Contact Toxicity Bioassays Research Articles

Sunflower seed hulls waste as a novel source of insecticidal product: Pyrolysis bio-oil bioactivity on insect pests of stored grains and products

The edible oil industry produces abundant sunflower seed hulls (SSH) as waste. Pyrolysis offers a sustainable method for producing high-value bioproducts from this lignocellulosic residue. This paper reports on the bioefficacy of SHH pyrolysis bio-oils from raw SSH (named SSH bio-oil) and acid pretreated hulls (named PTH bio-oil) as bioinsecticides against Sitophilus oryzae, Lasioderma serricorne and Tribolium castaneum. Raw SSH and pretreated hulls with 10% H3PO4 were subjected to fast pyrolysis in a vertical reactor at 450 °C. Results show that PTH bio-oil is a furfural enriched bio-liquid with storage stability and a yield of 33%. SSH bio-oil was unsuitable for evaluating biological activity since it produce high variability in mortality data. In contrast, PTH bio-oil produces high insecticidal activity in S. oryzae (LC50 = 0.51 mg cm−2) by contact toxicity bioassay, followed by L. serricorne and T. castaneum. In behavioral assays, PTH bio-oil shows a slight repellent effect and mobility reduction. Moreover, PTH bio-oil affects the nutritional physiology of S. oryzae and T. castaneum producing a modification of nutritional indices and antifeedant effects. Our study provides information on the potential of fast pyrolysis bio-oils from SSH waste to develop novel bioinsecticides as an alternative to the use of conventional synthetic pesticides.

Toxicity of the essential oil from Thymus serpyllum and thymol to larvae and pupae of the housefly Musca domestica L. (Diptera: Muscidae).

The essential oil (EO) of Thymus serpyllum and thymol were evaluated for their insecticidal activity against the housefly (Musca domestica) larvae and pupae. Contact toxicity and fumigation bioassays were used. Chemical composition analysis of T. serpyllum EO by gas chromatographic mass spectrometry (GC-MS) revealed that thymol (41.6%), p-cymene (21.9%), and γ-terpinene (19.2%) were the major components. For larval assays, the LC50 value of T. serpyllum EO was 0.4 μl/cm2 for contact toxicity and 20.9 μl/l for fumigation toxicity. For thymol, the contact toxicity LC50 value was 0.035 μl/cm2 and the fumigation LC50 value was 2.0 μl/l. For the pupal assay, T. serpyllum EO had a percentage inhibition rate (PIR) value of 100% for both contact toxicity (1.0 μl/cm2) and fumigation toxicity assay (25 μl/l), whereas thymol had a PIR of 100% for contact toxicity (0.1 μl/cm2) and fumigation assay (5 μl/l). This study shows that T. serpyllum EO and thymol are toxic to housefly larvae and pupae and have the potential for use in the population control of this species.

Ecofriendly Approach for the Control of a Common Insect Pest in the Food Industry, Combining Polymeric Nanoparticles and Post-application Temperatures.

One of the most common insect pests is Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae), which affects different food commodities. A new effective approach for the management of insect pests is the development of new formulations based on essential oils (EO). However, few works informed about the relationship between insecticidal activity of EO or essential oils loaded polymeric nanoparticles (EOPN) and post-application temperature. In our work, palmarosa [Cymbopogon martinii (Roxb.) Watson], geranium (Geranium maculatum L.), and peppermint (Mentha piperita L.) oils were formulated in a polyethylene glycol 6000 matrix to obtain EOPN. Geranium and palmarosa EOPN had sizes of 259 and 191 nm, respectively; the encapsulation efficiency (EE) was close to 90%, and the samples were monodisperse. The sizes from peppermint EOPN were around 380 nm, with an EE of 72%, and were polidisperse. In a contact toxicity bioassay, the insecticidal effect of the oils was increased by all EOPN, with palmarosa oil being the most toxic. In addition, the oils and their nanoparticles showed a significantly negative temperature coefficient when applied by contact. In a fumigant bioassay, just palmarosa and peppermint EOPN enhanced the oil activity and palmarosa EO and EOPN showed the highest toxic effect. In this case, the EO and EOPN insecticidal activity was unaffected by environmental temperature variation.

Bioactivity of Common Pesticidal Plants on Fall Armyworm Larvae (Spodoptera frugiperda).

The fall armyworm (FAW), Spodoptera frugiperda (Lepidoptera: Noctuidae) is a recent invasive pest species that has successfully established across sub-Saharan Africa where it continues to disrupt agriculture, particularly smallholder cereal production. Management of FAW in its native range in the Americas has led to the development of resistance to many commercial pesticides before its arrival in Africa. Pesticide use may therefore be ineffective for FAW control in Africa, so new and more sustainable approaches to pest management are required that can help reduce the impact of this exotic pest. Pesticidal plants provide an effective and established approach to pest management in African smallholder farming and recent research has shown that their use can be cost-beneficial and sustainable. In order to optimize the use of botanical extracts for FAW control, we initially screened ten commonly used plant species. In laboratory trials, contact toxicity and feeding bioassays showed differential effects. Some plant species had little to no effect when compared to untreated controls; thus, only the five most promising plant species were selected for more detailed study. In contact toxicity tests, the highest larval mortality was obtained from Nicotiana tabacum (66%) and Lippia javanica (66%). Similarly, in a feeding bioassay L. javanica (62%) and N. tabacum (60%) exhibited high larval mortality at the highest concentration evaluated (10% w/v). Feeding deterrence was evaluated using glass-fibre discs treated with plant extracts, which showed that Cymbopogon citratus (36%) and Azadirachta indica (20%) were the most potent feeding deterrents among the pesticidal plants evaluated. In a screenhouse experiment where living maize plants infested with fall armyworm larvae were treated with plant extracts, N. tabacum and L. javanica were the most potent species at reducing foliar damage compared to the untreated control whilst the synthetic pesticide chlorpyrifos was the most effective in reducing fall armyworm foliar damage. Further field trial evaluation is recommended, particularly involving smallholder maize fields to assess effectiveness across a range of contexts.

Chemical profile, characterization and acaricidal activity of essential oils of three plant species and their nanoemulsions against Tyrophagus putrescentiae, a stored-food mite.

Essential oils of Ocimum basilicum (L.), Achillea fragrantissima (Forssk.) and Achillea santolina (L.) were obtained by hydrodistillation and analyzed using gas chromatography (GC) and GC/mass spectrometry (MS). Oil-in-water nanoemulsions (10% active ingredient) were prepared through a high-energy (ultrasonication) emulsification process. Nanoemulsions were characterized by viscosity, pH, thermodynamic stability, droplet size, polydispersity index (PDI) and scanning electron microscopy (SEM) measurements. The plant oils and their nanoemulsions showed considerable acaricidal activity against the mold mite, Tyrophagus putrescentiae (Schrank) (Sarcoptiformes: Acaridae). In a contact toxicity bioassay and 48h post treatment, O. basilicum oil was the most toxic, followed by A. fragrantissima and A. santolina, where LC50 values were 8.4, 14.1 and 21.8µl/cm2, respectively. LC50 for benzyl benzoate, a standard acaricide was 9.8µl/cm2. Upon fumigation, responses also varied according to the test oil. Based on the 48-h LC50 values, the same manner of activity was also observed, where O. basilicum was the most toxic followed by A. fragrantissima and A. santolina. When prepared as nanoemulsions (particle size from 78.5 to 104.6) and tested as fumigants, toxicity of the oils was increased drastically with LC50 values of 2.2, 4.7, and 9.6µl/l air for O. basilicum, A. fragrantissima and A. santolina, respectively. The oils showed a moderate to strong residual acaricidal activity, where O. basilicum oil was the most effective. The results suggest that appropriate nanoemulsions containing the tested oils can be developed to control T. putrescentiae after the required toxicological assessments.

Chemical composition and toxicity of Jatropha curcas seed oil against Sitophilus zeamais Motschulsky as affected by pre-extraction treatment of seeds

This study evaluated the chemical composition and toxicity of fixed oils obtained from Jatropha curcas seeds pre-treated with different methods (cooking, roasting and raw) against maize weevil, Sitophilus zeamais Motschulsky. Palmitic acid was the predominant compound, being 86.60, 69.98 and 54.04%, in oil obtained from cooked, raw and roasted seeds, respectively. Glycerol 1-palmitate was identified in all oil samples (13.40. 16.43 and 27.06% for the oil extracted from cooked, raw and roasted seeds, respectively). Other compounds identified in oils obtained from raw seeds and roasted seeds were palmitoleic acid (2.36 and 2.16%, respectively), linoleic acid (3.13 and 5.80%, respectively) and 9 Octadecenal, (Z)- (8.10 and 10.94%, respectively). At the exposure of the weevils to 200 μl/L air for 24 h, weevil mortality observed in oil obtained from roasted seeds (84.68%) was significantly (p < 0.05) higher than 40.28 and 47.80% observed in oils obtained from cooked and raw seeds, respectively. In contact toxicity bioassay, application of 1.50 μl/cm2 for 3 h evoked 47.52, 46.96 and 47.36% mortality for oil obtained from roasted, cooked and raw seeds, respectively; being higher than the values observed in untreated control and n-hexane. According to these results, pre-extraction seed treatment affected the chemical composition and toxicity of the oil against Sitophilus zeamais.

Biological activity of Dittrichia viscosa (L.) Greuter extracts against adult Sitophilus granarius (L.) (Coleoptera, Curculionidae) and identification of active compounds

Dittrichia viscosa (L.) Greuter, a perennial weed of the Mediterranean area, was reported to be source of active substances. Here, by means of both ingestion and contact assays, the biological activity of three different extracts (n-hexane, methanol, and distilled water) of D. viscosa aerial part has been evaluated against Sitophilus granarius (L.) adults, an important pest of stored grains. Ingestion assays showed negligible mortality and food deterrence for all the extracts, whereas only a slight reduction of some nutritional parameters (relative growth rate, relative consumption rate, food efficiency conversion) was recorded for water extract. High contact toxicity was found only for the n-hexane extract (24 h median lethal dose LD50 = 53.20 μg/adult). This extract was further subfractioned by silica gel column chromatography and then by thin layer chromatography. Further contact toxicity bioassays highlighted two active subfractions which were analyzed by GC-MS. This revealed the occurrence, in both subfractions, of two major peaks that were identified as α- and γ- costic acid isomers. Moreover, D. viscosa active subfractions, did not cause acetylcholinesterase (AChE) inhibition; therefore, in the light of progressive limitation of compounds acting by this mechanism of action, D. viscosa represents a promising eco-sustainable source of natural products for pest control.

Evaluating insecticide coverage in almond and pistachio for control of navel orangeworm (Amyelois transitella) (Lepidoptera: Pyralidae).

Insecticide application is essential to control navel orangeworm (Amyelois transitella) in California almond and pistachios. Coverage is difficult because of tree height and applicator practices. Studies were conducted to characterize insecticide deposition by both ground and air, and to develop alternatives to the use of water-sensitive cards to assess spray coverage. We used almond challenge bioassays to demonstrate that insecticide application failed first in the upper canopy (5.2-6.1 m) when application speed exceeded 2.9 kph. In pistachios, we used filter paper and insecticide extraction from hulls to demonstrate that deposition increased with application volume. Typically, in ground applications, coverage decreased with height, whereas for application by air, coverage was greatest at the top of the canopy (6 m) and decreased as the spray penetrated the canopy. In the best ground applications there was no loss over height. We were able to demonstrate a dose-response relationship for methoxyfenozide using contact toxicity bioassays. Coverage was best at or below the recommended speed of 3.2 kph and improved when water volume increased. There was a 50% loss in insecticide efficacy at the height of 4-4.8 m; we suggest that future monitoring concentrate on this portion of the canopy. The best ground application provided uniform deposition throughout the canopy, whereas the applications by air were most effective in the upper canopy. The use of filter paper can provide information for chemical deposition and enable contact toxicity bioassays, whereas water-sensitive paper cannot do this. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.

Lethal and behavioral effects of synthetic and organic insecticides on Spodoptera exigua and its predator Podisus maculiventris.

BackgroundThe beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae), is a key insect pest of edible vegetables around the world and it is resistant to insecticide of different classes. Insecticides that are effective to this pest and selective to predator stinkbugs are required for the integrated management of S. exigua.MethodsThe toxicity of four commercial insecticide formulations azadirachtin + pyrethrin, spinosad, pyrethrin and chlorantraniliprole was tested on the target pest and their side effect were evaluated on the spined soldier bug, Podisus maculiventris (Heteroptera: Pentatomidae) through different bioassays.ResultsSpinosad and chlorantraniliprole were more toxic to S. exigua than to the predator P. maculiventris but opposite results were obtained for pyrethrin and azadirachtin + pyrethrin in contact toxicity bioassay. Chlorantraniliprole was the most toxic to S. exigua in oral toxicity bioassay, followed by spinosad, pyrethrin and azadirachtin + pyrethrin. Spinosad in oral toxicity bioassay was the most toxic to P. maculiventris, followed by pyrethrin, azadirachtin + pyrethrin and chlorantraniliprole. Spinosad caused irritability to the predator while pyrethrin to the pest. The insecticide repellency was not observed over the tested insect species. The synthetic insecticide chlorantraniliprole was less toxic than the natural pyrethrin, azadirachtin + pyrethrin and spinosad to the predator.ConclusionsThis work provides useful information on the combination of commercial insecticides with the predator P. maculiventris to controlling S. exigua in integrated pest management (IPM) programs.

Cinnamaldehyde and related phenylpropanoids, natural repellents, and insecticides against Sitophilus zeamais (Motsch.). A chemical structure-bioactivity relationship.

The insecticidal and repellent effects on adult Sitophilus zeamais of 12 cinnamaldehyde-related compounds was evaluated by contact toxicity bioassays and a two-choice olfactometer. To determine non-toxicity in mammals, body weight, serum biochemical profiles, liver weight, physiological parameters, sperm motility, and histopathological data were obtained as complementary information in C57BL/6 mice treated with the best natural compound. Based on 24 h LC95 and LC50 values, α-methyl-cinnamaldehyde and cinnamaldehyde exhibited better insecticidal action than the other compounds. The best repellent effect was observed with α-bromo-cinnamaldehyde, which even repelled at the lowest concentration studied (0.28 µmol L-1 ). The evaluation of a quantitative structure-activity relationship found a linear relationship between the LC50 values for adult weevil toxicity and dipolo with Q values (giving the difference between orbital electronegativity carbon 1 and orbital electronegativity carbon 3 of the molecule) in cinnamaldehyde-related compounds. The polar surface and Log P descriptors also revealed a linear relationship with the S. zeamais repellent effect for cinnamaldehyde analogues. Cinnamaldehyde did not show toxicity in the parameters evaluated in mice. From the phenylpropanoid components studied, the natural compound that had the best insecticidal and repellent action against S. zeamais was cinnamaldehyde. It presented no mammalian toxicity. © 2018 Society of Chemical Industry.

Bioactivity of Pistacia atlantica desf. Subsp. Kurdica (Zohary) Rech. F. and Pistacia khinjuk stocks essential oils against Callosobruchus maculatus (F, 1775) (Coloeptera: Bruchidae) under laboratory conditions

One of the major storage insect pests of cowpea and many other grains is Callosobruchus maculatus (F.) (Col.: Bruchidae). The use of plant materials rather than conventional pesticides to control these pests is a promising alternative to neurotoxic insecticides. In this study, for the first time, the fumigant, contact toxicity and repellent activity of Pistacia atlantica Desf. Subsp. kurdica (Zohary) Rech. f. (gum, fruit and leaves) and Pistacia khinjuk Stocks (fruit and leaf) essential oils were tested against adults of C. maculatus. The essential oil from P. khinjuk fruit showed a stronger fumigant activity against C. maculatus after 24 h exposure (LC50 = 22 μl/l air) compared to the leaves (LC50 = 29 μl/l air). As for P. atlantica subsp. kurdica, the essential oil from the gum showed the highest activity at 24 h (LC50 = 7.0 μl/l air) compared to the fruit (LC50 = 18 μl/l air) and leaves (LC50 = 24 μl/l air). In contact toxicity bioassays, the P. khinjuk fruit and leaf oils caused significant mortality to C. maculatus adults upon contact for 24 h (LC50 = 0.12 μl/cm2 and LC50 = 0.14 μl/cm2, respectively), while the P. atlantica subsp. kurdica gum was the most toxic at 24 h (LC50 = 0.07 μl/cm2) compared to the fruit oil (LC50 = 0.11 μl/cm2) and leaf oil (LC50 = 0.08 μl/cm2). At the highest concentration of 0.0234 μl/cm3, the respective repellency percentages for P. atlantica subsp. kurdica gum, leaves and fruit oils at 24 h were 82%, 77% and 70%. For P. khinjuk, the respective repellency percentages for the leaf and fruit oils at 24 h were 76% and 67% at the highest concentration (0.0234 μl/cm3). These results indicate strong fumigant and contact toxicity, and repellent activity for all the tested essential oils against C. maculatus. Hence, the data can be exploited further to develop a management strategy against C. maculatus.

Bioinsecticidal Activity of Eucalyptol and 1R-Alpha-Pinene Rich Acetonic Oils of &amp;lt;i&amp;gt;Eucalyptus saligna&amp;lt;/i&amp;gt; on &amp;lt;i&amp;gt;Sitophilus zeamais&amp;lt;/i&amp;gt; Motschulsky, 1855 (Coleoptera: Curculionidae)

Exploration of plants, animals, microbes and their products for green pesticides have been the mainstay of modern agriculturalists. Plant bioactive oils have been utilized in formulation of green pesticides, which are less toxic, least deleterious on biocontrol agents, readily biodegraded and have no or few ecological effects as compared to synthetic equivalents. This study evaluated the bioinsecticidal activity of Eucalyptol and 1R-Alpha-Pinene rich acetonic essential oils of dry leaves of the Sydney Blue gum (Eucalyptus saligna Smith) on common granivorous maize weevil. Fresh leaves of Eucalyptus saligna were harvested and the essential oils extracted from its dry powder by hydrodistillation. The chemical composition of the essential oil was analyzed by tandem GC/MS. Twelve components were identified, and the main components were Eucalyptol (34.36%) and 1R-alpha pinene (17.92%). Acetonic essential oils of 2µL, 4µL, 6µL and 8µL in 1ml acetone were used in contact toxicity, fumigant and repellent bioassays. In contact toxicity, 8µL/ml oil exerted a rapid effect on the weevils giving 100% mortality in the first day of exposure; 6µL/ml achieved 100% mortality 96 hours after treatment. Both fumigant and repellent activities showed a gradual increase in insect mortality and repellency with time of exposure as the concentrations of the essential oils were increased; 100% repellency was achieved at 8µL in the second hour and this remained constant with time. The lowest repellency of 20% was obtained at 2µL. In fumigant toxicity, the highest mortality was 70% recorded at 8µL on the third day of exposure. The results indicated that the acetonic essential oil of dry Eucalyptol and 1R-Alpha-Pinene rich Eucalyptus saligna leaves can be developed into a bioinsecticide for controlling maize weevil as a repellent, toxicant and fumigant candidate.

Potential of four tropical plant powders as Grain Protectants Against Callosobruchus maculatus (Coleoptera: Chrysomelidae)

Effects of four tropical plant (Aframomum melegueta, Zanthoxylum zanthoxyloides, Piper guineense and Eugenia aromatica) were investigated under tropical laboratory storage conditions for the protection of cowpea seeds against insect infestation. The plant materials were pulverised into fine powder after air drying and admixed with 20 g of cowpea seeds at the rates of 0.2, 0.3, 0.4 and 0.5 g in 125 ml plastic containers for contact toxicity experiment and 0.5 g of each plant powder to 50 g cowpea seeds for the fumigant toxicity experiment. Ten unsexed Callosobruchus maculatus were used for contact toxicity experiment, while two copulating pairs of C. maculatus were used for fumigant toxicity experiment. Callosobruchus maculatus response to the plant powders was recorded at 24 and 48 hrs post treatment for contact toxicity bioassay, while observation for fumigant activity was recorded at 24, 48, 72 and 96 hrs after treatment. All plant powders significantly (P < 0.05) exerted adult mortality in relations to dosage and exposure time. Cowpea seeds treated with 0.5g of E. aromatica had highest mortality of 90% and 100% at 24 and 48 hrs after exposure respectively for contact toxicity, while A. melegueta recorded the highest adult mortality for all exposure periods for the fumigant toxicity. The insects’ reactions to the plant powders admixed with cowpea seeds were restlessness, loss of coordination, knock-down and eventual death. The study indicated that the plant powders could be used as suitable alternative to synthetic insecticides to suppress C. maculatus infestation in stored cowpea seeds among the resource-poor farmers.

Comparative toxicity of Helosciadium nodiflorum essential oils and combinations of their main constituents against the cabbage looper, Trichoplusia ni (Lepidoptera)

The chemical composition of the essential oils from the aerial parts of Helosciadium nodiflorum Apiaceae), obtained from two different localities in Italy, were analyzed by gas chromatography/mass spectrometry (GC/MS). Sample 1 (collected from Sulmona) was dominated by phenylpropanoids (49.1%) with myristicin (49.1%), (Z)-β-ocimene (19.0%), limonene (7.8%) and terpinolene (7.1%) as major constituents. Sample 2 (collected from Colfiorito) was mainly composed of monoterpene hydrocarbons (58.7%) and the main compounds of the oil were limonene (40.6%), myristicin (24.3%), dillapiol (9.4%) and β-pinene (5.5%). In order to determine relationships between the chemical composition and insecticidal activity of the oils, comparative and synergistic interactions of the main constituents of H. nodiflorum essential oils were investigated in third-instar larvae of the cabbage looper, Trichoplusia ni, via a contact toxicity bioassay. In the case of sample 1, myristicin was identified as a major active principle while in sample 2, limonene, myristicin and dillapiol were main insecticidal constituents. Several combinations of these compounds were synergistic when topically applied, especially myristicin and (Z)-β-ocimene, or limonene.

Screening the insecticidal effect of thirty plant extracts from Jabel Akhdar region northeast Libya against adults of confused flour beetle, Tribolium confusum du Val (Coleoptera: Tenebrionidae) using contact toxicity bioassay and fumigation toxicity bioa

At the last forty years the world directing to replaceing the conventional pesticides by economic alternatives are more safty for health and suitable for different cases, the plant extracts (Green Pesticides) were in the front of these alternatives, in this study, thirty plant extracts were isolated from ten plant they are endemic in Jabel Akhdar region northeast Libya using three different solvents (hexane, ethanol and water). The efficacy of these extracts against the confused flour beetle, Tribolium confusum were evaluated by two methods for bioassay a contact toxicity bioassay (C.T.B.) on filter paper and fumigation toxicity bioassay (F.T.B.). The results showed that, ethanol extracts were the best comparing with others two solvents and the ethanol extracts of Caper, Thyme, Nerium and Nabq were more effective than others in the both bioassays methods, when the ethanol extracts of Rosmary was grate effective by (C.T.B.) with 100% mortality whereas it give only 50% mortality by (F.T.B.). However everyone who ethanol extract of Harmel, and ethanol extract of Juniper showed high efficacy by 100% mortality for each one with (F.T.B.) bioassay, while they give only 73.33% and 50% mortality with (C.T.B.) for each one respectively.

Comparison between two bioassay methods for detect the insecticidal activity of some plant extracts against adults of Tribolium confusum du Val (Coleoptera: Tenebrionidae).

The plant derived products are become the more popular ingredients for use as domain component in the medicaments, cosmetic products and pesticides and many thing ells, that for their nice properties and their wiled spread. The scientists need a good methods for bioassay the plant derived compounds as insecticides for detect their effect as contact or fumigant insecticides, in this study two methods for bioassay a contact toxicity bioassay (C.T.B.) and fumigation toxicity bioassay (F.T.B.) were examined using seven ethanolic extracts that are the superior toxic against adults of T. confusum, the results showed that, concerning the LT50 values the difference between the two methods was statistically significant only with ethanol extract of Thyme when the difference between these methods were significant with ethanol extracts for all of Caper, Thyme and Nabq using the LT90 values, Generally with these subjected extracts (Caper ; Thyme ; Nabq ; Nerium) the C.T.B. was the best method for bioassay.

Lethal and sublethal effects of the chitin synthesis inhibitor chlorfluazuron on Bradysia odoriphaga Yang and Zhang (Diptera: Sciaridae)

Bradysia odoriphaga Yang and Zhang is the primary insect pest that affects Chinese chive in northern China. Nevertheless, very few studies have been conducted on the use of chitin synthesis inhibitors (CSIs) for the control of B. odoriphaga. Here, lethal and sublethal effects of the CSI chlorfluazuron on B. odoriphaga were studied to explore the use for integrated pest management (IPM) of B. odoriphaga. A contact and ingestion toxicity bioassay showed that chlorfluazuron was more active against B. odoriphaga than three other CSIs, with a 72h LC50 of 0.1593mg/L. Treatment with the LC50 dose of chlorfluazuron decreased both the intrinsic and finite rates of increase of B. odoriphaga, in addition to reproduction rate, survival rate, and fecundity, and the mean generation time, total preovipositional period and larval development duration were shortened, compared with those of the control and LC10 groups. The mean generation time, total preovipositional period and larval development duration were all also markedly decreased by treatment with chlorfluazuron at the LC10. Furthermore, chlorfluazuron inhibited the feeding of the final instar larvae for a short period. Glutathione S-transferase and microsomal mixed function oxidase activities increased after exposure to the chemical. These results showed that chlorfluazuron at the sublethal LC50 treatment inhibited B. odoriphaga population growth, whereas the danger of causing rapid population growth by using a lower sublethal concentration was demonstrated with the sublethal LC10 treatment. Therefore, chlorfluazuron should be used with caution in an IPM program for B. odoriphaga.

Joint acute toxicity of the herbicide butachlor and three insecticides to the terrestrial earthworm, Eisenia fetida.

The herbicide butachlor and three insecticides phoxim, chlorpyrifos, and lambda-cyhalotrhin are widely used pesticides with different modes of action. As most previous laboratory bioassays for these pesticides have been conducted solely based on acute tests with a single compound, only limited information is available on the possible combined toxicity of these common chemicals to soil organisms. In this study, we evaluated their mixture toxicity on the terrestrial earthworm, Eisenia fetida, with binary, ternary, and quaternary mixtures. Two different types of bioassays were employed in our work, including a contact filter paper toxicity test and a soil toxicity test. Mixture toxicity effects were assessed using the additive index method. For all of the tested binary mixtures (butachlor-phoxim, butachlor-chlorpyrifos, and butachlor-lambda-cyhalothrin), significant synergistic interactions were observed after 14days in the soil toxicity assay. However, greater additive toxicity was found after 48h in the contact toxicity bioassay. Most of the ternary and quaternary mixtures exhibited significant synergistic effects on the worms in both bioassay systems. Our findings would be helpful in assessing the ecological risk of these pesticide mixtures to soil invertebrates. The observed synergistic interactions underline the necessity to review soil quality guidelines, which are likely underestimating the adverse combined effects of these compounds.

The mortality and repellency effect of a formulation of spearmint essential oil on the cotton-melon aphid under greenhouse conditions

In recent years, application of essential oils derived from aromatic plants has been considered as low-risk insecticides. These compounds have repellency, insecticidal and growth-reducing effects on immature stages of a variety of insects. Since it is not possible to use pure essential oils in agricultural fields and greenhouses, development of commercial formulations essential-oils is necessary. In this study, the insecticidal activity and repellency effect of essential oil from spearmint (Mentha spicata) and its formulation was tested against the melon aphid (Aphis gossypii), which is one of the key pests of greenhouse crops. The LC50 values of fumigation bioassay of the essential oil against the first instar nymph, third instar nymph and adult of A. gossypii were 2.70, 3.41 and 5.24 μl/L, respectively. For contact toxicity bioassay, based on preliminary tests, a formulation of essential oil from spearmint was used in four concentrations (8000, 12500, 16000 and 25000 mg/L). Results revealed that spearmint essential-oil formulation caused 88.7% adult mortality when applied at a concentration of 25000 mg/L. The repellency index was calculated when aphids were exposed for 24 h to LC20 concentration. This index was -10%. These results showed that formulation of spearmint essential oil could be used as a commercial substitute for chemical insecticides to control A. gossypii under greenhouse conditions.

EFFECT OF DRYING ON YIELD, CHEMICAL COMPOSITION AND INSECTICIDAL ACTIVITY OF LEAF ESSENTIAL OILS OF SWEET ORANGE (Citrus sinensis)

Pulverized fresh and dried leaves of Citrus sinensis (500 g) that were dried for five consecutive days during dry season were separately hydro-distilled for 3 hours. Oil yields from the samples ranged from 0.10 - 0.37% (w/w). Characterization of the oils using Gas chromatography - mass spectrometry showed that the oils were predominated by monoterpenoids (56.7 – 90.2%). Car-3-ene was the most abundant compound in the oils from fresh and the leaves dried for four days. Interestingly, the oils from other dried leaves had α-fenchene, α-terpinolene and β-pinene as their major constituents. The insecticidal activities of the oils against Callosobruchus maculatus were also determined via contact toxicity bioassay. Regardless of the level of dryness, the oils were observed to be toxic to C. maculatus. Oil obtained from the leaves dried for five days was found to be more active against the insect than other oils.