecast of 50% hatch but observations in 1966 suggested that this might be predicted from the total eggs hatched in an incubator expressed as a percentage of total healthy eggs.