Insecticide Tests Research Articles

Function analysis of Ac-PCNA and Sf-PCNA during the Autographa californica multiple nucleopolyhedrovirus infection process.

The baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV) possesses a gene, ac-pcna or ac49, which encodes a protein with similarity to proliferating cell nuclear antigen (PCNA). Homologs of this gene code for DNA polymerase processivity factors and are essential in the DNA replication systems. But the function of ac-pcna still remains unclear. To define the function of Ac-pcna in AcMNPV and Sf-pcna in host Sf9 cells, Bac-to-Bac baculovirus expression system was used to generate two recombinant baculoviruses: AcMNPV-Ac-pcna-EGFP and AcMNPV-Sf-pcna-EGFP. Results indicated that AcMNPV-mediated overexpression of Ac-PCNA and Sf-PCNA could stimulate replication of AcMNPV genome in the host Sf9 cells. Meanwhile, either AcMNPV-Ac-pcna-EGFP or AcMNPV-Sf-pcna-EGFP had a significant stimulating effect on Sf9 genome replication during infection. We also found that Ac-PCNA and Sf-PCNA could promote the production of budded virus. Ac-PCNA could improve the transcription level of ie2 gene dramatically and further improved the transcription of late gene, for example 38K and vp39, at 12h p.i.. Moreover, insecticidal potency test showed that the larvae of Beet armyworm in the AcMNPV-Ac-pcna-EGFP and AcMNPV-Sf-pcna-EGFP groups had a higher mortality rate (83.33 and 91.67%), a lower pupation rate (16.67 and 8.33%), and a lower emergence rate (6.67 and 3.33%), compared with those in AcMNPV-EGFP group. The function of Ac-PCNA and Sf-PCNA was confirmed in this study, which provided the theoretical foundation for using and modifying AcMNPV.

Cytotoxicity of chemical constituents from Torricellia tiliifolia DC. on Spodoptera litura (SL-1) cells

In this study, we evaluated cytotoxicity of chemicals isolated from Torricellia tiliifolia DC. on Spodoptera litura (SL-1) cell line. Among the isolated compounds, 4-hydroxy-3-methoxycinnamaldehyde, 3,5-dimethoxy-4-hydroxycinnamaldehyde, and syringaresinol inhibited SL-1 cell survival in both dose- and time-dependent manners. Meanwhile, the in vivo insecticidal activity test revealed that 4-hydroxy-3-methoxycinnamaldehyde and 3,5-dimethoxy-4-hydroxycinnamaldehyde showed obvious insecticidal activities. These two compounds exhibited toxicity to SL-1 cells by inducing cellular morphological changes including shape change, cell shrinkage, vacuolation, cell membrane blebbing and chromatin condensation and apoptosis. 4-hydroxy-3-methoxycinnamaldehyde and 3,5-dimethoxy-4-hydroxycinnamaldehyde showed the most effect on mitochondrial membrane depolarization at 24h and 72h respectively and induced the apoptosis at a late time point 72h. Our results suggest that 4-hydroxy-3-methoxycinnamaldehyde and 3,5-dimethoxy-4-hydroxycinnamaldehyde inhibit SL-1 survival by inducing apoptosis.

Synthesis and insecticidal activity of diacylhydrazine derivatives containing a 3-bromo-1-(3-chloropyridin-2-yl)-1H-pyrazole scaffold

BackgroundThe diacylhydrazine derivatives have attracted considerable attention in recently years due to their simple structure, low toxicity, and high insecticidal selectivity. As well as 3-bromo-1-(3-chloropyridin-2-yl)-1H-pyrazole is an important scaffold in many insecticidal molecules. In an effort to discover new molecules with good insecticidal activity, a series of diacylhydrazine derivatives containing a 3-bromo-1-(3-chloropyridin-2-yl)-1H-pyrazole scaffold was synthesized and bio-assayed.ResultsBioassays demonstrated that some of the title compounds exhibited favorable insecticidal activities against Helicoverpa armigera and Plutella xylostella. The insecticidal activity of compounds 10g, 10h, and 10w against H. armigera were 70.8, 87.5, and 79.2%, respectively. Compounds 10c, 10e, 10g, 10h, 10i, 10j and 10w showed good larvicidal activity against P. xylostella. In particular, the LC50 values of compounds 10g, 10h, and 10w were 27.49, 23.67, and 28.90 mg L−1, respectively.ConclusionsA series of diacylhydrazine derivatives containing a 3-bromo-1-(3-chloropyridin-2-yl)-1H-pyrazole scaffold was synthesized and bio-assayed. The results of insecticidal tests revealed that the synthesized diacylhydrazine derivatives possessed weak to good insecticidal activities against H. armigera and P. xylostella. Compounds 10g, 10h, and 10x showed much higher insecticidal activity than tebufenozide, and exhibited considerable prospects for further optimization. Primary structure–activity relationship revealed that phenyl, 4-fluoro phenyl and four fluorophenyl showed positive influence on their insecticidal activities, and introduction of a heterocyclic ring (pyridine and pyrazole) showed negative impacts on their insecticidal effects.

Evaluating the Toxicity of Candidate Organic and Conventional Insecticides on Western Grape Leafhopper and Virginia Creeper Leafhopper (Hemiptera: Cicadellidae) under Vineyard and Laboratory Conditions

Abstract The western grape leafhopper (Erythroneura elegantula Osborn) and the Virginia creeper leafhopper (Erythroneura ziczac Walsh) are the two leafhopper pests frequently observed in Washington State vineyards. Organic viticulturists have difficulties controlling these leafhopper pests, and outbreaks can result in economic loss. We vineyard-tested the efficacy of several candidate bioinsecticides and conventional insecticides against the western grape leafhopper and the Virginia creeper leafhopper. This study included the initial testing of several alternative candidate insecticides for leafhopper control. Controlled laboratory bioassays also were completed, and the 50% and 90% lethal concentrations were calculated for the nonsystemic insecticides tested. Of the bioinsecticides tested, pyrethrum (PyganicTM, Valent Bioscience Corporation, Libertyville, IL) was the only product that provided effective control of leafhoppers in both the vineyard and laboratory components of this study. In vineyard effic...

LARVICIDAL AND ENZYME INHIBITORY EFFECTS OF ACALYPHA FRUTICOSA (F.) AND CATHARANTHUS ROSEUS L (G) DON. LEAF EXTRACTS AGAINST CULEX QUINQUEFASCIATUS (SAY.) (DIPTERA: CULICIDAE)

ABSTRACTObjective: The prime objective of this study is to evaluate the larvicidal and enzyme inhibitory effects of Acalypha fruticosa and Catharanthus roseusleaf extracts against Culex quinquefasciatus.Methods: Insecticidal susceptibility tests were carried out using the World Health Organization standard method, and the mortality was observedafter 24 hrs exposure.Results: The tested extracts showed a significant larvicidal activity depending on the dose of the plant extracts. However, maximum larval mortalitywas detected in ethyl acetate extract of A. fruticosa with a lethal concentration (LC50) value of 253.08 ppm and (LC90) value of 455.40 ppm followedby hexane extract of C. roseus with LC50 value of 645.33 ppm and LC90 value of 1452.88 ppm against the larvae of C. quinquefasciatus. In control, therewere five different fractions of α-carboxylesterases resolved in the gel with the mobilities ranging between 0.14 and 0.66. β-carboxylesterase isozymeprofile of larvae treated with hexane extract of A. fruticosa showed higher enzyme activities by way of intense staining of fractions both at 1/4 and1/10 LC50 value of 48 hrs treatments. A. fruticosa ethyl acetate extract, and C. roseus hexane extract exposed larvae indicated increased quantitiesof β-Est4/5 isozymes in the concentration of 1/4 and 1/10 of LC50 value of 24 hrs treatment when compared to control. The protein quantity in themajority of treatments decreased compared to control.Conclusion: The results revealed that the organic leaf extract of A. fruticosa and C. roseus had significant larvicidal and enzyme inhibitory effectsagainst C. quinquefasciatus.Keywords: Acalypha fruticosa, Catharanthus roseus leaves extract, β-carboxylesterase, Culex quinquefasciatus, Lethal concentration50.

English

Larvicidal effects of plant extracts against larvae of Anopheles gambiae were studied in the malaria entomology laboratory at Mendefera. The aim of the study was to evaluate ethanol and hot water extracts from leaves of seven different plants, viz., Azadirachta indica, Eucalyptus globulus, Tagetes minuta, Datura stramonium, Lantana camara, Ricinus communis and Jatropha curcas, as natural larvicides against third instar larvae of An. gambiae. Insecticidal susceptibility tests were carried out using WHO standard method and the mortality was observed after 24 and 48 h (h) of exposure. The experiment was conducted in complete randomized design in three replications. Data were collected on mortality of mosquito larvae in all the treatments and then subjected to statistical analysis using one-way ANOVA. Most of the tested extracts showed more than 50% mortality. J. curcas (100±0.00%) and R. communis (99.44±0.56) gave significantly higher larval mortalities at 1000 ppm concentration after 48 h of exposure. The experiment also showed that ethanol extracts gave higher larval mortality than hot water extracts and the efficiency of the extracts increased with an increase in the exposure period of the larvae. Key words: Mosquito vector, malaria, larvicidal activity, leaf extracts

The influence of different substrates on the reproduction traits of Folsomia candida (Collembola) in an insecticide test

The standard OECD tests for Folsomia candida should be performed on the standard OECD soil. However, if it is necessary to measure more parameters than the juvenile number and mortality, the use of different substrates is necessary. But these substrates can modify the results of the experiments comparing to the standard OECD soil, resulting in different toxicity values. In our research, we tested the toxicity of an insecticide, Trebon® 10F to F. candida (Collembola). We tested the dose-dependent effect of Trebon® 10F on the egg number and the egg size on the substrates of (i) plaster of Paris mixed with activated charcoal and (ii) in standard OECD soil on two generation of collembolas. Similarly to our previous study, the insecticide had a dose-dependent negative effect on the parent’s egg size in the OECD soil, but on plaster of Paris, no response was found. The egg number did not show any response to the treatments. On the contrary, in the offspring generation, the egg size increased both in OECD and plaster of Paris tests. In the soil test, parent collembolas laid significantly more eggs, while the offspring laid much fewer, compared to the plaster of Paris test. Similar results were found in the case of egg size. In the soil test parent collembolas laid larger, while the offspring laid smaller eggs, compared to the plaster of Paris test. In multigenerational tests (i) Trebon 10F could affect the different generations in the opposite way. The experiment performed on the plaster of Paris (ii) could underestimate toxicity compared to the OECD soil test. This should be taken into account when Ecotoxicologists interpret their data.

Susceptibility of Anopheles gambiae to insecticides used for malaria vector control in Rwanda.

BackgroundThe widespread emergence of resistance to pyrethroids is a major threat to the gains made in malaria control. To monitor the presence and possible emergence of resistance against a variety of insecticides used for malaria control in Rwanda, nationwide insecticide resistance surveys were conducted in 2011 and 2013.MethodsLarvae of Anopheles gambiae sensu lato mosquitoes were collected in 12 sentinel sites throughout Rwanda. These were reared to adults and analysed for knock-down and mortality using WHO insecticide test papers with standard diagnostic doses of the recommended insecticides. A sub-sample of tested specimens was analysed for the presence of knockdown resistance (kdr) mutations.ResultsA total of 14,311 mosquitoes were tested and from a sample of 1406 specimens, 1165 (82.9%) were identified as Anopheles arabiensis and 241 (17.1%) as Anopheles gambiae sensu stricto. Mortality results indicated a significant increase in resistance to lambda-cyhalothrin from 2011 to 2013 in 83% of the sites, permethrin in 25% of the sites, deltamethrin in 25% of the sites and DDT in 50% of the sites. Mosquitoes from 83% of the sites showed full susceptibility to bendiocarb and 17% of sites were suspected to harbour resistance that requires further confirmation. No resistance was observed to fenitrothion in all study sites during the entire survey. The kdr genotype results in An. gambiae s.s. showed that 67 (50%) possessed susceptibility (SS) alleles, while 35 (26.1%) and 32 (23.9%) mosquitoes had heterozygous (RS) and homozygous (RR) alleles, respectively. Of the 591 An. arabiensis genotyped, 425 (71.9%) possessed homozygous (SS) alleles while 158 (26.7%) and 8 (1.4%) had heterozygous (RS) and homozygous (RR) alleles, respectively. Metabolic resistance involving oxidase enzymes was also detected using the synergist PBO.ConclusionThis is the first nationwide study of insecticide resistance in malaria vectors in Rwanda. It shows the gradual increase of insecticide resistance to pyrethroids (lambda-cyhalothrin, deltamethrin, permethrin) and organochlorines (DDT) and the large presence of target site insensitivity. The results demonstrate the need for Rwanda to expand monitoring for insecticide resistance including further metabolic resistance testing and implement an insecticide resistance management strategy to sustain the gains made in malaria control.

Assessment of insecticides and Cry2AB toxin resistance development in Karnataka population of Plutella xylostella (Linn.)

Insecticidal resistance studies against third instar larvae of DBM (Plutella xylostella L.) were carried out to know the rate of development of resistance from F1 to F3 generations in Karnataka population. The third instar larvae obtained from field were subjected to bioassay studies with tested against acephate, cypermethrin, spinosad, cartap hydrochloride and Cry2Ab toxin using leaf dip method to calculate LC50 values. The LC50 values of the insecticides were further used to quantify the resistance in P. xylostella of parental generation (F0) from Karnataka field population. The survivals from F0 generation were reared to next generation (F1). Resistance development studies was assessed from F1 to F3 generation with third instar larvae in every generation with a concentration that caused 80.00 % mortality for all the test insecticides and Cry2Ab toxin. Results revealed that ((0.17 folds) no resistance was developed against acephate in F3 generation. In case of cypermethrin 2.33 folds. Resistance studies further revealed that 1.50 folds resistance was developed against spinosad, 2.28 folds against cartap hydrochloride and Cry2Ab toxin 1.49 folds resistance was recorded in F3 generation. The rate of development of resistance from F1 to F3 generations increased in all the test insecticides and Cry toxin, except against acephate in Karnataka population. This data will be useful in the development of insecticide resistance management approach for DBM.

Control of root aphid (Pemphigus bursarius L.) in witloof chicory culture (Cichorium intybus L. var. foliosum)

Pemphigus bursarius L. is a serious pest of the witloof chicory (Cichorium intybus L. var. foliosum) during its growing phase in the field. Trials investigating many ways of improving control of this aphid were carried out, including improved knowledge of the pest's life cycle and of beneficial insects, tests of biological and chemical insecticides, impact of plants' growing conditions in the field (water stress) and research for resistance in different chicory families. The work showed that the winged flights of P. bursarius should be monitored in Northern France according to the temperature-based model established at Horticulture Research International, Wellesbourne (now Warwick Crop Center). An insecticide spray with spirotetramat during the fundatrigeniae migration strongly reduced the wingless colonies in summer. Beneficial insects also contributed to limiting the populations of P. bursarius, particularly several species of a genus of a fly (Thaumatomyia spp.) whose larvae are able to predate on about 100 wingless aphids on the root chicory. The use of an insecticide has been authorized based partly on efficacy results obtained in these reported trials. Italian chicories were more resistant than witloof chicories (“Belgian endive”) and could be used in breeding programs. Data on the life cycle of some species of the genus Thaumatomyia have been recorded and will be useful for biological management programs in the future.

Salvia officinalis essential oil in bean weevil control

ABSTRACT Bean weevil [Acanthoscelides obtectus Say (Coleoptera: Bruchidae)] is considered the main storage pest of the bean crop. Its control is performed mainly by chemical treatment, which has potential to cause resistance in pests, as well as environmental contamination. This study aimed at evaluating the insecticidal and repellent effect of Salvia officinalis L. essential oil against bean weevil. The doses used for the insecticidal test were: 0 L t-1, 0.5 L t-1, 1.0 L t-1, 1.5 L t-1, 2.5 L t-1 and 5.0 L t-1 of bean grains. For the mortality test, the experimental design was completely randomized, in a 6 × 7 (dose × time) factorial scheme, with five replications. The number of dead insects was counted at 2, 6, 12, 24, 48, 72 and 96 h after the insect introduction. The repellency test was conducted in arenas, under a completely randomized design, using the same doses applied to evaluate the insecticidal effect. Counts were performed 24 h after the introduction of insects. The insecticidal effect of the S. officinalis essential oil on A. obtectus resulted in mortality rates higher than 95 %, after 6 h of insect introduction, for all doses tested. Repellency effect was also detected for all doses tested.

First evaluation of bendiocarb in experimental huts using different substrates in Madagascar.

BackgroundIndoor residual spraying with insecticide is recommended for malaria control in high-transmission settings. Determination of residual activity of insecticides is essential for the selection of appropriate indoor spraying policy. The present study was undertaken to evaluate the residual effect of bendiocarb, a carbamate insecticide used in Madagascar, on different indoor surfaces in order to elaborate future vector control interventions.MethodsThe residual activity of bendiocarb was evaluated in both experimental huts and houses. Tests in experimental huts on different substrates represented a small scale-field trials. The houses IRS performed in parallel of experimental huts IRS, was done to compare semi-field results and field results. Bioassays according to the World Health Organization (WHO) standard protocol were carried out on different substrates impregnated with bendiocarb using susceptible strains of Anopheles arabiensis and Aedes albopictus.ResultsBendiocarb induced significantly high mortality in treated huts against exposed mosquito (p < 0.005) compared to untreated huts. The mortality is up to the WHO threshold of 80 % during 5 months post-treatment. Using a multivariate analysis, Ae. albopictus mortality decreased significantly from the 3rd month post-treatment. However, An. arabiensis mortality decreased significantly from the 4th month after treatment. Comparing mosquito mortality results from the mud experimental huts and the mud houses showed no significant difference regarding the persistence of bendiocarb on wall.ConclusionsCurrent data suggest variable persistence of bendiocarb according to the type of wall surfaces, highlighting the importance of testing insecticide for IRS in local context before using them in large scale. Data from this study validate also the importance of using experimental huts as representative tool to evaluate the effectiveness of an insecticide.

Multiple insecticide resistances and kdr mutation of Culex pipiens pallens in north-central Anhui Province

To understand the status of resistance to multiple insecticides and the frequencies of kdr mutations in Culex pipiens pallens from north-central Anhui Province. From July to September, 2014, the C. pipiens pallens mosquito larvae were collected in Huaibei, Bengbu and Chuzhou cities of the north-central Anhui Province and reared to adults. The female adult mosquitoes at 3-5 days post emergence were tested for susceptibility to the four insecticides, namely 0.05% deltamethrin, 5% malathion, 0.1% bendiocarb and 4% DDT, by using the standard WHO resistance tube bioassay. The detection of the point mutations of the kdr gene at codon 1014 was conducted by PCR and DNA sequencing in the deltamethrin-resistant and -susceptible mosquitoes. High levels of resistance to all the four insecticides were found in all the three tested populations, although mosquito mortality varied among populations and test insecticides. Among the test insecticides, DDT showed lowest mortality with no significant difference (F = 1.027, P > 0.05) in all test populations, whereas significantly different mortalities were observed among populations for the remained three insecticides tested (deltamethrin, malathion, and bendiocarb) (F = 23.823, 33.955, 128.841; all P < 0.01). Two types of non-synonymous kdr mutation at codon position 1014 (L1014F and L1014S) were observed. A positive correlation between L1014F mutation frequencies and deltamethrin resistance levels were detected in the three mosquito populations (r2 = 0.718, P < 0.01). The observed high levels of resistance to multiple-insecticides coupled with the occurrence of medium to high kdr frequencies in populations of C. pipiens pallens could profoundly affect the mosquito vector control programme in China. The local health departments need to strengthen vector dynamic monitoring and implement rational resistance management strategies.

Post harvest seed quality of greengram as influenced by pre-harvest spray of insecticides

The experiment was conducted to study the effect of insecticides and stages of insecticidal sprays on seed yield and yield components in greengram. The investigation was carried out in Department of Genetics and Plant Breeding, during &lt;italic&gt;Kharif&lt;/italic&gt; 2012. The experiment was laid in factorial randomized block design (FRBD) consisted of 15 treatment combinations involving two factors with three replications. Among the five test insecticides, spraying of malathion @ 2 ml/l recorded significantly more number of pods/plant (20.75), pod weight (20.45g), seed yield/plant (3.17 g), seed yield/hectare (949 kg) and less percentage of infested pods (5.35%) as well as infested seeds/plant (2.66%). It was followed by nimbicidine and methyl parathion. Whereas reciprocal values for these seed yield parameters were noticed in the unsprayed control plants (16.13, 16.53g, 1.84g, 725 kg, 14.13% and 7.89%, respectively). Similar results were recorded in spraying of insecticides at 20 and 10 Days before harvest compare to 20 or 10 Days before harvest. Interaction effect between insecticides and stages of insecticidal spraying were found non-significant for most of the seed yield and quality parameters.

Efficacy of different bio-pesticides against sucking pests of okra (Abelmoschus esculentus L. Moench)

The field experiment was carried out in the pre-kharif season of 2013 at Bidhan Chandra Krishi Viswavidyalaya, Kalyani, Nadia, West Bengal, India to evaluate the efficacy of different bio-pesticides against sucking pests of okra. The experiment was laid out in randomized complete block design with three replications for each treatment. The treatments viz. annonin 1% EC, karanjin 2% EC, Azadirachtin 1% EC, Metarrhizium anisopliae, Verticillium lecanii , Beauveria bassiana , Bacillus thuringiensis var Kurstaki, spinosad 45 % SC and imidacloprid 17.8% SL were applied at 15 days interval starting from seedling stage when whitefly and jassid infestation started. Results revealed that the overall best performance of insecticides against whitefly was recorded in imidacloprid treated plots with lowest mean population of whitefly (3.91 whitefly/15 leaves) followed by karanjin (4.16 whitefly/15 leaves) and azadirachtin (5.16 whitefly/15 leaves while the order of efficacy aginst jassid were imidacloprid (15.27 jassids/15 leaves) &gt; karanjin (33.91jassids/15leaves)&gt;azadirachtin(40.38jassids/15leaves). Effectiveness of test insecticides on the yield of okra wasspinosad&gt;Bt&gt;B. bassiana&gt;azadirachtin&gt;imidacloprid&gt;annonin&gt;karanjin&gt;M. anisopliae.

Evaluation of Mosquito Repellent Activity of Isolated Oleic Acid, Eicosyl Ester from Thalictrum javanicum.

To evaluate the traditional use, the mosquito repellent property of Thalictrum javanicum and to confirm the predicted larvicidal activity of the isolated compound, oleic acid, eicosyl ester from its aerial parts by PASS software, the present study was carried out using 4th instar stage larvae of the mosquitoes, Aedes aegypti (dengue vector) and Culex quinquefasciatus (filarial vector). Insecticidal susceptibility tests were conducted and the mortality rate was observed after 24 h exposure. The chitinase activity of isolated compound was assessed by using purified β-N-acetyl glucosaminidase (chitinase). Ecdysone 20-monooxygenase assay (radioimmuno assay) was made using the same larval stage of A. aegyptiand C. quinquefasciatus. The results were compared with the crude methanol extract of the whole plant. The isolated compound, oleic acid, eicosyl ester was found to be the most effective larvicide against A. aegypti (LC50/24 h -8.51 ppm) and C. quinquefasciatus (LC50/24 h - 12.5 ppm) than the crude methanol extract (LC50/24 h - 257.03 ppm and LC50/24 h - 281.83 ppm, respectively). The impact of oleic acid, eicosyl ester on reducing the activity of chitinase and ecdysone 20-monooxygenase was most prominent in both the target species, A. aegyptiand C. quinquefasciatus than the control. The results therefore suggest that the compound, oleic acid, eicosyl ester from Thalictrum javanicum may be considered as a potent source of mosquito larvicidal property.

Comparison of the Insecticidal Activities of Three Plants against Two Devastating Insects: Callosobruchus maculatus and Sitophilus zeamais

To find the alternate ones with insecticides of synthesis, the extracts of plants are more and more used by the peasants to protect stocks from harvest against the devastating insects. Small fireclay cups phytochimic and insecticidal are made on three plants (Crataeva religiosa, Ficus thonningii and Tapinanthus bangwensis). The identification of the active ingredients present in the three plants show that they contain polyphenols, flavonoides, alkaloids, tannins, saponosides, etc. The insecticidal tests showed that the extract with the chloroform (HEY) of Crataeva religiosa is effective on Callosobruchus maculatus and Sitophilus zeamais while extracts with cyclohexan (EC) and methanolic (EM) are effective only on Callosobruchus maculatus. It sucked shown that the extract with chloroform gives a better mortality rate and that Callosobruchus maculatus is more sensitive to the treatments the strong amount (50 mg/mL). For the study of emergences, the methanolic extract of the sheets of Crataeva religiosa ensures a better protection of the medium on Sitophilus zeamais. It was also shown that the extracts with the cyclohexane and methanolic of Ficus thonnigii are more effective on Callosobruchus maculatus. Thus, the methanolic extract (EM) of Ficus thonningii reduces considerably the number of insects emerged in the short run on Callosobruchus maculatus. The tests relating to Tapinanthus bangwensis showed that the extracts cyclohexanic, chloroformic and methanolic are effective on Sitophilus zeamais. The extracts with the cyclohexan and the methanol of Tapinanthus bangwensis reduce considerably the number of insects emerged on Sitophilus zeamais and long-term. Broadly Tapinanthus bangwensis is more effective on the two studied insects and Callosobruchus maculatus is the species most sensitive to the treatments. It is thus the most promising plant.

Gene Replacement for the Generation of Designed Novel Avermectin Derivatives with Enhanced Acaricidal and Nematicidal Activities.

Avermectin (AVM) and ivermectin (IVM) are potent pesticides and acaricides which have been widely used during the past 30 years. As insect resistance to AVM and IVM is greatly increasing, alternatives are urgently needed. Here, we report two novel AVM derivatives, tenvermectin A (TVM A) and TVM B, which are considered a potential new generation of agricultural and veterinary drugs. The molecules of the TVMs were designed based on structure and pharmacological property comparisons among AVM, IVM, and milbemycin (MBM). To produce TVMs, a genetically engineered strain, MHJ1011, was constructed from Streptomyces avermitilis G8-17, an AVM industrial strain. In MHJ1011, the native aveA1 gene was seamlessly replaced with milA1 from Streptomyces hygroscopicus. The total titer of the two TVMs produced by MHJ1011 reached 3,400 mg/liter. Insecticidal tests proved that TVM had enhanced activities against Tetranychus cinnabarinus and Bursaphelenchus xylophilus, as desired. This study provides a typical example of exploration for novel active compounds through a new method of polyketide synthase (PKS) reassembly for gene replacement. The results of the insecticidal tests may be of use in elucidating the structure-activity relationship of AVMs and MBMs.

Chemical characterization and insecticidal properties of essential oils from different wild populations of Mentha suaveolens subsp. timija (Briq.) Harley from Morocco.

The present study is the first investigation of the volatile-oil variability and insecticidal properties of the endemic Moroccan mint Mentha suaveolens subsp. timija (mint timija). The yield of essential oils (EOs) obtained from different wild mint timija populations ranged from 0.20±0.02 to 1.17±0.25% (v/w). GC/MS Analysis revealed the presence of 44 oil constituents, comprising 97.3-99.9% of the total oil compositions. The main constituents were found to be menthone (1.2-62.6%), pulegone (0.8-26.6%), cis-piperitone epoxide (2.9-25.5%), piperitone (0.3-35.5%), trans-piperitone epoxide (8.1-15.7%), piperitenone (0.2-9.6%), piperitenone oxide (0.5-28.6%), (E)-caryophyllene (1.5-11.0%), germacrene D (1.0-15.7%), isomenthone (0.3-7.7%), and borneol (0.2-7.3%). Hierarchical-cluster analysis allowed the classification of the EOs of the different mint timija populations into four main groups according to the contents of their major components. This variability within the species showed to be linked to the altitude variation of the mint timija growing sites. The results of the insecticidal tests showed that all samples exhibited interesting activity against adults of Tribolium castaneum, but with different degrees. The highest toxicity was observed for the EOs belonging to Group IV, which were rich in menthone and pulegone, with LC50 and LC90 values of 19.0-23.4 and 54.9-58.0 μl/l air in the fumigation assay and LC50 and LC90 values of 0.17-0.18 and 0.40-0.52 μl/cm(2) in the contact assay.

The activity of the pyrrole insecticide chlorfenapyr in mosquito bioassay: towards a more rational testing and screening of non-neurotoxic insecticides for malaria vector control.

BackgroundThe rapid selection of pyrethroid resistance throughout sub-Saharan Africa is a serious threat to malaria vector control. Chlorfenapyr is a pyrrole insecticide which shows no cross resistance to insecticide classes normally used for vector control and is effective on mosquito nets under experimental hut conditions. Unlike neurotoxic insecticides, chlorfenapyr owes its toxicity to disruption of metabolic pathways in mitochondria that enable cellular respiration. A series of experiments explored whether standard World Health Organization (WHO) guidelines for evaluation of long-lasting insecticidal nets, developed through testing of pyrethroid insecticides, are suitable for evaluation of non-neurotoxic insecticides.MethodsThe efficacy of WHO recommended cone, cylinder and tunnel tests was compared for pyrethroids and chlorfenapyr. To establish bioassay exposure times predictive of insecticide-treated net (ITN) efficacy in experimental hut trials, standard three-minute bioassays of pyrethroid and chlorfenapyr ITNs were compared with longer exposures. Mosquito behaviour and response to chlorfenapyr ITN in bioassays conducted at night were compared to day and across a range of temperatures representative of highland and lowland transmission.ResultsStandard three-minute bioassay of chlorfenapyr produced extremely low levels of mortality compared to pyrethroids. Thirty-minute day-time bioassay produced mortality closer to hut efficacy of chlorfenapyr ITN but still fell short of the WHO threshold. Overnight tunnel test with chlorfenapyr produced 100% mortality and exceeded the WHO threshold of 80%. The endogenous circadian activity rhythm of anophelines results in inactivity by day and raised metabolism and flight activity by night. A model which explains improved toxicity of chlorfenapyr ITN when tested at night, and during the day at higher ambient temperature, is that activation of chlorfenapyr and disruption of respiratory pathways is enhanced when the insect is more metabolically and behaviourally active.ConclusionsTesting according to current WHO guidelines is not suitable for certain types of non-neurotoxic insecticide which, although highly effective in field trials, would be overlooked at the screening stage of evaluation through bioassay. Testing methods must be tailored to the characteristics and mode of action of each insecticide class. The WHO tunnel test on night-active anophelines is the most reliable bioassay for identifying the toxicity of novel insecticides.