Contact Bioassays Research Articles

Toxicity and bioactivity of essential oil of Cilantro (Eryngium foetidum L.) against red flour beetle [Tribolium castaneum (Herbst)

Grains and milling products are a major part of the daily diet of humans and animals but grain storage is heavily impacted by insect pests. Toxicity and bioactivity of essential oil (EO) from Cilantro, Eryngium foetidum L. were evaluated against the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), known as one of the most common stored-product insect pests worldwide. EO was extracted from fresh leaves of E. foetidum using a Clevenger type apparatus, and its toxicity and bioactivity against T. castaneum were investigated using the topical application test, the vapor phase test, and the impregnated paper test. Toxicity of E. foetidum EO on T. castaneum adults was investigated by direct contact and fumigation bioassays. E. foetidum EO was efficient with low estimated LD50 and LC50 as 31.34 μL/mg adult and 13.03 µL/L air, respectively. Insecticidal efficiency of E. foetidum EO on T. castaneum adults showed that a dosage of 25 μL/mg adult and a concentration of 32 µL/L air killed 62.5% after 120 h of exposure and 72.50% after 72 h of exposure. E. foetidum EO was strongly repellent to T. castaneum adults at 2.5 µL/L air, with highest repellent activity (100%) after 7 h of exposure. Results indicated that E. foetidum EO showed potential as a bio-insecticide for the control of T. castaneum

Side effects of insecticides applied to cotton on adult Trichogramma pretiosum by three exposure routes

AbstractBACKGROUNDTrichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) is released in extensive areas cultivated with cotton worldwide, but the use of synthetic insecticides threatens the establishment of augmented populations. Thus, an assessment of insecticides’ effects on T. pretiosum is required to establish their compatibility with mass releases of the parasitoid. We studied in the laboratory the impact of insecticides administered through different exposure routes (direct‐spraying, ingestion and residue contact) on T. pretiosum. Based on their toxicity, the insecticides were rated into four categories (harmless, slightly harmful, moderately harmful and harmful) as per the International Organization for Biological Control.RESULTSThe survival, parasitism ability and emergence of the treated adults and offspring (F1 and F2), in addition to the persistence of the toxic effects in semi‐field conditions, were assessed. Teflubenzuron did not reduce female survival and caused a lesser impact on T. pretiosum on both direct‐spraying and ingestion bioassays. In the residue contact bioassay, teflubenzuron and flupyradifurone were rated as harmless and slightly harmful, respectively. The other active substances (chlorfenapyr, thiodicarb and methomyl) were harmful to the parasitoid by all exposure routes and were persistent (with toxicity duration surpassing 30 days).CONCLUSIONFrom these findings, teflubenzuron is the insecticide most compatible with T. pretiosum releases and should be preferred over the other active substances. Further studies with the harmful insecticides (thiodicarb, chlorfenapyr and methomyl) are required to determine their toxicity under field conditions and confirm their incompatibility with T. pretiosum releases.

Lime sulfur to control citrus flat mite and its interactions with the entomopathogenic fungus Lecanicillium muscarium

Lime sulfur is one of the few products indicated to control Brevipalpus yothersi in Brazilian organic citrus orchards. Other strategies, such as the use of entomopathogenic fungi should be evaluated, and Lecanicillium muscarium is one of the basic choices for pest management. Knowledge of the interactions between lime sulfur and this entomopathogen is critical for developing control strategies. With this goal, it was conducted the toxicological characterization of lime sulfur to B. yothersi and the compatibility evaluation with L. muscarium. Finally, the effects of L. muscarium and lime sulfur mixtures on B. yothersi control were evaluated. Product evaluation for B. yothersi was done through direct and residual contact bioassay, and different concentrations of lime sulfur mixed in potato dextrose agar culture medium were used to evaluate compatibility with L. muscarium. Lime sulfur was effective against adults of B. yothersi and caused eggs unviability of up to 71.0%, at a dose of 80 L per 2,000 L of H2O. The lethal concentration (LC50 and LC99) of lime sulfur estimated for mite adults were 246.62 and 858.5 μg of sulfur per mL of H2O (ppm a.i.). Lime sulfur concentrations of 180 to 560 ppm a.i. showed promise for use in combination with L. muscarium. However, concentrations of 1,000 and 5,600 ppm significantly reduced colony size and the number of spores/colony. The mixture of 100 and 180 ppm a.i. of lime sulfur with L. muscarium (108 conidia·mL–1) was not able to reduce the lethal time of entomopathogen on B. yothersi.

A Direct Contact Bioassay Using Immobilized Microalgal Balls to Evaluate the Toxicity of Contaminated Field Soils

A Direct Contact Bioassay Using Immobilized Microalgal Balls to Evaluate the Toxicity of Contaminated Field Soils

Evaluation of Native Entomopathogenic Fungi Isolates for Microbial Control of the Mediterranean Fruit Fly (Ceratitis Capitata (Diptera: Tephritidae)) Pupae and Adults

Two isolates of the entomopathogenic fungi (EPF) Beauveria bassiana (Hypocreales: Cordycipitaceae), an isolate of Aspergillus flavus (Eurotiales: Trichocomaceae), of Verticillium sp. (Glomerellales: Plectosphaerellaceae) and of Aschersonia sp. (Hypocreales: Clavicipitaceae) were evaluated for their pathogenicity against the Mediterranean fruit fly Ceratitis capitata (Diptera: Tephritidae) pupae and adults under laboratory conditions, using four different concentrations. Pathogenicity towards pupae and adults was tested via spraying and body contact bioassays respectively. Average mortality of treated individuals ranged from 60 to 100% for pupae and from 39 to 100% for adults depending on the fungal isolates and concentrations. The highest mortality levels were observed for individuals treated by Verticillium sp., A. flavus and Aschersonia sp., while the B. bassiana isolates were the less effective against both adult and pupae. Estimated lethal concentrations 90 ranged from 3x105 to 3.8 x 107 conidia/ml for adults and from 6.58 x 103 to 2.5 x 105 conidia/ml for pupae with lower values calculated for A. flavus, Verticillium sp. and Aschersonia sp. Mean lethal times 90 were less than 79h for C. capitata adults and ranged from 94 to 273 hours for pupae according to the fungal isolates. Microscopic observation of treated pupae showed a mycelium growth on the bodies of death individuals, while visible signs of mycosis are less observed for adults. Results of these experiments demonstrated that native EPF isolates could be a promising biocontrol agent to manage safely C. capitata and might be used against pupae by soil application or against adults by cover or bait sprays.

Assessing Varroa destructor acaricide resistance in Apis mellifera colonies of Virginia

Survival of European honey bee (Apis mellifera) colonies has been threatened over the past few decades as Varroa destructor has become a growing concern on a near-global scale. Prominent treatment methods have included the synthetic acaricides amitraz, coumaphos, and tau-fluvalinate. Since widespread resistance to these compounds has been noted, this study sought to investigate V. destructor resistance in Virginia. V. destructor infestation levels in apiaries located in three geographic regions of Virginia were monitored throughout the 2018 field season. By autumn, all apiaries had mite populations above the recommended treatment threshold. The results of resistance screening with glass surface contact bioassays indicated no resistance to amitraz, coumaphos, or tau-fluvalinate. These results have implications in future control strategies and responsible use of these acaricides may offer an additional option to those battling these aggressive ectoparasites.

Metarhizium anisopliae blastospores are highly virulent to adult Aedes aegypti, an important arbovirus vector

BackgroundThe use of entomopathogenic fungi (EPF) for the control of adult mosquitoes is a promising alternative to synthetic insecticides. Previous studies have only evaluated conidiospores against adult mosquitoes. However, blastospores, which are highly virulent against mosquito larvae and pupae, could also be effective against adults.MethodsMetarhizium anisopliae (ESALQ 818 and LEF 2000) blastospores and conidia were first tested against adult Aedes aegypti by spraying insects with spore suspensions. Blastospores were then tested using an indirect contact bioassay, exposing mosquitoes to fungus-impregnated cloths. Virulence when using blastospores suspended in 20% sunflower oil was also investigated.ResultsFemale mosquitoes sprayed with blastospores or conidia at a concentration of 108 propagules ml−1 were highly susceptible to both types of spores, resulting in 100% mortality within 7 days. However, significant differences in virulence of the isolates and propagules became apparent at 107 spores ml−1, with ESALQ 818 blastospores being more virulent than LEF 2000 blastospores. ESALQ 818 blastospores were highly virulent when mosquitoes were exposed to black cotton cloths impregnated with blastospores shortly after preparing the suspensions, but virulence declined rapidly 12 h post-application. The addition of vegetable oil to blastospores helped maintain virulence for up to 48 h.ConclusionThe results showed that blastospores were more virulent to adult female Ae. aegypti than conidia when sprayed onto the insects or applied to black cloths. Vegetable oil helped maintain blastospore virulence. The results show that blastospores have potential for use in integrated vector management, although new formulations and drying techniques need to be investigated.Graphical abstract

Characterization and In vitro investigation of antiscabietic effect of phytosomes assimilating quercetin and naringenin rich fraction of Pistacia integerrima galls extract against Sarcoptes scabiei

Background: Global prevalence of scabies urge to develop phytochemicals based novel herbal dosage forms that can assist in treatment of scabies. Objective: Anti scabietic investigation of phytosomes assimilating acetone fraction of hydroalcoholic extract of Pistacia integerrima galls against Sarcoptes scabiei. Method: Flavonoids were screened in acetone fraction of galls extract and HPTLC profile of acetone fraction was studied to identify phenolics, using toluene: ethyl acetate: methanol: formic acid (60:30:07:03) as solvent system. Phytosomes were prepared with solvent evaporation method and characterized by SEM, TEM, particle size analysis, entrapment efficiency, partition coefficient, IR spectroscopy and differential scanning calorimetry. Scabicidal effect of phytosomes and acetone fraction were evaluated by mite repellent and contact bioassay. Result: Quercetin (Rf value = 0.43) and naringenin (Rf value = 0.61) were screened with HPTLC in the acetone fraction. Oval shape, particle size (1161 nm), zeta potential (26.10) and polydispersity index (0.175) of F3 phytosomes were observed during characterization of complex. Entrapment efficiency (78.04±1.75%) and partition coefficient (0.85±0.60) of F3 phytosomes was higher as compared to F1 and F2 phytosomes. Chemical interaction between phospholipids and phenolics was analyzed by infrared spectroscopy and DSC. Significant mite repellent percentage with 1000 mg (93.33±0.57%) and 750 mg (86.66±0.57%) of F3 complex was observed after 4 h. Additionally F3 complex (4g and 3g) possess significant mean mortality rate after 4 h in comparison to acetone fraction. On probit analysis, median lethal concentration (LC50) of F3 phytosome complex was observed to be 3.354, 2.455, 1.475 and 0.420 g/mL after 1, 2, 3 and 4 h, respectively. Conclusion: Phytosomes assimilating acetone fraction of galls extracts can facilitate enhancement in scabicidal effect in contrast to acetone fraction of galls extract.

Bioactivity of a Linoleic Acid–Rich Fraction of Ricinus communis L. (Euphorbiaceae) Leaves against the Yellow Sugarcane Aphid, Sipha flava (Hemiptera: Aphididae)

The insecticidal activity of a Ricinus communis leaf hexane extract and its fractions against adult yellow sugarcane aphids (Sipha flava) was evaluated using a contact bioassay after fumigation. The n-hexane extract at 10,000 ppm achieved the highest mortality (80%); the positive control had 100% mortality and the negative control had only 4% mortality over the 72-h experiment time. Chemical fractionation of the hexane extract of R. communis leaves produced multiple fractions, and 10,000 ppm of the F4 fraction resulted in 92% aphid mortality at 72 h. Gas chromatography-mass spectrometry of the F4 fraction revealed linoleic acid as the major compound (84.5%). The R. communis n-hexane extract and linoleic acid could be used for integrated pest control as an ecologically friendly alternative to synthetic chemical insecticides.

Variable residual activity of K-Othrine\xae PolyZone and Actellic\xae 300 CS in semi-field and natural conditions in the Democratic Republic of the Congo

BackgroundIndoor Residual Spray (IRS) against vector mosquitoes is a primary means for combating malaria transmission. To combat increased patterns of resistance to chemicals against mosquito vectors, alternative candidate insecticide formulations should be screened. With mortality as the primary endpoint, the persistence of residual efficacy of a polymer-enhanced pyrethroid suspension concentrate containing deltamethrin (K-Othrine® PolyZone—KOPZ) applied at 25 mg active ingredient (ai)/m2 was compared with a microencapsulated organophosphate suspension formulation of pirimiphos-methyl (Actellic® 300CS—ACS) applied at 1 g ai/m2.MethodsFollowing standard spray application, periodic contact bioassays were conducted for at least 38 weeks on four types of wall surfaces (unbaked clay, baked clay, cement, and painted cement) sprayed with either KOPZ or ACS in simulated semi-field conditions. Similarly, two types of existing walls in occupied houses (painted cement and baked clay) were sprayed and examined. A colonized strain of female Anopheles arabiensis mosquitoes were exposed to treated or untreated surfaces (controls) for 30 min. For each wall surface test period, 40 treatment mosquitoes (4 cones × 10) in semi-field and 90 (9 cones × 10) in ‘natural’ house conditions were used per wall. 30 mosquitoes (3 cones × 10) on a matching unsprayed surface served as the control. Insecticide, wall material, and sprayed location on wall (in houses) were compared by final mortality at 24 h.ResultsInsecticide, wall material, and sprayed location on wall surface produced significant difference for mean final mortality over time. In semi-field conditions, KOPZ produced a 72% mean mortality over a 38-week period, while ACS gave 65% (p < 0.001). Painted cement wall performed better than other wall surfaces throughout the study period (73% mean mortality). In the two occupied houses, KOPZ provided a mean mortality of 88%, significantly higher than ACS (p < 0.001). KOPZ provided an effective residual life (≥ 80% mortality) between 7.3 and 14 weeks on experimental walls and between 18.3 and 47.2 weeks in houses, while ACS persisted between 3 and 7.6 weeks under semi-field conditions and between 7.1 and 17.3 weeks in houses. Household painted cement walls provided a longer effective residual activity compared to baked clay for both formulations. Greater mortality was recorded at the top and middle sections of sprayed wall compared to the bottom portion near the floor.ConclusionKOPZ provided longer residual activity on all surfaces compared to ACS. Painted cement walls provided better residual longevity for both insecticides compared to other surfaces. Insecticides also performed better in an occupied house environment compared to semi-field constructed walls. This study illustrates the importance of collecting field-based observations to determine appropriate product active ingredient formulations and timing for recurring IRS cycles.

Bioefficacy of bendiocarb WP80 in vector-borne and zoonotic diseases areas in borderline of Iran and Pakistan.

Malaria and leishmaniasis are the public health problems in southern Iran. The main activity of vector control is indoor residual spraying using pyrethroids, using different insecticides as larviciding and impregnated bednets. The aim of study was to evaluate the biological assays of bendiocarb wettable powder (WP) at different surfaces of wall. The residual effect of bendiocarb WP80 at 400 milligram/meter square (mg/m2) was evaluated on various local surfaces of rooms such as mud and plaster as well as thatch roofs and wooden. World Health Organization standard cones using contact bioassays were carried out using laboratory reared sugar-fed, 48-72 h old females of Anopheles stephensi. Contact bioassays were carried out on sprayed surfaces for 150 days. Contact bioassay on surfaces treated with bendiocarb WP80 at different surfaces was estimated about 2 months. Fumigant tests of bendiocarb WP80 at 400 mg/m2 revealed 50-93.83% mortality with 1 month persistency. The results showed that carbamate insecticide could be used as rotation with pyrethroids for malaria vector control. Monitoring and evaluation of environmental toxicology of pesticides is important for decision making for choosing appropriate pesticides for disease vector control.

Evaluations of the new deltamethrin-treated all-in-one hermetic bag for the control of the Khapra beetle, Trogoderma granarium (Everts)

The khapra beetle, Trogoderma granarium (Everts), is a highly destructive stored product insect that presents a significant threat to stored bagged grain. Hermetic packaging is designed to maintain the quality and safety of stored grain, while continually protecting the grain from insect infestations during storage. The objective of this research was to evaluate a prototype deltamethrin, all-in-one treated hermetic bag on contact efficacy, larval mobility, and the control of T. granarium in artificially infested wheat. The insecticidal activity of the deltamethrin-treated packaging was tested against larvae and adults of T. granarium through contact bioassays. There was a significant reduction in responsive adults after 5 day and >86% of larvae were unresponsive after 9 d of exposure on the treated bag. Trogoderma granarium movement toward a food bait was <10% after a 24 h exposure on the treated bag compared to ~45% of larvae on untreated bag. Lots of 15 kg of wheat were artificially infested with 100 T. granarium larvae and placed inside treated and untreated storage bags, sealed, and stored in a semi-field warehouse, and observed after 2, 6, and 8-weeks for T. granarium survival and grain quality attributes. The weight and number of insect damaged kernels was lower across all storage intervals for grain held in the treated bags, as compared with control bags. Live adult T. granarium were observed at 2-weeks in treated and untreated bags, but there were no live adults observed after 8-weeks of storage in both bags. The new prototype hermetic bags maintained positive grain qualities, however more information on the hermetic parameters are needed to understand how some individuals survived.

A pilot study on the prevalence of lice in Irish beef cattle and the first Irish report of deltamethrin tolerance in Bovicola bovis

BackgroundPediculosis in cattle causes significant itching, irritation and stress to the animal, often resulting in skin damage and poor coat condition. The control of bovine pediculosis in Ireland is based predominantly on commercial insecticides belonging to one of two chemical classes, the synthetic pyrethroids and the macrocyclic lactones. In recent years, pyrethroid tolerance has been reported in a number of species of livestock lice in the United Kingdom and Australia.ResultsIn this pilot survey, lice were detected in 16 (94%) out of 17 herds visited. Two species of lice, Bovicola bovis and Linognathus vituli were identified. In vitro contact bioassays showed evidence of deltamethrin tolerance in Bovicola bovis collected from 4 farms. This was confirmed by repeatedly assessing louse infestations on treated animals on one farm.ConclusionsTo our knowledge this is the first record of insecticide tolerant populations of lice in Irish cattle. The results also provide new data on the species of lice infesting beef cattle in Ireland and the prevalence and control of louse infestations in Irish beef cattle herds.

Evaluation of Beta-Cyfluthrin Resistance of Cigarette Beetle (Coleoptera: Anobiidae) from Cigarette Manufacturing Factories of China and Underlying Metabolic Mechanisms Responsible for Resistance.

Beta-cyfluthrin, as a synthetic pyrethroid, has been widely used in cigarette manufacturing factories in China to control Lasioderma serricorne (F.) (Coleoptera: Anobiidae). In this study, spray toxicity bioassays and filter paper residual contact toxicity bioassays were conducted to investigate the beta-cyfluthrin sensitivity level of five field strains of L. serricorne collected from cigarette manufacturing factories in China. Bioassay results indicated that five field strains had developed different levels of resistance to beta-cyfluthrin with RR50 of 3.51-10.20 at 2 hr after application and 4.05-49.50 at 24 hr after application in spray toxicity bioassays, and RR50 of 4.74-14.47 at 2 hr exposure in filter paper residual contact bioassays. In addition, we examined CarE, GST, and CYP450 enzyme activity and content of L. serricorne adults and larvae. Enzyme-linked immunosorbent assay results suggested that there was no significant difference in GST, CYP450, and CarE content of L. serricorne adults between field strains and reference sensitive strain. Biochemical assay results indicated that CYP450 activity of L. serricorne adults and larvae of five field strains was significantly higher than that of reference sensitive strain, with increased CYP450 activity of 1.08-1.82-fold in adults and 1.08-2.12-fold in larvae. The results implied that elevated CYP450 activity may contribute to metabolic resistance of L. serricorne to pyrethroid. Our study indicated that there was no clear evidence that the enhanced CarE and GST activity was associated with pyrethroid resistance of L. serricorne.

Essential Oil from Flowering Tops of Lavandula dentata (L): Chemical Composition, Aantimicrobial, Antioxidant and Insecticidal Activities

In this study, the chemical composition, antioxidant, antimicrobial, and insecticidal activities of essential oil (EO) from Lavandula dentata (L. dentata) flowering tops collected from northern Tunisia were assessed. Forty-three compounds were identified. β-eudesmol (21.178 %), myrtenol (13.023 %), and sabinol (11.021 %) were the main compounds. The antibacterial potential was evaluated against three Gram-positive bacteria and three Gram-negative bacteria. The diameter of inhibition varied between 20.83±0.47 mm and 24.16±0.47 mm. The largest one was found in Salmonella typhimurium, however, the smallest one was found in Bacillus cereus. The minimal inhibition concentration (MIC) varied between 0.1 and 0.6 μg/ml. Furthermore, the antifungal potential was carried out. The mycelial growth of all the treated fungi was significantly different from the control ones (p<0.05), except in the case of P. notatum when treated with a dose of 1.25 mg/ml. Moreover, L. dentata EO was screened for its antioxidant activity using three methods. IC50 values were 113.29± 0.012 mg/ml, 53.029± 0.02 mg/ml, 43.20± 0.004 mg/ml, respectively for the DPPH test, the ABTS test and the reducing power test. The insecticidal activity was tested against adults of two major insect pests namely Rhyzopertha dominica and Sitophilus oryzae using contact, fumigant toxicity, and repellent bioassays. Results revealed that the L. dentata EO exhibited strong fumigant, repellent, and contact properties. For all tests, R. dominica was more sensitive compared to S. oryzae. This study revealed that EO from L. dentata flowering tops could be potentially valorized as a new antibacterial, antifungal, and bioinsecticide product.

A toxicogenomics approach reveals characteristics supporting the honey bee (Apis mellifera L.) safety profile of the butenolide insecticide flupyradifurone

Flupyradifurone, a novel butenolide insecticide, selectively targets insect nicotinic acetylcholine receptors (nAChRs), comparable to structurally different insecticidal chemotypes such as neonicotinoids and sulfoximines. However, flupyradifurone was shown in acute toxicity tests to be several orders of magnitude less toxic to western honey bee (Apis mellifera L.) than many other insecticides targeting insect nAChRs. The underlying reasons for this difference in toxicity remains unknown and were investigated here. Pharmacokinetic studies after contact application of [14C]flupyradifurone to honey bees revealed slow uptake, with internalized compound degraded into a few metabolites that are all practically non-toxic to honey bees in both oral and contact bioassays. Furthermore, receptor binding studies revealed a lack of high-affinity binding of these metabolites to honey bee nAChRs. Screening of a library of 27 heterologously expressed honey bee cytochrome P450 enzymes (P450s) identified three P450s involved in the detoxification of flupyradifurone: CYP6AQ1, CYP9Q2 and CYP9Q3. Transgenic Drosophila lines ectopically expressing CYP9Q2 and CYP9Q3 were significantly less susceptible to flupyradifurone when compared to control flies, confirming the importance of these P450s for flupyradifurone metabolism in honey bees. Biochemical assays using the fluorescent probe substrate 7-benzyloxymethoxy-4-(trifluoromethyl)-coumarin (BOMFC) indicated a weak, non-competitive inhibition of BOMFC metabolism by flupyradifurone. In contrast, the azole fungicides prochloraz and propiconazole were strong nanomolar inhibitors of these flupyradifurone metabolizing P450s, explaining their highly synergistic effects in combination with flupyradifurone as demonstrated in acute laboratory contact toxicity tests of adult bees. Interestingly, the azole fungicide prothioconazole is only slightly synergistic in combination with flupyradifurone – an observation supported by molecular P450 inhibition assays. Such molecular assays have value in the prediction of potential risks posed to bees by flupyradifurone mixture partners under applied conditions. Quantitative PCR confirmed the expression of the identified P450 genes in all honey bee life-stages, with highest expression levels observed in late larvae and adults, suggesting honey bees have the capacity to metabolize flupyradifurone across all life-stages. These findings provide a biochemical explanation for the low intrinsic toxicity of flupyradifurone to honey bees and offer a new, more holistic approach to support bee pollinator risk assessment by molecular means.

Toxicity of Rosmarinus Officinalis Essential Oil to the Pest Tetranychus Urticae Koch (Acari: Tetranychidae) and its Predator Phytoseiulus Persimilis Athias-Henroit (Acari: Phytoseiidae)

This study aims to determine the chemical composition of Rosmarinus officinalis (Lamiales: Lamiaceae) and its acaricidal effect on the pest mite Tetranychus urticae Koch (Acari: Tetranychidae). and its predator Phytoseiulus persimilis Athias-Henroit (Acari: Phytoseiidae). The analysis of the chemical composition of the essential oil extracted was carried out on gas chromatography coupled with mass spectrometry. Three major compounds found in the essential of R. officinalis were α-pinene (32.64%), β-Humulene (8.71%), and Camphene (5.95%). The toxicity of R. officinalis oil was performed using inhalation bioassay on both T. urticae and its predator P. persimilis. The results obtained showed high toxicity on the mite than to its predator with a mortality rate of 80% and 16.11% respectively at the dose of 4%. The fertility of females, the hatching of eggs, and the emergence of adults in T. urticae were also studied using contact bioassay where a total reduction of all three biological parameters was recorded at the dose of 4%. Besides, the application of this oil will also allow the conservation of P. persimilis. Altogether, the combination of toxicity on T. urticae and preservation of its predator gives R. officinalis essential oil a propitious potential for the control of the pest mite T. urticae and maintenance of environmental balance.

Chemical composition of Ricinus communis and Momordica charantia seeds extracts and its bioactivity against the sugarcane aphid, Melanaphis sacchari (Zehntner)

Melanaphis sacchari Zehntner (Hemiptera: Aphididae) is currently the most destructive pest insect of the sorghum crop (Sorghum bicolor L. Moench) and has caused economic losses worldwide. Strategies using natural products such as plant extracts can offer alternatives for the control of this pest. In this investigation, we evaluated the insecticidal effect of the hexane extract of Ricinus communis L. and Momordica charantia L. seeds on M. sacchari in contact bioassays. The results showed that the extract of R. communis presented a mortality rate of 100% in 48 h at 10,000 ppm, while M. charantia presented 80% in 72 h, at 10,000 ppm. Gas chromatography—mass spectrometry (GC–MS) identified the major compounds as squalene in R. communis (51.57%) and linalool oxide in M. charantia (30.45%). The hexanic extracts of these plant species could be considered an ecologically friendly alternative to control this pest, given the use of synthetic chemical insecticides.

Anti-oxidant, pediculicidal and pesticidal activities of leaves of Rhinacanthus nasutus (Linn) grown in Sri Lanka

Rhinacanthus nasutus is an ethnomedical plant used in the traditional system of medicine for treating skin diseases. As no adequate studies available on R. nasutus grown in Sri Lanka, this study aimed on exploring anti-oxidant, anti-parasitic and pesticidal activity of leaves of the plant. Antioxidant capacity of the crude extract of leaves was evaluated using DPPH free radical scavenging assay and FRAP assay using ascorbic acid and FeSO4.7H2O as the standards respectively. Pediculicidal efficacy was carried out against head lice using 0.0010% (w/v) methanolic, ethyl acetate and aqueous extracts of leaves by following modified filter paper diffusion bioassay. Pesticidal activity of leaves was evaluated using modified filter paper contact bioassay against mealybugs, P. marginatus, resides on papaw and guava trees. The IC50 value of DPPH assay was found to be 514.3 μgmL-1 and FRAP value was found to be 594.33±2.93 μmol Fe2+/g in anti-oxidant assay. The LT50 (median Lethal Time) values for 0.0010% (w/v) concentration of methanolic, ethyl acetate and aqueous extracts were 263, 347 and 676 min respectively in pediculicidal assay. LC50 (50% mortality) value was found to be 0.0011% (w/v) after 240 minutes whereas LT50 values of 0.0020% (w/v) of methanol, ethyl acetate and aqueous fractions of R. nasutus for adult were found as 31, 124 and 189 hours and for nymph were 14, 18 and 29 hours respectively in pesticidal assay. Accordingly, methanolic extract was effective in controlling nymph stage of mealybug life cycle than adults with the LC50 of 0.0015% (w/v) within 14 hours. This study confirmed promising pediculicidal and pesticidal activity and significant anti-oxidant capacity of leaves of R. nasutus.&#x0D; Asian J. Med. Biol. Res. December 2020, 6(4): 754-760

Impact of Insecticides and Bioagents on Indian Bee Apis Cerana Indica F.

Honey bees are subjected to several risks caused by synthetic and organic pesticides. Hence, this study evaluates through a laboratory experiment, the safety of some pesticides used in organic and inorganic farming. The workers of Indian (Asiatic) bee Apis cerana indica F. were subjected to contact and oral (feeding) bioassays. The results revealed that in the contact toxicity study treatment with thiamethoxam at 0.3g/ ml resulted in maximum mortality while, the least mortality was with B. thuringiensis @ 4g/ l. In the oral (feeding) toxicity study, neem oil soap with pungam oil soap (1:1 ratio) at 10% concentration exhibited maximum oral toxicity.