Relationship of phenotypic structures and allelochemical compounds of okra (Abelmoschus spp.) to resistance against Aphis gossypii Glover

The cotton aphid (Aphis gossypii) is one of the major pests of okra. Eleven okra varieties collected from farmers' fields in Cameroon and four aphid-resistant accessions from The World Vegetable Center (AVRDC, Asian Vegetable Research and Development Center) were evaluated from October 2012 to March 2013, and another seven aphid-resistant accessions from AVRDC were evaluated from March to July 2013 at AVRDC's Nkolbisson station, Yaoundé, Cameroon. Accessions selected from these trials were screened in an advanced confirmatory screening in autumn (October–December) 2013 in Shanhua, Taiwan. Results showed that none of the farmers' landraces were resistant to aphids. Two accessions (VI041210 and VI033824) with the lowest aphid populations had the highest trichome density. Analysis of various phytochemicals in selected okra accessions revealed that higher nitrogen and potassium levels made the okra accessions susceptible to aphids during the reproductive stage of the plants. Similarly, the total phenol content was lower in moderately resistant accessions during their reproductive stage. Aphid feeding induced an increase in phenols, and to a lesser extent, tannins. Accessions VI041210 and VI033824 could be incorporated into an integrated pest management strategy to enhance productivity of okra.     

Acaricide resistance and synergism between permethrin and amitraz against susceptible and resistant strains of Boophilus microplus (Acari: Ixodidae)

The control of the southern cattle tick, Boophilus microplus (Canestrini), in Mexico and many other countries relies on chemical acaricides. Boophilus microplus has developed resistance to all major classes of acaricides in recent years. To gain a better understanding of the resistance and to develop resistance management strategies that benefit both Mexican ranchers and USDA's cattle fever tick eradication program (CFTEP), the authors used larval bioassay techniques to determine levels of resistance to permethrin and amitraz and then evaluated synergism between these two acaricides in one susceptible laboratory tick strain and four resistant strains originating from Mexico and Brazil. To examine mechanisms of resistance to permethrin in these strains, the frequency of a mutated sodium channel gene was determined using a PCR assay. The tick strains from Mexico and Brazil demonstrated 49.4- to over 672.2-fold resistance to permethrin, and up to 94.5-fold resistance to amitraz. While the San Roman strain from Mexico was the most permethrin-resistant strain, the Santa Luiza strain from Brazil was the most amitraz-resistant strain. A significant correlation was found between the permethrin resistance ratio and the allelic frequency of the sodium channel mutation. Significant synergism between permethrin and amitraz was found when one acaricide was tested in the presence of another. Synergism ratios ranged from 1.5 to 54.9 when amitraz was tested as a synergist for permethrin. Similar synergism ratios were obtained when permethrin was tested as a synergist for amitraz. Permethrin caused virtually no mortality in the San Roman strain, even at the highest concentration (3294 microg cm(-2)). Adding amitraz (11.0 microg cm(-2)) to permethrin led to a dramatic increase in larval mortality, even at very low concentrations of permethrin.     

Repellent action of permethrin,cypermethrin and resmethrin against black flies (Simulium spp.) attacking cattle

Permethrin, cypermethrin, and resmethrin were tested under field conditions as repellents to protect cattle from black flies (Simulium spp.). The chemicals were applied topically to the entire body surface of steers. Ethanolic solutions of technical permethrin, at doses of 1, 2, 4 and 6 mg a. i. kg^?1 of body weight, effectively repelled black flies by preventing at least 70% of the flies present from taking a blood meal for up to 8 days, and for at least 11 days at a dose of 12 mg a. i. kg^?1. Aqueous mixtures of a 20% permethrin emulsifiable concentrate (e. c.), at doses of 1, 2 and 6 mg a. i. kg^?1, effectivelyrepelled black flies for 2, 10 and 11 days, respectively. Aready-to-use 5% permethrin dust, at doses of 1, 2, and 4 mg a. i. kg^?1, effectively repelled black flies for 4, 5 and 8 days, respectively. Ethanolic solutions of technical cypermethrin, at doses of 1 and 2 mg a. i. kg^?1, repelled black flies for 3 and 4 days, respectively. Aqueous mixtures of a 40% cypermethrin e. c., at doses of 2 and 4 mg a. i. kg^?1, repelled black flies for at least 5 days. Ethanolic solutions of technical resmethrin, at doses of 2 and 6 mg a. i. kg^?1, repelled black flies for 1 and 2 days, respectively.     

Relationship between chemical structure and biological activity of triazole fungicides against Botrytis cinerea

The inhibitory activity of commercial and experimental triazole fungicides on the target enzyme, sterol 14α-demethylase (P450_14DM), was studied in a cell-free sterol synthesis assay of Botrytis cinerea Pers. ex Fr. In order to assess structure-activity relationships, the inhibitory activities of the compounds on radial growth of the fungus were tested as well. The EC₅₀ values (concentrations of fungicide inhibiting radial growth of B. cinerea on PDA by 50%) of all triazoles tested ranged between 10^?8 and 10^?5 m. IC₅₀ values (concentrations of fungicide inhibiting incorporation of [2-¹⁴C]mevalonate into C4-desmethyl sterols by 50%) generally ranged between 10^?9 and 10^?7 M and correlated with inhibition of radial mycelial growth. However, differences in IC₅₀ values did not reflect quantitatively the observed differences in EC₅₀ values, since the ratio between EC₅₀ and IC₅₀ increased with decreasing fungitoxicity. For a limited number of compounds the correlation between intrinsic inhibitory activity and fungitoxicity was low. Both in-vitro tests were used to investigate structure-activity relationships for stereoisomers of cyproconazole, SSF-109 and tebucona-zole. Fungitoxicity and the potency to inhibit cell-free C4-desmethyl sterol synthesis correlated for all stereoisomers tested. Mixtures of isomers of tebucona-zole or cyproconazole were slightly less active than the most potent isomer. The high activity of several commercial triazoles in both experiments implies that poor field performance of triazole fungicides against B. cinerea is due neither to insensitivity of the P450_14DM nor to low in-vitro sensitivity of the fungus.     

Characterization of acetylcholinesterases of acaricide resistant and susceptible strains of the cattle tick Boophilus microplus (Can.): II. The substrate specificity and catalytic efficiency of the critical enzyme component

Concentrations and turnover numbers have been determined for the critical acetylcholinesterase component of the organophosphorus susceptible Yeerongpilly and resistant Biarra and Ridgelands strains. The lower specific activity for the substrate acetylthiocholine in the resistant strains was shown to be due to decreased catalytic efficiency and not to any change in the titer of the enzyme. Thioester analogs of acetylthiocholine, with additional methylene groups between the carbonyl carbon and the quaternary nitrogen of the molecule and in the alkyl moiety, have been used to derive K_m and V_max values for the enzymes from each strain. An hypothesis is proposed concerning the alteration of the active site that has occurred to produce the dissimilar aberrant enzymes of the resistant strains and the implications of this hypothesis for inhibitor design are discussed.     

Protective action of fenvalerate,deltamethrin, and four stereoisomers of permethrin against black flies (Simulium spp.) attacking cattle

Fenvalerate, deltamethrin, (1R)-cis-permethrin, (1R)-trans-permethrin and (1S)-trans-permethrin, applied topically to the entire body surface of steers at a rate of 1 mg a.i. kg⁻¹, provided 70% or better protection from black flies on cattle for 16, 9, 8, 6 and 6 days, respectively. The (1S)-cis stereoisomer of permethrin was ineffective as a protectant against black flies at a rate of 1 mg a.i. kg⁻¹ when applied as a total body spray. One poly(vinyl chloride) ear tag containing 10% permethrin, in each ear of steers, provided protection from black fly attack for up to 13 days under field conditions. Poly(vinyl chloride) ear tags containing 8% fenvalerate, installed in each ear of steers, did not provide satisfactory protection from black flies under field conditions.     

Insect deterrent activity of ethanolic leaf extracts of landrace maize and determination of active compounds against Spodoptera littoralis Boisduval (Lepidoptera: Noctuidae)

Journal of Plant Diseases and Protection - The present work was carried out to gain insight into the chemical defense of maize against phytophagous insects. Leaves of sixteen landrace populations...     

Characterization of acetylcholinesterases of acaricide-resistant and susceptible strains of the cattle tick Boophilus microplus (Can.): I. Extraction of the critical component and comparison with enzyme from other sources

The critical acetylcholinesterase component, that is responsible for the resistance mechanism of decreased sensitivity to the inhibitor in the cattle tick Boophilus microplus (Can.), has been isolated from the organophosphorus-susceptible Yeerongpilly and resistant Biarra and Ridgelands strains. With the substrate acetylthiocholine this enzyme component gave a pH activity profile similar for all strains. Optimal substrate concentration for Ridgelands was 1.73.10^?2M compared to 2.70.10^?4M for the other strains. Computed Km values were 1.98.10^?5M, 3.65.10^?5M, and 6.43.10^?6M for Yeerongpilly, Biarra, and Ridgelands strains, respectively, while the corresponding V_max figures were 336, 135, and 21 μmoles acetylthiocholine hydrolyzed per gram of larvae per hour. These results are discussed in relation to the resistance mechanism and compared with similar parameters derived for this enzyme from bovine erythrocytes, the sheep blowfly Lucilia cuprina, and the sheep nematode Trichostrongylus colubtiformis.     

香豆素类化合物对朱砂叶螨的触杀活性及定量构效关系研究

采用玻片浸渍法,测定并筛选了25种具有代表性的香豆素类化合物对朱砂叶螨Tetranychus cinnabarinus雌成螨的触杀活性,并构建了一个预测能力较强的定量构效关系(QSAR)模型。结果表明:所有供试化合物对朱砂叶螨均具有触杀活性,且随着处理时间的延长活性升高。处理48 h后,LC50值低于1000 mg/L的化合物有8个,分别是3-(2-苯并咪唑)-7-(二乙氨基)香豆素(1)、3-(2-苯并噻唑)-7-(二乙氨基)香豆素(2)、3-氨基香豆素(3)、3-乙酰基香豆素(4)、4-甲氧基香豆素(5)、6-硝基香豆素(8)、6,7-二甲氧基香豆素(13)和7,8-二羟基香豆素(21),其中化合物1、2、3、5和13的杀螨活性优于药剂对照螺螨酯或与其活性相当;活性最好的化合物为13,处理48 h和72 h后LC50值分别为284.8和122.2 mg/L,其毒力约为螺螨酯的2倍。通过计算得到25种香豆素类化合物的34种物化参数,以此为描述子,经过SPSS相关性剔除、逐步回归分析和校正,得到一个以扭转力、取向力、总能量和分子半径为自变量的QSAR模型,该模型复相关系数R达到0.987,复判定系数R2也达到0.967,通过F检验证明上述模型具有较高的预测能力。     

Toxicology and metabolism of some synthetic pyrethroids in larvae of susceptible and resistant strains of the cattle tick boophilus microplus (Can.)

Larvae of the Malchi and DDT-R pyrethroid-resistant strains of ticks, compared with larvae of the Yeerongpilly (susceptible) strain, exhibited knock-down resistance equally to (1 RS)-cis- and (1 RS)-trans-permethrin but little resistance to either (1 RS)-cis- or (1 RS)-trans-cypermethrin. Kill resistance was higher in Malchi than in DDT-R ticks and more pronounced against the permethrin isomers. The cis-isomers were more potent overall than the trans-isomers. Cypermethrin isomers penetrated more slowly than permethrin isomers, especially into Malchi larvae. Metabolic detoxication, mainly esteratic, was fastest in Malchi larvae, trans-isomers consistently being attacked faster than cis-isomers. The greatei resistance of Malchi ticks is therefore probably due to a combination of these two differences. Dual mechanisms of the toxic action of pyrethroids are discussed.     

Identification of the anthracnose fungus of walnut (Juglans spp.) and resistance evaluation through physiological responses of resistant vs. susceptible hosts

Walnut anthracnose is one of the most serious diseases of walnut globally. In this study, the pathogen was identified as Colletotrichum gloeosporioides by morphological and molecular approaches. Then, the resistance of 18 walnut genotypes was evaluated by field investigation as well as field and detached leaflet inoculation. A field inoculation assay was used as a benchmark for comparing field evaluation and the detached leaflet inoculation assay. Seven genotypes, Panhe1 and clones 71 and 200 of Juglans sigillata, Yanyuanzao and Qingxiang of J. regia, and Shujiang1 and Chuanzao1 of J. regia × J. sigillata, displayed high resistance in all assays, suggesting that they may be good candidates for further evaluation. Subsequently, two genotypes (Panhe1 with high resistance, and clone 199 with high susceptibility) were selected to analyse the different physiological responses between highly resistant and susceptible genotypes after inoculation. C. gloeosporioides infection induced the activities of superoxide dismutase (SOD), peroxidase (POD), polyphenol oxidase (PPO), and chitinase; they were all significantly increased in both Panhe1 and clone 199. However, the POD activity and its change rate in Panhe1 were significantly higher than those in clone 199. The change rates of PPO activity, and total phenol and proline content in Panhe1 were significantly higher than those in clone 199. Moreover, the change rates of SOD activity, malondialdehyde, and soluble sugar content in clone 199 were significantly higher than those in Panhe1. These findings not only enhance our understanding of the resistance of walnut to anthracnose, but also lay the foundation for breeding anthracnose-resistant walnuts in the future.     

The pyrethrins and related compounds part XXXIX— structure-activity relationships of pyrethroidal esters with cyclic side chains in the alcohol component against resistant strains of housefly (Musca domestica)

Activities of a range of pyrethroidal esters, incorporating structural variations in all regions of the acid and alcohol components, have been measured against two fully characterised and homozygous resistant strains of Musca domestica L. (kdr and super-kdr). The results, limited in this paper to esters of alcohols with cyclic side chains, indicate uniform resistance to the kdr strain across the whole range of structural variations. Against the super-kdr strain, while variation in the acid component has little effect, the resistance factor is sensitive to the nature of the alcohol component, in particular on whether it contains an α-cyano substituent.     

New and little-known lepidopteran (Lepidoptera) phytophages on the poplars (Populus spp.) in Bulgaria

Investigations were carried out during the period 1997-1999 on lepidopteran entomofauna deleterious to poplars (Populus spp.) in Bulgaria. The phytophages were collected in larval and pupal stage and were reared under laboratory con-ditions to the adult stage. In two regions of Bulgaria, Sofia and Montana, 18 new and little-known phytophages in seven families were established on the trees in Populus genus: Limenitis populi (L.) (Nymphalidae); Anacampsis populefia (Cl.), Gelechia turpella (Den. & Schiff.) (Gelechiidae); Synanthedon melliniformis (Lasp.) (Sesiidae); Euproctis similis (Fuessl.) (Lymantriidae); Drymonia velitaris (Hufn.), Notodonta tritophus (Den. & Schiff.) (Notodontidae); Amphipyra pyramidea (L.), Catocala nupta (L.), Cosmia trapezina (L.), Enargia paleacea (Esp.), Eupsilia transversa (Hufn.), Ipomorpha subtusa (Den. & Schiff.), Parastichtis ypsilon (Den. & Schiff.), Scoliopteryx libatrix (L.) (Noctuidae); Gastropacha quercifolia (L.), Phyllodesma tremulifolia (Hb.) and Poecilocampa populi (L.) (Lasiocampidae). G. turpella and S. melliniformis are new records for Bulgaria and D. velitaris was found for the first time in Northern Bulgaria. Thirteen species (L. populi, E. similis, D. velltaris, N. tritophus, A. pyramidea, C. nupta, C. trapezina, E. transversa, I. subtusa, P. ypsilon, G. quercifolia, P. tremulifolia and P. populi) were established for the first time in Bulgaria to have a trophic relationship with poplars. G. turpella and L subtusa were occurred in the highest population densities – up to 1.6 larvae/m and up to 1.1 larvae/m respectively. The remaining species occurred in low population densities in the studied habitats and were not considered to be pests on the poplars.     

New and little-known lepidopteran (Lepidoptera) phytophages on the poplars (Populus spp.) in Bulgaria

Investigations were carried out during the period 1997-1999 on lepidopteran entomofauna deleterious to poplars (Populus spp.) in Bulgaria. The phytophages were collected in larval and pupal stage and were reared under laboratory con-ditions to the adult stage. In two regions of Bulgaria, Sofia and Montana, 18 new and little-known phytophages in seven families were established on the trees in Populus genus: Limenitis populi (L.) (Nymphalidae); Anacampsis populefia (Cl.), Gelechia turpella (Den. & Schiff.) (Gelechiidae); Synanthedon melliniformis (Lasp.) (Sesiidae); Euproctis similis (Fuessl.) (Lymantriidae); Drymonia velitaris (Hufn.), Notodonta tritophus (Den. & Schiff.) (Notodontidae); Amphipyra pyramidea (L.), Catocala nupta (L.), Cosmia trapezina (L.), Enargia paleacea (Esp.), Eupsilia transversa (Hufn.), Ipomorpha subtusa (Den. & Schiff.), Parastichtis ypsilon (Den. & Schiff.), Scoliopteryx libatrix (L.) (Noctuidae); Gastropacha quercifolia (L.), Phyllodesma tremulifolia (Hb.) and Poecilocampa populi (L.) (Lasiocampidae). G. turpella and S. melliniformis are new records for Bulgaria and D. velitaris was found for the first time in Northern Bulgaria. Thirteen species (L. populi, E. similis, D. velltaris, N. tritophus, A. pyramidea, C. nupta, C. trapezina, E. transversa, I. subtusa, P. ypsilon, G. quercifolia, P. tremulifolia and P. populi) were established for the first time in Bulgaria to have a trophic relationship with poplars. G. turpella and L subtusa were occurred in the highest population densities – up to 1.6 larvae/m and up to 1.1 larvae/m respectively. The remaining species occurred in low population densities in the studied habitats and were not considered to be pests on the poplars.     

Potential physical and chemical barriers to infection by the burrowing nematode Radopholus similis in roots of susceptible and resistant banana (Musa spp.)

Resistance in banana roots against the burrowing nematode Radopholus similis has been correlated in the past with the phenylpropanoid pathway of secondary metabolism, but quantitative chemical analyses to support histological data are lacking. Therefore, healthy and infected roots of two susceptible (Grande naine and Obino l'ewai) and three resistant cultivars (Yangambi km5, Pisang jari buaya and Calcutta 4) were extracted and chemically analysed for their lignin content and phenylpropanoid profile using a quantitative lignin assay, high performance liquid chromatography and liquid chromatography/mass spectrometry. Through histochemical staining phenylpropanoids were localized in root tissue. Compared to the susceptible cultivars, the resistant cultivars had constitutively significantly higher levels of lignin in the vascular bundle and cell-wall bound ferulic acid esters in the cortex. Infection-induced lignification was observed in the vascular bundles of all cultivars. The catecholamine dopamine was identified as a major metabolite in banana roots. Levels varied from 2·8 to 8·4 mg per g root fresh weight and were significantly higher in the resistant cultivars. Other compounds, tentatively identified as anthocyanidin-related, were present in high quantities and may, besides dopamine, make up the substrates for polyphenol oxidation products in necrotic tissue.     

Effects of particle size and active ingredient content on residual activity of chlorpyrifos wettable powder formulations against codling moth,Cydia pomonella (L.)

In a laboratory experiment Cydia pomonella (L.) eggs, two days from eclosion, were placed on apples which had been sprayed five weeks previously with chlorpyrifos (125 mg/litre) from five formulations. Four were wettable powders (250 g a.i./kg) with particles ca 4, 5, 9 and 10 μm in diameter and one (500 g a.i./kg) with particles 2 μm in diameter. The treated apples were aged in direct sunlight. The percentage of apples without deep entries by first instar larvae one week after positioning of eggs, was greater the greater the ratio of active ingredient content of a formulation to total wettable powder particle surface area.