A bioassay for determining simazine in water using aquatic flowering plants (Ceratophyllum oryzetorum,Ranunculus trichophyllus and Alisma plantago-aquatica)

A simple and rapid bioassay for the measurement of simazine in water using aquatic flowering plants (Ceratophyllum oryzetorum Kom., Ranunculus trichophyllus Chaix. and Alisma plantago-aquatica L.) is reported in this paper. It is based on the effect of simazine on the amount of oxygen produced by photosynthesis which is measured directly using a Clark-type oxygen electrode. This method is rapid, sensitive, and capable of measuring a simazine concentration of 0.02 mg litre^?1 within 10 min of treatment. The precision of this method was examined with spiked river water by comparing the results obtained with HPLC. Mean recoveries of simazine measured by bioassay using C. oryzetorum were 96 to 100% which were comparable to those (98 to 100%) obtained with C18 column extraction and HPLC measurement. The results obtained by the two methods showed excellent agreement. Maintenance of stock cultures of the plants and the bioassay procedure itself were much simpler and more easily conducted than methods using algae.     

Removal of the phytotoxicity of uracil herbicides in water by photodecomposition

The efficiency of a photo-oxidation procedure for the detoxication of water containing herbicides of the uracil group was tested by bioassay. Treated herbicide solutions were checked for their inhibiting effect on germination and photosynthesis in sorghum (Sorghum bicolor). The treated solutions, and the main photodegradation products of bromacil and terbacil did not inhibit significantly either germination or seedling development at concentrations of up to 200 and 10 mg litre^?1, respectively. Preliminary tests with industrial waste effluents containing added uracil compounds showed that these compounds were rendered non-phytotoxic by the photo-oxidation procedure.     

Residualwirkung von Chlortriazin-Herbiziden im Boden an drei rumänischen Standorten. II. Prognose möglicher Folgekulturen bei Atrazinrükständen im Boden

Residual effects of chlorotriazine herbicides in soil at three Rumanian sites. II. Prediction of the phytotoxicity of atrazine residues to following crops Total and plant-available atrazine residues in the top 10 cm soil were measured 120 days after application of 3 kg ai ha^?1 to maize (Zea mays L.) at three sites in Rumania. At one site, similar measurements were made 3?5 years after application of 100 kg ai ha^?1. Plant-available atrazine residues were estimated by extraction of soil samples with water, and by bioassay using Brassica rapa as the test plant. It was calculated that between 30 and 120μg atrazine 1^?1 was potentially available to plants in the different soils. Dose-response relationships for atrazine and the most important rotational crops with maize in Rumania—sunflower, winter wheat, soybean and flax—were determined in hydroponic culture using herbicide concentrations corresponding with the plant-available fractions measured in the different soils. ED₅₀ values were determined by probit analysis and the results showed that sunflower (ED₅₀, 22μg 1^?1) was the most sensitive crop, and soybean (ED₅₀, 78μg 1^?1) was the least. The residual phytotoxicity of atrazine to succeeding crops in the different soils was predicted using the appropriate availability and phytotoxicity data, and the results showed good agreement with those observed. The results suggest that measurements of plant-available herbicide residues afford a rapid method of assessing possible phytotoxicity to following crops.     

Dissipation of metham-sodium from soil and its effect on the control of Orobanche aegyptiaca

The effect of metham-sodium on Orobanche aegyptiaca Pers. was tested in the laboratory and in soil columns. The laboratory experiment was carried out on O. aegyptiaca seeds placed in Petri dishes and germinated with GR₂₄, a synthetic strigol analogue. In soil columns, metham-sodium was applied by application of the chemical through the irrigation water to three different soils and its dissipation determined in three soil layers by gas chromatography, by a lettuce bio-assay to check the herbicide's phytotoxicity, and with a flax bioassay to check its effect on O. aegyptiaca. Results of the germination experiments showed an exponential decrease in O. aegyptiaca germination, parallel with the increase of metham-sodium concentration, with an average effective concentration (EC₅₀) of 18 mg L^?1. In a soil column, methylisothiocyanate (MIT, the metham active product) rapidly disappeared from the upper soil level (0–10 cm) within 24 h. Seven days after application only traces of MIT remained in all soil layers in all soils, except for the sandy Rehovot soil that contained low concentrations in the lower soil layer (20–30 cm). Flax bioassay confirmed the chemical analysis, showing that O. aegyptiaca tubercles developed only on plants grown in the upper soil layer of all three soils.     

Effects of repeated applications of ten soil-active herbicides on weed population,residue accumulation and nitrification*

Ten herbicides, bromacil, chlorthal-dimethyl, diphenamid, diuron, fluometuron, neburon, prometryne, pyrazon, simazine and trifluralin at two doses were repeatedly sprayed, in autumn and in spring, for 4 consecutive years on non-cultivated, sprinkler-irrigated field plots. Herbicidal effect was assessed at 1–2 month intervals on the natural weed population and after each observation a paraquat + diquat spray destroyed emerged weeds. The response of various weed species to herbicides varied markedly but a herbicide-induced shift in the composition of weed population did not occur, presumably because of the paraquat treatment. The overall phytotoxicity to weeds present was, in decreasing order: diuron, bromacil, simazine, trifluralin, prometryne, neburon, fluometuron, pyrazon, diphenamid, chlorthal-dimethyl. Persistence of herbicides was in decreasing order: diuron = bromacil, simazine, neburon (at higher rate), fluometuron, trifluralin, prometryne. Control produced by pyrazon improved with the number of applications, but that of diphenamid and chlorthal-dimethyl remained weak and short. After repeated applications, the activity of these herbicides increased or remained at similar level, but in no case decreased. Soil samples were taken 5 months after each application and bioassayed. Phytotoxic residues were detected beneath the disturbed top-soil from bromacil, diuron, fluometuron and simazine after the first application, and from neburon after the second application; residues from trifluralin were found in the top soil only after the fifth application. After the seventh spraying, residues of bromacil were found in the 45–60-cm soil layer. Ammonia content in soil samples taken from treated plots after the fourth, sixth and seventh application was generally similar to the untreated control. In these samples, nitrate content appeared to be correlated negatively with remaining weed number; the control thus contained less nitrate than efficient herbicidal treatments. Soil samples taken after the seventh application of bromacil, diuron, fluometuron, neburon and simazine, which contained appreciable residual concentrations, did not show significant differences from control, in an in vitro nitrification test.     

Analysis of metsulfuron‐methyl residues in wheat field soil: a comparison of HPLC and bioassay techniques

BACKGROUND: Metsulfuron‐methyl is a low‐application‐rate sulfonylurea herbicide that is widely used to control broad‐leaved weeds in wheat. Owing to its persistent nature, its residues may be present at phytotoxic levels for the next crop in rotation. Therefore, a comparative evaluation of HPLC and bioassay techniques was made for the analysis of this herbicide in wheat field soil. RESULTS: Metsulfuron‐methyl was applied to wheat crop at different rates (4, 8 and 12 AI ha^?1) at 28 days after sowing as a post‐emergence application, and the soil was analysed for metsulfuron‐methyl residues by HPLC and lentil seed bioassay techniques. The bioassay was found to be the more sensitive technique. At the recommended rate of application, 4 g AI ha^?1, the bioassay technique could detect the residue up to 30 days in surface soil, while, with HPLC, residues were not detectable on the 15th day. The half‐lives of metsulfuron‐methyl by HPLC and bioassay were calculated as 6.3–7.8 and 17.5 days respectively. Under field conditions, residues of metsulfuron‐methyl were also detected in subsurface soil by the bioassay technique at trace levels, but were not detected by the solvent extraction/HPLC method. CONCLUSION: Lentil seed bioassay is a more sensitive technique than HPLC. Traces of residues detected in subsurface soil indicated the mobility of metsulfuron‐methyl into lower layers. Copyright © 2009 Society of Chemical Industry     

EVALUATION OF HERBICIDE PERSISTENCE IN SOIL*

Summary. The persistence of ten herbicides in soil was tested in the glasshouse over a 5–month period, using an oat bioassay. Simazine and diuron were highly persistent, atrazine persistent, fluometuron, trifluralin, bromacil and noruron moderately persistent, and pyrazon, prometryne and ametryne of short persistence. Six of these herbicides were also included in a field experiment consisting of logarithmically sprayed strips on which oats were sown at ten intervals of 1 month; changes of herbicidal activity with time were evaluated by measuring the length of the strip showing herbicidal injury. Results corroborate those of the glasshouse experiments except for trifluralin which was more persistent in the field. Disappearance curves were generally sigmoidal. The more persistent compounds showed a long period of slow disappearance followed by rapid disappearance.     

Effects of Cry1Ac toxin of Bacillus thuringiensis and nuclear polyhedrosis virus of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) on larval mortality and pupation

In the laboratory, the percentage mortality and pupation of Helicoverpa armigera (Hübner) were investigated when larvae were exposed to Cry1Ac of Bacillus thuringiensis Berliner, nuclear polyhedrosis virus of H. armigera (HaNPV) or Cry1Ac and HaNPV together. The results revealed that interactions between Cry1Ac and HaNPV varied with bioassay method and concentration of the suspension. When larvae were infected using a suspension containing both HaNPV and Cry1Ac, most combinations of Cry1Ac (62.5, 125 and 250 microg mL(-1)) and HaNPV (1.2 x 10(6), 6.0 x 10(6) and 3.0 x 10(7) PIB mL(-1)) showed an antagonistic effect. In the bioassay procedure where larvae were force fed diet containing Cry1Ac 48 h after being infected by HaNPV, interaction between Cry1Ac (0.5, 1, 2, 4 and 8 microg mL(-1)) and HaNPV (6.0 x 10(6) and 3.0 x 10(7) PIB mL(-1)) showed an additive effect, while combinations of Cry1Ac (0.5, 1, 2 and 4 microg mL(-1)) and HaNPV (1.2 x 10(6) PIB mL(-1)) showed an antagonistic effect. In the bioassay procedure where larvae being infected by HaNPV were fed on Cry1Ac diet from neonate to death or pupation, the results suggested that Cry1Ac and HaNPV showed an additive interaction. The percentage mortality was lower in the treatment of larvae infected by transgenic Bt cotton leaf discs containing HaNPV suspension than in the treatment of larvae by conventional cotton leaf discs containing HaNPV, while the pupation rate was higher. The combination of Bt cotton and HaNPV showed antagonism. The present results showed that a combination of Cry1Ac and HaNPV usually resulted in mortality levels greater than in the case of Cry1Ac but not greater than with the virus alone.     

Detection of Colletotrichum coccodes and Helminthosporium solani in soils by bioassay

The sensitivity of a bioassay in detecting soil inoculum of Colletotrichum coccodes and Helminthosporium solani was examined using potato minitubers and microplants. Tests were conducted on soils which were collected from fields in which the interval after a previous potato crop differed, and which were also artificially infested with conidia or microsclerotia. For C. coccodes , determining plant infection based on the occurrence of infected roots after 9–12 weeks was a sensitive method for detecting and quantifying the amount of inoculum in soil. Infestations of less than 0·4 microsclerotia per g soil were detected in artificially infested soils. A semiselective medium, developed for isolating C. gloeosporioides from pepper, detected soil infestations by C. coccodes as low as nine conidia or one microsclerotium per g soil in artificially infested soil. For H. solani , infection on minitubers was a sensitive measure, with soil inoculum of fewer than 10 conidia per g soil being detected. Soil infestation could be quantified by assessing the percentage surface area of minitubers covered by sporulating lesions, which was strongly related to the amount of soil infestation. The results of these bioassay tests were compared with published results for real-time quantitative PCR assays on the same soils. The two methods were in good agreement in artificially infested soils, but the bioassay appeared to be more sensitive with naturally infested soils.     

Uptake and translocation of [14C]asulam and [14C]bromacil by roots of maize and bean plants

The uptake and translocation of ¹⁴C-ring-labeled asulam (methylsulfanilcarbamate) and bromacil (5-bromo-3-sec-butyl-6-methyluracil), were compared after root application to maize (Zea mays L.) and bean (Phaseolus vulgaris L.). Autoradiographs showed the distribution of bromacil throughout these and other plant species, and the retention of asulam in the roots. The recovery of both compounds in quantitative radioassays was between 90 and 100%. The absorption of bromacil and asulam was rather similar. Absorption of bromacil increased up to 20% of the applied dose in bean plants after 2 days of exposure, and up to 11% in maize plants after 4 days. Absorption of asulam in bean plants was 22% of the applied dose after 2 days, and 8% in maize plants after 4 days. The pattern of distribution of bromacil and asulam was completely different. After 4 h of exposure of the roots about half of the absorbed bromacil had accumulated in the shoots, while two-thirds or more was translocated to the shoots after exposure periods of 1 to 4 days. Not more than one-eighth of the absorbed asulam was found in the shoots. In consequence, the bromacil content in the transpiration stream relative to that in the ambient solution was much higher than that of asulam. The leakage of asulam from bean and maize roots into herbicide-free nutrient solution was lower than that of bromacil. The reasons for these differences are not yet clear. There was only some metabolism of asulam in maize, but not in bean plants. No metabolites of bromacil were detected in the two plant species.     

RATE OF DETOXIFICATION OF 4-AMINO-3,5,6-TRICHLOROPICOLINIC ACID IN SOIL

Summary. 4-Aniino-3,5,6-trichloropicolinic acid was incubated at 70° F in thirteen different soils for periods of up to 2 years at a concentration range of 0–023–24 ppm. Losses varied from complete to non-measurable by the bioassay technique employed. The percentage decomposed was generally greater for lower initial concentrations. The results were mathematically analysed in terms of zero-order, half-order, first-order and Michaclis-Menten kinetics. Half-order and Mirhaelis-Menten were found to be the kinetic expressions that most satisfactorily described the detoxification of the herbicide in soil.
Taux de deloxification de l'acide 4-amino-3,5,6-trichloropicolinique dans le sol     

Effets non compétitifs entre le chénopode blanc (Chenopodium album L.) et le mas (INRA 258)

Non-competitive effects between lamb's quarters (Chenopodium album L.) and maize (INRA 25H) Maize is extremely sensitive to competition from weeds, lamb's quarters (C.alhum) often being particularly competitive, Under controlled conditions in a growth chamber short term bioassay methods techniques have shown that lamb's quarters exerted inhibiting influences on maize growth which were not attributable to competition alone. These non-compctitive, specific influences became apparent mainly from the early flowering stage of lamb's quarters both in soil and in nutrient solution. With an identical concentration of lamb's quarters roots, the growth-inhibiting effects are more marked when the soil structure is modified than when it is not, similarly when the aqueous extract is obtained by placing soils in suspension, the inhibiting effects are more marked than when it is obtained by percolation. Finally, water leached from the leaves, roots or seeds of lamb's quaners shows inhibiting effects proport ional to the concentration on root growth of maize. The presence of phytotoxins in the culture media of lamb's quarters is discussed.     

Effect of inoculum type and timing of application of Coniothyrium minitans on Sclerotinia sclerotiorum: influence on apothecial production

The effects of different inocula of the mycoparasite Coniothyrium minitans on carpogenic germination of sclerotia of Sclerotinia sclerotiorum at different times of year were assessed. A series of three glasshouse box bioassays was used to compare the effect of five spore-suspension inocula of C. minitans , including three different isolates (Conio, IVT1 and Contans), with a standard maizemeal–perlite inoculum. Apothecial production, as well as viability and C. minitans infection of S. sclerotiorum sclerotia buried in treated soil, were assessed. Maizemeal–perlite inoculum at 10⁷ CFU per cm³ soil reduced sclerotial germination and apothecial production in all three box bioassays, decreasing sclerotial recovery and viability in the second bioassay and increasing C. minitans infection of sclerotia in the first bioassay. Spore-suspension inocula applied at a lower concentration (10⁴ CFU per cm³ soil) were inconsistent in their effects on sclerotial germination in the three box bioassays. Temperature was an important factor influencing apothecial production. Sclerotial germination was delayed or inhibited when bioassays were made in the summer. High temperatures also inhibited infection of sclerotia by C. minitans . Coniothyrium minitans survived these high temperatures, however, and infected the sclerotia once the temperature decreased to a lower level. Inoculum level of C. minitans was an important factor in reducing apothecial production by sclerotia. The effects of temperature on both carpogenic germination of sclerotia and parasitism of sclerotia by C. minitans are discussed.     

Induction of systemic resistance byPseudomonas fluorescens in radish cultivars differing in susceptibility to fusarium wilt,using a novel bioassay

Pseudomonas fluorescens-mediated induction of systemic resistance in radish against fusarium wilt (Fusarium oxysporum f. sp.raphani) was studied in a newly developed bioassay using a rockwool system. In this bioassay the pathogen and bacterium were confirmed to be confined to spatially separate locations on the plant root, throughout the experiment. Pathogen inoculum obtained by mixing peat with microconidia and subsequent incubation for four days at 22 °C, yielded a better percentage of diseased plants than a microconidial suspension drench, an injection of a microconidial suspension into the hypocotyl, or a talcum inoculum.Pseudomonas fluorescens strain WCS374 applied in talcum or peat, but not as a suspension drench, induced systemic resistance. A minimal initial bacterial inoculum density of 10⁵ CFU WCS374 root^–1 was required to significantly reduce the percentage diseased plants. At least one day was necessary between bacterization of strain WCS374 in talcum on the root tips and inoculation of the pathogen in peat on the root base, for an optimal induction of systemic resistance. Strain WCS374 induced systemic resistance in six radish cultivars differing in their susceptibility toF. oxysporum f. sp.raphani. Significant suppression of disease by bacterial treatments was generally observed when disease incidence in the control treatment, depending on pathogen inoculum density, ranged between approximately 40 to 80%. Strains WCS374 and WCS417 ofPseudomonas fluorescens induced systemic resistance against fusarium wilt, whereasP. putida WCS358 did not. This suggests that the induction of systemic resistance byPseudomonas spp. is dependent on strain-specific traits.Abbreviations CFU colony forming units - IFC immunofluorescence colony-staining - ISR induced systemic resistance - PBS phosphate buffered saline - SAR systemic acquired resistance     

七种杀虫剂对暗黑鳃金龟成虫和幼虫的毒力及田间防控效果

为筛选防治暗黑鳃金龟Holotrichia parallela的有效药剂,用浸虫法测定了7种药剂对暗黑鳃金龟幼虫的毒力,分别采用浸虫法、浸叶法、药膜法测定了7种药剂对其成虫的毒力,并通过大田试验作了进一步验证。浸虫法测得高效氯氟氰菊酯对成虫的毒力最高,LC₅₀值为1.38 mg/L;浸叶法测得辛硫磷毒力最高,为42.05 mg/L;药膜法测得毒死蜱毒力最高,为18.51 mg/L。其中,高效氯氟氰菊酯毒力值变化最大,浸虫法毒力是浸叶法毒力的61.86倍;氯虫苯甲酰胺、氟虫腈在3种生测方法中毒力相当,但均较低。丁硫克百威对暗黑鳃金龟幼虫的毒力最高,LC₅₀值为7.29 mg/L。田间试验结果显示,35%辛硫磷微囊悬浮剂4 500 g/hm²(有效成分,余同)防效达80.66%,对花生的保果、增产幅度分别为77.90%、17.56%;30%毒死蜱微囊悬浮剂2 250 g/hm²、20%丁硫克百威乳油3 000 g/hm²与辛硫磷防效相当,且显著高于其它药剂。因此,选用以上药剂于7月中下旬花生封垄前田间灌墩可以有效减轻暗黑鳃金龟为害。     

三叶鬼针草化感作用的初步研究

运用生物测定法,对三叶鬼针草的化感作用进行研究。比较了用不同部位及其不同浓度水浸提液对不同作物化感作用的差异,并初步探讨了三叶鬼针草对小麦和莴苣幼苗生长的化感机制。结果表明,三叶鬼针草不同部位水浸提液对2种受体植物影响均表现出抑制效应,其强弱为叶>茎>根。其水浸提液对2种受体植物的种子萌发、幼苗生长和光合色素均有显著的抑制作用。Peason相关性分析表明,叶绿素A和叶绿素b含量与水浸提液浓度存在显著的负相关性,类胡萝卜素无明显变化。丙二醛随浓度增加而有上升趋势,但差异不显著,说明三叶鬼针草对受体植物膜的透性影响不大。     

脂肽类抗生素fengycin在枯草芽胞杆菌NCD-2菌株抑制番茄灰霉病菌中的功能分析

 枯草芽胞杆菌NCD-2菌株及其无细胞发酵液对多种植物病原真菌具有较强的拮抗活性。为了明确NCD-2菌株抑菌作用机理,本研究利用快速蛋白液相色谱技术(FPLC)结合抑菌活性测定,对NCD-2菌株的脂肽类抑菌物质进行分离、纯化,经质谱鉴定,该抑菌物质为芬荠素(fengycin)。从NCD-2菌株中克隆出fengycin合成酶基因fenC及其上游启动子序列,通过同源重组技术对fenC基因进行了内缺失突变,同NCD-2野生型菌株相比,fenC基因缺失突变子丧失了fengycin的合成能力,同时该突变子显著降低了对番茄灰霉病菌的拮抗活性。进一步在离体叶片上比较了NCD-2野生型菌株和突变子之间脂肽提取物和菌体细胞对番茄灰霉病的保护作用,结果发现,突变子不论是脂肽提取物还是菌体细胞显著降低了对番茄灰霉病的防治作用。     

Phytotoxic effects of Parthenium hysterophorus residues on three Brassica species

A study was conducted to assess the phytotoxicity of residues of Parthenium hysterophorus , an exotic invasive weed, towards the growth of three Brassica species ( Brassica campestris, Brassica oleracea and Brassica rapa ). The early growth of crops, measured in terms of seedling length and dry weight, was significantly reduced when grown in soil amended with varying amounts of Parthenium residues. A direct relationship was observed between the amount of residue incorporated in the soil and growth reduction. This adverse effect on Brassica crops indicates the presence of some growth-retardatory substances which are possibly released by the residues into the soil medium. In order to test this, aqueous extracts (1, 2, and 4%) of residues were prepared. It was observed that, in a laboratory bioassay, these extracts severely reduced the early growth of Brassica species, thereby indicating the presence of some water-soluble, inhibitory principles in Parthenium residues. A significant amount of the phenolics, the largest group of secondary metabolites usually implicated in allelopathy, was estimated in residue extracts, as well as in residue-incorporated soil. The phenolic content increased with increasing residue concentration, thereby showing their direct involvement in the observed growth inhibitions. Therefore, the study establishes that Parthenium residues exert an allelopathic influence on the early growth of Brassica crops by releasing water-soluble phenolics into the soil.     

Quantitative Aspects of Infection of Sclerotinia sclerotiorum Sclerotia by Coniothyrium minitans – Timing of Application, Concentration and Quality of Conidial Suspension of the Mycoparasite

White mould disease leads to production of sclerotia, which subsequently survive in soil and may be responsible for future epidemics. The effect of the mycoparasite Coniothyrium minitans in decreasing survival of sclerotia of Sclerotinia sclerotiorum was studied. Infection of sclerotia of S. sclerotiorum by C. minitans can be achieved by a single conidium. Under optimal conditions, 2 conidia per sclerotium produced 63% of the maximum infection (ca. 90%) of sclerotia produced by up to 1000 conidia. Similar results were observed on the infection of stem pieces infected by S. sclerotiorum. In field trials, application of conidial suspensions of C. minitans to a bean crop soon after white mould outbreak led to a higher percentage of sclerotial infection than later applications. Ninety per cent infection of sclerotia was obtained within 3 weeks of application by C. minitans suspensions in the range of 5 × 10⁵ and 5 × 10⁶ conidia ml^–1 at 1000 l ha^–1. The concentration of the conidial suspensions and the isolate used were of less importance. The result was marginally affected by the germinability of the conidia (75% against 61% infected sclerotia at 91% and 16% viability of isolate IVT1, respectively). Less apothecia of S. sclerotiorum developed in soil samples collected after 2 months from plots sprayed immediately after disease outbreak than from those treated 11–18 days later. It is concluded that a suspension of 10⁶ conidia ml^–1 in 1000 l ha^–1 (= 10¹² conidia ha^–1) sprayed immediately after the first symptoms of disease are observed, results in > 90% infection of sclerotia of S. sclerotiorum. The infection of sclerotia, which prevents their carry-over, occurs within a broad range of inoculum quality.     

An oral bioassay for the toxicity of hydramethylnon to individual workers and queens of Argentine ants,Linepithema humile

We have developed an oral bioassay to determine the toxicity of hydramethylnon to individual workers and queens of the Argentine ant, Linepithema humile. We fed seven concentrations of hydramethylnon in suspension to individual workers or queens, determined the amount of hydramethylnon ingested and evaluated the individual ants for mortality 14 days later. At concentrations ≥0.37 g liter^?1, the amount of liquid the queens ingested decreased dramatically, indicating that Argentine ant queens may detect hydramethylnon. Significantly larger volumes of the two highest concentrations of the hydramethylnon suspension were ingested by the workers, compared to the lower concentrations, suggesting that hydramethylnon may act as a feeding stimulant for the workers. Worker mortality was higher than queen mortality at the highest concentrations tested. The highest worker mortality resulted when the ants ingested 1.03 µg of hydramethylnon per mg of ant tissue. At the highest concentration (1.0 g liter^?1) tested, workers ingested almost 12 times as much active ingredient per mg of body weight as did queens, suggesting that, in order to increase mortality of queens, multiple feedings must occur. © 2001 Society of Chemical Industry