Genetics of resistance to parathion and demeton-S-methyl inTetranychus urticae Koch (Acarina)

Out of a strain, resistant to organophosphorous insecticides, a dominant factor has been isolated by repeated backcrossings with a susceptible strain under selection pressure. This factor, calledOP, gives a large resistance to parathion and a much smaller resistance to demeton-S-methyl. Modifiers toOP increase the demeton-S-methyl resistance to a high level. Evidence is given that the resistance to the mentioned insecticides of the well known Leverkusen resistant strain has a similar inheritance.Abbreviations used OP organophosphorus - R resistant - S susceptible     

Organophosphorus resistance in Aphis gossypii (Hemiptera: Aphididae) on chrysanthemum in the UK

The FAO standard dip-test was used to test resistance of glasshouse populations of Aphis gossypii from chrysanthemums to the organophosphorus insecticides heptenophos and diazinon. Compared with a susceptible population collected in 1981, resistance factors to diazinon of up to 538 were found in populations collected after 1984. Resistance to heptenophos was less than that to diazinon but some populations collected after 1984 were 34 times as resistant as the susceptible strain. Possible reasons for the sudden increase in resistance in A. gossypii and current prospects for control of resistant populations are discussed.     

Susceptibility of two bulb mites,Rhizoglyphus robini andR. setosus (Acarina: Acaridae), to some acaricides and insecticides

The susceptibility of two field-collected bulb mites,Rhizoglyphus robini andR. setosus to some organophosphorus, carbamates, pyrethroids and other compounds with acaricidal activity was evaluated. In general,R. setosus was more tolerant to these compounds thanR. robini. Among the 58 commercially formulated compounds tested,R. robini was susceptible to chlorpyrifos 22.5% EC, EPN 45% EC, ethion 46.5% EC, fenitrothion 50% EC, methamidophos 50% S, methidathion 40% EC, mevinphos 25.3% EC, omethoate 25% EC, parathion 47% EC, phosmet 50% WP, profenofos 43% EC, prothiophos 50% EC, benfuracarb 20% EC, carbofuran 40.64% F, carbosulfan 48.34% EC, formetanate 50% SP, methiocarb 50% WP, azocyclotin 25% WP and cyhexatin 50% WP. Demeton-S-methyl 25% EC, methidathion 40% EC, phosmet 50% WP, profenofos 43% EC, prothiophos 50% EC, azocyclotin 25% WP and cyhexatin 50% WP gave good toxicity toR. setosus. Both species were tolerant to avermectin 1.8% EC and some newly developed synthetic pyrethroids, which were proved to have acaricidal activity. In addition, two bioassay methods were also evaluated for these two mites.Contribution No. 1354 from Taiwan Agricultural Research Institute     

Speed of action and in vitro efficacy of spinosad against sheep body lice, Bovicola ovis (Schrank) (Phthiraptera: Trichodectidae), resistant to pyrethroid, organophosphate or insect growth regulator insecticides

Abstract  Results of laboratory bioassays indicated that spinosad was equally effective against sheep lice populations that were susceptible to insecticides or resistant to pyrethroid, organophosphorus or insect growth regulator (IGR) insecticides. Spinosad had similar toxicity against susceptible strains of lice to that previously reported for diazinon, but lower toxicity than cypermethrin. Lethal concentrations of spinosad and diazinon caused knock down of lice within 6 h of exposure and death within 24 h. Prior to the current phasing out of diazinon as a sheep dip, most wool producers, needing to control pyrethroid- or IGR-resistant lice infestations in short-wool, would have chosen to use diazinon. Our results suggest that spinosad is an effective alternative for treatment of lice resistant to other chemical groups.     

Genotypic variation in susceptibility of honey bees (Apis mellifera) to infestation by tracheal mites (Acarapis woodi)

Two-way selection for lines of honey bees (Apis mellifera L.) susceptible and resistant to infestation by tracheal mites (Acarapis woodi Rennie) was conducted for two generations. Individuals of the susceptible line were 1.4 and 2.4 times more likely to become infested by female mites after the first and second generations, respectively. These results demonstrate that genotypic variability exsts within North American populations and that selection for resistance is feasible. The mechanisms of resistance are unknown.     

Identification and characterization of chlorpyrifos-methyl and 3,5,6-trichloro-2-pyridinol degrading Burkholderia sp. strain KR100

A chlorpyrifos-methyl (CM) degrading bacterium (designated strain KR100) was isolated from a Korean rice paddy soil and was further tested for its sensitivity against eight commercial antibiotics. Based on morphological, biochemical, and molecular characteristics, this bacterium showed greatest similarity to members of the order Burkholderiales and was shown to be most closely related to members of the Burkholderia cepacia group. Strain KR100 hydrolyzed CM to 3,5,6-trichloro-2-pyridinol (TCP) and utilized TCP as the sole source of carbon for its growth. The isolate was also able to degrade chlorpyrifos, dimethoate, fenitrothion, malathion, and monocrotophos at 300 μg/ml but diazinon, dicrotophos, parathion, and parathion-methyl at 100 μg/ml. The ability to degrade CM was found to be encoded on a single plasmid of ~50 kb, pKR1. Genes encoding resistance to amphotericin B, polymixin B sulfate, and tetracycline were also located on the plasmid. This bacterium merits further study as a potential biological agent for the remediation of soil, water, or crop contaminated with organophosphorus compounds because of its greater biodegradation activity and its broad specificity against a range of organophosphorus insecticides.     

Differences in Biological Characteristics in Organophosphorus-Resistant Strains of the Phytoseiid Mite Typhlodromus Pyri

Strains of Typhlodromus pyri were collected from orchards in SW England, where populations differed in their response to organophosphorus insecticides compared with strains collected in the SE. Biological characteristics of these strains were compared with those in OP-resistant strains collected from the SE and OP- susceptible strains. There were significant differences in size of eggs and adult mites from the different strains, but these differences did not appear to be related to resistance status of the mites. Female OP-susceptible mites had a longer development time than other strains. Over all strains total development time for female mites was 0.8 day less than for males. There were significant differences between strains for pre-oviposition period, but not oviposition or post-oviposition periods. There were significant differences in total numbers of eggs produced between strains, with a standard OP-resistant strain producing the most and an OP-susceptible strain the fewest eggs. There were significant differences in male longevity between strains, but this did not appear to be related to resistance status. This study highlights the fact that strains may differ in biological characteristics that contribute to fitness regardless of their pesticide resistance status.     

Stability of insecticide resistance in Frankliniella occidentalis to acrinathrin, formetanate and methiocarb

1 The stability of the resistance in the Western Flower Thrips, Frankliniella occidentalis (Pergande) to selective insecticides (acrinathrin, formetanate and methiocarb) was studied in both laboratory and field conditions.
2 In laboratory strains reared over a sufficient number of generations in insecticide free-conditions, levels of resistance were stable.
3 Laboratory strains selected for resistance showed moderate to very high levels of resistance. In the strain ACR9, very highly resistant to acrinathrin [resistance factor (RF) > 1000-fold], resistance was maintained with little change after 5 and 8 months without acrinathrin exposure. In the MET9 strain, resistance to methiocarb (RF = 40) was maintained after 5 months without selection pressure (RF = 33). However, 3 months later, there was a significant increase in the susceptibility to this insecticide (RF = 10). The formetanate resistance in the FOR7 strain showed a no significant decline during the 8 months without selection (from RF = 31 to RF = 17).
4 The field-collected strains from sweet pepper greenhouses (PTF4, PP2 and PM5) showed a marked fall in the LC₅₀ to acrinathrin and methiocarb, and a slight decrease to formetanate, after being reared in the laboratory in the absence of selection pressure for 8 months.
5 In greenhouses, a significant fall in resistance to the selected insecticides was produced when insecticide pressure was withdrawn, at the end of the season, probably caused by the immigration of thrips from nearby crops or weeds, and the dilution of resistance through interbreeding with susceptible individuals.
6 Factors influencing stability or reversion of insecticide resistance are discussed.     

Susceptibility and detoxifying enzyme activity in two spider mite species (Acari: Tetranychidae) after selection with three insecticides

Changes in the susceptibility and detoxifying enzyme activity were measured in laboratory strains of Banks grass mite, Oligonychus pratensis (Banks), and twospotted spider mite, Tetranychus urticae Koch, that were repeatedly exposed to three insecticides. Three strains of each mite species were exposed to one of two pyrethroids, bifenthrin, and lambda-cyhalothrin, or an organophosphate, dimethoate, for 10 selection cycles at the LC60 for each insecticide. A reference or nonselected strain of each mite species was not exposed to insecticides. After 10 cycles of exposure, susceptibility to the corresponding insecticides, bifenthrin, lambda-cyhalothrin, and dimethoate, decreased 4.5-, 5.9-, and 289.2-fold, respectively, relative to the reference strain in the respective O. pratensis strains, and 14.8-, 5.7-, and 104.7-fold, respectively, relative to the reference strain in the respective T. urticae strains. In the bifenthrin-exposed O. pratensis strain, there was a 88.9-fold cross-resistance to dimethoate. In the dimethoate-exposed T. urticae strain, there was a 15.9-fold cross-resistance to bifenthrin. These results suggest that there may be cross-resistance between dimethoate and bifenthrin. The reduced susceptibility to dimethoate remained stable for three months in the absence of selection pressure in both mites. The decrease in susceptibility in the O. pratensis strains exposed to bifenthrin, lambda-cyhalothrin, and dimethoate was associated with a 4.7-, 3.0-, and 3.6-fold increase in general esterase activity, respectively. The decrease in susceptibility in the T. urticae strains exposed to bifenthrin and lambda-cyhalothrin was associated with a 1.3- and 1.1-fold increase in general esterase activity, respectively. The mean general esterase activity was significantly higher in the pyrethroid-exposed O. pratensis and T. urticae strains than in the nonselected strain. There was no significant increase in esterase activity in the dimethoate-exposed T. urticae strain. The decrease in susceptibility to insecticides was also associated with reduced glutathione S-transferase 1-chloro-2, 4-dinitrobenzene conjugation activity, but this did not appear to be related to changes in insecticide susceptibility. These results suggest that in these mites, the general esterases may play a role in conferring resistance to pyrethroids. However, some other untested mechanism, such as target site insensitivity, must be involved in conferring dimethoate resistance.     

Development and stability of insecticide resistance in the leafminer Liriomyza trifolii (Diptera: Agromyzidae) to cyromazine, abamectin, and spinosad

Three populations of the leafminer, Liriomyza trifolii (Burgess), were collected from commercial ornamental production greenhouses in the United States and tested for susceptibility to three commercial insecticides. A leaf dip bioassay of leaves containing young (1-2-d-old) larvae was used. Based on larval mortality and compared with a susceptible laboratory reference colony, the three strains varied in spectrum and level of resistance to the insecticides. CA-1, collected from Gerbera daisy, was moderately resistant to cyromazine (18.1-fold) and abamectin (22.0-fold), but highly resistant to spinosad (> 188-fold). CA-2, collected from chrysanthemums, was not resistant to abamectin, had a low level of resistance to cyromazine (8.2-fold), but was extremely resistant to spinosad (1,192-fold). GA-1, collected from chrysanthemums, had very low levels of resistance to cyromazine (5.4-fold) and spinosad (1.9-fold) but was moderately resistant to abamectin (30.6-fold). When reared in the absence of insecticide selection pressure, all three strains reverted to approximately the level of the reference strain. The CA-1 strain reverted in nine generations to cyromazine; however, the lowest levels of abamectin and spinosad resistance reverted to was 3.1-fold at F8 and 3.2 at the F10, respectively. The CA-2 strain reverted in five generations to both cyromazine and spinosad. GA-1 reverted in five generations to abamectin. Based on the results, resistance to these three insecticides was unstable. Additionally, there was no cross-resistance among these three insecticides.     

Organophosphorus insecticides synergize pyrethroids in the resistant strain of cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) from West Africa

Helicoverpa armigera (Hübner) populations from West Africa recently developed resistance to pyrethroid insecticides through enhanced metabolism by mixed-function oxidases. The combination index method was used to study the synergism of pyrethroids by organophosphorus insecticides. Several mixtures of insecticides currently registered to control cotton pest complex in West Africa were tested, including: cypermethrin/ethion, cypermethrin/profenofos, deltamethrin/ triazophos, deltamethrin/chlorpyriphos, cyfluthrin/chlorpyriphos, and betacyfluthrin/chlorpyriphos. In the resistant strain, the organophosphorus insecticides significantly increased the toxicity of pyrethroids suppressing the resistance effect, either by additive or synergistic effects. Significant synergism was shown for the following mixtures: cypermethrin/ethion, deltamethrin/triazophos, and deltamethrin/chlorpyriphos. The use of synergism from these insecticide mixtures should prove to be an additional tool in the overall resistance management strategy because the pyrethroid resistance in H. armigera from West Africa is not yet stable, decreasing between cotton seasons and increasing with treatments. In absence of selection, the susceptibility of H. armigera to insecticides should be restored.     

Studies on the resistance to various insecticides of a house fly strain (Diptera: Muscidae) selected with azamethiphos.

A colony of azamethiphos-resistant house flies, Musca domestica (L.), was obtained from Denmark and further selected in the laboratory with azamethiphos for four generations. LD50s for various insecticides were determined and compared with those of a susceptible house fly strain. The selected flies showed cross-resistance to all insecticides evaluated. The flies were highly resistant to most organophosphorus, carbamate, and chlorinated hydrocarbon insecticides except prothiophos, p,p'-DDT, and the pyrethroids. We conclude that the main mechanisms responsible for resistance are presumed to be factors other than acetylcholinesterase sensitivity and nerve sensitivity due to knockdown resistance.     

Accelerated Mineralization of Two Organophosphate Insecticides in the Rhizosphere

Numerous xenobiotic compounds, including the organophosphate insecticides O, O-diethyl-O-(2-isopropyl-6-methyl-4-pyrimidinyl) phosphorothioate (diazinon) and O, O-diethyl-O-p-nitrophenyl phosphorothioate (parathion), appear to be degraded in the soil environment by an initial cometabolic attack. Comparing the mineralization rates of radiolabeled diazinon and parathion in root-free and in rhizosphere soil, we tested our hypothesis that, because of the presence of root exudates, the rhizosphere is an especially favorable environment for such co-metabolic transformations. The insecticides were added individually at 5 μg/g to sealed flasks containing either soil permeated by the root system of a bush bean plant or identical soil without roots. Periodically, the flask atmospheres were flushed through traps and the evolved ¹⁴CO₂ was quantitated. Bush bean plant roots without associated rhizosphere microorganisms failed to produce a significant amount of ¹⁴CO₂. During 1 month of incubation, rhizosphere flasks mineralized 12.9 and 17.9% of the added diazinon and parathion radiocarbon, respectively, compared to 5.0 and 7.8% by the soil without roots. The mineralization of parathion but not of diazinon was stimulated in a similar manner when soil without roots was repeatedly irrigated with a root exudate produced in aseptic solution culture. Viable counts of microorganisms on soil extract agar were not significantly altered by root permeation or by root exudate treatment of the soil, leaving population selection and/or enhanced cometabolic activity as the most plausible interpretations for the observed stimulatory effects. Rhizosphere interactions may substantially shorten the predicted half-lives of some xenobiotic compounds in soil.     

Insecticide Susceptibilities of Anopheles sinensis (Diptera: Culicidae) Larvae from Paju-shi, Korea

A study was conducted to determine the susceptibility of Anopheles sinensis larvae, malaria vector, from Paju‐shi (Gyonggi‐do) to 24 pesticides including 11 pyrethroids, 11 organophosphates, 1 pyrazole analogue and another pesticide. The mosquito larvae showed the most highly susceptible to chlorfenapyr with LC₅₀ of 0.0063 ppm followed by spinosad, temephos, fenthion and beta‐cyfluthrin with 0.03, 0.0366, 0.0367 and 0.0998 ppm, respectively, and fluvalinate (>128 ppm) was the least susceptible. Also, 11 pesticides of them were compared with Goyang strain (Gyonggi‐do) of data 1992. The development of resistance was noticed to cypermethrin and permethrin as much of 73.59 and 6.23 folds at LC₅₀, respectively, and also fluvalinate was showed high resistance development. In generally, the pyrethroid insecticides were showed higher development of resistance than organophosphorus insecticides.     

Stability of spinosad resistance in Frankliniella occidentalis (Pergande) under laboratory conditions

The stability of spinosad resistance in western flower thrips (WFT), Frankliniella occidentalis (Pergande), populations with differing initial frequencies of resistance was studied in laboratory conditions. The stability of resistance was assessed in bimonthly residual bioassays in five populations with initial frequencies of 100, 75, 50, 25 and 0% of resistant individuals. There were no consistent changes in susceptibility of the susceptible strain after eight months without insecticide pressure. In the resistant strain, very highly resistant to spinosad (RF50>23,000-fold), resistance was maintained up to eight months without further exposure to spinosad. In the absence of any immigration of susceptible genes into the population, resistance was stable. In the case of the population with different initial frequency of resistant thrips, spinosad resistance declined significantly two months later in the absence of selection pressure. With successive generations, these strains did not change significantly in sensitivity. Spinosad resistance in F. occidentalis declined significantly in the absence of selection pressure and the presence of susceptible WFT. These results suggest that spinosad resistance probably is unstable under field conditions, primarily due to the immigration of susceptible WFT. Factors influencing stability or reversion of spinosad resistance are discussed.     

Patterns of insecticide resistance to organo-phosphorus compounds in strains of houseflies from various sources

Four strains of housefly (Musca domestica L.), resistant to organo-phosphorus insecticides, have been maintained in laboratory culture, together with a normal colony. Resistance in one strain had been developed by laboratory selection and in the others by field usage of insecticides followed by laboratory selection. They originated in Denmark, Italy and U.S.A., mainly by the use of parathion, diazinon and malathion respectively. The resistance spectra of these strains were determined by measuring their relative resistance to 14 organo-phosphorus compounds, by a microdrop application test. The strains selected by parathion and diazinon gave rather similar resistant patterns, showing highest resistance to parathion, paraoxon and diazinon and low resistance to malathion. The American strain produced a different pattern with high resistance to malathion and low resistance to parathion, paraoxon and diazinon. It is believed that these two patterns reflect different resistance mechanisms.A detailed comparison of the two European strains revealed more divergence in compounds containing (EtO)₂P-groups than in those with (MeO)₂P—groups.Injection of parathion reduced its resistance level considerably and the resistance to paraoxon on injection was even more reduced.

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Zusammenfassung Vier gegen organische phosphorhaltige Insektizide resistente Stubenfliegen-Stämme wurden zusammen mit einer normalen Kolonie in Laboratoriumkultur gehalten. Die Resistenz des einen Stammes hatte sich durch Selektion im Laboratorium entwickelt, die der anderen durch den Feldgebrauch von Insektiziden und nachfolgender Selektion im Labor. Sie stammten aus Dänemark, Italien und USA, hauptsächlich nach Anwendung von Parathion, Diazinon bzw. Malathion. Die Resistenzspektren dieser Stämme wurden durch Messung ihrer relativen Resistenz gegenüber 14 organischen Phosphorverbindungen mit Hilfe eines Mikrotropfen-Applikator-Tests bestimmt. Die durch Parathion und Diazinon selektierten Stämme ergaben ziemlich ähnliche resistente Eigenschaften; sie zeigten höchste Resistenz gegen Parathion, Paraoxon und Diazinon und niedrige gegen Malathion. Der amerikanische Stamm ergab abweichendes Verhalten mit hoher Resistenz gegen Malathion und niedriger gegen Parathion, Paraoxon und Diazinon. Es wird vermutet, daß diese beiden Typen auf verschiedenen Resistenzmechanismen beruhen.Ein eingehender Vergleich der zwei europäischen Stämme erbrachte größere Unterschiede in Verbindungen mit (EtO)₂P-Gruppen als in solchen mit (MeO)₂P-Gruppen.Injektion von Parathion verminderte seinen Resistenzspiegel beträchtlich und die Resistenz gegen Paraoxon wurde bei Injektion noch mehr reduziert.

     

Non-stable resistance to demeton-methyl in a strain of Myzus persicae

The progeny of one viviparous aptera from a strain of Myzus persicae which appeared to have become resistant to organophosphorus insecticides, were bred asexually in an environment free from these materials. At approximately the 7th generation, the clone when compared with a susceptible strain had a 25-fold resistance to demeton-methyl. With subsequent generations the resistance gradually declined and within 30 generations from its establishment the clone was no longer resistant.

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Zusammenfassung Die Nachkommen einer viviparen Aptera von Myzus persicae, die offenbar resistent gegen organische Phosphorverbindungen geworden waren, wurden in einer insektizidfreien Umwelt geschlechtslos vermehrt. Ungefähr in der siebenten Generation, wenn der Klon mit einem normalen Stamm verglichen wurde, hatte er eine 25-fache Resistenz gegen Demeton-methyl. Mit weiteren Generationen nahm die Resistenz allmählich ab und 30 Generationen nach seiner Gründung war der Klon überhaupt nicht mehr resistent.

     

Candidate natural enemies for control of Rhizoglyphus robini Claparède (Acari: Astigmata) in lily bulbs: exploration in the field and pre-selection in the laboratory

To find suitable candidates for biological control of the bulb mite, Rhizoglyphus robini Claparède (Acari: Astigmata) on lilies, exploration was undertaken in areas where the bulb mite is an established pest (The Netherlands, Taiwan and Japan). Among the predators, found in association with R. robini in the field and under storage conditions, mesostigmatic mites predominate. The most abundant species were Hypoaspis aculeifer (Canestrini), Lasioseius bispinosus Evans and Parasitus fimetorum (Berlese). These predators appeared to feed and reproduce on a diet of exclusively R. robini and they were able to control the bulb mite in small-scale population experiments initiated with a 1:20 predator-prey ratio. Under laboratory conditions corresponding to lily bulb propagation (lily scales mixed with vermiculite and stored at 23°C and >90% RH) the laelapid mite, H. aculeifer, was the most effective predator; the ascid predator, L. bispinosus, was much less effective, but being relatively small and being successful in attacking the juvenile stages of the bulb mite it may be better able to search for bulb mites hidden inside the lily bulb. The parasitid predator, P. fimetorum, failed to control the bulb mite when vermiculite was used as a medium, but turned out to suppress this prey when peat was used instead. Various strains of H. aculeifer or closely related species were compared with respect to their impact and performance on bulb mites as prey: two Dutch strains, one obtained from Breezand and the other from 'tZand, a Taiwanese strain, a German strain that in contrast to the previously mentioned strains was not collected from lily bulbs, but from agricultural areas near Bremen and, in addition, a Canadian strain of a related species (Hypoaspis miles Berlese), known to control sciarid fly larvae. These comparative experiments showed that H. miles died out without noticeable impact on the bulb mite population whereas all strains of H. aculeifer were able to suppress the bulb mites to very low numbers. However, the numerical responses of the H. aculeifer strains differed in that those collected in association with the pest (Breezand > Taiwan > 'tZand) were superior to the strain from Bremen. These results do not provide support to the Hokkanen and Pimentel hypothesis, which states that predators forming an evolutionary new association with the pest are often more effective in biological control.     

Laboratory evaluation of resistance to pesticides in the phytoseiid predator Typhlodromus pyri from English apple orchards

Typhlodromus pyri, reared on plate cultures and fed on pollen of Vicia faba, were bioassayed using a taped-slide technique. Mite stocks from isolated unsprayed orchards were used to establish base-line susceptibility to azinphos-methyl, parathion, carbaryl and permethrin. Stocks from English orchards with a spray history of organophosphates and carbaryl showed resistance of 4 to 6x to azinphos-methyl, c 50 x to parathion, >20x to carbaryl, and no resistance to permethrin. An orchard population derived from T. pyri imported from New Zealand in 1977 responded similarly. In other tests, mites exposed to spray residues on glass and on apple leaves were killed by lower concentrations than in taped-slide tests (glass < apple leaf < taped-slide technique); but for all three assay techniques the resistance factors to azinophos-methyl and carbaryl, comparing two stocks, were similar. All stocks from sprayed orchards were resistant to both azinphos-methyl and carbaryl, suggesting cross-resistance; and resistance to both these pesticides appeared to be stable in the field when selection pressure was relaxed. The results are discussed in relation to earlier work on T. pyri and two other resistant orchard-inhabiting phytoseiid species.