Stage-specific action of juvenile hormone analogs

The discovery of juvenile hormones (JH) and their synthetic analogs (JHA) generated excitement and hope that these compounds will replace first- and second-generation insecticides that have not so desirable environmental and human safety profiles. However, JHAs used commercially during the past four decades did not meet these expectations. The recent availability of advanced molecular and histological methods and the discovery of key players involved in JH action provided some insights into the functioning of JHA in a stage and species-specific manner. In this review, we will summarize recent findings and stage-specific action of JHA, focusing on three commercially used JHA, methoprene, hydroprene and pyriproxyfen and economically important pests, the red flour beetle, Tribolium castaneum, and the tobacco budworm, Heliothis virescens, and disease vector, the yellow fever mosquito, Aedes aegypti.     

Impact of celery age and infection byBotrytis cinerea on linear furanocoumarin (Psoralens) content in stored celery

The concentration of psoralens in celery (Apium graveolens L.), variety ‘Tender Crisp’, harvested 120 days after planting, was 12 μg g^-1 f.wt, compared with 18 μg g^-1 f.wt in celery harvested 150 days after planting. After 1 month of storage at 2°C, concentrations of psoralens in the 120- and 150-day-old celery were 82 and 118 μg g^-1 f.wt, respectively. Concentrations of psoralens in the 120- and 150-day-old celery inoculated withBotrytis cinerea Pers., after 1 month of storage at 2°C, were 266 and 294 μg g^-1 f.wt, respectively.     

Effects of juvenile hormone analog formulations on development and reproduction in the bed bug Cimex lectularius (Hemiptera: Cimicidae)

BACKGROUND: Bed bugs (Cimex lectularius L.) have become a common insect pest in urban areas and are often difficult to manage. Eradication is made more problematic by widespread insecticide resistance, raising interest in alternative control products. Juvenile hormone analogs (JHAs) such as methoprene and hydroprene are relatively harmless to non‐arthropods and have proved to be effective against other urban insect pests. Two JHA products (Gentrol^® and Precor^®, Central Life Sciences, Schaumburg, IL) were tested for efficacy against various bed bug stages as direct spray and as dry residue using three bed bug strains. RESULTS: At 1× and 2× the label rate, Precor^® [active ingredient (S)‐methoprene] had no significant effect on the development or fecundity of bed bugs. At 2× the label rate, confinement to residues of Gentrol^® [active ingredient (S)‐hydroprene] had no significant effect, but residues at 3× and 10× the label rate caused a reduction in fecundity and impaired development. Field strains were more susceptible to the reproductive effects of (S)‐hydroprene than a long‐maintained laboratory strain. CONCLUSIONS: While JHAs are attractive alternatives for pest management because of their inherent safety and distinct mode of action, these JHA formulations would have little impact on bed bug populations without relabeling to allow for higher application rates. Copyright © 2012 Society of Chemical Industry     

Excretion and residues of the pyrethroid insecticide cypermethrin in lactating cows

Two radiolabelled forms of racemic [¹⁴C]cypermethrin (¹⁴C at the benzylic carbon or at C-1 of the cyclopropane ring) were separately administered twice daily to lactating cows in portions of the feed. The amounts dosed were equivalent to 0.2, 5 and 10 μg of cypermethrin per g of feed. The radioactivity eliminated in the milk indicated that the ingestion and elimination of radioactivity were in balance at about day 4 after the start of dosing. Urine and faeces were equally the major routes of elimination, and only a fraction of a percent of the dose appeared in the milk. The residue in the milk was unchanged cypermethrin and was found at a concentration that was proportional to the dose. At the high cypermethrin intake of 10 μg g^?1 of diet, the residue in the milk was 0.03 μg g^?1. Concentrations of residues in the tissues, measured after 7, 20 or 21 days of treatment, were low and in the order: liver>kidney>renal fat>subcutaneous fat>blood>muscle>brain. The major residue in the liver and kidney of a cow that received 10 μg of cypermethrin per g of diet was N-(3-phenoxybenzoyl)glutamic acid. Other conjugates of 3-phenoxybenzoic acid and of 3-(4-hydroxyphenoxy)benzoic acid (unidentified, with the exception of the glycine conjugate) were also present. The residue in fat (about 0.1 μg g^?1 from an intake of 10 μg g^?1 of feed) consisted mainly of cypermethrin.     

三重PCR检测黄瓜炭疽病菌、菌核病菌和细菌性萎蔫病菌

 本试验建立一种可同时检测黄瓜炭疽病(Colletotrichum orbiculare)、黄瓜菌核病(Sclerotinia sclerotiorum(Lib.)de Bary)和黄瓜细菌性萎蔫病(Erwinia tracheiphila)等黄瓜主要病害病原菌的三重PCR检测体系。采用正交试验设计方法, 对三重PCR的影响因素分析研究, 进行退火温度优化, 并以3个引物组、Taq DNA聚合酶、dNTP和Mg²⁺ 共6因素3水平进行多重PCR体系优化, 成功建立了适合黄瓜主要病害的三重PCR最佳检测体系, 即25 μL的反应体系中含有0.24 μmol·L^-1 CY1/CY2;0.72 μmol·L^-1 SSFWD/SSREV;0.336 μmol·L^-1 ET-P1/ ET-P2;1 U Taq聚合酶;0.15 mmol·L^-1 dNTP;1 mmol·L^-1 MgCl₂, 最适退火温度为63℃。该方法能够快速从田间黄瓜发病植株和根围土壤中将黄瓜炭疽病菌、黄瓜菌核病菌和黄瓜细菌性萎蔫病菌检测出来, 灵敏度可以达到10 pg·μL^-1。     

The toxicity of cyromazine to Chironomus zealandicus (chironomidae) and Deleatidium sp. (leptophlebiidae)

The toxicity of cyromazine and a commercial formulation, ‘Vetrazin’®, to Chironomus zealandicus (thummi) Hudson and Deleatidium sp. was investigated. Under acute test conditions, the LC₅₀ values for each species were quite comparable. For C. zealandicus, the value varied according to instar, 100–400 mg litre^?1 for second- and third-instar to 1000–10000 mg litre^?1 for older fourth-instars. For the one size class of Deleatidium tested (c.10 mm long), the value was 300–400 mg litre^?1. High control mortalities of C. zealandicus limit that species' usefulness as an acute bioassay candidate. Under chronic test conditions, cyromazine showed a high toxicity to eggs or early-instar larvae of C. zealandicus. The maximum acceptable toxicant concentration for cyromazine against C. zealandicus was approximately 17.5 μg litre^?1. The possibility of water contamination at this level is discussed. Whole-of-life chronic tests with C. zealandicus indicated that the most susceptible stage was in the egg or soon after larval emergence. These results highlight the dangers of using short-term acute toxicity results to formulate environmental exposure limits for modern pesticides that do not have dysfunction of the nervous system as their mode of action.     

Structural modifications increase the insecticidal activity of ryanodine

The toxicity of ryanodine ( 1 ) and 9,21-didehydroryanodine ( 2 ) (the principal active ingredients of the botanical insecticide ryania) to adult female house flies (Musca domestica L.) is attributable to binding to the ryanodine receptor (ryr) and thereby disrupting the Ca²⁺-release channel. These ryanoids, assayed in house flies with piperonyl butoxide (PBO) to suppress cytochrome P450-dependent detoxification, give injected KD₅₀ values of 0·07–0·11 μg g^-1, injected LD₅₀ values of 0·39–0·45 μg g^-1 and topical LD₅₀ values of 12– 50 μg g^-1. They inhibit the [³H]ryanodine binding site of house fly and rabbit muscle with IC₅₀ values of 3–10 nM . This study examines the effect of structure on potency, with 15 variants of the cyclohexane substituents, two 4,6-cyclic boron and two methylated derivatives, and four modifications of the isopropyl and ester substituents. The most effective compound examined was 10-deoxy- 2 ( 3 ) which was more potent than 2 by 2–4-fold on injection and 29-fold applied topically following PBO (LD₅₀ 0·41 μg g^-1). Additional high-potency compounds were 10-oxo- 1 and the cyclohexane variants with lactam, 21-nor-9-oxo and 21-nor-10-deoxy substituents. Other modifications usually reduced toxicity. The injected knockdown potency of the ester ryanoids was generally related to their effectiveness in competing with [³H]ryanodine at the ryr of rabbit skeletal muscle. Two non-ester ryanoids, ryanodol and 9,21-didehydroryanodol, were found to be more toxic than predicted from their potency at the ryr and may therefore act in a different manner such as at a K⁺ channel, as suggested by Usherwood and Vais. Clearly ryanoids are challenging prototypes for a potential new generation of insecticides. © 1997 SCI.     

Insecticide resistance management of Bemisia tabaci (Hemiptera: Aleyrodidae) in Australian cotton – pyriproxyfen,spirotetramat and buprofezin

BACKGROUND

Bemisia tabaci is a globally significant agricultural pest including in Australia, where it exhibits resistance to numerous insecticides. With a recent label change, buprofezin (group 16), is now used for whitefly management in Australia. This study investigated resistance to pyriproxyfen (group 7C), spirotetramat (group 23) and buprofezin using bioassays and available molecular markers.

RESULTS

Bioassay and selection testing of B. tabaci populations detected resistance to pyriproxyfen with resistance ratios ranging from 4.1 to 56. Resistance to spirotetramat was detected using bioassay, selection testing and sequencing techniques. In populations collected from cotton, the A2083V mutation was detected in three populations of 85 tested, at frequencies ≤4.1%, whereas in limited surveillance of populations from an intensive horticultural region the frequency was ≥75.8%. The baseline susceptibility of B. tabaci to buprofezin was determined from populations tested from 2019 to 2020, in which LC₅₀ values ranged from 0.61 to 10.75 mg L⁻¹. From the bioassay data, a discriminating dose of 200 mg L⁻¹ was developed. Recent surveillance of 16 populations detected no evidence of resistance with 100% mortality recorded at doses ≤32 mg L⁻¹. A cross-resistance study found no conclusive evidence of resistance to buprofezin in populations with high resistance to pyriproxyfen or spirotetramat.

CONCLUSIONS

In Australian cotton, B. tabaci pest management is challenged by ongoing resistance to pyriproxyfen, while resistance to spirotetramat is an emerging issue. The addition of buprofezin provides a new mode-of-action for whitefly pest management, which will strengthen the existing insecticide resistance management strategy. © 2023 Commonwealth of Australia. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Pyriproxyfen,a novel insect growth regulator for controlling whiteflies: Mechanisms and resistance management

Pyriproxyfen, a novel juvenile hormone mimic, is a potent suppressor of embryogenesis and adult formation of the sweetpotato whitefly, Bemisia tabaci (Gennadius), and the greenhouse whitefly, Trialeurodes vaporariorum (Westwood). Dipping of cotton or tomato seedlings infested with 0 to 1-day-old eggs in 0.1 mg litre^?1 resulted in over 90% suppression of egg hatch of both B. tabaci and T. vaporariorum. Older eggs were affected to a lesser extent. Exposure of whitefly females to cotton or tomato seedlings treated with pyriproxyfen resulted in oviposition of non-viable eggs. The LC90 values for egg viability of B. tabaci and T. vaporariorum exposed to treated plants were 0.05 and 0.2 mg litre^?1, respectively. Treatment of whitefly larvae with 0.04–5 mg litre^?1 resulted in normal development until the pupal stage; however, adult emergence was totally suppressed. Second instars of B. tabaci exposed to 5 mg litre^?1 pyriproxyfen, excreted honeydew at a level similar to the control level until the fourth instar (pupation), after which a strong reduction was observed. Inhibition of egg-hatch on the lower surface of cotton leaves was observed when their upper surface was treated with 1–25 mg litre^?1, indicating a pronounced translaminar effect. These findings indicate that pyriproxyfen is an efficient control agent of both B. tabaci and T. vaporariorum. The compound has been used successfully for controlling whiteflies in Israeli cotton fields since 1991. Adults of B. tabaci collected from a rose greenhouse and from adjacent cotton fields were monitored during 1991–1993 for their susceptibility to pyriproxyfen. A high level of resistance was recorded in whiteflies collected from a greenhouse after three successive applications of pyriproxyfen. Based on LC50 values, the resistance ratio for egg-hatch suppression was 554-fold and, for adult emergence failure, 10-fold. However, a single treatment of pyriproxyfen in cotton fields during the summer season (according to an insecticide resistance management (IRM) strategy) did not alter appreciably the susceptibility of B. tabaci to this compound. In order to prevent development of resistance, an attempt should be made to restrict its use to one treatment per crop season applied during the peak activity of the pest. Pyriproxyfen can be alternated with other novel compounds such as buprofezin and diafenthiuron for controlling whiteflies in cotton, vegetables and ornamentals as part of integrated pest management (IPM) and IRM strategies. In pyriproxyfen- or buprofezin-resistant strains of B. tabaci or T. vaporariorum, no appreciable cross-resistance was observed among pyriproxyfen, buprofezin and diafenthiuron.     

The response of pyriproxyfen-resistant and susceptible Bemisia tabaci Genn (Homoptera: Aleyrodidae) to pyriproxyfen and fenoxycarb alone and in combination with piperonyl butoxide

Pyriproxyfen was effective against susceptible Bemisia tabaci eggs at a LC₅₀ of 0.003 mg litre⁻¹ and against nymphs at 0.02 mg litre⁻¹. In comparison, eggs of a laboratory selected, pyriproxyfen-resistant B tabaci strain, originating in an Israeli greenhouse, exhibited 6500-fold resistance and nymphs exhibited 1100-fold resistance. Eggs and nymphs of a strain from an Israeli sunflower field exhibited 450 and 210-fold resistance in comparison to the susceptible standard. Fenoxycarb was generally less effective than pyriproxyfen against B tabaci eggs and nymphs but was unaffected by pyriproxyfen resistance. Piperonyl butoxide (PB) was antagonistic to pyriproxyfen, and this increased with increasing pyriproxyfen resistance. PB had no effect on the toxicity of fenoxycarb. Collectively, these data imply that the modes of action of pyriproxyfen and fenoxycarb are distinct, despite the structural similarities of these molecules. Possible reasons for the antagonism of PB against pyriproxyfen are discussed. © 1999 Society of Chemical Industry     

Sublethal effects of environmentally relevant run‐off concentrations of glyphosate in the root zone of Ludwigia peploides (creeping water primrose) and Polygonum hydropiperoides (smartweed)

As one of the most widely applied agricultural chemicals in the world, glyphosate has many effects on the environment. The present study quantified plant responses to exposure by glyphosate through the root zone for a range of concentrations (0, 10, 100 and 1000 μg L^?1). Ludwigia peploides and Polygonum hydropiperoides were grown in a greenhouse and given a single exposure to glyphosate via the root zone. The growth and physiological parameters were measured before exposure and for 18 days postexposure. The growth variables that were measured included the relative growth rate, stem length increase, biomass and root‐to‐shoot‐ratios. The physiological variables that were measured were the chlorophyll content index and chlorophyll fluorescence. The data analyses revealed that the root‐zone glyphosate affected some of the measured variables in P. hydropiperoides more than for L. peploides. Polygonum hydropiperoides showed a significant decrease in the root‐to‐shoot ratios for the 100 μg L^?1 treatment, compared to the 10 μg L^?1 treatment. The chlorophyll content index of the treated plants was significantly reduced in P. hydropiperoides, compared to the untreated plants on Days 7 and 18. Ludwigia peploides was affected only on the day after exposure, with the chlorophyll fluorescence parameters being significantly less for the 1000 μg L^?1 treatment, compared to the 10 μg L^?1 treatment. Glyphosate‐treated P. hydropiperoides showed a decreased chlorophyll content and reduced chlorophyll fluorescence parameters. In contrast, L. peploides showed a decrease in the chlorophyll fluorescence parameters but no reduction in its chlorophyll content. In addition to demonstrating the adverse effects of root exposure to glyphosate for the study species, these data help to partially explain the highly invasive and persistent nature of L. peploides in marginal aquatic environments, such as agricultural ditches.     

Lethal and sublethal effects of the neem insecticide formulation, ‘Margosan-O’, on the pea aphid

The effects of ‘Margosan-O’ (MO) on the pea aphid, Acyrthosiphon pisum (Harris), were determined. MO significantly reduced population increase of A. pisum in a concentration-dependent manner. At a concentration equivalent to 100 mg litre^?1 of azadirachtin, population increase was c. 3.5 times lower than the control. In more detailed studies, MO significantly reduced the number of molts, longevity, and fecundity of A. pisum that had been reared on treated broad bean. Viciafaba L., plants. MO also reduced the longevity and fecundity of young adult A. pisum exposed to MO-treated broad bean. MO was slow-acting against A. pisum. Mortality caused by MO stabilised seven days after newborn A. pisum were exposed to treated broad bean and 10 days for adults. The seven day LC₅₀ for individuals exposed from birth was 27.50 mg azadirachtin liter^?1 while the 10 day LC₅₀ for adults was 53.32 mg liter^?1. Contrary to previous studies suggesting that neem insecticides are not contact toxicants, we found that MO applied topically to adult A. pisum caused effects similar to those found in individuals that fed upon treated plants. However, MO was slower-acting when applied topically. Mortality in adult A. pisum caused by topically applied MO stabilised 17 days after treatment with a resultant LD₅₀of 2.91 μg azadirachtin g^?1.     

Cross resistance to juvenile hormone analogues in insecticide-resistant strains of Musca domestica L

Five juvenile hormone analogues (JHAs) were tested by topical application to prepupae of a susceptible (S) and 8 insecticide-resistant (R) strains of the housefly. Activity was measured by the inability to completely emerge from the puparium. Aitosid (isopropyl 11-methoxy-3,7,1l-trimethyldodeca-2,4-dienoate) was the most active compound against the S strain (ED₅₀ 0.0033 μg/prepupa) followed by Ro 7-9767 [6,7-epoxy-3,7-diethyl-(3,4-(methylenedioxy)phenoxy)-2-cis/trans-octene], R-20458 [trans l-(4-ethylphenoxy)-6,7-epoxy-3,7-dimethyl-2-octene], sesamex, and NIA 23509 (10,11 -epoxy-N-ethyl-3,7,11-trimethyI-2,6-dodecadienamide). The R strains, designated by the name of the selecting insecticide, have been under pressure for over 10 years and are considered maximally resistant. The dimethoate-R and OMS-15-R (carbamate-resistant) strains exhibited high levels of cross resistance to all JHAs often exceeding 100x at the ED₉₅ The fenthion-R strain showed high cross resistance toward all JHAs except Altosid, toward which it manifested an intermediate level (17.5x). The DDT/lindane-R demonstrated only negligible tolerance to Aitosid but an intermediate response to all the other JHAs. The OMS-12-R strain (phosphoramidothioate-R) exhibited intermediate to high levels of cross resistance toward all JHAs, whereas the parathion-R, Chlorthion-R and a multi-resistant field-collected strain showed only low to intermediate levels of cross resistance. On the basis of known degradative mechanisms of the OMS-15-R strain, mixed function oxidases apparently play an important role in deactivating JHAs.     

Uptake,metabolism and effects of DDT,fenitrothion and chlorpyrifos on Tetrahymena pyriformis

The uptake and metabolism of DDT, fenitrothion and chlorpyrifos were studied in cultures of the ciliate protozoan Tetrahymena pyriformis. When cultures were treated with DDT in concentrations varying from 0.01 to 0.5 μg ml⁻¹, concentrations found in T. pyriformis were 3.8 to 335 μg g⁻¹ dry weight. The accumulation of fenitrothion ranged from 28.7 μg g⁻¹ in cultures treated with 1 μg ml⁻¹ to 2260 μg g⁻¹ in cultures treated with 10 μg ml⁻¹. Under similar experimental conditions chlorpyrifos was accumulated from 24.7 to 15400 μg g⁻¹. The patterns of uptake were dependent on the growth cycle, the ability of the organism to metabolise insecticide and the type of the insecticide used. Maximum accumulation of DDT, fenitrothion and chlorpyrifos occurred in 2, 4 and 6 h respectively. Tetrahymena metabolised DDT to DDD and DDE but failed to metabolise fenitrothion and chlorpyrifos. The effects on growth and morphology of T. pyriformis were studied over a period of 5 days. Higher concentrations (10, 50 and 100 μg ml⁻¹) of DDT inhibited only the growth of the organisms and did not change cell morphology. Fenitrothion was extremely toxic to the organisms and at 5 and 10 μg ml⁻¹ cells became more or less spherical and died after 48 h. However, concentrations of 0.5, 1 and 2.5 μg ml⁻¹ fenitrothion caused growth inhibition, but only at 2.5 μg ml⁻¹ was this permanent. Chlorpyrifos inhibited the growth of the organisms at 1, 5 and 10 μg ml⁻¹ but the morphology was affected only at 5 and 10 μg ml⁻¹.     

Effect of Adjuvants on the Therapeutic Activity of Dimethomorph in Controlling Vine Downy Mildew. I. Survey of Adjuvant Types

The effect of adjuvants on the performance of emulsifiable concentrate (EC) and wettable powder (WP) formulations of dimethomorph, a new systemic Oomycete fungicide, has been investigated using a two-day therapeutic (curative) assay with downy mildew (Plasmopara viticola, Berl. & de T.) on vines (Vitisvinifera L., cv. Cabernet Sauvignon) in glasshouse trials. The EC formulation had some therapeutic activity in this type of test. This activity was increased by the spray tank incorporation of 6 g litre⁻¹ of either emulsifiable rape seed oil (‘Atplus’ 412) or emulsifiable paraffinic oil (‘Atplus’ 411F). However, these improvements in performance were overshadowed by those brought about by incorporation of 3 g litre⁻¹ of a series of C₁₃/C₁₄ alcohol ethoxylates varying in ethylene oxide content from 5 to 20 moles:(‘Marlipal’ 34/6EO, 34/11EO, 34/20EO). Nearly complete fungal control was obtained in the presence of these adjuvants with a dimethomorph application rate of 25 g ha⁻¹ compared with only around 90% control at 400 g ha⁻¹ without adjuvants. The WP formulation was inactive in this therapeutic test but the presence of the adjuvants improved the performance of this formulation towards the high levels observed with the EC plus adjuvants, demonstrating that adjuvants could markedly influence the performance of solid, otherwise therapeutically inactive, dimethomorph formulations. Further trials examined other types of adjuvants (nonylphenol, alkylamine and silicone ethoxylates) but either they were no better than the alcohol ethoxylates or they induced unacceptable phytotoxicity. Trials with alcohol ethoxylates (‘Genapols’) from another source demonstrated activity equivalent to the ‘Marlipal’ surfactants. A two-factorial matrix experiment with ‘Genapol’ C050 showed that, under glasshouse conditions, >90% control could be obtained with the dimethomorph EC at 25 g AI ha⁻¹ with 375 g ha⁻¹ ‘Genapol’ C050. Applications of the WP formulation required slightly higher rates of either 50 g AI ha⁻¹ plus 375 g ha⁻¹ ‘Genapol’ C050 or 25 g AI ha⁻¹ plus 750–1500 g ha⁻¹ ‘Genapol’ C050. The overall conclusion was that alcohol ethoxylates varying in alkyl chain length from C₁₂ to C₁₈ and ethylene oxide content between 5 and 20 moles for the C₁₂ surfactants and ∽15 moles for the C₁₈ surfactants were effective adjuvants in promoting the therapeutic activity of dimethomorph formulationsagainst P. viticola on glasshouse-propagated vines.     

Uptake and translocation of 14C-glyphosate in Alternanthera philoxeroides (Mart.) Griseb. (alligator weed) I. Rhizome concentrations required for inhibition

Rhizome segments from Alternanthera philoxeroides were shaken in solutions of ¹⁴C-glyphosate for 24 h to establish a range of internal tissue concentrations. Rhizomes were killed at concentrations of 16 μg g^?1 dry weight and above and survived at concentrations of 8 μg g^?1 dry weight and below. Plants grown in the field for 10 weeks in declining photoperiod were used to investigate the uptake and translocation of ¹⁴C-glyphosate after application of a constant dosage in either 1.0-or 0.2-μl droplets corresponding to concentrations of 1.06 and 5.3 g 1^?1, of glyphosate acid, respectively. Use of smaller droplets of higher concentration increased absorption of ¹⁴C, but did not improve translocation. Uptake by treated leaves was 25 and 41% of the applied glyphosate for the large and small droplets respectively, but translocation to underground parts of the plant was about 7% of applied ¹⁴C-activity. Radiolabel accumulated in new rhizomes was equivalent to about 0.5 μg g^?1 dry weight of glyphosate, at least 30 times below the concentration required for tissue death. Absorption et transport de glyphosate C14 chez Alternanthera philoxeroides (Mart.) Griseb. I.Concentrations dans les rhizomes nécéssaires pour l'inhibition Des fragments de rhizome d'Alternanthera philoxeroides ont été trempés dans des solutions de glyphosate C14 pour aboutir à un éventail de concentrations internes des tissus, Les rhizomes ont été tués à des concentrations de 16 μg g^?1 PS et plus, et ont survécu à des concentrations de 8 μg g^?1 PS et en-dessous. Des plantes cultivées en plein champ pendant 10 jours en photopériode décroissante ont été utilisées pour étudier l'absorption et le transport du glyphosate C14 après l'application d'une dose constante dans des gouttelettes de 1 ou 0,2 μl correspondant à des concentrations de 1,06 et 5,3 g l^?1 de glyphosate C14 acide respectivement, L'utilisation de gouttelettes plus petites de concentrations plus é1evées a augmenté l'absorption du C14, mais n'en a pas amélioré le transport. L'absorption par les feuilles traitées était de 25 et 41% du glyphosate appliqué pour les grandes et les petites gouttelettes respectivement, mais le transport vers les parties souterraines de la plante était d'environ 7% du C14 appliqué. Le radio-marqueur dans les nouveaux rhizomes était équivalent à environ 0,5 μg g^?1 PS de glyphosate, soit au moins 30 fois en-dessous de la concentration nécessaire à la mort des tissus. Aufnahme und Translokation von ¹⁴C-Glyphosat in Alternanthera philoxeroides (Mart.) Griseb. I. Für die Hemmung erforderliche Konzentration im Rhizom Rhizomteile von Alternanthera philoxeroides wurden 24 Stunden lang in ¹⁴C-Glyphosat-Lösungen geschüttelt, um eine Reihe von Konzentrationen in den inneren Geweben einzustellen. Die Rhizome wurden bei Konzen-trationen von 16 und mehr μg g^?1 TM abgetötet und überlebten bei Konzentrationen von 8 μg g^?1 TM und weniger. Die Aufnahme und Translokation von ¹⁴C-Glyphosat nach der Applikation einer konstanten Dosis in 1,0-oder 0,2-μl-Tröpfchen, entsprechend Konzentrationen von 1,06 und 5,3 g l^?1 Glyphosat-Säure, wurden an Pflanzen untersucht, die im Freiland 10 Wochen lang bei abnehmender Photoperiode gewachsen waren. Der Gebrauch kleinerer Tropfen höherer Konzentration führte zu mehr Absorption von ¹⁴C, förderte aber nicht die Translokation. Das Glyphosat wurde von den behandelten Blättern zu 25 bzw. 41% aus den großen Oder den kleinen Tröpfchen aufgenommen, aber die Translokation in die unterirdischen Pflanzenteile war etwa 7% der ausgebrachten ¹⁴C-Aktivität. Die in neuen Rhizomen akkumlierte Radioaktivität entsprach 0,5 μg g^?1 TM Glyphosat, mindestens 30mal weniger als für die Abtötung von Gewebe erforderlich.     

注射大肠杆菌后草地贪夜蛾高龄幼虫的免疫应激反应

为采用生物技术防控草地贪夜蛾Spodoptera frugiperda的扩散为害,对草地贪夜蛾5龄和6龄幼虫注射浓度为1×109CFU/mL的大肠杆菌Escherichia coli菌液,并以注射等量磷酸盐缓冲液(phosphate buffer solution,PBS)和未做任何处理(CK)为对照,24 h后测定幼虫体重、集结数和酚氧化酶(phenoloxidase,PO)活性。结果显示,注射大肠杆菌菌液24 h后,草地贪夜蛾5龄和6龄幼虫体重均受到抑制,其体重分别为0.170 g和0.411 g,均显著低于CK的0.181 g和0.484 g;注射大肠杆菌菌液24 h后,草地贪夜蛾5龄和6龄幼虫集结数分别为135.0、338.4个索引集结数(the indexed nodules,INs),前者极显著低于后者,且均显著高于CK和PBS处理,分别为0.4、10.2个INs和0.3、10.9个INs;注射大肠杆菌菌液24 h后,草地贪夜蛾5龄幼虫PO活性为0.156 ABS·min-1·mg-1,显著高于CK和PBS处理,分别为0.046 ABS·min-1·mg-1和0.066 ABS·min-1·mg-1,但草地贪夜蛾6龄幼虫的PO活性为0.050 ABS·min-1·mg-1,显著低于CK和PBS处理,分别为0.066 ABS·min-1·mg-1和0.069 ABS·min-1·mg-1,且草地贪夜蛾5龄幼虫的PO活性显著高于6龄幼虫的PO活性。表明细菌侵染后草地贪夜蛾不同高龄幼虫的免疫应激反应存在差异,而这种差异可能受幼虫生长发育及细胞免疫和体液免疫功能之间权衡现象的影响。     

Chlorpyrifos degradation in soil at termiticidal application rates

Chlorpyrifos [O,O-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate] is an organophosphorus insecticide applied to soil to control pests both in agricultural and in urban developments. Typical agricultural soil applications (0.56 to 5.6 kg ha^?1) result in initial soil surface residues of 0.3 to 32 μg g^?1. In contrast, termiticidal soil barrier treatments, a common urban use pattern, often result in initial soil residues of 1000 μg g^?1 or greater. The purpose of the present investigation was to understand better the degradation of chlorpyrifos in soil at termiticidal application rates and factors affecting its behaviour. Therefore, studies with [¹⁴C]chlorpyrifos were conducted under a variety of conditions in the laboratory. Initially, the degradation of chlorpyrifos at 1000 μg g^?1 initial concentration was examined in five different soils from termite-infested regions (Arizona, Florida, Hawaii, Texas) under standard conditions (25°C, field moisture capacity, darkness). Degradation half-lives in these soils ranged from 175 to 1576 days. The major metabolite formed in chlorpyrifos-treated soils was 3,5,6-trichloro-2-pyrid-inol, which represented up to 61% of applied radiocarbon after 13 months of incubation. Minor quantities of [¹⁴C]carbon dioxide (< 5%) and soil-bound residues (? 12%) were also present at that time. Subsequently, a factorial experiment examining chlorpyrifos degradation as affected by initial concentration (10, 100, 1000 μg g^?1), soil moisture (field moisture capacity, 1.5 MPa, air dry), and temperature 15, 25, 35°C) was conducted in the two soils which had displayed the most (Texas) and least (Florida) rapid rates of degradation. Chlorpyrifos degradation was significantly retarded at the 1000 μg g^?1 rate as compared to the 10 μg g^?1 rate. Temperature also had a dramatic effect on degradation rate, which approximately doubled with each 10°C increase in temperature. Results suggest that the extended (3–24 + years) termiticidal efficacy of chlorpyrifos observed in the field may be due both to the high initial concentrations employed (termite LC ₅₀ = 0.2– 2 μg g^?1) and the extended persistence which results from employment of these rates. The study also highlights the importance of investigating the behaviour of a pesticide under the diversity of agricultural and urban use scenarios in which it is employed.     

Reinvestigating adjuvants for the wild oat herbicide,flamprop-M-isopropyl. II: Field performance

A field trials programme was conducted in which the performance of a new emulsifiable concentrate formulation (ECI) of flamprop-M-isopropyl containing the adjuvant, ‘Dobanol’ 25-7, in a ratio of 2:1 (by weight) with the AI, was compared with the current commercial formulation of ‘Commando’, in combination with its recommended adjuvant, ‘Swirl’, for the control of wild oat (Avena fatua L.) in wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.). A further treatment, in which the ‘Dobanol’ 25-7: AI ratio was increased to 4:1 by the spray tank addition of the former, was also included. The mean results from six trials (five wheat, one barley) showed that the addition of ‘Swirl’ to ‘Commando’ was beneficial, increasing wild oat floret control from a mean value of 80% to 92% at current recommended rates (flamprop-M-isopropyl, 600 g ha^?1; ‘Swirl’, 2.5 litre ha^?1). However, combinations of flamprop-M-isopropyl and ‘Dobanol’ 25-7 gave superior levels of control even at lower AI application rates. For example, a mean level of 96% control of Avena spp. was obtained at 300 g AI ha^?1 with 1200 g ha^?1 ‘Dobanol’ 25–7; with even better control at higher rates of application of both components. This improvement in performance was accompanied by a higher risk of crop phytotoxicity than observed with the ‘Commando’/‘Swirl’ mixtures. Symptoms initially were scorch and subsequently growth depression, particularly of tillers. None of the mean values in the six ‘efficacy’ trials reached commercially unacceptable levels, but in a further six ‘crop effects’ trials (three wheat, three barley), in which double rates were applied, the levels of phytotoxicity did become unacceptable and subsequently reduced grain yields. In contrast, two barley ‘crop effects’ trials gave yields higher than the control plots, possibly through the effects of reducing stem length and lodging thereby enabling more efficient harvesting. Nevertheless, there were rates of application of flamprop-M-isopropyl in the range 300–400 g ha^?1 with ratios of ‘Dobanol’ 25-7 in the range 2:1 to 4:1 that would achieve high levels of control of Avena spp. without undue risk of crop phytotoxicity and further trials are planned to support this new adjuvant system.     

Complementary effect of Phloxine B on the insecticidal efficacy of Isaria fumosorosea SFP‐198 wettable powder against greenhouse whitefly,Trialeurodes vaporariorum West.

BACKGROUND: Insecticidal activities of five photoactive dyes against greenhouse whitefly (GWF), Trialeurodes vaporariorum West., in tomatoes were investigated to improve the control efficacy of an entomopathogenic fungal product, Isaria fumosorosea SFP‐198 wettable powder (WP). Azorubine, Eosin B, Erythrosine, Brilliant Green and Phloxine B were used in this work, accompanying pyriproxyfen emulsifiable concentrate (EC) as a commercial standard for comparison. RESULTS: Phloxine B had the highest control efficacy in glasshouse conditions. The most suitable dose of Phloxine B was determined as 0.005 g L^?1, given the dosage‐dependent control efficacy and phytotoxicity of the dye, and its influence on the germination of SFP‐198 conidia. In field conditions, SFP‐198 WP + Phloxine B (2 + 0.005 g L^?1; tank mix) showed 89.1 and 95.3% control efficacy 7 and 14 days post‐application, which was significantly higher than the efficacy of SFP‐198 WP alone (43.5 and 64.0%), Phloxine B (47.5 and 30.7%) or pyriproxyfen EC (67.7 and 80.2%). CONCLUSION: Phloxine B cooperates with SFP‐198 WP complementarily, possibly in the order of killing action (early: Phloxine B; late: SFP‐198 WP). The dye can be incorporated into SFP‐198 WP to improve its efficacy and applied to other Hypocrelean entomopathogenic fungal products. Copyright © 2010 Society of Chemical Industry