Acaricide Dicofol Research Articles

Detection and biochemical characterization of acaricide resistance in field populations of tea red spider mite, Oligonychus coffeae (Acari: Tetranychidae), in Assam tea plantation of India

ABSTRACTThe red spider mite, Oligonychus coffeae, (RSM) is one of the most damaging pests of tea in most tea-producing countries. The use of synthetic acaricide, the main strategy for controlling RSM, has increased year by year. In this study, eight field populations of RSM were evaluated for resistance against five different acaricides (ethion, dicofol, propargite, fenazaquin, and fenpropathrin) using the leaf-dip method. The results showed that almost all the tested field populations had developed a high to very high level of resistance to ethion and dicofol. The highest level of resistance for RSM was found to ethion and dicofol with a resistance ratio of 134.27 and 65.38, respectively in the Cachar population as compared to the laboratory susceptible population. Propargite and fenazaquin were very effective against RSM in all tested populations, whereas a minor level of tolerance was evident against fenpropathrin at the recommended dose. Biochemical assays using detoxifying enzymes indicated that general esterase, glutathione-S- transferase, and cytochrome P450 monooxygenase activities were higher in all conventional field populations than in the susceptible population and also had a significantly positive correlation with the LC50 values for ethion and dicofol. Synergism assays were therefore performed using ethion and dicofol in combination with common synergists like piperonylbutoxide (PBO), S.S.S.-Tributylphosphorotrithioate (DEF), and ethacrynic acid (EA). Results showed that mixing of PBO with ethion ensured about 36.73 times higher toxicity against RSM. DEF was moderately effective in revamping the effect of ethion whereas only EA was able to reduce the tolerance of RSM population to dicofol up to 11.71 times. The present studies infer that general esterase and cytochrome P450 monooxygenase may play a major role in imparting resistance to ethion whereas only glutathione-S-transferase plays an important role in dicofol resistance in RSM. The present study indicates the need for adopting integrated resistance management programmes to effectively control RSM in the tea plantations of Assam.

Organochlorine pesticides in agricultural soils and associated biota

The behavior of organochlorine pesticides (OCPs), such as DDTs, endosulfans, HCHs, heptachlors, drins and chlordanes, has been evaluated in the Quequen Grande River agricultural watershed including different matrices. Soil profiles from fields dedicated to soybean cultures and the associated terrestrial biota (earthworms, coleopteran larvae, collembolan and mites), stream water, suspended particle matter and surface sediment were sampled during the pre-application pesticide period. Pesticide analyses were carried out using gas chromatography with an electron capture detector. Soils samples showed a differential pesticide pattern throughout the profile. Control soils, settled 200 m from agricultural plots showed similar pesticide levels but with higher variety of compounds, denoting the historical use of OCPs in the zone. However, in agricultural plots DDTs and endosulfans constituted 90 % of the pesticides found with a further enrichment of endosulfan sulfate at depth. The relatively high p,p′-DDT levels in surface agricultural soil would be a consequence of pesticide impurities in technical acaricide Dicofol, which is widely used in the region; and it represents a new threat of fresh p,p′-DDT input into environment despite its use being forbidden. Terrestrial biota, mainly mesofauna showed high capacity to OCP accumulation, the aforementioned organisms being a good option in the monitoring of trace pesticides. Furthermore, the high OCP levels found constitute a hazard to food web since these organisms are one of the first steps in the food chain and the biomagnification is a common process with these compounds. As a result of runoff and volatilization the occurrence of OCPs in the aquatic environment was observed, draining a load of around 7.3 kg of pesticides into the river annually. As a whole, these results suggest the importance of using terrestrial biota for studying recalcitrant pesticides and a continuous monitoring is strongly advised as a first step in minimizing environmental risks.

Relative Toxicity of Fenazaquin Against Two-Spotted Spider Mite on Okra

Continuous use of previous generation acaricides in okra [Abelmoschus esculentus (L.) Moench] has increased resistance to pesticides and pest resurgence. The project was undertaken to evaluate a new acaricide, fenazaquin 10 EC, for effective control of two-spotted spider mites [Tetranychus urticae Koch (Acari: Tetranychidae)] in pot culture and under field conditions. Fenazaquin was used at 75, 100, 125, or 150 g·ha−1 a.i. and compared with the standard acaricide dicofol 18.5 EC at 250 g·ha−1 a.i. and an untreated control. The adulticide bioassay, ovicidal action to T. urticae and safety of Dwarf honey bees (Apis florea Fabricius), was performed under laboratory conditions. Pot culture and two field trials were conducted to evaluate efficacy. Impact on okra yield and phytotoxicity were determined. The LC50 was 1.440 mg·L−1 and LT50 at 1.50 mg·L−1 was ˜8 hours. Fenazaquin produced more than 70% egg mortality in all doses for T. urticae. Fenazaquin at 125 and 150 g·ha−1 a.i. caused the highest reduction in numbers of mites in pot culture and field experiments. Fruit yields (9.89 Mt·ha−1, 10.59 Mt·ha−1) and cost–benefit ratio (1:3.25, 1:3.48) were higher in fenazaquin-treated plants at 150 g·ha−1 a.i in field experiments. No test doses were phytotoxic and all doses were relatively safe to Dwarf honey bees.

Dicofol degradation to p,p′-dichlorobenzophenone – A potential antiandrogen

In the present investigation, the degradation of the acaricide dicofol (also known as kelthane) was investigated with special emphasis on generation of p,p′-dichlorobenzophenone (DCBP) under alkaline conditions as well as induced by UV-light. Dicofol was also incubated in the presence and absence of microsomal preparations to measure potential metabolic formation of DCBP. The results indicate that the degradation of dicofol to DCBP primarily proceeds as an abiotic process via hydroxide ion catalysed elimination of a trichloromethyl anion. The generated anion picks up a proton from the solvent to generate chloroform. Microsomal metabolism does not appear to play a major role in the degradation of dicofol. DCBP is structurally analogous to the antiandrogen p,p′-dichlorodiphenylethene (DDE). We therefore investigated whether DCBP displays antiandrogenic properties. In an in vitro transactivation system utilising transiently transfected African green monkey kidney (COS-7) cells, DCBP showed potent antiandrogenic efficacy. This finding was confirmed by further studies in T47D human mammary carcinoma cells by measuring mRNA and protein expression of androgen dependent genes i.e. TRMP-2 (testosterone-repressed prostate message-2) mRNA and PSA (prostate-specific antigen) protein.

Production of Monoclonal Antibody to Acaricide Dicofol and Its Derivatives

In Thailand detection of acaricide dicofol residues has been sporadically performed due to the limitation of analytical techniques. Conventional analytical methods for detecting dicofol residues most often use chromatographic-based techniques. Our ultimate aim is to develop an alternative method for rapidly analyzing dicofol residues in vegetables and fruit samples. Here we report the production of monoclonal antibodies specific to dicofol and its derivatives. Hapten-protein carriers were prepared by linking succinic anhydride to dichlorobenzhydrol (DCBH), which was then conjugated to bovine serum albumin (BSA) and oval albumin (OVA). DCBH-BSA conjugate was used as immunogen while DCBH-OVA conjugate was used as capture antigen for competitive inhibition assay. Female BALB/c mice were immunized with DCBH-BSA conjugate subcutaneously, and antibody (Ab) level was determined 2 weeks after the last immunization. Spleen cells producing high titer antibody were isolated and fused with myeloma cells of P3.X6.Ag8.653. After limiting dilutions, antibody produced by one clone had high affinity, which was found to be of IgG1 with κ light chain. Specificity and inhibition concentrations of the monoclonal antibody (MAb) were determined by competitive indirect ELISA with dicofol, and its 50% (IC(50)) was 0.28 μg/mL. Working ranges of the developed immunoassay were from 0.07 to 25 μg/mL. Hence, the prepared MAb will be able to be applied for immunoassay development for detecting dicofol residue in vegetables and fruits far below the maximum residue limit such that 5 g of fruits and berries can be detected below 0.1 mg/kg.

An acaricide-treated net to control phytophagous mites

A new technique to control phytophagous mites was tested in West Africa on the African eggplant Solanum macrocarpon. This technique consisted of covering plants with a net impregnated with the acaricide dicofol. The net was applied during the night to protect the net fabric and the active ingredient from UV degradation and to avoid interference of the net with overhead watering. The technique was evaluated in three trials at the INRAB research station and in a grower's field in 2006 and 2007. Results showed that the broad mite Polyphagotarsonemus latus (Banks), the major pest of S. macrocarpon which causes severe damage to leaves, and spider mites ( Tetranychus spp.), were completely controlled by the dicofol-treated net. Very few mites and practically no mite injury were observed on plants covered with the dicofol-treated net compared to 12–94% damaged leaves in the unprotected control plots. The acaricide-treated net was as efficient when used temporarily (once every three nights) as when used every night. No difference in the percentages of leaves damaged by mites was apparent at harvest between plots covered with a non-acaricide deltamethrin-treated net (40%) and unprotected control (32%). This new concept of mite control using an acaricide-treated net temporarily covering vegetable crop appears to be an efficient tool which is easy to use. It can be used repeatedly reducing costs and poses a very low risk of environmental pollution when used in the dry season or in greenhouses.

Toxicidade de Acaricidas sobre Diferentes Estágios de Vida de Tetranychus urticae Koch (Acari: Tetranychidae) em Mamoeiro

The two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), is one of the most important pests of papaya in Brazil. It causes leaf yellowing, necrosis, and leaf drop, reducing the papaya yield. In the present work, the effects of the acaricides fenpyroximate (50 g.L-1), lufenuron (50 g.L-1), tetradifon (80 g.L-1), azocyclotin (500 g.L-1), carbosulfan (200 g.L-1), dicofol (185 g.L-1), sulfur (800 g.kg-1), and chlorfenapyr (240 g.L-1) on eggs viability and adult female were tested at the 25, 50, and 75% ratios of recommended dosages from the commercial formulations. The effects of these acaricides at 75% ratio on the immature forms (larvae, protonymphs, deutonymphs) were evaluated also. Leaf discs (d (o) = 3.5 cm), with 30 eggs each, were dipped into the respective treatments and distilled water (control) for 5 sec. All treatments were left to dry at room temperature for 30 min. For effects on adults, leaf discs were infested with 15 females each. Egg viability was determined after counting the number of living larvae at 96h after disc treatment. Adult mortality was evaluated after 72h of infestation and individuals were considered dead if they did not move when prodded with a fine pointed brush. The same method was applied to the active immature forms. The acaricides tetradifon, dicofol, and fenpyroximate were the most efficient in the control of eggs, while dicofol and azocyclotin were most efficient to control adult females. For the immature forms, activities of azocyclotin, chlorfenapyr, fenpyroximate, dicofol, and tetradifon are highlighted.

Compatibilidade de inseticidas e acaricidas com o percevejo predador Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae) em algodoeiro

Os objetivos deste trabalho foram estudar a ação dos inseticidas espinosade, lambdacialotrina e monocrotofós no controle do curuquerê-do-algodoeiro Alabama argillacea (Hübner), sua compatibilidade com o percevejo predador Podisus nigrispinus (Dallas), e os efeitos dos inseticidas e acaricidas metiocarbe, pimetrozine, tiametoxam, abamectim, diafentiurom, dicofol e propargite na predação de A. argillacea por P. nigrispinus no campo. Inseticidas e concentrações utilizadas proporcionaram controle de A. argillacea acima de 90% no dia da aplicação. O controle de A. argillacea por lambdacialotrina (20 g i.a./ha) e monocrotofós (240 e 320 g i.a./ha) foi observado até três dias após aplicação, enquanto espinosade (30 e 60 g i.a./ha) prolongou o controle acima de 90% até cinco dias. Monocrotofós e lambdacialotrina foram significativamente mais tóxicos para P. nigrispinus comparado a espinosade. O efeito residual de monocrotofós e lambdacialotrina para P. nigrispinus foi evidente até três dias após a aplicação. A sobrevivência de P. nigrispinus foi afetada por metiocarbe, tiametoxam, diafentiurom, abamectim e enxofre após um dia, e apenas por tiametoxam após três dias da aplicação. Pimetrozine, dicofol e propargite não afetaram a sobrevivência de P. nigrispinus. A predação de lagartas de A. argillacea por P. nigrispinus não foi observada no dia da aplicação em plantas tratadas com metiocarbe e afetada por tiametoxam, abamectim, diafentiurom e enxofre, mesmo três dias após a aplicação. Os inseticidas pimetrozine e espinosade, bem como os acaricidas dicofol e propargite mostraram-se compatíveis com P. nigrispinus, e devem ser priorizados em programas de manejo integrado de pragas do algodoeiro.

Mistura de dicofol com fempiroximato no manejo da resistência de Brevipalpus phoenicis (Geijskes) (Acari: Tenuipalpidae) ao dicofol

A mistura dos acaricidas dicofol e fempiroximato para o manejo da resistência de Brevipalpus phoenicis (Geijskes) ao dicofol foi avaliada no presente estudo. Inicialmente, a interação de dicofol e fempiroximato foi testada a partir das CL25s de cada produto para as linhagens de B. phoenicis suscetível (S) e resistente (R) ao dicofol. Foi observada uma interação sinérgica da mistura para as duas linhagens. Posteriormente, a persistência da atividade biológica dos resíduos de dicofol (na concentração comercial de 360 g de ingrediente ativo [I.A.] / 1.000 L de água), fempiroximato (50 g de I.A. / 1.000 L de água) e mistura de dicofol e fempiroximato (240 e 25 g de I.A. / 1.000 L de água, respectivamente) foi avaliada em um pomar comercial de citros. Após a aplicação dos produtos, frutos foram coletados periodicamente e infestados com as linhagens S e R no laboratório. Resíduos de dicofol e da mistura discriminaram as linhagens, ou seja, maior mortalidade da linhagem S em relação à R foi observada em todas as avaliações. Resíduos de fempiroximato não discriminaram as linhagens, porém a concentração aplicada do produto não proporcionou controle eficiente de B. phoenicis. O sinergismo entre o dicofol e fempiroximato não foi eficiente no manejo da resistência de B. phoenicis ao dicofol.

Detecção e monitoramento da resistência de Brevipalpus phoenicis (Geijskes) (Acari: Tenuipalpidae) ao dicofol

Um método de bioensaio residual foi utilizado para caracterizar a resistência de Brevipalpus phoenicis (Geijskes) ao acaricida dicofol. Arenas confeccionadas com folhas de laranjeira foram pulverizadas com diferentes concentrações de dicofol com o auxílio da torre de Potter. Posteriormente, as arenas foram acondicionadas em placas de acrílico contendo uma solução a 2,3% de ágar-água. Após a transferência de ácaros adultos para a arena pulverizada, as placas foram mantidas a 25±1ºC, umidade relativa de 70±10% e fotofase de 14h. A avaliação da mortalidade foi realizada 24h após a infestação dos ácaros. As CL50s estimadas para as linhagens susceptível e resistente ao dicofol foram 7,44 µg de dicofol / mL de água destilada [ppm (I.A.)] (IC 95% 6,74 - 8,23) e 422,45 ppm (I.A.) (IC 95% 369,41 - 482,80), respectivamente; resultando numa razão de resistência de aproximadamente 57 vezes. Concentrações discriminatórias entre 32 e 100 ppm (I.A.) foram definidas para um programa de monitoramento da resistência de B. phoenicis ao dicofol. Resultados de um levantamento da susceptibilidade de populações de B. phoenicis coletadas em diversos pomares comerciais de citros do estado de São Paulo evidenciaram uma grande variabilidade entre as populações com relação à resposta ao dicofol.

Mobility of the Organochlorine Compound Dicofol in Soil Promoted by Pseudomonas fluorescens

The genetic modified Pseudomonas fluorescens Br 12, resistant to kanamycin and rifampycin, was used to follow the co-transport of the organochlorine acaricide dicofol through a nonsterilized soil column. P. fluorescens was found to bioaccumulate dicofol with the highest bioconcentration factor of 279 within 30 min. Separate soil column experiments where applied P. fluorescens or [14C]dicofol were submitted to heavy rain simulation did not reveal any correlation between the distribution patterns of P. fluorescens and [14C]dicofol in the leachate fractions (r=0.3). Similar experiments with P. fluorescens that previously had bioaccumulated [14C]dicofol demonstrated a high correlation of these bacteria and radioactivity in the leachate fractions (r=0.8). The total recovery of radioactivity in the leachate, when [14C]dicofol was previously bioaccumulated in bacteria, was more than two times higher (4.5%) than the total recovery of radioactivity in the leachate when [14C]dicofol was directly applied in the soil (2%). This indicates cotransport by Pseudomonas. Fractionation and analysis of soil columns indicated that most of the bioaccumulated dicofol was rapidly released and adsorbed in soil, while bacteria moved down by leaching.

14C]Dicofol association to cellular components ofAzospirillum lipoferum

The bacterium Azospirillum lipoferum is able to survive in high concen-trations of the organochlorine acaricide dicofol [1,1-bis-(4-chlorophenyl)-2,2,2-trichloroethanol]. It accumulates this chemical in the cell envelope where it is protected against hydrolysis. We investigated the nature of cell envelope molecules with which [14C]dicofol is associated; no indication of [14C]dicofol–saccharide bonds was found. We concluded that about 80% of the total [14C]dicofol found in the cells was associated with lipids and the remaining 20% with proteins. Electrophoresis did not indicate any correlation of a specific protein band with [14C]dicofol radioactivity peaks. After Folch partition, [14C]dicofol distribution in TLC analysis showed 60% of [14C]dicofol–lipid bonds related to neutral lipids, 20% to phospholipids and the remaining 20% of the bonds associated with other lipids. Experimental results suggested that [14C]dicofol associates mainly with membrane domains near proteins and that this association influences membrane fluidity as well as enzymatic activity. © 1998 SCI

Bioaccumulation and enhanced persistence of the acaricide Dicofol by Azospirillum lipoferum

The purpose of this paper is to study the influence of the Gram-negative nitrogen-fixing bacterium Azospirillum lipoferum in the persistence of the organochlorine acaricide Dicofol [1,1-bis(4′-chlorophenyl)2,2,2-tricholoro-ethanol]. This microorganism bioaccumulates dicofol and the bioconcentration factor reaches 577 at the maximum after 3 days of incubation as measured by GC-MS. Cell uptake of (U- 14C) Dicofol measured by photo-induced binding technique shows similar results. Incorporation of (U- 14C)Dicofol in A. lipoferum reaches equilibrium in 20 minutes, it is not temperature dependent, and acaricide-cell interactions occur preferentially to cell envelope. Dicofol is easily hydrolised in aqueous cell-free medium (67%) and was less degraded in the presence of A. lipoferum cells (31%). This means that Dicofol bioaccumulation in A. lipoferum protected this acaricide against hydrolysis. As a consequence Dicofol-cell interactions can enhance the persistence of this chemical in the soil.

Interface Between Citrus Rust Mite (Acari: Eriophyidae) and Dicofol: Implications for Resistance Management

Laboratory and field studies were conducted to characterize the interface between citrus rust mite, Phyllocoptruta oleivora (Ashmead), and the acaricide dicofol. Direct and residual (continuous and discontinuous residues) contacts of dicofol on susceptible (S) and dicofol-resistant (R) strains of citrus rust mite were evaluated. The decay in biological activity of different formulations of dicofol was also measured with both strains. Differences between S and R strains were less pronounced in direct contact than residual contact with dicofol. When dicofol was used at high concentrations in residual bioassays (500-1,280 microgram [AI]/ml of water [ppm]), the expression of resistance was very poor on fresh residues of dicofol. However, as residues decayed, we observed substantially greater mortality of the S strain than the R strain. Field studies showed that dicofol on citrus fruits becomes biologically inactive to citrus rust mite relatively fast after its application (concentration of 1,280 ppm [AI]). Both S and R strains survived totally when transferred to a 6-d residue. The formulation of dicofol had an significant effect on the rate of decay in biological activity. Differences in the rate of decay observed in bioassays were consistent with the field performance of dicofol in controlling citrus rust mite.

Laboratory and Field Evaluation of the Selective Acaricides Dicofol and Propargite for Control of Tetranychus urticae Koch (Acari: Tetranychidae) in Australian Cotton

ABSTRACTEfficacy of the selective acaricides dicofol (960 g a.i./ha) and propargite (1,500 g a.i./ha) for control of twospotted spider mite, Tetranychus urticae Koch, on cotton was compared to profenofos (750 g a.i./ha), a broad‐spectrum acaricidal organophosphate which was the industry standard. Ground and aerial applications of propargite reduced mite populations to lower levels for longer than the other compounds. Ground applications of dicofol and profenofos provided equivalent efficacy, but it was only about half that of propargite. A side dressing of the granular insecticide aldicarb (1,500 g a.i./ha) was included at one site and, although it suppressed mite populations, was less efficacious than propargite and uneconomic for commercial use. Dicofol and propargite are now registered for commercial use in cotton. Results of laboratory bioassays suggest that T. urticae populations collected from several cotton farms in New South Wales are presently susceptible to both compounds. the incorporation of these products into the insecticide resistance management strategy for cotton is discussed.

Susceptibility of Various Stages ofTrichogrammatoidea armigeraNagaraja to Some Pesticides and Effect of Residues on Survival and Parasitizing Ability

The toxicity, persistence and effect on parasitism of 10 insecticides, eight fungicides and one acaricide on Trichogrammatoidea armigera Nagaraja, an egg parasitoid of a Helicoverpa armigera (Hb), were investigated in the laboratory and under field conditions. At field recommended dosages, the fungicides oxycarboxin, copperoxychloride, streptomycin sulphate + tetracycline hydrochloride and 2‐bromo‐2‐nitropropane‐1,3‐diol and the acaricide dicofol were safe, while the insecticide phosalone and fungicide tridemorph were moderately toxic to adults. All other insecticides tested, namely dimethoate, fenitrothion, monocrotophos, phosphamidon, endosulfan, cypermethrin, decamethrin, fenvalerate and fluvalinate, and the fungicides carbendazim, methyl thiophenate and carboxin were toxic to adults. A high level of parasitism was recorded for all fungicide treatments and for dicofol and fluvalinate. The larval stage of the parasitoid was more tolerant than other stages. The residual toxicity of all fungicides, and di...

RESIDUAL TOXICITY OF DICOFOL, FORMETANATE HCl, PROPARGITE, HEXYTHIAZOX, AND CLOFENTEZINE TO EUROPEAN RED MITE ON PEACH

AbstractThe persistence of toxic effects of the contact acaricides dicofol, propargite, and formetanate HCl and the ovicides clofentezine and hexythiazox to the European red mite, Panonychus ulmi (Koch), were tested by bioassays of disks cut from treated peach foliage. Effects of dicofol were more persistent than propargite or formetanate HCl to susceptible mites. Mortality on dicofol-treated foliage was >50% for more than 15 days. Propargite killed >50% of females for 10 days after application, whereas the toxicity of formetanate HCl deposits declined rapidly after 7 days. Mortality of dicofol-resistant mites was less than for susceptible mites. However, resistant mites were affected (>50% killed) by dicofol residues up to 7 days old. The toxic effects of the ovicides clofentezine and hexythiazox persisted for at least 30 days and at the rates tested were approximately equally toxic.Formetanate HCl and propargite residues were less persistent (half-life 8–9 days) than the other compounds. Dicofol residues had a half-life of about 15 days but approximately 10% of residues persisted for 65 days. Residues of clofentezine and hexythiazox declined more gradually (half-life = 15–20 days) than other compounds and persisted at approximately 10% of initial residues after 65 days.

Behavioral Response and Mortality of Nursery Populations of Two spotted Spider Mite (Acari: Tetranychidae) to Residues of Six Acaricides

Residue bioassays of six acaricides (cyhexatin, propargite, dicofol, carbophenothion, hexakis, and abamectin) were conducted against three populations of the two spotted spider mite (TSSM), Tetranychus urticae Koch. Two separate bioassays were done to examine the behavioral responses and physiological tolerance levels of the three TSSM populations to the acaricides. In a third bioassay, we determined if responses were indicative of behavior that would allow mites to disperse successfully from treated surfaces. Behavioral responses (walk-off or spin-down) significantly greater than that of the control occurred with some concentrations of hexakis, cyhexatin, and carbophenothion. Mortality of mites that walked off was very low, whereas mortality of those that spun down was high. Irritancy to four of the sixcompounds was evident in the preliminary bioassay, but successful behavioral response appeared to be directly related to the physiological tolerance levels of the mites.

Metabolism of a dicofol impurity alpha-chloro-DDT, but not dicofol or dechlorodicofol, to DDE in mice and a liver microsomal system.

1. The important acaricide dicofol and two related compounds, alpha-chloro-DDT (an impurity in dicofol) and dechlorodicofol (DCD) (a photolysis product of dicofol), as [phenyl-14C]-labelled preparations, were administered i.p. to male mice (30 mg/kg) and incubated with rat-liver microsomes alone and with NADPH, both aerobically and anaerobically, and with rat-liver cytosol alone and with glutathione. 2. alpha-Chloro-DDT is metabolically dechlorinated to DDE in the following systems: in vivo, based on analyses of mouse brain, fat and liver; in vitro, with anaerobic rat-liver microsomes plus NADPH; and with reduced haematin. Trace amounts of DDT are also detected in vivo in mouse liver. 3. Dicofol is reductively dechlorinated to DCD, and both compounds are metabolized to dichlorobenzophenone and dichlorobenzhydrol in vivo in the mouse tissues examined, and also in vitro exclusively with anaerobic rat-liver microsomes in the presence of NADPH. Liver cytosol with glutathione is less effective or inactive. 4. The in vivo metabolic dechlorinations of alpha-chloro-DDT and dicofol probably involve a reduced porphyrin in liver microsomes.

The impact of cotton plant resistance on spider mites and their natural enemies

A spider mite-resistant and a spider mite-susceptible variety of cotton were planted in the field in a replicated design. An acaricide (dicofol) and an insecticide (acephate) were used to manipulate numbers of spider mites and their natural enemies. In general, numbers of spider mites remained low until just before midseason when 650 °D air temperature had accumulated. At 650 °D, mite numbers began to increase more sharply and reached significantly (P<0.001) greater levels on susceptible plants than on resistant plants. Although natural enemies, such as Geocoris pallens Stål, Orius tristicolor (White), and Frankliniella occidentalis (Pergande), were slightly more apparent on susceptible plants than on resistant plants, these differences were not statistically significant, and cotton varietal resistance was compatible with biological control. Acephate significantly (P<0.05) reduced predator densities for up to 2 weeks following each application, and after 550 °D mite populations had begun to explode on plants sprayed with acephate. Predators had a greater impact on mites on susceptible plants than on resistant plants, which was attributed to greater densities of spider mite prey on susceptible plants. After 900 °D, spider mites were out of control on susceptible plants treated with acephate, and the acaricide dicofol had no observable effect on mite numbers. Rapidly increasing mite populations appear to exhibit acaricide resistance, solely by attaining very high densities. Dicofol efficacy was relatively high on spider mite-resistant plants, because mite growth rates were slower, and thus mite populations could not “outgrow” the effect of the acaricide. Hence, there appeared to be a synergistic interaction between acaricide and varietal resistance. In untreated plots, yield was significantly (P<0.05) higher in the susceptible variety than in the resistant variety. However, this trend was reversed in plots treated with acephate, and yield from resistant plants was significantly (P<0.05) greater than yield from susceptible plants. On crops heavily treated with insecticides, resistant varieties may offer the best alternative for pest management.