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.     

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.     

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.     

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.     

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.     

Positive correlation of methamidophos resistance between Lipaphis erysimi and Diaeretilla rapae and effects of methamidophos ingested by host insect on the parasitoid

Temporal and spatial correlated variations on the methamidophos resistance and biomolecular rate constant of acetylcholinesterase to insecticides were found between the turnip aphid, Lipaphis erysimi and its endoparasitoid, Diaeretilla rapae , collected from field colonies and an insecticide-free field insectarium in Fujian, China. Compared to the related susceptible insectarium population, L. erysimi and D. rapae displayed 7.4–29.2- and 2.6–9.2-fold resistance ratios, respectively. In addition, two populations of L. erysimi with different methamidophos resistance levels, that is, a field (with 5.8-fold resistance ratio) and an insectarium population, were used to study the effects of methamidophos ingested by the host insect on D. rapae development. The percentage of D. rapae cocoon formation decreased significantly when the parasitized L. erysimi were fed on cauliflower leaves treated with methamidophos at lethal concentration dosages 10 (LC₁₀) or LC₅₀. At LC₅₀ dosages the percentage of D. rapae cocoon formation and adult emergence decreased significantly. When the parasitized L. erysimi were fed on methamidophos at LC₉₀ dosage, no D. rapae cocoons were found. When the field or insectarium L. erysimi were treated with methamidophos at LC₁₀, the susceptibility to methamidophos in the adult D. rapae emerged from the treated host insect was similar to the control. However, the susceptibility to methamidophos in the adult D. rapae became lower than the control when the host insects were treated at LC₅₀ dosages. The data thus suggested that the methamidophos ingested by the host insect L. erysimi could be an important factor in the endoparasitoids' insecticide resistance development. The natural selectivity would favor the parasitoids that had developed an insensitivity to the insecticide(s).     

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.     

Life history and life table analysis of the whitefly predator Delphastus catalinae （Coleoptera： Coccinellidae） on collards

Abstract The ladybeetle, Delphastus catalinae (Horn), is one of the most commonly used predacious natural enemies being commercially reared for controlling whiteflies, including Bemisia tabaci (Gennadius) biotype B (= B. argentifolii Bellows & Perring), on various ornamental and vegetable crops under greenhouse conditions. The development, survivorship, and fecundity of D. catalinae feeding on B. tabaci biotype B on collard plants were determined in the laboratory, and the age-specific life table parameters were analyzed based on the life history data. Developmental time was 4.0, 1.9, 1.1, 1.4, 5.2, and 5.3 days for eggs, first, second, third, fourth instars, and pupae, respectively, with an average of 18.9 days from oviposition to adult emergence for both sexes, 19.0 days for females, and 18.8 days for males. Adult longevities averaged 146.6 days for both sexes, 122.6 days for females, and 170.5 days for males. After an average 4.9 days preoviposition period, females laid a mean of 5.6 eggs per day over a 97.0-day period. Net reproductive rate ( R ₀) and gross reproductive rate (ΣM m_x ) were estimated by life table analysis at 276.8 and 325.1, respectively. Generation time (T) and doubling time (DT) were 35.6 and 4.8 days respectively, and the intrinsic rate of natural population increase ( r_m ) was estimated at 0.158, or l = 1.171 for the finite rate of increase. The r_m value of D. catalinae is similar to or higher than those of the whitefly feeding on most vegetable and ornamental crops, indicating that the ladybeetle is capable of regulating populations of B. tabaci biotype B and other whiteflies under greenhouse conditions.     

Adult survival of Delphastus catalinae (Coleoptera: Coccinellidae), a predator of whiteflies (Hemiptera: Aleyrodidae), on diets of whiteflies, honeydew, and honey

Delphastus catalinae (Horn) is a coccinellid predator that is commercially sold for the management of whiteflies. A study was conducted to assay the effect of selected diets on the survival of adult D. catalinae. Treatments of water (as a control), 10% honey, honeydew, and whiteflies [Bemisia tabaci (Gennadius)] were provided to the beetles in laboratory assays. Newly emerged, unfed adult insects were used at the start of a survival experiment with trials lasting 50 d. Another survival experiment used mixed-aged adults from a greenhouse colony, and the trials lasted 21 d. Survival was poor on a diet of solely water; ~1% survived beyond a week at 26°C. Survival using the newly emerged insects was similar between those fed honeydew and honey diets, but those on the whitefly diet had the greatest survival (~60% on day 50). However, in the experiment with mixed-aged beetles, adults on honey, and whitefly diets performed the same over a 21-d experiment. Excluding those on the water diet, survival of beetles on the various diets ranged from ~50-80% after 21 d. In an open choice assay across 7 h, D. catalinae adults were found on the whitefly diet in a much greater incidence than on the other diets, and the number of beetles found on the whitefly diet increased over time. The data supports that when D. catalinae are employed in greenhouses or fields for whitefly management, during low prey populations, honeydew from the whitefly can help sustain the population of this predator. Moreover, a supplemental food such as a honey solution can help sustain the population of D. catalinae when the prey is decreased to low numbers. These results may help in the development of strategies to enhance the utility of predators for the management of whiteflies.     

Susceptibility of various developmental stages of the maize weevil, Sitophilus zeamais Motschulsky (Col., Curculionidae) to methyl iodide in brown rice

Abstract:  The efficacy of methyl iodide (MI) as a fumigant against all developmental stages of the maize weevil, Sitophilus zeamais Motsch. was investigated. Tests were conducted with concentrations of 1.5, 1.8, 2.1, 2.4, 2.7 and 3.0 mg/l, for a 6-h exposure period. Values of LC₅₀, LC₉₅ and LC₉₉ of MI for immatures and adult stages were determined. The present laboratory tests showed that MI was toxic to various life stages of S. zeamais at relatively short exposure periods. At the LC₅₀ and LC₉₅ levels, the most susceptible stage was the egg stage followed by larvae, pupae and adults (1-day mortality). The egg was found to be most susceptible to MI, requiring 0.81 and 2.16 mg/l for 50 and 99% mortality, respectively, while the adult was most tolerant, requiring 2.30 and 3.02 mg/l for 50 and 99% mortality, respectively, based on 1-day mortality count. Pupae were less susceptible to MI than egg and larvae, requiring 1.47 and 3.19 mg/l for 50 and 99% mortality, respectively. Based on the present toxicity tests, MI has the potential for use as a fumigant to control all developmental stages of the maize weevil, S. zeamais .     

Roles of endothermy in niche differentiation for ball-rolling dung beetles (Coleoptera: Scarabaeidae) along an altitudinal gradient

Abstract.  1. An analysis of whether niche differentiation in ball-rolling dung beetles can be explained by the way in which they regulate their body temperature was conducted.
2.  A priori assumptions were: (i) if thermoregulation affects niche partitioning, sympatric species must have different endothermic strategies that minimise encounters; or, alternatively (ii) if two co-occurring species show the same thermoregulation pattern and their flight periods overlap, they might be avoiding competition by exhibiting different resource preferences or different food relocation behaviour.
3. The ball-rolling dung beetles studied showed a hierarchical structure based on the species' endothermic capacity, measured as temperature excess [ T _ex= difference between body temperature ( T _b) and ambient temperature ( T _a)]. Those with a high T _ex (10–15 °C) were located exclusively at altitudes >1000 m a.s.l. On the coastal plains, species with a high T _ex were restricted to flying at night when the T _a was lower. Species with a lower T _ex (less than 10 °C higher than T _a) were found in the coastal plains zone.
4. Where there was sympatry with similar trophic habits, the species involved showed very different thermal niches, and where there was significant overlap of thermal niches between sympatric species, trophic habits of species were very different.
5. The results suggest that it is possible to use the concept of the thermal niche as a tool to explain interspecific interactions and the spatial distribution of species.     

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.     

Insecticide resistance in Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) collected from horticulture and cotton in Turkey

Abstract  The sensitivity of three reference strains of the western flower thrips Frankliniella occidentalis from Australia, Israel and Turkey was evaluated and their response did not differ significantly and so they are considered typical of susceptible F. occidentalis . Field strains of F. occidentalis from Antalya, Turkey were tested for resistance against five classes of insecticide during the years 2001–2003. Difference in the field strains response to abamectin, endosulfan, malathion and methomyl was low (<3.0-fold) and in many cases not significant. However, all strains were likely resistant to cypermethrin (1.6- to 12.2-fold at LC₅₀ (lethal concentration)). The established agricultural practices and ecosystem patterns in the Antalya province are assumed to contribute to delay in insecticide resistance in F. occidentalis .     

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.     

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.     

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.     

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.     

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.     

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.     

Synthesis and Cytotoxic Profile of a Diphtheria Toxin-Neurotrophin-4 Chimera

Abstract: A diphtheria toxin-neurotrophin-4/5 (NT-4/5) chimera (DAB₃₈₉-NT4), in which the native receptor binding domain of diphtheria toxin was replaced with a synthetic gene encoding rat NT-4/5, was expressed, refolded, and purified. This fusion toxin has a deduced molecular mass of 60,163 and is formed by joining the first 389 amino acids of diphtheria toxin to amino acids 1–130 of mature rat NT-4/5, using an NH₂-terminal bridge of 33 additional amino acids including six consecutive histidines. Neural cell types expressing only p75^LNGFR or p75^LNGFR and full-length or truncated TrkB were used to evaluate the cytotoxic efficacy of DAB₃₈₉-NT4. The fusion toxin produced a concentration-dependent killing of all cell populations, with LC₅₀ values that largely reflected the known NT-4/5 binding affinities for these receptor proteins. Mean LC₅₀ values ranged from 2,960 p M in p75^LNGFR-expressing neuro-2a neuroblastoma cells to 1,075 and 70 p M , respectively, in hippocampal astrocytes (p75^LNGFR+/truncated TrkB⁺) and cerebellar granule cells (p75^LNGFR+/TrkB⁺). The LC₅₀ for DAB₃₈₉-NT4 in receptor-negative 3T3 fibroblasts was 20 n M . NT-4/5 and brain-derived neurotrophic factor but not ciliary neurotrophic factor added in excess neutralized DAB₃₈₉-NT4 cytotoxicity. NT-4/5, however, did not reduce the cytotoxicity of intact diphtheria toxin.