Depression of the minimum concentration of methyl bromide effective against diapausing warehouse moth larvae at 15°c by prior exposure at a moderate concentration

Warehouse moth (Ephestia elutella) larvae in diapause were exposed at 15°C to methyl bromide at 8 mg litre^?1 for 14.5 h and then immediately exposed at a lower concentration. The exposure at 8 mg litre^?1 killed 44–69% of the larvae treated. Subsequent concentrations down to 1.1 mg litre^?1 obeyed Haber's rule (concentration × time= k, a constant for mortality), but a higher concentration-time product (ct) was required for over 90% kill at 0.8 mg litre^?1. Only concentrations down to 1.9 mg litre^?1 obey Haber's rule if there is no prior exposure at a higher concentration. Although minimum effective concentrations are lower at 15°C than at 25°C, exposure at a higher concentration depresses the subsequent level to a similar extent at each temperature. The contribution to the efficacy of a treatment, of low concentrations persisting at the end of fumigation, is thus likely to be even greater at moderate to low temperatures than at 25°C. The implications for the development of resistance to methyl bromide are discussed.     

Minimum concentration levels of methyl bromide required for full efficacy against seven species of stored-product beetle at two temperatures

The dosages of methyl bromide required to control insect pests can be expressed as concentration, time (Ct) products for concentrations down to a certain minimal level, here defined as the efficacy threshold, below which Habers Ct rule (C×t=k,a constant for mortality) no longer applies. Twelve strains of seven species of stored-product beetle were tested to identify efficacy threshold concentrations at 15°C and 25°C. For each strain the efficacy threshold was higher at 25°C than at 15°C. Different species differed widely in the threshold levels identified. Strains with a higher than usual tolerance to methyl bromide than their standard stock counterparts had slightly higher efficacy thresholds at 25°C but not at 15°C. The order of tolerance of the standard stocks to methyl bromide at 15°C was Tribolium confusum> T. castaneum> Oryzaephilus surinamensis> Rhyzopertha dominica> Sitophilus granarius> S. zeamais> S. oryzae, and at 25°C Tribolium castaneum > T. confusum> R. dominica> O. surinamensis> S. granarius> S. zeamais> S. oryzae. The order of efficacy thresholds largely reflected the order of susceptibility, S. oryzae and S. zeamais having the lowest efficacy thresholds of about 0.6 mg litre^?1 at 15°C and 1.3-2.0 mg litre^?1 at 25°C, while Tribolium spp. had the highest, 1.3-2.0 mg litre^?1 at 15°C and 2.5-4.0 mg litre^?1 at 25°C.     

Effect of short exposures to a high concentration on the subsequent toxicity of low concentrations of methyl bromide to diapausing larvae of the warehouse moth,Ephestia elutella (Hübner)

Ephestia elutella larvae in diapause were exposed at 25°C to methyl bromide at 12 mg litre^?1 for 3.5 or 7.5 h and then immediately exposed to a lower concentration. The minimum effective concentration (that at which Haber's rule, concentration × time = k, a constant for mortality, still applied) was about 3 mg litre^?1 in tests with no previous exposure toa high concentration, but it was about 2.5 mg litre^?1 for individuals surviving a 3.5 h exposure to 12 mg litre^?1, and was about 1.6 mg litre^?1 for those surviving a 7.5 h exposure to 12 mg litre^?1. These exposures to 12 mg litre^?1, respectively, killed 2–20% and 50–75% of larvae exposed, and hence the smaller the proportion of survivors of exposure to a high concentration, the lower the minimum effective concentration needed against them. Thus the low concentration persisting at the end of a practical fumigation should contribute significantly to the success of the treatment and be much more effective than any similar low concentration present soon after the introduction of gas.     

Breakdown rates of dimethoate in fruit and vegetable dips

In order to determine the effect of pH and temperature on post-harvest dip solutions of dimethoate (500 mg litre^?1), the half-lives and pseudo first-order rate constants were calculated from measurements at pH 4, 6, 8, 10, 11.5, and at two temperatures 25 and 52°C. The half-lives ranged from 206 days to 39.3 min at 25°C, and from 5.6 days to 205s at 52°C; the rate constants ranged from 3.9 × 10^?8 s^?1 to 2.9 × 10^?4 s^?1 at 25°C, and from 1.4 × 10^?6 s^?1 to 3.4 × 10^?3 s^?1 at 52°C. The results show that the water used in dips should have a pH≤7. The addition of benomyl to the dip solutions at two concentrations (0.5 and 1.0 g litre^?1) had no effect on the half-lives and rate constants. The use of hard and salted waters in dips also showed no major effect. A formula was developed that gives the half-life of the dimethoate as a function of the pH and temperature.     

Relation between volatility rating and composition of phenoxy herbicide ester formulations

A CIPAC/AOAC test with tomato plants is used to specify the volatility ratings of herbicide ester formulations. This work compares the tomato plant test with an alternative chemical one. The concentrations of esters and the effective molecular weight and density of each formulation were used with the ester vapour pressures to calculate its herbicide vapour pressure as complete, and evaporated formulations. The range was from 28.8 mPa (at 257deg;C) for a mixture of 2,4–D esters to 0–07 mPa (at 25°C) for a 2,4,5–T-(iso-octyl) formulation, as complete formulations, and 35-5 and 0–16 mPa (at 25°C) as evaporated ones. A value of 0–6 mPa (at 25°C) was selected on the basis of the tomato plant test as the cut-off area for low-volatile esters and is recommended to be included in specifications for herbicide esters. Formulations with a herbicide vapour pressure above 3.3 mPa (at 25°C) are high-volatile ones according to the tomato plant test, while between 0–6–3.3 mPa (at 25°C) is a borderline region where the test gives mixed results. Levels of 2,4–D-ethyl and methyl were added to pure 2–ethylhexyl esters of 2,4–D and a 2,4,5–T-(iso-octyl) formulation to find what level of contamination would change the rating of these esters from low to high volatile. Formulations of 2,4–D-(iso-octyl) should not contain more than 11 g litre^?1 2,4–D as methyl ester or 2.0 g litre^?1 2,4–D as ethyl ester. Formulations of 2,4,5–T-(iso-octyl) should not contain more than 26 g litre^?1 2,4–D as methyl ester or 4.7g litre^?1 2,4–D as ethyl ester.     

Ethyl formate plus methyl isothiocyanate--a potential liquid fumigant for stored grains

BACKGROUND: Methyl bromide is being phased out for use on stored commodities, as it is listed as an ozone‐depleting substance, and phosphine is the fumigant widely used on grains. However, phosphine resistance occurs worldwide, and phosphine fumigation requires a long exposure period and temperatures of > 15 °C. There is an urgent requirement for the development of a fumigant that kills insects quickly and for phosphine resistance management. This paper reports on a new fumigant formulation of 95% ethyl formate plus 5% methyl isothiocyanate as an alternative fumigant for stored grains. RESULTS: The formulation is stable for at least 4 months of storage at 45 °C. A laboratory bioassay with the formulation showed that it controlled all stages of Sitophilus oryzae (L.), Sitophilus granarius (L.), Tribolium castaneum (Herbst), Rhyzopertha dominica (F.), Trogoderma variabile Ballion and Callosobruchus maculatus (Fabricius) in infested wheat, barley, oats and peas at 80 mg L^?1 for 5 days, and in canola at both 40 mg L^?1 for 5 days and 80 mg L^?1 for 2 days at 25 ± 2 °C. After an 8–14 day holding period, residues of ethyl formate and methyl isothiocyanate in wheat, barley, peas and canola were below the experimental permit levels of 1.0 and 0.1 mg kg^?1. However, fumigated oats needed an 18 day holding period. CONCLUSIONS: The findings suggest that the ethyl formate plus methyl isothiocyanate formulation has potential as a fumigant for the control of stored‐grain insect pests in various commodities. Copyright © 2011 Society of Chemical Industry     

Use of a field-scale biofilter for the degradation of the organophosphate insecticide coumaphos in cattle dip wastes

Insecticide wastes generated from livestock dipping operations are well suited for biodegradation processes since these wastes are concentrated, contained, and have no other significant toxic components. A field-scale biofilter capable of treating 15000-litre batches of dip waste containing the acaricide coumaphos was used to reduce the coumaphos concentration in two successive 11000-litre batch trials from 2000 mg litre^-1 to 10 mg litre^-1 in approximately 14 days at 25–29°C. Removal of coumaphos from the biofilter effluent is a function of both physical filtration and biodegradation by the biofilter. However, stoichiometric increases in chloride levels in the effluent as coumaphos concentrations decreased confirmed that coumaphos was being degraded by the biofilter rather than just being filtered out. In subsequent 5500-litre batch experiments, the addition of a vitamin supplement to the biofilter-treated dip resulted in a further decrease in coumaphos concentration to approximately 1 mg litre^-1. Results from incubations of two representative Texas soils with biofilter-treated dip spiked with [benzo-U-¹⁴C] coumaphos revealed that 32–36% of the spiked [¹⁴C] coumaphos was mineralized in the soils after 110 days at 30°C. © 1998 SCI.     

Sensitivity of Botrytis cinerea to chitosan and acibenzolar‐S‐methyl

BACKGROUND: The antifungal properties of chitosan and acibenzolar‐S‐methyl were evaluated to assess their potential for protecting grapes against Botrytis cinerea Pers.: Fr. isolated from Vitis vinifera L. The objectives were to determine the effects of these compounds on the in vitro development of B. cinerea and to assess their effectiveness at controlling grey mould on grapes stored at different temperatures. RESULTS: Both agents significantly inhibited the radial growth of this fungus species. The EC₅₀ was 1.77 mg mL^?1 for chitosan and 3.44 mg mL^?1 for acibenzolar‐S‐methyl. In addition, single grapes treated with aqueous solutions of chitosan (1.0 and 2.5 mg mL^?1) and acibenzolar‐S‐methyl (1.0 and 3.0 mg mL^?1) were inoculated with B. cinerea and incubated at both 4 and 24 °C. After 4 days at 24 °C, all the concentrations of chitosan and acibenzolar‐S‐methyl significantly reduced B. cinerea growth. However, at 4 °C, significant differences were only observed between chitosan at 2.5 mg mL^?1 and acibenzolar‐S‐methyl at both 1.0 and 3.0 mg mL^?1 and the corresponding controls. After 3 days at 24 °C, the greatest reduction in lesion size was obtained in grapes pretreated with acibenzolar‐S‐methyl at 3.0 mg mL^?1. Only the highest doses of these products significantly reduced the lesion diameters when grapes were stored for 3 days at 4 °C. CONCLUSIONS: Chitosan and acibenzolar‐S‐methyl could directly inhibit the growth of Botrytis cinerea in vitro and confer resistance on grapes against grey mould. Pretreatment with these compounds could be an alternative to traditional fungicides in post‐harvest disease control in grapes. Copyright © 2010 Society of Chemical Industry     

N-Nitrosodimethylamine content of aqueous dimet hylamine and phenoxy herbicide/dimethylamine formulations during storage

N-Nitrosodimethylamine (NDMA) levels in samples of 600 g litre^?1 aqueous dimethylamine (DMA) solution stored at 4, 25 and 40°C, in formulations of the DMA salt of 2, 4-dichlorophenoxyacetic acid (2, 4-D) and of the DMA salt of 4-chloro-2-methylphenoxyacetic acid (MCPA) at 40°C were monitored using a gas-liquid chromatograph coupled with a thermal energy analyser (g.l.c./t.e.a.). The NDMA content of aqueous DMA at 4°C increased from 0.32μgg^?1 to 8.6μgg^?1 in 156 days. At 25°C it increased from 0.20μgg^?1 to 10.5 μgg^?1 in 156 days and at 40°C from 0.76μgg^?1 to 7.12μgg^?1 in 54 h. At 40°C, the NDMA in the 2, 4-D/DMAsalt increased from 0–53μgg^?1 to 2.79μgg^?1 in 96 days and in the MCPA/DMA salt from 0.48μgg^?1 to 5.51 μgg^?1 in 21 days.     

A monoclonal antibody‐based ELISA for the analysis of the insecticide flucythrinate in environmental and crop samples

A competitive enzyme‐linked immunosorbent assay (ELISA) has been developed for the detection of the insecticide flucythrinate in environmental and food samples. Two types of haptens, the acid moiety that is the hydrolyzed product of flucythrinate, and the carboxylated propyl derivative of the alcohol moiety, were used to prepare monoclonal antibodies (MAbs). Five MAbs, which raised against the former hapten, were reactive with flucythrinate. Among them, MAb F1A27‐4 showed the highest activity toward flucythrinate, and did not cross‐react with other pyrethroids such as cycloprothrin, fenvalerate, fluvalinate, etofenprox and silafluofen. The assay conditions of indirect competitive ELISA with MAb F1A27‐4 were studied to optimize the detection of flucythrinate in environmental and food samples. Incubation at 4 °C in the assay buffer, pH 8, with 300 mM sodium chloride improved the sensitivity. The addition of rabbit serum albumin or rabbit antiserum and the presence of 50 ml litre^?1 of methanol reduced matrix effects of the samples. Under optimized conditions, the ELISA detected flucythrinate spiked in water, soil, and extracts of apple and tea samples down to 10 mg litre^?1, 0.2 mg litre^?1, 0.3 mg litre^?1 and 0.3 mg litre^?1, respectively. The mean recovery and CV ranged from 91% to 120% and from 5% to 12%, respectively. The ELISA results in apple samples correlated well with those from LC–MS analysis (r² = 0.99, n = 12). © 2001 Society of Chemical Industry     

Effect of ABT on the activity and rate of degradation of isoproturon in susceptible and resistant biotypes of Phalaris minor and in wheat

The effect of the monooxygenase inhibitor, 1-aminobenzotriazole (ABT) on isoproturon phytotoxicity and metabolism was studied in resistant (R) and susceptible (S) biotypes of Phalaris minor and in wheat (Triticum aestivum). Addition of ABT (2·5, 5 and 10 mg litre^-1) to isoproturon (0·25, 0·5, 1, 2 and 4 mg litre^-1) in the nutrient solution significantly enhanced the phytotoxicity of isoproturon against the R biotype. Isoproturon at 0·25 mg litre^-1 reduced the dry weight (DW) of the S biotype by 77%, whereas the R biotype required 4·0 mg litre^-1 for similar reduction. Addition of 10 mg litre^-1 of ABT to the 0·25 mg litre^-1 isoproturon caused 71 and 82% reduction in DW of R and S biotypes, respectively. Wheat was more sensitive to the mixture of isoproturon and ABT than the R biotype of P. minor. Reduced concentrations of ABT in the mixture from 10 to 2·5 mg litre^-1 increased the DW of the R biotype more than that of the S biotype. The R biotype metabolised [¹⁴C]isoproturon at a faster rate than the S biotype. ABT (5 mg litre^-1) inhibited the degradation of [¹⁴C]isoproturon in both biotypes of P. minor and in wheat. In the presence of ABT, about half of the applied [¹⁴C]isoproturon remained as parent herbicide in all the three species after two days. The metabolites were similar in the R and S biotypes and wheat as determined by co-chromatography with reference standards and mass spectroscopy (MS). ABT inhibited the appearance of the hydroxy and monomethyl metabolites and their conjugates in all the test plants. These results suggest that the activity of the enzymes responsible for the degradation of isoproturon is greater in the R than in the S biotype of P. minor, resulting in its rapid detoxification. Incorporation of the monooxygenase inhibitor ABT into the nutrient solution greatly inhibited the degradation of [¹⁴C]isoproturon in the R biotype and increased its phytotoxicity. Both hydroxylation and N-dealkylation reactions were found to be sensitive to ABT; inhibition of hydroxylation was greater than that of demethylation. Since ABT could not completely suppress isoproturon degradation, it is possible that more than one monooxygenase is involved. © 1998 SCI     

DPX-MP062—a potent compound for controlling the Egyptian cotton leafworm Spodoptera littoralis (Boisd.)

The effects of DPX-MP062 [methyl 7-chloro-2,3,4a,5-tetrahydro-2-[methoxycarbonyl(4-trifluoromethoxyphenyl)carbamoyl] indeno[1,2-e][1,3,4] oxadiazine-4a-carboxylate] a broad-spectrum insecticide with a novel mode of action, on the Egyptian cotton leafworm, Spodoptera littoralis, were studied in laboratory experiments. Egg hatch was affected by high concentrations (125 mg AI litre^-1) of DPX-MP062. Larvae that hatched from treated eggs were significantly affected at concentrations of 12·5 mg AI litre^-1 and greater. Larvae were fed castor bean leaves treated with DPX-MP062; 1st-instar larvae were the most susceptible development stage. Pupation and adult formation were determined in assays with 5th-instar larvae. There was strong suppression of adult formation; 65 and 91% at 0·5 and 0·75 mg AI litre^-1, respectively. Highly affected larvae died before pupation; slightly affected ones reached pupation 2–4 days later, were smaller than larvae in the untreated control, and were sometimes unable to develop into normal adults. Comparatively high concentrations (50 and 100 mg AI litre^-1) of the test compound were necessary to affect adults by ingestion, but no effects from contact application could be determined at a concentration of 100 mg AI litre^-1. © 1998 Society of Chemical Industry     

Gas-liquid chromatographic determination of hydrazine in maleic hydrazide formulations and in samples stored at an elevated temperature

A method is described for the analysis of small amounts of hydrazine in maleic hydrazide formulations. Following derivative formation with pentafluorobenz-aldehyde, the pentafluorobenzaldehyde azine was extracted with hexane and determined by gas-liquid chromatography with electron-capture detection. Recoveries of 72-80% were obtained from samples fortified with 1 and 10 μg of hydrazine. The limit of detection was 0.05 mg kg^?1. Fourteen commercial formulations with maleic hydrazide concentrations ranging from 180-360 g litre^?1 were investigated. The hydrazine content of the maleic hydrazide used in these formulations ranged from less than 0.05 to 53 mg kg^?1. During the storage of two samples at 50°C for 10 weeks, the hydrazine contents increased from 2.2 to 124 and 0.4 to 54 mg litre^?1, respectively.     

The algaecidal activity of some substituted 1,3-diphenylureas, 1-phenyl-3-(2-pyridyl)ureas and the corresponding thioureas

Twelve ureas and thioureas with 1,3-diphenyl- and 1-phenyl-3-(2-pyridyl) were tested as potential herbicides in a simple screen against two species of algae Chlorella fusca and Anabaena variabilis. Several were shown to inhibit growth at 100 mg litre^?1 but only 1-[2,4-bis(azidosulphonyl)phenyl]-3-(2-pyridyl)urea and 1,3-bis(4-isopropyl- idenehydrazinosulphonylphenyl)thiourea showed any activity at 1 mg litre^?1. This compares with the well-established urea herbicide diuron which, in identical tests, gives similar inhibition of growth at concentrations as low as 0.01 mg litre^?1.     

Some physicochemical factors influencing foliar uptake enhancement of glyphosatemono(isopropylammonium) by polyoxyethylene surfactants

Structure-concentration–foliar uptake enhancement relationships between commercial polyoxyethylene primary aliphatic alcohol (A), nonylphenol (NP), primary aliphatic amine (AM) surfactants and the herbicide glyphosatemono(isopropylammonium) were studied in experiments with wheat (Triticum aestivum L.) and field bean (Vicia faba L.) plants growing under controlled-environment conditions. Candidate surfactants had mean molar ethylene oxide (EO) contents ranging from 5 to 20 and were added at concentrations varying from 0·2 to 10 g litre^?-1 to [¹⁴C]glyphosate formulations in acetone–water. Rates and total amounts of herbicide uptake from c. 0·2–μl droplet applications of formulations to leaves were influenced by surfactant EO content, surfactant hydrophobe composition, surfactant concentration, glyphosate concentration and plant species, in a complex manner. Surfactant effects were most pronounced at 0·5 g acid equivalent (a.e.) glyphosate litre^?-1 where, for both target species, surfactants of high EO content (15–20) were most effective at enhancing herbicide uptake: surfactants of lower EO content (5–10) frequently reduced, or failed to improve, glyphosate absorption. Whereas, at optimal EO content, AM surfactants caused greatest uptake enhancement on wheat, A surfactants gave the best overall performance on field bean; NP surfactants were generally the least efficient class of adjuvants on both species. Threshold concentrations of surfactants needed to increase glyphosate uptake were much higher in field bean than wheat (c. 2 g litre^?-1 and < 1 g litre^?-1, respectively); less herbicide was taken up by both species at high AM surfactant concentrations. At 5 and 10 g a.e. glyphosate litre^?-1, there were substantial increases in herbicide absorption and surfactant addition could cause effects on uptake that were different from those observed at lower herbicide doses. In particular, the influence of EO content on glyphosate uptake was now much less marked in both species, especially with AM surfactants. The fundamental importance of glyphosate concentration for its uptake was further emphasised by experiments using formulations with constant a.i./surfactant weight ratios. Any increased foliar penetration resulting from inclusion of surfactants in 0·5 g litre^?-1 [¹⁴C]glyphosate formulations gave concomitant increases in the amounts of radiolabel that were translocated away from the site of application. At these low herbicide doses, translocation of absorbed [¹⁴C]glyphosate in wheat was c. twice that in field bean; surfactant addition to the formulation did not increase the proportion transported in wheat but substantially enhanced it in field bean.     

Transformation of aldicarb sulfoxide and aldicarb sulfone in four water-saturated sandy subsoils

The transformation of aldicarb sulfoxide and aldicarb sulfone was studied in incubations with water-saturated subsoils under simulated field conditions at 10°C. The subsoils were collected at four locations from beneath the water table at a depth of 2.5 to 3.5 m. In three of the subsoils, the half-life of sulfoxide, incubated at concentrations of 0.14-0.17 mg litre^?1, ranged from 0.7 to 2.8 years. At higher concentrations (8-13 mg litre^?1), its half-life ranged from 3.4 to 6.4 years. At the lower concentration, a large fraction of sulfoxide was transformed into sulfone. The rates of transformation of the sulfone at the lower concentration in the three subsoils corresponded to half-lives of 3.3 to 8.1 years, but in only one subsoil was a significant transformation rate (half-life 6.7 years) measured at the higher concentration during the 2.3-year incubation period. The half-lives at the lower concentrations were more like those in field studies, and perhaps would still underestimate transformation rates under field conditions. After a year, 2.5-15% of the higher sulfoxide and sulfone doses had been trapped as [¹⁴C] carbon dioxide. In the fourth subsoil, with more anaerobic conditions, the half-life of sulfoxide at both concentrations was less than 0.02 year and that of sulfone was about 0.04 year. Four or five radio-labelled transformation products could be traced in this subsoil and about half of the dose of both compounds was trapped as [¹⁴C] carbon dioxide.     

In-transit control of Liriomyza trifolii in chrysanthemum cuttings1

Individual cuttings and leaves of chrysanthemum infested with eggs and larvae of the alien leaf miner Liriomyza trifolii (Burgess) and batches of pupae, were treated in the laboratory in order to find an effective quarantine treatment to control the pest in imported cuttings. Cold treatment for 2 days at 1–2°C followed by methyl bromide fumigation at 15°C with a range of concentration time products (CTPs) was used to obtain accurate dose-response lines and estimate the LD99 and LD99.9 for each stage of the insect. The largest estimates of the LD99 for eggs, larvae and pupae up to 3 days old were less than the CTP specified in the existing (as at September 1983) United Kingdom statutory fumigation treatment designed to prevent the entry of Spodoptera littoralis (Boisd.). This statutory schedule for unrooted cuttings consists of cold storage for 2 days at 1–2°C and then fumigation with methyl bromide at a CTP of not less than 54 g·h/m³ with a minimum treatment period of 4 h at a minimum air temperature of 15°C. Our results indicate that the Spodoptera treatment should give high levels of kill for most stages of L. trifolii provided a CTP of 54 g·h/m³ and a temperature of 15°C (throughout the fumigation) arc achieved uniformly within packs of cuttings when they are fumigated in their transit boxes in commercial practice. The practicality of the technique will depend on whether it is possible to achieve this without causing unacceptable phytotoxicity. The LD99 values for pupae more than 3 days old were greater than those for eggs, larvae and young pupae. Therefore, if this treatment were adopted as a quarantine measure against L. trifolii, good prophylactic treatments and rigorous prc-packing inspections in exporting countries would still need to be maintained, to minimize any risk of importing pupae. The results are presented in full by Mortimer E.A. & Powell, D.F. (1984). Development of a combined cold storage and methyl bromide fumigation treatment to control the American serpentine leaf miner Liriomyza trifolii (Diptera: Agromyzidae) in imported chrysanthemum cuttings. Annals of Applied Biology 105 , (3), 443–454.     

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.     

The effects of temperature and humidity on the toxicity of three organophosphorus insecticides to adult Oryzaephilus surinamensis (L.)

The toxicities, to a laboratory susceptible strain and to a resistant strain of Oryzaephilus surinamensis (L.), of water-dispersible powder formulations of pirimiphos-methyl, fenitrothion or chlorpyrifos-methyl under constant conditions of 25°C and 70% r. h. were compared to the toxicities when the insects were exposed to a diurnal cycle of 12.5–20–12.5°C and 70–50–70% r. h. to simulate grain store conditions in the UK during spring and autumn. All the insecticides were more effective at 25°C and 70% r. h. The LD₅₀ values for the susceptible strain were low, being 4.4 and 1.4 mg m^?2 at 12.5-20°C and 25°C, respectively, for chlorpyrifos-methyl, 18.3 and 4.1 mg m^?2, respectively, for pirimiphos-methyl, and 4.0 and < 1.O mg m^?2, respectively, for fenitrothion. The LD₅₀ values obtained from the two sets of environmental conditions for a resistant strain (484) differed by factors of 1.8 for chlorpyrifos-methyl, 4.8 for pirimiphos-methyl, and 7.3 for fenitrothion. Toxicity studies were also made with chlorpyrifos-methyl under various constant conditions of temperature and humidity from 5–30°C (5°C intervals) and 30, 50, 70 and 90% r. h., and also at O°C and 60% r. h. Chlorpyrifos-methyl was very effective and there was little or no cross resistance to chlorpyrifos-methyl in the resistant strain. From 15 to 30°C, mortality was high, and differences in mortality at the LD₅₀ level for the various humidities were slight, but there was a decrease in mortality with decreasing humidity at any one temperature, in particular, at 5°C, 50 and 70% r. h., and 10°C and 50% r. h. Chlorpyrifosmethyl was more toxic to both strains at the highest humidity (90%) throughout the whole temperature range. The LD₅₀ values for each strain decreased at each temperature as the water vapour concentration was increased. At O°C and 60% r. h., all the insects from both strains died but the cause of death was not clear.     

Fumigation of gypsophila flowers against Liriomyza trifolii1

Gypsophila cut flowers were fumigated with methyl bromide against Liriomyza trifolii. Complete control was obtained at a dose of 40 g/m³ methyl bromide, for 3 h at 15–18°C. To get satisfactory results without injuring the flowers they had to be conditioned at the above temperature for 6 h prior to fumigation.