Insecticidal activities of leaf and twig essential oils from Clausena excavata against Aedes aegypti and Aedes albopictus larvae

BACKGROUND: The current study investigates, for the first time, the mosquito larvicidal activities of leaf and twig essential oils from Clausena excavata Burm. f. and their individual constituents against Aedes aegypti L. and Aedes albopictus Skuse larvae. The yields of essential oils obtained from hydrodistillation were compared, and their constituents were determined by GC‐MS analyses. RESULTS: The LC₅₀ values of leaf and twig essential oils against fourth‐instar larvae of Ae. aegypti and Ae. albopictus were 37.1–40.1 µg mL^?1 and 41.1–41.2 µg mL^?1 respectively. This study demonstrated that C. excavata leaf and twig essential oils possess mosquito larvicidal activity, inhibiting the growth of mosquito larvae for both species at a low concentration. In addition, results of larvicidal assays showed that the effective constituents in leaf and twig essential oils were limonene, γ‐terpinene, terpinolene, β‐myrcene, 3‐carene and p‐cymene. The LC₅₀ values of these constituents against both mosquito larvae were below 50 µg mL^?1. Among these effective constituents, limonene had the best mosquito larvicidal activity, with LC₅₀ of 19.4 µg mL^?1 and 15.0 µg mL^?1 against Ae. aegypti and Ae. albopictus larvae respectively. CONCLUSION: The findings suggested that the essential oils from Clausena excavata leaf and twig and their effective constituents may be explored as a potential natural larvicide. Copyright © 2008 Society of Chemical Industry     

Ovicidal,larvicidal and juvenilizing activity of a picolinephenoxyanilide against Cydia pomonella

N‐(4‐phenoxyphenyl)‐2‐pyridinecarboxamide (1) was synthesized from commercially available materials and its ovicidal and larvicidal activity against Cydia pomonella (L) was tested. The compound showed a LC₅₀ of 0.98 mg ml⁻¹ when eggs less than 24 h were sprayed using a Potter Tower, but it had no effect when eggs older than this were sprayed. The compound did not have larvicidal activity when larvae were treated with 1200 µg g⁻¹. However, the larval head capsules were smaller than those in the controls when treated at this concentration. To assess its possible juvenile‐hormone‐like activity, the compound was topically applied to young pupae of Tribolium confusum duVal, where it produced clear juvenilization effects, which were dependent on the applied dose. © 2000 Society of Chemical Industry     

Larvicidal and oviposition‐altering activity of monoterpenoids,trans‐anithole and rosemary oil to the yellow fever mosquito Aedes aegypti (Diptera: Culicidae)

BACKGROUND: Aedes aegypti L. is the major vector of dengue fever and dengue hemorrhagic fever. In an effort to find effective tools for control programs to reduce mosquito populations, the authors assessed the acute toxicities of 14 monoterpenoids, trans‐anithole and the essential oil of rosemary against different larval stages of Ae. aegypti. The potential for piperonyl butoxide (PBO) to act as a synergist for these compounds to increase larvicidal activity was also examined, and the oviposition response of gravid Ae. aegypti females to substrates containing these compounds was evaluated in behavioral bioassays. RESULTS: Pulegone, thymol, eugenol, trans‐anithole, rosemary oil and citronellal showed high larvicidal activity against all larval stages of Ae. aegypti (LC₅₀ values 10.3–40.8 mg L^?1). The addition of PBO significantly increased the larvicidal activity of all test compounds (3–250‐fold). Eugenol, citronellal, thymol, pulegone, rosemary oil and cymene showed oviposition deterrent and/or repellent activities, while the presence of borneol, camphor and β‐pinene increased the number of eggs laid in test containers. CONCLUSIONS: This study quantified the lethal and sublethal effects of several phytochemical compounds against all larval stages of Aedes aegypti, providing information that ultimately may have potential in mosquito control programs through acute toxicity and/or the ability to alter reproductive behaviors. Copyright © 2008 Society of Chemical Industry     

Synergistic and antagonistic interactions of terpenes against Meloidogyne incognita and the nematicidal activity of essential oils from seven plants indigenous to Greece

BACKGROUND: Biorational means for phytonematode control were studied within the context of an increasingly ecofriendly pest management global approach. The nematicidal activity and the chemical composition of essential oils (EOs) isolated from seven plants grown in Greece and ten selected compounds extracted from them against second‐stage juveniles (J2) of Meloidogyne incognita (Kof. & White) Chitwood were evaluated using juvenile paralysis experiments. Additionally, synergistic and antagonistic interactions between nematicidal terpenes were studied using an effect addition model, with the comparison made at one concentration level. RESULTS: The 96 h EC₅₀ values of Foeniculum vulgare Mill., Pimpinella anisum L., Eucalyptus meliodora A Cunn ex Schauer and Pistacia terebinthus L. were 231, 269, 807 and 1116 µg mL^?1, respectively, in an immersion bioassay. Benzaldehyde (9 µg mL^?1) was the most toxic compound, followed by γ‐eudesmol (50 µg mL^?1) and estragole (180 µg mL^?1), based on 96 h EC₅₀ values. The most potent terpene pairs between which synergistic actions were found, in decreasing order, were: trans‐anethole/geraniol, trans‐anethole/eugenol, carvacrol/eugenol and geraniol/carvacrol. CONCLUSION: This is the first report on the activity of F. vulgare, P. anisum, E. meliodora and P. terebinthus, and additionally on synergistic/antagonistic nematicidal terpene interactions, against M. incognita, providing alternative methods for nematode control. Copyright © 2010 Society of Chemical Industry     

The mode of action of RH‐1965: a new phenylpyrimidinone bleaching herbicide

RH‐1965 is a new bleaching herbicide which causes newly developing leaf tissue to emerge devoid of photosynthetic pigments. Mode‐of‐action studies revealed that RH‐1965 inhibited the accumulation of both total chlorophyll and β‐carotene. Concomitantly, it induced the accumulation of the β‐carotene precursors, phytoene, phytofluene and, in particular, ξ‐carotene. Inhibition of chlorophyll accumulation by RH‐1965 is attributed to the photo‐oxidative destruction of chlorophyll in the absence of β‐carotene because RH‐1965 blocked chlorophyll accumulation to a greater extent under high light (50–330 µE m⁻² s⁻¹) than under low light (0.8 µE m⁻² s⁻¹) conditions. Radish (Raphanus sativus L) and barnyardgrass (Echinochloa crus‐galli (L) Beauv) were very senstive to RH‐1965. Under high light (330 µE m⁻² s⁻¹), the I₅₀ values for inhibition of chlorophyll accumulation were 0.10 and 0.15 µM , respectively. Wheat (Triticum aestivus L), on the other hand, was much less sensitive to RH‐1965 (I₅₀ = 1.4 µM ). It is concluded that the mode of action of RH‐1965 involves the inhibition of ξ‐carotene desaturation. © 2000 Society of Chemical Industry     

Toxicity of formic acid to red imported fire ants, Solenopsis invicta Buren

BACKGROUND: Ants often compete with other ants for resources. Although formic acid is a common defensive chemical of formicine ants, it does not occur in any other subfamilies in Formicidae. No information on toxicity of formic acid to red imported fire ants, Solenopsis invicta, is available. This study examined its contact and fumigation toxicity to S. invicta in the laboratory. RESULTS: In a contact toxicity bioassay, 24 h LD₅₀ values of formic acid for workers ranged from 124.54 to 197.71 µg ant⁻¹. Female alates and queens were much less sensitive to formic acid than workers. At a concentration of 271.72 µg ant⁻¹, which killed 81.09 ± 16.04% of workers, the 24 h mortality was up to 39.64% for female alates and 38.89% for queens. In fumigation bioassays, 24 h LC₅₀ values ranged from 0.26 to 0.50 µg mL⁻¹ for workers, 0.32 µg mL⁻¹ for male alates and 0.70 µg mL⁻¹ for female alates. Complete mortality (100%) in queens occurred 24 h after they had been exposed to 1.57 µg mL⁻¹ of formic acid. At a concentration of 2.09 µg mL⁻¹, KT₅₀ values ranged from 23.03 to 43.85 min for workers, from 37.84 to 58.37 min for male alates, from 86.06 to 121.05 min for female alates and from 68.00 to 85.92 min for queens. CONCLUSION: When applied topically, formic acid was significantly less toxic than bifenthrin to red imported fire ants. Although its fumigation toxicity was lower than that of dichlorvos, formic acid had about an order of magnitude higher toxicity to S. invicta than to other insects studied so far. It may be worth investigating the use of formic acid for managing imported fire ants. Published 2012 by John Wiley & Sons, Ltd.     

Effect of pyriproxyfen,a juvenile hormone mimic,on egg hatch,nymph development,adult emergence and reproduction of the Asian citrus psyllid,Diaphorina citri Kuwayama

BACKGROUND: The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, is a vector of bacteria presumably responsible for huanglongbing (HLB) disease in citrus. In this laboratory study, an investigation was made of the activity of pyriproxyfen, a juvenile hormone mimic, on ACP eggs, nymphs and adults to evaluate its potential as a biorational insecticide for inclusion in an integrated pest management (IPM) program for ACP. RESULTS: Irrespective of egg age, timing or method of treatment, a significantly lower percentage of eggs (5–29%) hatched after exposure to 64 and 128 µg mL^?1 of pyriproxyfen. Only 0–36% of early instars (first, second and third) and 25–74% of late instars (fourth and fifth) survived to adults following exposure to 16, 32 and 64 µg mL^?1 of pyriproxyfen. However, 15–20% of adults that emerged following treatment as late instars exhibited morphological abnormalities. Furthermore, pyriproxyfen adversely affected reproduction (fecundity and fertility) of adults that emerged from treated fifth instars or that were treated topically with 0.04 µg as adults. CONCLUSIONS: Application of pyriproxyfen at 64 µg mL^?1 resulted in greater inhibition of egg hatch and suppression of adult emergence compared with lower rates. Pyriproxyfen also markedly reduced female fecundity and egg viability for adults that were exposed either as fifth instars or as newly emerged adults. The ovicidal, larvicidal and reproductive effects against ACP suggest that pyriproxyfen is suitable for integration into an IPM program for ACP. Copyright © 2009 Society of Chemical Industry     

Effectiveness of Carvacrol Derived from Thujopsis dolabrata var. hondai Sawdust against Thecodiplosis japonensis (Diptera: Cecidomyiidae)

The larvicidal component from sawdust of Thujopsis dolabrata var. hondai (Family Cupressaceae) against the pine needle gall midge (Thecodiplosis japonensis) was isolated by chromatographic techniques and characterized by spectral analysis as carvacrol. In a laboratory study using the impregnated filter paper method, carvacrol was more toxic to T. japonensis larvae than β-thujaplicine, cedrol, α-terpinol, thujone or thymol. In field studies with soil injections of carvacrol, this compound exhibited potent larvicidal activity, suggesting that this activity might be attributable to fumigant action. In a test with trunk implantation, a mixture of carvacrol and phosphamidon (0·15+0·15 ml cm^-1 diameter at breast height) revealed much more potent larvicidal activity than phosphamidon alone (0·3 ml cm^-1 DBH) in spite of little or no larvicidal activity of carvacrol alone (0·3 ml cm^-1 DBH), indicating a possible synergistic effect. As a naturally occurring insecticide, carvacrol could be useful as a new preventive agent against damage caused by T. japonensis. © 1997 SCI.     

A new aqueous suspension concentrate formulation of cis‐permethrin and its insecticidal activity

Isomers of pyrethroids usually have different insecticidal activities. Permethrin, a non‐cyano pyrethroid, is not an exception and cis‐permethrin is much more active than the trans‐isomer against Triatoma infestans, vector of Chagas' Disease in Argentina. The large‐scale separation of cis‐ and trans‐permethrin was performed by successive recrystallizations from ethanol‐water mixtures. An aqueous suspension concentrate (flowable) formulation of pure crystalline cis‐permethrin was prepared and assayed for its insecticidal activity on wood and ceramic surfaces against nymph V of T infestans. This formulation was at least three times more effective than deltamethrin, with LC₅₀ values on ceramic of 0.11 µg cm⁻² and 0.33 µg cm⁻² respectively. On wood surfaces, the LC₅₀ value was 0.57 µg cm⁻² compared with 3.20 µg cm⁻² for deltamethrin. Against other insect species such as Periplaneta americana, Aedes aegypti and Culex quinquefasciatus, the suspension concentrate formulation of cis‐permethrin was, however, less effective than similar formulations of deltamethrin or β‐cypermethrin. © 2000 Society of Chemical Industry     

Resistance to pyraclostrobin, boscalid and multiple resistance to Pristine® (pyraclostrobin + boscalid) fungicide in Alternaria alternata causing alternaria late blight of pistachios in California

Pristine® (pyraclostrobin + boscalid) is a fungicide registered for the control of alternaria late blight in pistachio. A total of 95 isolates of Alternaria alternata collected from orchards with and without a prior history of Pristine® sprays were tested for their sensitivity towards pyraclostrobin, boscalid and Pristine® in conidial germination assays. The EC₅₀ values for 35 isolates from orchards without Pristine® sprays ranged from 0·09 to 3·14 µg mL^?1 and < 0·01 to 2·04 µg mL^?1 for boscalid and Pristine®, respectively. For pyraclostrobin, 27 isolates had EC₅₀ < 0·01 µg mL^?1 and six had low resistance (mean EC₅₀ value = 4·71 µg mL^?1). Only one isolate was resistant to all three fungicides tested, with EC₅₀ > 100 µg mL^?1. Among 59 isolates from the orchard with a history of Pristine® sprays, 56 were resistant to pyraclostrobin; only two were sensitive (EC₅₀ < 0·01 µg mL^?1) and one was weakly resistant (EC₅₀ = 10 µg mL^?1). For the majority of these isolates EC₅₀ values ranged from 0·06 to 4·22 µg mL^?1 for boscalid and from 0·22 to 7·74 µg mL^?1 for Pristine®. However, seven isolates resistant to pyraclostrobin were also highly resistant to boscalid and Pristine® and remained pathogenic on pistachio treated with Pristine®. Whereas strobilurin resistance is a common occurrence in Alternaria of pistachio, this is the first report of resistance to boscalid in field isolates of phytopathogenic fungi. No cross resistance between pyraclostrobin and boscalid was detected, suggesting that Pristine® resistance appears as a case of multiple resistance.     

Composition and biological activity of essential oils from Labiatae against Nezara viridula (Hemiptera: Pentatomidae) soybean pest

BACKGROUND: Plant essential oils have been recognised as an important natural source of insecticide. This study analysed the chemical constituents and bioactivity of essential oils that were isolated via hydrodistillation from Origanum vulgare L. (oregano) and Thymus vulgaris L. (thyme) against eggs, second instar and adults of Nezara viridula (L.). RESULTS: The major component of oregano was p‐cymene, and, for thyme, thymol. The ovicidal activity was tested by topical application; the essential oil from thyme was more effective. The fumigant activity was evaluated in an enclosed chamber; the LC₅₀ values for oregano were 26.8 and 285.6 µg mL^?1 for nymphs and adults respectively; for thyme they were 8.9 µg mL^?1 for nymphs and 219.2 µg mL^?1 for adults. To evaluate contact activity, a glass vial bioassay was used; the LC₅₀ values for oregano were 1.7 and 169.2 µg cm^?2 for nymphs and adults respectively; for thyme they were 3.5 and 48.8 µg cm^?2 respectively. The LT₅₀ analyses for contact and fumigant bioassays indicated that thyme was more toxic for nymphs and adults than oregano. Both oils produced repellency on nymphs and adults. CONCLUSION: These results showed that the essential oils from O. vulgare and T. vulgaris could be applicable to the management of N. viridula. Copyright © 2011 Society of Chemical Industry     

Mefenoxam sensitivity and fitness analysis of Phytophthora nicotianae isolates from nurseries in Virginia, USA

Mefenoxam is one of the most commonly used fungicides for managing diseases caused by Phytophthora spp. on ornamentals. The objectives of this study were to determine whether Phytophthora nicotianae, a destructive pathogen of numerous herbaceous annual and perennial plant species in nurseries, has developed resistance to mefenoxam, and to evaluate the fitness of mefenoxam‐resistant isolates. Ninety‐five isolates of P. nicotianae were screened for sensitivity to mefenoxam on 20% clarified V8 agar at 100 a.i. µg mL^?1. Twenty‐five isolates were highly resistant to this compound with EC₅₀ values ranging from 235·2 to 466·3 µg mL^?1 and four were intermediately resistant with EC₅₀ values ranging from 1·6 to 2·9 µg mL^?1. Sixty‐six isolates were sensitive with EC₅₀ values less than 0·04 µg mL^?1. Nine resistant and seven sensitive isolates were tested for mefenoxam sensitivity on Pelargonium × hortorum cv. White Orbit. Mefenoxam provided good protection of pelargonium seedlings from colonization by sensitive isolates, but not by any resistant isolates. Four resistant and four sensitive isolates were compared for fitness components and their relative competitive ability on Lupinus Russell Hybrids in the absence of mefenoxam. Resistant isolates outcompeted sensitive ones within 3 to 6 sporulation cycles on lupin seedlings, regardless of their initial proportions in mixed zoospore inoculum. Resistant isolates exhibited greater infection rate and higher sporulation ability than sensitive ones when they were applied separately onto lupins. These results suggest that fungicide resistance may pose a serious challenge to the continued effectiveness of mefenoxam as a control option for nursery growers.     

Residues in apples and sweet cherries after methyl bromide fumigation

Methyl bromide fumigations are used to treat apples, Malus domestica Borkh, and sweet cherries, Prunus avium (L), before export to Japan. In order to expand existing markets, additional cultivars are being prepared for export to Japan. As part of the approval process, residue analyses must be conducted and residues must be at acceptable levels. Five apple cultivars (‘Braeburn,’ ‘Fuji,’ ‘Gala,’ ‘Jonagold,’ and ‘Granny Smith’) were fumigated at 40 g m⁻³ for 2 h at 10 °C, and six sweet cherry cultivars (‘Brooks,’ ‘Garnet,’ ‘Lapin,’ ‘Rainier,’ ‘Sweetheart,’ and ‘Tulare’) were fumigated for 2 h with 64 g m⁻³ at 6 °C, 48 g m⁻³ at 12 °C, 40 g m⁻³ at 17 °C, and 32 g m⁻³ at 22 °C. Three replicates of fruit from each fumigation were analyzed for methyl bromide and bromide ion residues periodically with time. Methyl bromide residues for both apples and cherries were the highest immediately after fumigation, but rapidly declined so that only ‘Braeburn’ had residues >8 µg kg⁻¹ after 13 days and, except for ‘Lapin,’ all cherries were <1 µg kg⁻¹ after seven days. Average bromide ion residues were between 3.3 and 4.9 mg kg⁻¹ among apple cultivars, and between 3.7 and 8.0 µg kg⁻¹ among cherry cultivars. Published in 2000 for SCI by John Wiley & Sons, Ltd     

In vivo control and in vitro antifungal activity of rhamnolipid B,a glycolipid antibiotic,against Phytophthora capsici and Colletotrichum orbiculare

The glycolipid antibiotic rhamnolipid B isolated from Pseudomonas aeruginosa strain B5 was evaluated for in vitro antifungal activity and in vivo control against phytophthora blight and anthracnose under glasshouse conditions. Rhamnolipid B showed antifungal activity against Cercospora kikuchii, Cladosporium cucumerinum, Colletotrichum orbiculare, Cylindrocarpon destructans, Magnaporthe grisea and Phytophthora capsici. Microscopic observation revealed that the high level of antifungal activity (10 µg ml ⁻¹) against P capsici was mainly due to a lytic effect on zoospores. Zoospore lysis began in the presence of 10 µg ml ⁻¹ of rhamnolipid B and most of the zoospores were collapsed at 25 µg ml ⁻¹. Rhamnolipid B showed inhibitory activity against the germination of zoospores and hyphal growth of P capsici at concentrations of 50 µg ml ⁻¹. Spore germination of the anthracnose plant pathogen C orbiculare was also inhibited in the presence of 50 µg ml ⁻¹ of rhamnolipid B, although hyphal growth was not affected at this concentration. In the glasshouse, the efficacy of rhamnolipid B against phytophthora blight was similar to that of metalaxyl on pepper plants when treated just before inoculation with P capsici. Treatment with either at 500 µg ml ⁻¹ completely protected pepper plants from phytophthora blight. Rhamnolipid B also suppressed the development of C orbiculare infection on leaves of cucumber plants. © 2000 Society of Chemical Industry     

Effects of buprofezin and diflubenzuron on various developmental stages of Asian citrus psyllid, Diaphorina citri

BACKGROUND: Diaphorina citri populations in Florida are developing resistance to commonly used neurotoxic insecticides. Alternatives to neurotoxins, such as insect growth regulators, are needed to control this season-long subtropical pest to prevent or delay development of insecticide resistance. In the present investigation, two insect growth regulators (IGRs), buprofezin and diflubenzuron, were evaluated against various developmental stages of D. citri. RESULTS: The 0–1-day-old D. citri eggs were more susceptible to buprofezin and diflubenzuron than the 3–4-day-old eggs. Adult emergence was completely suppressed by treating first- or third-instar nymphs with buprofezin or diflubenzuron at 30–240 or 23–184 µg mL⁻¹ rates respectively. Treatment of fifth-instar nymphs with diflubenzuron at a rate of 184 µg mL⁻¹ and with buprofezin at 30–240 µg mL⁻¹ rates resulted in approximately 20 and 15–80% reductions in adult emergence respectively. The mean number of eggs per plant was reduced at 5 days after topical treatment with diflubenzuron. Mean egg hatch per plant was reduced at 5 and 6–15 days after topical treatments with buprofezin and diflubenzuron respectively. CONCLUSION: Buprofezin and diflubenzuron effectively suppressed D. citri adult emergence. D. citri were more susceptible as early (first–third-instar) than late (fifth-instar) nymphs. Both IGRs inhibited egg production and egg hatch. Reduction in the number of subsequent offspring suggests reduced vertical transmission of Candidatus Liberibacter asiaticus, the pathogen thought to cause citrus greening disease. The present results indicate that both IGRs tested here should be effective tools for rotation in insecticide-based D. citri management programs. Copyright © 2012 Society of Chemical Industry     

Synthesis of 2-amino-6-oxocyclohexenylsulfonamides and their activity against Botrytis cinerea

BACKGROUND: With the objective of exploring the fungicidal activity of 2‐oxocyclohexylsulfonamides (2), a series of novel 2‐amino‐6‐oxocyclohexenylsulfonamides (6 to 23) were synthesised, and their fungicidal activities against Botrytis cinerea Pers. were evaluated in vitro and in vivo. RESULTS: The compounds were characterised by IR, ¹H NMR and elemental analysis. Bioassay results of mycelial growth showed that compounds 6 to 23 had a moderate antifungal activity against B. cinerea. N‐(2‐methylphenyl)‐2‐(2‐methylphenylamino)‐4,4‐dimethyl‐6‐oxocyclohexenylsulfonamide (13) and N‐(2‐chlorophenyl)‐2‐(2‐chlorophenylamino)‐6‐oxocyclohexenylsulfonamide (21) showed best antifungal activities, with EC₅₀ values of 8.05 and 10.56 µg mL^?1 respectively. Commercial fungicide procymidone provided an EC₅₀ value of 0.63 µg mL^?1. The conidial germination assay showed that most of compounds 6 to 23 possessed excellent inhibition of spore germination and germ‐tube elongation of conidia of B. cinerea. For in vivo control of B. cinerea colonising cucumber leaves, the compound N‐cyclohexyl‐2‐(cyclohexylamino)‐4,4‐dimethyl‐6‐oxocyclohexenylsulfonamide (19) showed a better control effect than the commercial fungicide procymidone. CONCLUSION: The present work demonstrated that 2‐amino‐6‐oxocyclohexenylsulfonamides can be used as possible new lead compounds for further developing novel fungicides against B. cinerea. Copyright © 2011 Society of Chemical Industry     

Inheritance of resistance to Bacillus thuringiensis Cry1Ac toxin in Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) from India

BACKGROUND: The cotton bollworm, Helicoverpa armigera (Hübner), is one of the most serious insect pests of cotton. It has developed resistance to almost all groups of chemical insecticides because of their intensive use. The failure of insecticides to control H. armigera has been a strong incentive for the adoption of transgenic cotton (Bt cotton). However, the value of Bt could be diminished by widespread resistance development to Bt toxins in insect populations. Therefore, understanding the genetic basis of resistance is essential for developing and implementing strategies to delay and monitor resistance. RESULTS: A resistant strain designated as BM‐R was obtained from the cross of adults from Bathinda () and Muktsar (), Punjab, India, which showed the highest survival (60.68%) and LC₅₀ value (1.396 µg mL^?1 diet). Similarly, a laboratory‐maintained strain from Hoshiarpur, Punjab, showed maximum susceptibility to Cry1Ac toxin with the lowest LC₅₀ value (0.087 µg mL^?1), and was designated as HP‐S. The genetic purity of both strains was confirmed by RAPD profile analysis at each generation, and genetic similarity reached more than 90% after the third generation. Continuous maintenance of the resistant BM‐R strain on Cry1Ac resulted in an increase in LC₅₀ from 0.531 µg mL^?1 in F₀ to 4.28 µg mL^?1 in F₁₄ and 7.493 µg mL^?1 in F₁₉, while the LC₅₀ values for HP‐S larvae on diet without Cry1Ac increased to 0.106 and 0.104 µg mL^?1, which lay within the fiducial limits of the baseline LC₅₀ value. The mode of inheritance of resistance was elucidated through bioassay response of resistant, susceptible heterozygotes and backcross progeny to Cry1Ac incorporated in semi‐synthetic diet. CONCLUSION: Based on dominance, degree of dominance and backcross values, resistance was inferred to be polygenic, autosomal and inherited as a recessive trait. Copyright © 2011 Society of Chemical Industry     

Fumigant toxicity of volatile natural products from Korean spices and medicinal plants towards the rice weevil,Sitophilus oryzae (L)

The fumigant toxicity of various volatile constituents of essential oils extracted from sixteen Korean spices and medicinal plants towards the rice weevil, Sitophilus oryzae L (Coleoptera: Curculionidae), was determined. The most potent toxicity was found in the essential oil from Mentha arvensis L var piperascens (LC₅₀ = 45.5 µl litre^?1 air). GC–MS analysis of essential oil from M arvensis showed it to be rich in menthol (63.2%), menthone (13.1%) and limonene (1.5%), followed in abundance by β‐pinene (0.7%), α‐pinene (0.6%) and linalool (0.2%). Treatment of S oryzae with each of these terpenes showed menthone to be most active (LC₅₀ = 12.7 µl litre^?1 air) followed by linalool (LC₅₀ = 39.2 µl litre^?1 air) and α‐pinene (LC₅₀ = 54.9 µl litre^?1 air). Studies on inhibition of acetylcholinesterase activity of S oryzae showed menthone to have a nine‐fold lower inhibitory effect than menthol, despite menthone being 8.1‐fold more toxic than menthol to the rice weevil. Different modes of toxicity of these monoterpenes towards S oryzae are discussed. © 2001 Society of Chemical Industry     

Biological activity of the succinate dehydrogenase inhibitor fluopyram against Botrytis cinerea and fungal baseline sensitivity

BACKGROUND: Succinate dehydrogenase inhibitors (SDHIs) constitute a fungicide class with increasing relevance in crop protection. These fungicides could play a crucial role in successful management of grey mould disease. In the present study the effect of fluopyram, a novel SDHI fungicide, on several developmental stages of Botrytis cinerea was determined in vitro, and the protective and curative activity against the pathogen was determined on strawberry fruit. Furthermore, fungal baseline sensitivity was determined in a set of 192 pathogen isolates. RESULTS: Inhibition of germ tube elongation was found to be the most sensitive growth stage affected by fluopyram, while mycelial growth was found to be the least sensitive growth stage. Fluopyram provided excellent protective activity against B. cinerea when applied at 100 µg mL^?1 96, 48 or 24 h before the artificial inoculation of the strawberry fruit. Similarly, fluopyram showed a high curative activity when it was applied at 100 µg mL^?1 24 h post‐inoculation, but, when applications were conducted 48 or 96 h post‐inoculation, disease control efficacy was modest or low. The measurement of baseline sensitivity showed that it was unimodal in all the populations tested. The individual EC₅₀ values for fluopyram ranged from 0.03 to 0.29 µg mL^?1. In addition, no correlation was found between sensitivity to fluopyram and sensitivity to other fungicides, including cyprodinil, fenhexamid, fludioxonil, iprodione, boscalid and pyraclostrobin. CONCLUSIONS: The obtained biological activity, baseline sensitivity and cross‐resistance relationship data suggest that fluopyram could play a key role in grey mould management in the near future and encourage its introduction into spray programmes. Copyright © 2011 Society of Chemical Industry