Relative toxicity of nC24 agricultural mineral oil to Tetranychus urticae Koch (Acari: Tetranychidae) and Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae) and its possible relationship to egg ultrastructure

The relative toxicity (LC₅₀ values based on µg oil/cm²) is evaluated of aqueous n C24 agricultural mineral oil (AMO) emulsions to the egg, six-legged nymph (larva), eight-legged protonymph and adult stages of two-spotted mite ( Tetranychus urticae ) and its predator, Phytoseiulus persimilis , on French bean leaf discs, using a Potter spray tower to apply of the oil. The egg of P. persimilis was the least susceptible stage (LC₅₀ 444.84) and its LC₅₀ was significantly higher than all other stages tested of either P. persimilis or T. urticae . The LC₅₀ for adult female T. urticae (LC₅₀ 63.89) was significantly lower than the larva (LC₅₀ 93.86); however, there was no significant difference in response between the protonymph (LC₅₀ 70.44) and the larva, which were both higher than T. urticae eggs (LC₅₀ 17.55). LC₅₀s for P. persimilis larva (LC₅₀ 43.87), protonymph (LC₅₀ 41.55) and adult female (LC₅₀ 53.34) were similar. Scanning electron microscopy showed that the egg surface of T. urticae is usually well covered with fine silk that may trap more oil and increase AMO efficacy. Other possible differences in AMO efficacy between T. urticae and P. persimilis may be due to differences in egg size, egg incubation period, egg surface structure and the presence of vulnerable respiratory cones in T. urticae eggs. Dose of 0.2–0.3% (w/w) is considered to be the most appropriate for n C24 AMOs use against T. urticae in combination with P. persimilis in integrated pest management programs.     

Early life stage toxicity of extracts from the African fish poison plants Tephrosia vogelii Hook. f. and Asystasia vogeliana Benth. on zebrafish embryos

Embryos of Danio rerio are highly susceptible to extracts of the plants Tephrosia vogelii and Asystasia vogeliana . The concentration of the dried extracts at which 50% of the embryos were affected (EC₅₀) after 24 h exposure were 320 and 572 μg l⁻¹, respectively; corresponding 50% mortality (LC₅₀) values after 48 h exposure were 493 and 869 μg l⁻¹. Results indicate that the use of these ichthyotoxic plants might have a severe impact on the survival of fish larvae in the field.     

Production of mosquito larvicidal Bacillus thuringiensis serotype H-14 on raw material media from Nigeria

Bacillus thuringiensis serotype H-14 de Barjac, a potent larvicide of many mosquito and blackfly species, was grown on various media compounded from fermented cassava ( Mannihot esculenta ), ground and whole maize ( Zea mays ) grains and whole cowpeas ( Vigna unguiculata ) in shake flask fermentations. The liquors obtained from 100g/l of the whole cowpea and maize grains as well as combinations of these were used for further fermentations in 1 and 5 1 fermenters. The final whole cultures obtained were bioassayed against L11/111 of Aedes aegypti and the concentration-effects estimated. The potency of the preparations (estimated as LC₅₀, strength that showed 50% mortality of the mosquito larvae) ranged from 10.5 mg/l for the 1:3 combination of cowpea steep liquor:maize steep liquor to 90 mg/l for the 2:1 combination at 95% confidence limits. The LC₅₀ of a standard nutrient broth-yeast extract medium was 18 mg/l. The juice of Citrus aurantifolia and an extract from Elaeis guiniensis were used as acid and alkali respectively while bleached deodorized palm olein was used as antifoam.     

Ovicidal and larvicidal effectiveness of several insect growth inhibitors and regulators on the codling moth Cydia pomonella L. (Lep., Tortricidae)

Several insect growth inhibitors (IGIs) and regulators (IGRs) were tested in the laboratory for their ovicidal and larvicidal properties on the codling moth C. pomonella , by dipping apples in solutions of them. The IGIs which block chitin synthesis – diflubenzuron, hexaflumuron and teflubenzuron – were noticeably more effective against eggs than on newborn larvae with preventive ovicidal 50% lethality concentrations (LC₅₀) values of approximately 0.6, 1.3 and 15 p.p.m., respectively, and larvicidal LC₅₀ values of 104, 1208 and 204 p.p.m. Flufenoxuron, on the other hand, is almost as effective on larvae (LC₅₀ : 9.9 p.p.m.) as on eggs (LC₅₀ : 5.4 p.p.m.). Fenoxycarb, an IGR juvenile hormone analogue, acts as an excellent ovicidal product with an LC₅₀ value of 0.05 p.p.m. Tebufenozide, an IGR ecdyson (moulting hormone) agonist, is exclusively larvicidal with an LC₅₀ at 0.4 p.p.m. Methoxyfenozide, an IGR of the same family and currently being developed, acts as effectively on eggs as on larvae with ovicidal and larvicidal LC₅₀ values of about 0.6 and 0.8 p.p.m., respectively. When ovicidal products are applied as a curative treatment on eggs less than 24 h old, their effectiveness is much lower than that obtained from preventive application.     

Inheritance of resistance and cross resistance pattern in indoxacarb-resistant diamondback moth Plutella xylostella L.

Leaf-dip assay of Plutella xylostella against indoxacarb showed that the concentration that produced 50% mortality (LC₅₀) of indoxacarb ranged from 20.1 to 11.9 ppm, with highest in Nasik and lowest levels in Coimbatore strains. In selection studies, the LC₅₀ of indoxacarb was 18.5 ppm at generation 1 (G1), which increased to 31.3-fold (167.8 ppm) resistance after ten exposed generations (G10) as compared to unexposed. The LC₅₀ of quinalphos was 74.4 ppm, which increased to 10.0-fold (631.5 ppm) resistance after G10. The LC₅₀ of cypermethrin resistant strain resulted in an 11.5-fold increase in resistance after G10. In P. xylostella , heritability (h²) after ten generations of selection was estimated at 0.4. The number of generations required for tenfold increase in LC₅₀ (1/R) were 6.7. The response to indoxacarb selection in P. xylostella was 0.2 and the selection differential was estimated as 0.4. The phenotypic standard deviation was 0.2. Reciprocal crosses between indoxacarb-resistant and susceptible strains showed that the inheritance of indoxacarb resistance was autosomal. The degree of heritability (D_LC) (0.4, 0.4) indicated incomplete recessive inheritance of indoxacarb resistance.     

Insecticide susceptibility and resistance of larvae of the Anopheles sinensis Group (Diptera: Culicidae) from Paju, Republic of Korea

The susceptibility of members of the Anopheles sinensis Group in Korea to insecticides was evaluated under laboratory conditions using 15 insecticides currently used by local public health centers in Korea. The insecticides included eight pyrethroids, six organophosphates and a pyrazol analogue. Based on their LC₅₀ values, the order of susceptibility of An. sinensis larvae to the insecticides was bifenthrin, chlorfenapyr, α-cypermethrin and λ-cyhalothrin, with values of 0.009, 0.04, 0.06 and 0.08 p.p.m., respectively. The least susceptibility was obtained with fenitrothion, with an LC₅₀ of 7.7 p.p.m. In the comparative resistance test, the resistance ratios (RR) of 14 insecticides were compared to each other using two strains of members of the An. sinensis Group collected in the locality in 2001 and 2008. Anopheles spp. demonstrated higher RR to organophosphates such as fenthion, and low RR for the pyrethroids. Among the organophosphates, fenthion had the highest RR of 33.3 and 270.0 fold differences for LC₅₀ and LC₉₀ values, respectively. Among the pyrethroids, permethrin was observed to have the highest RR of 3.8 and 1.8 fold differences for LC₅₀ and LC₉₀ values, respectively. However, there were no significant differences in susceptibility to chlorfenapyr, chlorpyrifos, deltamethrin and fenitrothion. An. sinensis s. l. was more susceptible to the six insecticides bifenthrin, λ-cyhalothrin, α-cypermethrin, cypermethrin, cyfluthrin and pyridafenthion, showing 0.03, 0.06, 0.3, 0.3, 0.4 and 0.4 fold differences in resistance rates (RR LC₅₀), respectively.     

Insecticidal activity influence of destruxins on the pathogenicity of Paecilomyces javanicus against Spodoptera litura

Abstract:  The bioactivities of destruxins (dtx), depsipeptides isolated from Metarhizium anisopliae , against Spodoptera litura were tested in laboratory. For contacting toxicities, dtx-E was more effective than dtx-A and dtx-B. The LC₅₀s values of dtx-A, B and E were 197.98, 292.00 and 113.99 mg/l at 48 h after treatment, while the LT₅₀s were 42.65, 59.45 and 23.68 h at 300 mg/l. In the experiment of antifeedant activity, dtx-A, dtx-B and dtx-E at five concentrations (200, 100, 50, 25 and 12.5 mg/l) were bioassayed. Destruxins in a dose-dependent manner gave an apparent antifeedant activity. Generally, dtx-A, over dtx-B and dtx-E had the significant (P < 0.05) larger choice and no-choice antifeedant indexes (CAIs and NCAIs). At the concentration of 200 mg/l, the CAIs or NCAIs of dtx-A, dtx-B and dtx-E were 96.78, 84.93 and 85.90 or 89.75, 62.42 and 72.28 respectively. Furthermore, the synergistic activity of crude destruxin (CD) for pathogenicity of Paecilomyces javanicus strain Pj01 was detected. The LC₅₀s values of single Pj01 and the mixtures of Pj01 plus CD at 100 or 200 mg/l (Pj01-CD100 or Pj01-CD200) were respectively 474.63 × 10⁵, and 197.45 × 10⁵ or 113.11 × 10⁵ spores/ml at the fifth day after treated. Meanwhile, Pj01, Pj01-CD100 and Pj01-CD200 gave the LT₅₀s values of 6.99 day, 5.49 day and 4.21 day at 100 × 10⁵ spores/ml. Clearly, dtx decreased the values of LC₅₀ and LT₅₀ of the strain Pj01.     

Pathogenicity of six isolates of Beauveria bassiana (Balsamo) Vuillemin (Deuteromycotina, Hyphomycetes) to Perillus bioculatus (F) (Hem., Pentatomidae)

Abstract:  The two-spotted stink bug, Perillus bioculatus (F) (Hem., Pentatomidae) is considered an important predator of Colorado potato beetle egg masses and small larvae. The susceptibility of P. bioculatus second instar nymphs to six isolates of Beauveria bassiana (Balsamo) Vuillemin, which are highly pathogenic to Colorado potato beetle, was tested in the laboratory. Five isolates were highly pathogenic and caused more than 77% mortality after 8 days at a concentration of 10⁶ conidia/ml. However, isolate IPP46 showed low pathogenicity and caused only 11% mortality of nymphs. The pathogenicity of isolates was independent of their host, source or country of origin. Isolate IPP46 was tested at six different concentrations. A linear relationship between the concentration of B. bassiana and the mortality of nymphs was observed. The 50% lethal concentration (LC₅₀) value was 3.4 × 10⁷ conidia/ml. The LT₅₀ decreased with increase of conidia concentration used. The present results suggest that isolate IPP46 has good potential as a biological control agent within an integrated pest management programme.     

Baseline toxicity of emamectin and spinosad to Helicoverpa armigera (Lepidoptera: Noctuidae) for resistance monitoring

Acute toxicity studies of emamectin and spinosad against Helicoverpa armigera revealed that the pest is highly susceptible to both the insecticides. The median lethal dose (LD₅₀) of emamectin is 3.86 × 10⁻³ µg per larva. The median lethal concentrations (LC₅₀) of emamectin and spinosad were found to be 0.09 and 2.94 ppm, respectively. The discriminating doses were fixed based on the LC₉₅ of the susceptible population of H. armigera as 0.80 ppm for emamectin and 10 ppm for spinosad. Resistance was not observed when the discriminating doses of emamectin and spinosad were applied on field-collected populations of H. armigera from two intensive cotton growing areas, Coimbatore and Madurai, India.     

紫茎泽兰提取物对四种储粮害虫的杀虫活性

紫茎泽兰提取物对米象、玉米象、绿豆象和蚕豆象等 4种储粮害虫成虫具有强烈的熏杀活性 ,用 4 4.4 4mg L的浓度熏蒸处理 4 8小时后 ,每种成虫死亡率均达到 1 0 0 .0 0 %。熏蒸毒力测定结果表明 ,紫茎泽兰提取物对上述 4种成虫 2 4小时的LC50 分别为 1 4 .65,1 2 .80 ,2 5.0 7和 1 2 .2 0mg L ,4 8小时的LC50 分别为 1 1 .79,9.67,1 3 .2 9和 9.76mg L。     

Evaluation of insecticidal and genotoxic effects of imidacloprid and acetochlor in Drosophila melanogaster

Two pesticides, the insecticide imidacloprid and the herbicide acetochlor, were evaluated for their insecticidal and genotoxic effects in Drosophila melanogaster . Their insecticidal effects were assessed by calculating LC₅₀ values after acute or chronic exposure of larvae and adults to different concentrations of the test compounds. After acute exposure, the LC₅₀ of imidacloprid was 7.59 × 10⁻⁵ M for larvae and 1.43 × 10⁻⁴ M for adults, and after chronic exposure, it was 2.67 × 10⁻⁵ M and 6.09 × 10⁻⁵ M for larvae and adults, respectively. On the contrary, the herbicide acetochlor showed no acute or chronic insecticidal effect against either larvae or adults, even at very high concentrations (8 × 10⁻³ M). For the evaluation of genotoxic properties of the two pesticides, the Somatic Mutation and Recombination Test in D. melanogaster was used. Our results suggest that neither imidacloprid nor acetochlor exhibits mutagenic or recombinogenic activity at applicable concentrations.     

Seasonal and geographical toxicity of Indoxacarb against Helicoverpa armigera and influence of different host plants against Indoxacarb in India, 2005–2007

Indoxacarb, an oxadiazine insecticide, was evaluated for its effectiveness against Helicoverpa armigera collected from selected locations in India. Determination of Indoxacarb efficacy was done using a log-dose probit (LDP) bioassay against third instars collected from cotton ( Gossypium arborium ) fields near Akola, India. Monthly levels of toxicity of Indoxacarb were determined from July 2005 to March 2007. The maximum tolerance level of Indoxacarb was reported for the Amaravati strain (5.09 p.p.m.) and the minimum tolerance level for the Fatehbad strain (0.22 p.p.m.). Seasonal monitoring of Indoxacarb toxicity revealed an increased trend in tolerance from July 2005 to February 2006, which decreased from March 2006. The LC₅₀ of Indoxacarb was 2.71 p.p.m. in July 2005 and 17.14 p.p.m. in February 2006. During 2006–2007, the LC₅₀ was 3.84 p.p.m. at the start of the season and in March 2007 it was 13.51 p.p.m. The minimum LC₅₀ of Indoxacarb was reported for H. armigera larvae fed on Legasca spp. (1.62 p.p.m.) and the maximum LC₅₀ was reported for H. armigera reared on chickpea ( Cicer arietium ) (8.45 p.p.m.). LC₅₀ of 2.73 and 4.56 p.p.m. were reported for H. armigera fed on cotton ( Gossypium arborium ) and pigeonpea ( Cajanus cajan ), respectively.     

Potential of some Metarhizium anisopliae isolates for control of Culex quinquefasciatus (Dipt., Culicidae)

Abstract: The potential of some isolates of Metarhizium anisopliae and Beauveria bassiana for use in the integrated management of Culex quinquefasciatus was evaluated. Metarhizium anisopliae isolate 1037 was selected in initial bioassays with a 50% lethal concentration (LC₅₀) of 1.97 × 10⁴ conidia/ml. This fungus caused higher mosquito larva mortality when applied as a conidial suspension to the surface of the water than as dry conidia, with a time to 50% lethal (LT₅₀) of 1 day compared with 3.6 days for the dry conidial application. However, results with UV- and heat-inactivated conidia did not confirm a possible role of fungal toxins in causing mortality when ingested by C. quinquefasciatus larvae. Metarhizium anisopliae did not remain active for as long as the bacterium Bacillus sphaericus isolate 2362. At 24 h after application, the fungus-induced mortality on mosquito larvae was significantly lower than the mortality caused by the bacterium. By the second day, almost no activity by the fungus was observed. Results suggest that M. anisopliae isolate 1037 has potential for use in mosquito control programmes.     

Morphological changes in the gills of Lophiosilurus alexandri exposed to un-ionized ammonia

The average lethal concentration of un-ionized ammonia (48-h LC₅₀NH₃) has been determined by the static assay for larvae (0.48 mg l⁻¹) and alevins (0.92 mg l⁻¹) of 'pacamã' Lophiosilurus alexandri. Studies by light and scanning electron microscopes at the greatest concentration of NH₃ (0.99 mg l⁻¹ for larvae and 1.5 mg l⁻¹ for alevins) have shown that the changes in the cells and branchial tissue were more intense in the alevins.     

Fumigant toxicity of Eucalyptus intertexta, Eucalyptus sargentii and Eucalyptus camaldulensis against stored-product beetles

Abstract:  Three essential oils extracted from the species of the family Myrtaceae found in Kashan (centre regions of Iran) were shown to have potent fumigant toxicity against three major stored-product insects: Callosobruchus maculatus (Fab.), Sitophilus oryzae (L.) and Tribolium castaneum (Herbst). These were the essential oils from Eucalyptus intertexta R.T. Baker, Eucalyptus sargentii Maiden and Eucalyptus camaldulensis Dehnh. The mortality of 1- to 7-day-old adults of the insect pests increased with concentration from 37 to 926  μ l/l air and with exposure time from 3 to 24 h. The LC₅₀ values to the selected essential oils were between 2.55 and 3.97  μ l/l air for C. maculatus , 6.93 and 12.91  μ l/l for S. oryzae and 11.59 and 33.50  μ l/l air for T. castaneum . Fumigant effects of these essential oils were considered to warrant further research into their potential for commercial use.     

Larvicidal and smoke repellency effect of Toddalia asiatica and Aegle marmelos against the dengue vector, Aedes aegypti (Insecta: Diptera: Culicidae)

Investigations were made to evaluate the larvicidal activity and smoke repellent potential of Toddalia asiatica (L.) and Aegle marmelos at different concentrations (20, 40, 60, 80 and 100 p.p.m.) against first to fourth instar larvae and pupae of Aedes aegypti (L.). The LC₅₀ of A. marmelos and T. asiatica against first instars was 50.960 and 47.893 p.p.m., respectively; against second instars, 52.979 and 50.922; third instars, 56.653 and 54.461; and fourth instars, 60.778 and 61.278. The LC₅₀ and LC₉₀ for A. marmelos and T. asiatica against pupae were 56.634 and 112.992, and 53.64 and 116.22 p.p.m., respectively. The smoke toxicity of T. asiatica against Ae. aegypti was greater than that of A. marmelos . Smoke-exposed gravid females oviposited fewer eggs when compared to those that were not exposed to smoke. Smoke-exposed females hatched a lower percentage of eggs compared to unexposed females.     

Screening of Brazilian Bacillus sphaericus strains for high toxicity against Culex quinquefasciatus and Aedes aegypti

Abstract:  In this work, 246 Bacillus sphaericus strains were evaluated against Aedes aegypti and Culex quinquefasciatus larvae to select the most effective ones to be used as the basis of a national product. All strains were isolated from different regions of Brazil and they are stored in a Bacillus spp. collection at Embrapa Genetic Resources and Biotechnology. The selected strains were characterized by biochemical and molecular methods. Based on selective bioassays, 87 strains were identified as toxic to one or both target species. All of these strains contain genes that encode the 42, 51 kDa proteins that constitute the binary toxin and the 100 kDa Mtx1 toxin. All toxic strains presented a very high LC₅₀ against A. aegypti , so, a product based on any of these B. sphaericus strains would not be recommended for use in programmes to control A. aegypti . S201 had highest activity against C. quinquefasciatus , presenting the lowest LC₅₀ and LC₉₀ in bioassays.     

Enhancement of Bacillus thuringiensis with monosodium glutamate against larvae of obliquebanded leafroller (Lep.:Tortricidae)

Abstract:  Monosodium glutamate, a taste enhancer widely used in food industry, was tested in the laboratory to determine its phagostimulatory effects on larvae of Choristoneura rosaceana (Harris). Larvae fed apple leaves treated with 50–700  μ g/l monosodium glutamate increased leaf tissue consumption by approximately 40%. The stimulatory effect of monosodium glutamate (at 675  μ g/l concentration) was maintained throughout 10 days of continuous exposure. Adding 675  μ g/l monosodium glutamate to commercial formulation of Bacillus thuringiensis ssp. kurstaki, (DiPel^®2X DF), lowered LC₅₀ from 450 to 150  μ g/l (P < 0.05, Lethal Ratio Significance Test), indicating good potential for monosodium glutamate to enhance B. thuringiensis -based formulations.     

Nematicidal Activity of Honokiol and Magnolol Isolated from Magnolia tripetala

Ethyl acetate extract of the branches of Magnolia tripetala exhibited nematicidal activity against Bursaphelenchus xylophilus , Panagrellus redivivus and Caenorhabditis elegans . Two nematicidal phenolic compounds magnolol ( 1 ) and honokiol ( 2 ) were isolated from the extract based on bioassay-guided fractionation. The median lethal concentrations (LC₅₀) of compounds 1 – 2 were 149.3 and 63.7 mg/l, respectively, against B. xylophilus , 74.5 and 75.9 mg/l, respectively, against P. redivivus , 64.7 and 57.8 mg/l, respectively, against C . elegans at 48 h.     

Genetics of Indoxacarb resistance in Helicoverpa armigera (Hubner)

The present investigation was done with the aim of studying the genetics of Indoxacarb resistance. Selection of Helicoverpa armigera (Hubner) with Indoxacarb was done for eight generations to develop resistance. Reciprocal crosses between resistant and susceptible populations were made to understand the population genetics of Indoxacarb resistance in H. armigera . Generation-wise selection with Indoxacarb was evaluated for resistance development in H. armigera . The LC₅₀ of Indoxacarb was 2.81 p.p.m. for the first selected generation, and it increased to 272.55 p.p.m. after eight selected generations, which is a 1238.86-fold resistance compared to the susceptible strain. The estimated realized heritability (h²) after eight generations of selection with Indoxacarb was 0.45. The number of generations required for a tenfold increase in LC₅₀ (1/R) was estimated to be 2.59. The response to Indoxacarb selection in H. armigera was 0.39, the estimated selection differential (S) was 0.87, and the phenotypic standard deviation (σp) was 0.03. Reciprocal crosses between Indoxacarb resistant and susceptible strains revealed that the inheritance of Indoxacarb resistance was autosomal: neither maternal effect nor linkage was evident. The values of D_LC (0.10 and 0.09) indicated completely recessive inheritance of Indoxacarb resistance.