Effects of deltamethrin on walking, flight and potato virus Y-transmission by pyrethroid-resistant Myzus persicae

In laboratory tests with moderately pyrethroid-resistant (R₁) Myzus persicae, more walked or flew from excised leaves pre-treated with the pyrethroid deltamethrin, or its aqueous formulation ‘Decis’ at 10 mg a.i. litre^-1 than from untreated leaves. Neither a carbamate (pirimicarb) nor an organophosphate (demeton-S-methyl) induced flight. R₁ alatae and apterae which had dispersed from deltamethrin-treated leaves rarely transmitted potato virus Y (PVY); however transmission by the more pyrethroid-resistant R₂ alatae was only halved and that by R₂ apterae undiminished. Treatment with deltamethrin decreased spread of PVY both in flight chamber and field experiments.     

The toxicity of aphicide residues to beneficial invertebrates in cereal crops

The toxicity of dimethoate, deltamethrin and pirimicarb residues to Bembidion lampros and Coccinella septempunctata was evaluated by confining groups of insects to winter wheat foliage and soil for 24 h at different times after treatment in the field. Flag leaf residues were found to be more toxic than first leaf residues: soil residues were the least toxic with pirimicarb showing virtually no soil toxicity. In general, dimethoate and deltamethrin showed similar levels of foliar toxicity with flag leaf toxicity on the first day after treatment being in the range 60–80% for B. lampros; deltamethrin was however, less toxic than dimethoate at ground level. Both of these products were more toxic than pirimicarb. The long-term exposure of insects, surviving the 24 h bioassays, to treated soil at different times following application resulted in further mortality and provided estimates of the maximum levels of mortality that populations of predators might suffer migrating into the crop at different times following application. Dimethoate was shown to be particularly harmful at the current recommended field application rate and reduced doses were proposed to limit the severity of the initial effects.     

Effects of the pyrethroid deltamethrin on the acquisition and inoculation of viruses by Myzus persicae

The pyrethroid, deltamethrin, alone or as an emulsifiable formulation, hindered infection of healthy plants with the persistent beet mild yellowing virus (BMYV) and both acquisition of, and infection with, the non-persistent potato virus Y (PVY) and the semi-persistent sugar beet yellows virus (BYV) by Myzus persicae in glasshouse tests.
Another pyrethroid, RU-15525, also protected against infection with PVY. Even sub-lethal amounts of deltamethrin decreased virus transmission by rapidly incapacitating the aphids, the effect being least with aphids most resistant to organophosphorous insecticides and to certain pyrethroids including deltamethrin. Demeton-S-methyl hindered infection only with BMYV. This work shows that deltamethrin restricts transmission of persistent, semi-persistent and perhaps more importantly of non-persistent viruses in the glasshouse, and has potential for doing the same in the field.     

The Ability of Aphis craccivora, A. gossypii and A. citricola to Transmit Single and Mixed Viruses to Cowpeas

The ability of populations of adult apterous Aphis craccivora, A. gossypii and A. citricola to transmit the cowpea aphid-borne virus (CAMV) and cucumber mosaic virus (CMV) to cowpea was investigated. CMV was more readily transmitted than CAMV by all three aphid species, but was most readily transmitted by A. craccivora and A. citricola, with transmissions ranging from 64–71 %. With CAMV, the infection level with A. gossypii was higher than with A. craccivora and both were more efficient than A. citricola, although the differences were not significant. With mixed infections of CAMV and CMV, there was a higher level of CAMV transmission using A. craccivora from sequential feeding when CMV-infected plants were fed on first followed by CAMV-infected plants, suggesting that cowpea plants were more prone to infection by CAMV when already infected by CMV.     

Propagation of lettuce (Lactuca sativa) breeding material by tissue culture

A tissue culture method using Murashige and Skoog's (MS) medium was devised to propagate healthy plants from field grown lettuce plants selected for seed production. Explants (2–3 mm long) from axillary buds were successfully grown on MS + 1.0 or 2.0 mg litre^-1 kinetin and 6.4 mg litre^-1 IAA to promote shoot growth. Concentrations of 0.5 and 4.0 mg litre^-1 kinetin gave poor shoot growth. The cultures were successfully rooted after 3–4 wk on MS + 6.4 mg litres^-1 IAA after transfer from MS + 1.0 mg litre^-1 kinetin and on MS + 4.8 mg litre^-1 IAA after transfer from MS + 2.0 mg litre^-1 kinetin. Concentrations of 3.2 and 8.0 mg litre^-1 IAA gave poor root initiation. Root initiation was more successful when cultures were grown at 40 Wm^-2 than in cultures grown at 5 Wm^-2. Rooted cultures were established in compost with a 90–95% success rate and the regenerated plants flowered c. 18 wk after the cultures were initiated.     

Comparison of different insecticides and fabrics for anti-mosquito bednets and curtains

Abstract. Various formulations of six insecticides (a carbamate and five pyrethroids), were impregnated into bednets and curtains made from cotton, polyester, polyethylene or polypropylene fabric. For bioassays of insecticidal efficacy, female Anopheles gambiae mosquitoes were made to walk on the fabrics for 3 min and mortality was scored after 24 h. The main concentrations tested were: bendiocarb 400 mg/m², cyfluthrin 30–50 mg/m², deltamethrin 15–25 mg/m², etofenprox 200 mg/m², lambda-cyhalothrin 5–15 mg/m² and permethrin 200–500 mg/m². Field trials in Tanzania used experimental huts (fitted with verandah traps) entered by wild free-flying Anopheles gambiae, An. funestus and Culex quinquefasciatus mosquitoes. Results of testing the impregnated fabrics in experimental huts showed better personal protection provided by bednets than by curtains. Permethrin cis:trans isomer ratios 25:75 and 40:60 were equally effective, and the permethrin rate of 200 mg/m² performed as well as 500 mg/m². Bioassay data emphasized the prolonged insecticidal efficacy of lambda-cyhalothrin deposits, except on polyethylene netting. Most of the impregnated nets (including the ‘Olyset’ net with permethrin incorporated during manufacture of the polyethylene fibre) and an untreated intact net performed well in preventing both Anopheles and Culex mosquitoes from feeding on people using them overnight in the experimental huts. Anopheles showed high mortality rates in response to pyrethroid-treated nets, but only bendiocarb treated curtains killed many Culex. Holed nets treated with either cyfluthrin (5 EW formulation applied at the rate of 50 mg a.i./m²) or lambda-cyhalothrin (2.5 CS formulation at 10 mg a.i./m²) performed well after 15 months of domestic use. Treatment with deltamethrin SC or lambda-cyhalothrin CS at the very low rate of 3 mg/m² gave good results, including after washing and re-treatment.     

Effects of carbonyl sulfide, methyl iodide, and sulfuryl fluoride on fruit phytotoxicity and insect mortality

Three potential chemical fumigants: carbonyl sulfide (COS), methyl iodide (MI) and sulfuryl fluoride (SF) were tested at selected dosages on lemons against California red scale (Aonidiella aurantii) and MI and COS were tested on nectarines against codling moth (Cydia pomonella). In nectarines, COS was tested at 0, 20, 40, 60 and 80 mg litre^?1, MI at 0, 10, 15, 20 and 25 mg litre^?1. Both fumigants intensified nectarine peel color, delayed fruit softening, but did not alter overall fruit quality. COS at 80 mg litre^?1 resulted in 87% codling moth mortality, but the fumigant dosage was insufficient to reach the desired probits 9 level (99.9968%). MI gave 100% codling moth mortality at 25 mg litre^?1. Lemons were treated with MI at 0,10,20,40,60 mg litre^?1, SF at 0,10,20,40, 80 mg litre^?1 and COS at 0,20,40, 60 and 80 mg litre^?1. MI gave 100% red scale mortality at ≥40 mg litre^?1 but caused significant fruit injury. Conditioning lemons at 15°C for 3 days before MI fumigation lessened lemon phytotoxicity. Forced aeration at 3.5 standard litres per minute of lemons for 24 h following MI fumigation at 20 mg litre^?1 significantly reduced phytotoxicity compared to 2 h postfumigation aeration after MI treatment. SF at ≥40 mg litre^?1 gave 100% red scale mortality but resulted in commodity phytotoxicity. Lemons treated with the highest selected dose of 80 mg litre^?1 COS gave only 87% kill of red scale, but failed to reach the desired probit 9 level.     

Efficacy of various synthetic pyrethroid-impregnated encasement materials against house dust mite under laboratory conditions

The acaricidal activity of synthetic pyrethroid and benzyl benzoate against Dermatophagoides pteronyssinus was examined in the laboratory, using a specially designed test set up. On the basis of median lethal dose (LD₅₀) values, the compound found to be most toxic to D. pteronyssinus was benzyl benzoate (LD₅₀ = 50 mg/m²), followed by permethrin (LD₅₀ = 76.7 mg/m²), deltamethrin (LD₅₀ = 146.7 mg/m²), esbioallenthrin (LD₅₀ = 186.6 mg/m²) and lamdacyhalothrin (LD₅₀ = 756.6 mg/m²). Very low toxicity was observed with bifenthrin (LD₅₀ = 5157.8 mg/m²). A laboratory control trial was also carried out to compare the acaricidal activity (residual effect) of four pyrethroids impregnated on woven and non-woven encasement materials against house dust mites during a 4-month period. Of the pyrethroids used in this study, esbioallenthrin demonstrated the highest acaricidal activity, and of the pyrethroid impregnated materials, the non-woven encasement material was more effective than the woven encasement material.     

Direct plant regeneration from leaf explants of Plumbago species and its genetic fidelity through RAPD markers

In vitro plant regeneration was achieved from leaf explants of Plumbago rosea and Plumbago zeylanica on Murashige & Skoog (1962) medium supplemented with 1.5 mg litre^?1 6‐benzylaminopurine, 0.25 mg litre^?1 indole‐3‐acetic acid, 50 mg litre^?1 adenine sulfate and 3% (w/v) sucrose. The shoot initials developed within 2–3 wk on the leaf margin as well as from the wounds of the leaf. High frequency shoot‐bud regeneration was achieved on similar medium in subsequent subcultures. The semi‐mature leaves produced more shoot‐buds as compared to the younger leaves. Mature leaves did not show any response for shoot bud initiation. More than 85% of the semi‐mature explants produced shoot‐buds per leaf explant within 4 wk of culture. Shoots rooted easily on medium having half‐strength basal Murashige & Skoog (1962) medium supplemented with 0.25 mg litre^?1 indole‐3‐butyric acid and 2% (w/v) sucrose; 84–92% of the in vitro rooted plantlets survived in the greenhouse. The regenerated plantlets appeared morphologically similar to the mother plants. No variation was detected among the regenerated plants by the use of Randomly Amplified Polymorphic DNA (RAPD) markers. This method might be useful for assessing plant improvement programmes.     

Effect of imidacloprid on the sivlerleaf whitefly, Bemisia argentifolii Bellows and Perrring (Homoptera: Aleyrodidae), and whitefly parasitism

Bioassays were conducted under greenhouse conditions to determine the effect of imidacloprid on adult and nymphal stages of the silverleaf whitefly, Bemisia argentifolii Bellows and Perring, and parasitism by Encarsia formosa (Gahan). A flowable formulation (24Oglitre^-1) of imidacloprid at six rates (0.09, 0.04 and 0.02 g a.i. litre^-1 pot volume for experiments 1 and 2; 0.009, 0.004, and 0.002 g a.i. litre^-1 pot volume for experiment 3) was evaluated. After a 48 h exposure to treated plants, high mortality of adult whitefly (>94%) was observed. Adults exposed to poinsettias treated 150 days earlier also had significantly greater mortality (>79%) than the adults on control plants. When exposed to treated plants for only 6 h, >65% of adults were killed. All three rates of imidacloprid caused >97% mortality of immature whiteflies by day 19. When treated plants were continually exposed to adult whiteflies, immature mortality was 100% for the three higher rates of imidacloprid up to and including 88 days after treatment. During the same time, emerging adults were reduced significantly. Immatures reinfested on plants treated 161 days earlier, incurred 80% mortality at the higher rate 0.09 g a.i. litre^-1 pot volume and 38% mortality at 0.02 g a.i. litre^-1 pot volume. At lower treatment rates, results varied. At 0.009 g a.i. litre^-1 of pot volume, mean percentage whitefly mortality (65%) 25 days after treatment was significantly higher than the controls; however, whitefly mortality at 0.004 and 0.002 g a.i. litre^-1 pot volume was not significantly different from controls or plants treated with the higher rate. Parasitoids could develop to the adult stage on whiteflies infesting imidacloprid treated plants. Parasitism occurred at low levels (< 10%), doe to high levels of whitefly mortality on treated plants. No phytotoxicity was observed for any treatment throughout the length of the trials that lasted through flowering.     

The effects of sowing date and choice of insecticide on cereal aphids and barley yellow dwarf virus epidemiology in northern England

During the mid-1980s, Sitobion avenae became recognised as an important vector of barley yellow dwarf virus (BYDV) in the Vale of York. A field trial at the University of Leeds Farm, North Yorkshire, was carried out during the autumn/winter of 1984-85 to evaluate different control procedures against S. avenae-transmitted BYDV and to investigate its epidemiology. Winter barley was sown on three dates in September, and plots were sprayed with either deltamethrin, demeton-S-methyl or pirimicarb on one of three dates between mid-October and mid-November, making a factorial design. Rhopalosiphum padi, the main vector of BYDV in southern England, were rarely found during the experiment, but the numbers of S. avenae were much higher, reaching a peak of 21% of plants infested in the unsprayed plots of the first sowing date. Single applications of each insecticide reduced populations of S. avenae to zero. Some treatments, particularly in the early sown plots and those treated with pirimicarb, however, did allow some recolonisation, and thus led to increased virus incidence and decreased yields. Sprays applied before the end of the migration of S. avenae were more efficient at controlling BYDV if the insecticide was persistent, otherwise a spray after this period, in November, was more effective. Virus incidence, although reduced by sprays, was generally low in plots sown on 18 and 27 September. In contrast, about 11% of plants were infected in unsprayed plots sown on 6 September and a small yield benefit was obtained with insecticidal treatments. Enzyme-linked immunosorbent assay (ELISA) of plants taken from the plots indicated that MAV- and PAV-like strains were present, and were most likely to have been transmitted by S. avenae.     

Nitrogen fertilisation and light effects on growth and photosynthesis of lodgepole pine seedlings

Seedlings of Pinus contorta were grown for 16 wk without ectomycorrhizas in the greenhouse at three levels of irradiance (100, 210 and 470 μEm^-2s^-1) and three levels of ammonium nitrate (3, 62 and 248 mg litre^-1 of N). Measurements at 5, 10 and 16 wk of age indicated that plants receiving the highest levels of irradiance and nitrogen had significantly larger biomass, a higher total foliar N and P content and net photosynthesis per unit leaf area than those at lower levels of each factor. Although the root/shoot ratio also increased from low to high irradiance at each harvest, nitrogen application resulted in an increased ratio from 3 to 62 mg litre^-1 N, but decreased ratio at 248 mg litre^-1 N.     

Interaction between two synthetic pyrethroids and the spread of two non-persistent viruses in cowpea

The effectiveness of the synthetic pyrethroids deltamethrin and lambda-cyhal-othrin in preventing (i) aphid colonisation of four cowpea cultivars with different levels of aphid resistance and (ii) the introduction and subsequent spread of cowpea aphid-borne mosaic virus and cucumber mosaic virus was investigated under tropical field conditions. Sprays of these pyrethroids eight days apart prevent aphid colonisation and within crop spread of virus by the colonising Aphis craccivora. However, neither deltamethrin nor lambda-cyhalothrin prevented the initial introduction of virus into the cowpea crop and, when incoming alate incidence was high, virus incidence was higher in the sprayed than in the unsprayed plots. In addition, the degree of aphid resistance of each cultivar affected secondary virus spread within the crop, with greatest spread in the most resistant cultivar.     

Pyrethroid-sprayed tents for malaria control

Field trials were undertaken in the North West Frontier Province of Pakistan to determine the effects of pyrethroid-sprayed tents on feeding success, mortality and biting-rates of wild mosquitoes attracted to bait cows confined within the tents. Under natural conditions, endophagic mosquitoes rested only briefly in untreated tents during the night, followed by complete exodus at dawn. In tents sprayed on the interior surface with permethrin 0.5 mg/m² or with deltamethrin 0.03 g/m² the biting rate of Anopheles stephensi was reduced by about 40%; detergency against culicines and other anophelines was much less. Mortality-rates of bloodfed mosquitoes from the treated tents were 75%An.stephensi, 65%An. subpictus but only 10% of culicines. Outer fly-sheets prolonged the effective life of the treatment; bioassays on the sprayed inner-sheets showed that insecticidal efficacy remained high for over a year, whereas on tents without fly-sheets permethrin residual efficacy declined rapidly 20–40 weeks post-treatment. It is concluded that tent-spraying with fast-acting photostable residual pyrethroid insecticide would probably provide effective protection against malaria transmission for the inhabitants of tents in any part of the world where the vector mosquitoes are endophilic and susceptible to pyrethroids.     

Soil contact toxicity of insecticides to the european earwigForficula auricularia [Dermaptera]

The soil contact effects of several commonly used agricultural insecticides on 2nd instar and adultForficula auricularia (L.) were studied in the laboratory. The earwigs were individually confined on soil surfaces sprayed under a track sprayer. Pirimicarb had no effect on either adult or 2nd instar earwigs. The LD_50,s of 2nd instar earwigs for γ HCH, fenitrothion, DDT and dimethoate were all lower than their normal field rates. Second instars were more susceptible to dimethoate and cypermethrin than adults. The pyrethroids cypermethrin and deltamethrin had LD_50,s above normal field rates. However, high levels of knockdown were induced by both insecticides at concentrations below normal application rates. The effects of this in the field remain unknown.     

Effects of three modern insecticides, pyriproxyfen, spinosad and tebufenozide, on survival and reproduction of Chrysoperla carnea adults

Three novel insecticides, pyriproxyfen, spinosad and tebufenozide, were evaluated for their effect on survival and reproduction of Chrysoperla carnea adults using two methods of exposure: direct contact and ingestion. Pyriproxyfen and tebufenozide proved to be harmless to adult survival, whereas spinosad 72 h after treatment reduced the number of adults by 39.8% and 87.2% in topical and ingestion treatment at the maximum concentration recommended (800 mg a.i. litre^?1). Fecundity was not affected irrespective of the insecticide or time of application (before or after the onset of oviposition). Concerning fertility, only pyriproxyfen exerted a negative effect on hatching when the eggs were deposited by females treated by ingestion in the post‐oviposition period at the highest concentration tested (150 mg a.i. litre^?1).     

Pyrethroid insecticides: Actions of deltamethrin and related compounds on insect axonal sodium channels

The actions of deltamethrin and eight other pyrethroids were tested on isolated giant axons of the cockroach Periplaneta americana, using microelectrode and oil-gap, single-fibre electrophysiological recording techniques. Deltamethrin at micromolar concentrations induced a slow progressive depolarization of the axon membrane accompanied by a gradual reduction in action potential amplitude. The deltamethrin-induced depolarization was enhanced by an increase in stimulation frequency and was reduced in the presence of the sodium channel blocking agent saxitoxin (1 × 10^?7 M).Other synthetic pyrethroids (biopermethrin and its 1S enantiomer, biotetramethrin, s-bioallethrin, bioresmethrin and its 1S enantiomer, cismethrin and kadethrin) were also studied. In contrast to the findings with deltamethrin all other compounds, apart from the 1S isomers which were inactive, induced prolonged negative (depolarizing) after-potentials. Deltamethrin appears to affect a small fraction of sodium channels which are held in a modified open-state, whereas the pyrethroids which generate large negative after-potentials appear to induce a brief alteration of the open-state sodium channels with a larger number of channels affected. Differences between the actions of pyrethroids on insect axonal sodium channels and whole insects are discussed.     

Pyrethroid action on calcium channels: neurotoxicological implications

Actions of cismethrin versus deltamethrin were compared using two functional attributes of rat brain synaptosomes. Both pyrethroids increased calcium influx but only deltamethrin increased Ca²⁺-dependent neurotransmitter release following K⁺-stimulated depolarization. The action of deltamethrin was stereospecific, concentration-dependent, and blocked by ω-conotoxin GVIA. These findings delineate a separate action for deltamethrin and implicate N-type rat brain Ca_v2.2 voltage-sensitive calcium channels (VSCC) as target sites that are consistent with the in vivo release of neurotransmitter caused by deltamethrin. Deltamethrin (10⁻⁷ M) reduced the peak current (approx. −47%) of heterologously expressed wild type Ca_v2.2 in a stereospecific manner. Mutation of threonine 422 to glutamic acid (T422E) in the α₁-subunit results in a channel that functions as if it were permanently phosphorylated. Deltamethrin now increased peak current (approx. +49%) of T422E Ca_v2.2 in a stereospecific manner. Collectively, these results substantiate that Ca_v2.2 is directly modified by deltamethrin but the resulting perturbation is dependent upon the phosphorylation state of Ca_v2.2. Our findings may provide a partial explanation for the different toxic syndromes produced by these structurally-distinct pyrethroids.     

Post-harvest age-induced seed dormancy of Acer ginnala and its alleviation by growth regulator and low temperature treatments

One-month-old fruits of Acer ginnala with winged pericarp attached gave 44% germination and this was not increased by cold treatment at 4°C for 0, 10, 20, or 30 days, gibberellic acid treatment at 0, 1, 10, 100 or 1000 mg litre^-1, or ethephon treatment at 0, 2, 20, 200 or 2000 mg litre^-1. After 6 months of storage at 20–25 °C, germination of untreated fruits fell to 5% but could be restored to that of 1-month-old fruits by incubation at 4 °C for 30 days. After 9 months storage, no germination occurred in untreated fruits. Cold treatment (30 days at 4 °C partially restored germination (26%). Treatment with either gibberellic acid (1000 mg litre^-1) and 30 days at 4 °C (40%) or ethephon (100 mg litre^-] and 30 days at 4 °C improved germination (69%). The combination of all three treatments, i.e. 100 mg litre^-1 gibberellic acid, 100 mg litre^-1 ethephon and 30 days at 4 °C, optimised germination (86%). Thus, dormancy of A. ginnala developed during storage but could be reversed by a combination of treatment with low temperature and growth regulators. The highest germination (86%) was achieved after low temperature and growth regulator treatment of stored fruit.     

六种常用杀虫剂对八种蚜虫的选择毒性

作者自1982年开始研究了乐果、氧化乐果、抗蚜威、氰戊菊酯、溴氰菊酯和氯氰菊酯等6种杀虫剂对8种蚜虫的选择毒性.以桃粉大尾蚜Hyalopterus amygdali Blanchard为标准,氧化乐果对桃粉大尾蚜和瓜蚜Aphis gossypii Glover之间的选择毒性指数最高为163.77,乐果和抗蚜威分别是373.24和34.70,而氰戊菊酯仅为1.37.氰戊菊酯最高的选择毒性指数是在桃粉大尾蚜和麦长管蚜Sitobionavenae(F.)之间,也只有6.86,有机磷和氨基甲酸酯杀虫剂对不同蚜虫的选择毒性与乙酰胆碱酯酶(AChE)对巯基试剂(DTNB)的敏感度有明显的相关性,说明其选择毒性与AChE的巯基结合部位有关.同时还发现,抗蚜威对洋槐蚜Aphis robiniae Macchiati和瓜蚜AChE的1₅₀值与其LC₅₀值表现一致.这些都说明了这两类杀虫剂对不同种蚜虫的选择毒性与AChE有关.氰戊菊酯和溴氰菊酯对蚜虫的选择毒性与α-乙酸萘酯羧酸酯酶的活性具有明显的相关性,而与β-乙酸萘酯羧酸酯酶的活性则无任何关系.氯氰菊酯的选择毒性与上述两种酯酶的活性没有任何相关性.