Nerve insensitivity resistance to cypermethrin in larvae of the tobacco budworm Heliothis virescens from USA cotton field populations

Spontaneous neuronal activity was recorded from the peripheral nerves of third-instar larvae of strains of Heliothis virescens (F.) obtained directly from cotton fields in the USA. Following a control period the preparations were exposed to increasing concentrations of cis-cypermethrin in a cumulative dose-response assay. A positive response was defined as an increase of at least five-fold in the rate of neuronal activity over that seen during the control period. Up to 35 individuals of each strain were assayed and the responses used to construct a phenotypic profile categorising the individuals from nerve-susceptible to highly nerve-insensitive. An EC₅₀ for the action of cis-cypermethrin was also obtained. There was a positive, significant correlation between non-synergisable resistance to cypermethrin and nerve insensitivity as defined in the neurophysiological assay. It was shown that nerve insensitivity to cypermethrin increased throughout the cotton-growing season.     

Time related factors in Heliothis control on cotton

Most factors in Heliothis control on cotton are crucially related to time but all are interrelated one with another and form two complex interactions hinging on the pest life cycle. One is the crop-pest interaction and the other the control strategy. This paper reviews most of the factors and reports work carried out in Swaziland to elucidate some of them. In the crop-pest interaction the timing of the initial attack and a cue for spraying can be indicated by development of an alternate host and, in Swaziland, by reference to the average date of maize tassellation. Later infestations are measured by scouting and a comparison is made of the two main systems, the first based on a small part of many plants and used in the USA, and the second based on the whole of a few plants in Africa. Their respective purposes are discussed and economic spray thresholds based on them are presented. The compensatory ability of the plant diminishes as the season progresses but in Swaziland manual bud/flower removal experiments over 3 years on raingrown and irrigated cotton showed that prior to 12 January (9-12 weeks from planting) removal increased the yield in half the cases whilst later removal could cause a decrease. The natural Heliothis infestation was allowed to remove fruits in an experiment by leaving spray gaps and the results confirmed those of the previous manual experiments except that damage continued for about 2 weeks after spraying restarted. This advanced the critical date to 31 December but up to three sprays could be saved without loss of yield and possibly with a yield bonus. In the control strategy the different stages of the life cycle are considered as targets but the most obvious is normally the first instar larvae. Rapid plant growth can dictate frequent spray applications regardless of deposit persistence which may need to be longer when using aircraft in spite of Heliothis oviposition occurring predominantly on exposed surfaces. Temperature-independent or fumigant insecticides or those affecting the adult may best be sprayed in the evening when cooler and calmer post-treatment conditions occur and adults are starting to fly.     

Pyrethroid insecticide residues on vegetable crops

Pyrethroid insecticides were applied on various vegetable crops as foliar treatments to determine dissipation rates. On Chinese broccoli (Guy Lon), Chinese mustard (Pak Choi) and Chinese cabbage (Kasumi, napa), fenvalerate was persistent with residues of 0.10, 0.14 and 0.11 mg kg-1, respectively, by day 21. Cypermethrin residues on head lettuce were below 0.1 mg kg-1 by day 10 but on the leafier romaine and endive varieties it was more persistent and required 14-19 days to dissipate below this concentration. After three applications, residues of cypermethrin in harvested carrots and of permethrin in eggplant were not detected on the day of application. On asparagus, deltamethrin and cypermethrin residues declined to less than 0.1 mg kg-1 by days 1 and 2, respectively; permethrin was more persistent, requiring more than 2 days to decline to less than 0.1 mg kg-1. Deltamethrin on dry (cooking) and Spanish onions was not detected on the day of application. On tomatoes, the concentration of permethrin was 0.093 mg kg-1 on the day of application and declined to about 0.05 mg kg-1 after 2-4 days. In general, permethrin, cypermethrin and deltamethrin residues declined to acceptable concentrations within an acceptable pre-harvest interval. Fenvalerate may be too persistent on these speciality crops unless a maximum residue limit > 0.1 mg kg-1 is permitted.     

Chemical residues and bioactivity of tebufenozide applied to apple foliage

Tebufenozide, an insect growth regulator that acts as an ecdysone agonist, was applied at recommended label rate to apple trees in August 1997 and May 1998. Foliar residues were determined by high-performance liquid chromatography from samples collected 2, 24, 48 and 96 h post-spray, and at weekly intervals thereafter for 9 weeks in 1997 and 11 weeks in 1998. Foliage sampled at the same times was used in bioassays to determine residual toxicity to first-instar obliquebanded leafrollers, Choristoneura rosaceana (Harris). Residue decay followed first-order kinetics in both years, with residual half-life of 36.3 days in 1997 and 7.2 days in 1998. Estimates of the time needed to reduce bioactivity to 50% in bioassays were 18.7 days in 1997 and 36.3 days in 1998. The accuracy of equations describing decay of tebufenozide residues and bioactivity over time was not improved by using degree-day accumulations as the independent variable.     

Comparison of insecticide absorption and detoxification in larvae of the bollworm,Heliothis zea,and the tobacco budworm,H. virescens

Rates and nature of metabolism of several insecticides were compared in larvae of the bollworm, Heliothis zea (Boddie), and the tobacco budworm, H virescens (F.). Both species are resistant to organochlorine compounds. In addition, H. virescens is resistant to carbamate and organophosphate insecticides. All test insecticides were metabolized by larvae of both species under in vivo conditions. In most instances, metabolism was more rapid in H. virescens larvae.A series of in vivo and in vitro assays implicated high levels of NADPH-dependent oxidative enzymes as a major metabolic factor in resistance. Other work demonstrated that H. virescens larvae absorbed insecticides at a slower rate than did H. zea larvae. High resistance to organophosphates present in H. virescens may be due to interaction of factors for increased rate of detoxification and decreased rate of absorption.     

不同寄主植物棉蚜酯酶对杀虫剂不敏感性的频率分布

通过生物测定和生化分析研究了花椒棉蚜(HA)和棉花棉蚜(MA)种群对杀虫剂的抗性及其α-乙酸萘酯(α-NA)酯酶和乙酰胆碱酯酶(AChE)对杀虫剂的不敏感性。结果表明,MA种群对甲基对硫磷、辛硫磷和灭多威的耐药性均高于HA种群;MA种群中具有高α-NA酯酶活力的个体比HA种群多,甲基对硫磷对HA和MA种群α-NA酯酶的抑制率达30％时的个体累计频率分别为37％和65％;抑制率大于50％时的累计频率分别为18％和1％;灭多威对HA种群棉蚜AChE的抑制作用高于MA种群。说明MA种群对有机磷的抗性可能与α-NA酯酶活力的增高和对杀虫剂的不敏感性有关,对灭多威的抗性与AChE敏感度的降低有关。滤纸酯酶反应法和微量滴度酶标板法均能快速、有效地测定棉蚜个体酯酶的频率分布,准确地反映两种群棉蚜酯酶活力的差异。     

Persistence and performance of esfenvalerate residues on broccoli

The efficacy of esfenvalerate (84 g litre-1 EC; Asana XL) at 7.0 g AI ha-1 on broccoli was tested against the flea beetle, Phyllotreta cruciferae Goeze (Chrysomelidae: Coleoptera) and the imported cabbage worm, Pieris rapae L (Pieridae: Lepidoptera) under field conditions. Insect populations were monitored before and after treatment. Periodic sweep-net collections and examination of the leaves in treated and untreated broccoli plots revealed mean reductions of P cruciferae levels of nearly 98% 1 week post-application compared with untreated plots. The residual toxicity of esfenvalerate was also effective for 2 weeks in reducing population density of P rapae by 69% on broccoli leaves. The impact of esfenvalerate on feeding damage to broccoli leaves was established by counting the number of feeding holes made by P cruciferae on spring broccoli and P rapae on fall broccoli. As the leaf area ingested increased, a linear relationship was seen between the number of holes and number of insects. Results indicated that forage destruction by the two pests was significantly reduced by esfenvalerate application. Esfenvalerate was extracted from broccoli at 1 h and 1, 3, 7, 10, and 14 days post-application for residue analysis. Residues on spring broccoli were 12.2, 5.2 and 2.9 micrograms cm-2 on the leaves and 0.13, 0.05 and 0.02 microgram g-1 on the heads at 1 h, 1 and 3 days, respectively. Only trace levels (0.001 microgram g-1) were detected in/on the heads 14 days after spraying. On the basis of half-life (T1/2) values, persistence of esfenvalerate on spring broccoli leaves (T1/2 = 1 day) was shorter than on fall broccoli (T1/2 = 1.6 days). T1/2 values were 2.1 and 3.6 days on spring and fall broccoli heads, respectively. The implications of these residue levels on re-entry times into treated fields are discussed.     

Photodegradation of the pyrethroid insecticide fenpropathrin in water,on soil and on plant foliage

The photodegradation of fenpropathrin [(RS)-α-cyano-3-phenoxybenzyl 2,2,3,3-tetramethylcyclopropanecarboxylate] ( I ), in water, on soil and on plant foliage, was investigated using ¹⁴C-preparations labelled separately at the cyano group, cyclopropyl-C₁ or in the benzyl ring. On exposure to sunlight, I was photodecomposed with initial half-lives of >6 weeks in distilled water, 6.0 weeks in humic acid aqueous solution, 2.7 weeks in river water, 1.6 weeks in sea water and 0.5 of a day in 2% aqueous acetone. A triplet photosensitiser, acetone, together with naturally occurring substances in river and sea water, including humic acid, enhanced the photodegradation of I . On three kinds of soil, I was rapidly photodegraded with initial half-lives of 1–5 days, whereas it was fairly photostable on a mandarin orange leaf. The photoreactions involved were: decarboxylation, hydration of the cyano group to carboxamide, cleavage of the ester or the diphenyl ether linkage, hydrolysis of the carboxamide group to carboxyl, and hydroxylation at either or both of the gem dimethyl groups. The predominant reactions in water were decarboxylation, ester bond cleavage and photo-induced evolution of [¹⁴C] carbon dioxide from the [¹⁴C] cyano label; on soil, hydration or ester bond cleavage predominated. The hydration was also of importance in river and sea water. Decarboxylation did not occur on soil and plant foliage.     

不同杀菌剂对棉花枯萎病病原菌室内毒力的研究

采用抑制病原菌菌丝生长法在室内测定了多菌灵,甲基托布津,菌毒清等１２种杀菌剂对棉花枯萎病病原菌的毒力作用,结果显示,多种杀菌剂对该病原菌丝生长有明显的抑制作用,其中以多菌灵作用最强,其抑制中浓度（ＥＣ５０值）为０．７７ｐｐｍ（沪产）和０．９６ｐｐｍ（杜邦公司产品）,其余杀菌剂品种ＥＣ５０值在１．１４ｐｐｍ￣５２．６５ｐｍ之间。     

Persistence of fenthion residues in olive oil

The level of fenthion residues was followed for up to one year in olive oil samples. The concentration of the parent compound decreased slowly following a double-phase first-order decay model, both in the freezer and laboratory, while the total concentration (parent compound and its sulfoxide) remained unchanged. Storage, therefore, cannot be used as a decontamination technique for oil containing higher than the toxicologically acceptable residues of this compound.     

Influence of oil droplet size on the toxicity of bifenthrin on cotton to tobacco budworm (Heliothis virescens)

Sprays of bifenthrin and paraffinic oil mixtures were applied to cotton leaves (Gossypium hirsutum L.) to investigate droplet size effects on the mortality of Heliothis virescens (F.). An air-assisted nozzle applied mixtures at 9.4 litre ha ?1 spray rate with volume median diameters (VMD) of 96 and 337 μm, as verified with a Malvern laser diffraction analyzer. An hour after spraying, susceptible 3rd-instars walked for 2-min through wet droplets of spray mixtures applied at bifenthrin rates of 22, 45, 67, 90. and 112 g a.i. ha ?1. Mortality was assessed at 21, 26, 45, 50, 74, and 117h after exposure. Final mean mortality was affected (P =0.01) by bifenthrin rate and droplet size. Bifenthrin applied in 337 μm VMD droplets caused 75.8% mortality, whereas 96-μm VMD droplets resulted in a mortality of 67.9%. Also, the 337 μm VMD droplets killed larvae in 13% less time than the 96μm VMD droplets, based on analysis (P =0.01) using the mean elapsed time till death as the dependent factor.     

Systemic effects of a neem insecticide onLiriomyza huidobrensis larvae

In an effort to expand the spectrum of larvicides effective against the pea leafminer,Liriomyza huidobrensis (Blanchard), we studied the effects of a neem-based insecticide (Neemix-45) on the development of the leafminer under laboratory conditions. Bean plants were treated with a soil drench of 1, 5, 10 or 25 ppm azadirachtin or by dipping leaves in 1 or 15 ppm azadirachtin at various times before or during the development of the leafminer. Treating the plants with the neem insecticide before exposure to egg-laying adults had a greater effect on inhibiting the development of pupae and adult eclosion than treatment at the 1st-instar larval stage. The systemic effects from a soil drench had a greater adverse effect on pupation and adult eclosion than leaf dipping. Drenching plants with 1 ppm azadirachtin 24 h before exposure to adults had a greater effect (0% adult eclosion) than leaf dipping at the same time period and concentration (15. 6% adult eclosion). Similar results were obtained when drenching plants infested with lst-instar larvae with 1 ppm azadirachtin (11. 7% eclosion)vs dipping leaves at the same time period and concentration (44. 7% eclosion).     

Transfer of insecticide residues to food stored on or near plywood impregnated with organochlorine insecticides

Formulations of aldrin and dieldrin have been used for a number of years to treat exposed timber components used in the construction of freight containers. The extent to which these insecticides migrate to foodstuffs stored on or near treated plywood has been examined under laboratory conditions and is reported here. A limited survey of organochlorine insecticide residues in samples of foodstuffs, taken from commercial loads carried in freight containers, indicated that residue levels are unlikely to present a health hazard.     

Time trends in mortality of Conophthorus ponderosae (Hopkins) exposed to insecticide residues

The protection of the female cones of Pinus monticola (Dougl. ex D. Don) from attack by Conophthorus ponderosae (Hopkins) requires that the beetles be killed before they enter the cone. This encourages consideration of the distributions of length of time to death and how these distributions are changed with different concentrations of various candidate insecticides. In this study a three-parameter Weibull function was employed to depict the distributions for data originally collected for a probit analysis. The time to achieve 90% mortality as defined by the Weibull function was taken as a dependent variable, and a regression evaluation was used to define relationships with concentration for selected insecticides. The mode Y = b0 + b1 · X⁻1, in which Y = LT90 and × = insecticide concentration in g litre⁻1, proved useful when a sufficient range of concentrations was included in the testing.     

Persistence and frequency of application of an insecticide in relation to the rate of evolution of resistance

In an earlier paper, it was demonstrated that in order to delay the evolution of resistance, it is important to ensure that heterozygous carriers of resistance genes are killed so that the R gene is made effectively recessive. How this may be achieved is considered here, with (a) a persistent insecticide declining in effectiveness with time, and (b) a non-persistent insecticide (or fumigant). The relationship between the time taken for the dosage to decline to one-tenth (NGI) and the interval between insecticide applications (N12) was investigated. The optimal value of N12 was found to depend not only on the rate of decline but also on the shape of the degradation curve. Other important factors were (a) the dosage of insecticide applied (the initial effective dominance); (b) the initial frequency of the R gene; (c) the proportion of insects per generation that escaped exposure; and (d) whether selection occurred before or after mating. When considering non-persistent insecticides, it was necessary to distinguish between the short-lived deposit and the space spray, the latter being much less likely to lead to resistance.     

Analysis and dissipation of dislodgable residues of acephate,dimethoate and formetanate hydrochloride on citrus foliage

Dislodgable residues of acephate and its hydrolysis product methamidophos, dimethoate and its oxygen analogue omethoate (dimethoxon), and formetanate hydrochloride on citrus foliage were determined by gas–liquid chromatography. The use of 5% OV-101 coated on a Carbowax 20M surface-modified support (Ultra-Bond 20M) allowed the reproducible analysis of dimethoate and omethoate residues. Formetanate hydrochloride residues were analysed as the free base, without preparation of a derivative, on a column packed with 5% Apiezon N coated on 80–100 mesh Ultra-Bond 20M. The dissipation of the residues of the three pesticides applied to citrus trees was studied. Acephate and formetanate hydrochloride dissipation curves followed first-order kinetics; dimethoate residues were best characterised by two first-order kinetic processes. The half-life values were 8.2 days for acephate, undeterminably long for formetanate hydrochloride, and 2.2 days (the 1–10 days portion) and 7.0 days (the 10–49 days portion) for dimethoate.     

A colorimetric method for the determination of eight carbamate insecticide residues

A simple, quick and reliable method is described for the colorimetric estimation of residues of eight carbamate insecticides. The method is applicable to carbamates which on hydrolysis yield phenols with free para-positions suitable for coupling with a diazo reagent to yield coloured solutions. Optimum conditions for the development and measurement of the colour are described. Analytical data including graphs and some results from mud-bricks and cloth are presented to show the wide applicability of the method.     

Excretion and residues of the pyrethroid insecticide cypermethrin in laying hens

Laying hens were treated daily for 14 days with oral doses of [¹⁴C-phenoxy]cypermethrin (1.52 mg day^?1, 0-7 mg kg^?1) formulated on a small quantity of diet. Radioactivity in the eggs reached a plateau value of 0.05 μg equivalents g^?1 8 days after the start of dosing. Most of the residue was found in the yolk and was a mixture of cypermethrin and material which was closely associated with neutral lipids and phosphatidyl cholines. Four and a half hours after the last dose, the birds were killed and selected tissues were taken for analysis. The highest residue was found in the liver. This was composed of cypermethrin and a mixture of very polar metabolites which were not hydrolysed to significant amounts of 3-phenoxybenzoic acid or its 4-hydroxy derivative.     

Excretion and residues of the pyrethroid insecticide cypermethrin in lactating cows

Two radiolabelled forms of racemic [¹⁴C]cypermethrin (¹⁴C at the benzylic carbon or at C-1 of the cyclopropane ring) were separately administered twice daily to lactating cows in portions of the feed. The amounts dosed were equivalent to 0.2, 5 and 10 μg of cypermethrin per g of feed. The radioactivity eliminated in the milk indicated that the ingestion and elimination of radioactivity were in balance at about day 4 after the start of dosing. Urine and faeces were equally the major routes of elimination, and only a fraction of a percent of the dose appeared in the milk. The residue in the milk was unchanged cypermethrin and was found at a concentration that was proportional to the dose. At the high cypermethrin intake of 10 μg g^?1 of diet, the residue in the milk was 0.03 μg g^?1. Concentrations of residues in the tissues, measured after 7, 20 or 21 days of treatment, were low and in the order: liver>kidney>renal fat>subcutaneous fat>blood>muscle>brain. The major residue in the liver and kidney of a cow that received 10 μg of cypermethrin per g of diet was N-(3-phenoxybenzoyl)glutamic acid. Other conjugates of 3-phenoxybenzoic acid and of 3-(4-hydroxyphenoxy)benzoic acid (unidentified, with the exception of the glycine conjugate) were also present. The residue in fat (about 0.1 μg g^?1 from an intake of 10 μg g^?1 of feed) consisted mainly of cypermethrin.