Filter Paper Bioassay Research Articles

Role of secondary metabolites of wild marigold in suppression of Johnson grass and Sun spurge

ObjectiveTo analyze the wild marigold [(Tagetes minuta L.) (T. minuta)] leaf extract with respect to phytochemicals and allelopathic activity. MethodsThe aqueous extracts of T. minuta leaves at concentrations of 50%, 75% and 100% were prepared. Preliminary phytochemical analysis was carried out and then allelopathic effect of T. minuta on root length, shoot length, germination, fresh and dry weight of Johnson grass and Sun spurge was tested on filter paper and in soil. ResultsQualitative phytochemical analysis showed the presence of alkaloids, tannins, saponins, flavonoides and terpenoids. The higher concentrations proved to be significantly effective in reducing almost all the parameters of Sun spurge and Johnson grass in filter paper bioassay. Supplemented with the soil, all concentrations of leaf extract showed reduction in germination, root and shoot growth, fresh and dry weight of Sun spurge; however, 100% concentration significantly reduced the germination of Johnson grass. ConclusionsThis study suggests that marigold allelochemicals can be used as an integrated weed management for the production of better crop yield.

Methyl eugenol bioactivities as a new potential botanical insecticide against major insect pests and their natural enemies on rice (Oriza sativa)

The bioactivities of methyl eugenol (ME) against rice insect pests, the brown planthopper (BPH), Nilarparvata lugens, the leaf folder (RLF), Cnaphalocrocis medinalis, the striped stem borer (SSB), Chilo suppressalis, and their major natural enemies, a predator Cyrtorhinus lividipennis and parasitoids Anagrus nilaparvatae and Trichogramma japonicum were determined under laboratory conditions. The results showed ME had repellent, systemic and contact insecticidal activities against BPH. The nymphal mortality increased with raised ME concentrations. The LC50 value for BPH using an impregnated filter paper bioassay was 1025 mg/L which was much lower than that of 3778 mg/L obtained from an immersion bioassay. ME also had a contact toxicity against RLF larvae with a LC50 of 250 mg/L. However, bioactivity of ME against SSB larvae was much lower than against RLF. Only 21.8% of 2nd instar SSB larvae died at 24 h after being treated with 8000 mg/L ME. In addition, ME also had contact toxicity to predator C. lividipennis and parasitic natural enemies A. nilaparvatae, T. japonicum, with LC50 values of 527, 105 and 123 mg/L, respectively. Even so, the toxicity of ME to natural enemies was much lower than that of chemical insecticides.

Acaricidal Activity of Constituents Derived from Peppermint Oil against Tyrophagus putrescentiae

The acaricidal activities of peppermint oil and menthol isomers against mites in stored food were evaluated using fumigant and contact bioassays and were compared with the activity of benzyl benzoate as a synthetic acaricide. Based on the 50% lethal dose (LD50) values against Tyrophagus putrescentiae in the fumigant bioassay, menthol (0.96 μg/cm(2)) was approximately 12.18 times more effective than benzyl benzoate (11.70 μg/cm(2)), followed by (+)-neomenthol (1.33 μg/cm(2)), (-)-menthol (1.60 μg/cm(2)), and (+)-menthol (1.90 μg/cm(2)). In the filter paper bioassay, menthol (0.55 μg/cm(2)) was about 15.18 times more active than benzyl benzoate (8.35 μg/cm(2)), followed by (-)-menthol (0.84 μg/cm(2)), (+)-menthol (0.92 μg/cm(2)), and (+)-neomenthol (1.72 μg/cm(2)). However, (+)-isomenthol did not exhibit any acaricidal activity against T. putrescentiae in the fumigant and filter paper bioassays. These results indicate that peppermint oil and menthol isomers could be effective natural acaricides for managing mites in stored food.

Toxic and antifeedant activities of prenylated flavonoids isolated from Tephrosia apollinea L. against three major coleopteran pests of stored grains with reference to their structure–activity relationship

Four prenylated flavonoids, isoglabratephrin, (+)-glabratephrin, tephroapollin-F and lanceolatin-A, were isolated from Tephrosia apollinea L. and tested against three stored grain insects. Using the filter paper bioassay, compounds showed adulticidal activity against Sitophilus oryzae (L), Rhyzopertha dominica (F) and Tribolium castaneum (Herbst) at concentrations of 0.875, 1.75 and 3.5 mg mL− 1. At 3.5 mg mL− 1, tephroapollin-F was the most toxic (78.6%, 64.6% and 60.7% mortality was recorded after 10 days exposure of S. oryzae, R. dominica and T. castaneum, respectively). The F1 progeny production of insects was affected after parental exposure to flavonoids, where S. oryzae was the most susceptible. A nutritional bioassay, employing a flour disc and test concentrations of 0.65, 1.3 and 2.6 mg g− 1, revealed a significant reduction in the relative growth rate, relative consumption rate and efficiency of conversion of ingested food by all insects. The structure–activity relationship among the tested flavonoids was discussed.

Acaricidal activities of bicyclic monoterpene ketones from Artemisia iwayomogi against Dermatophagoides spp.

The acaricidal properties of 1,7,7-trimethylbicyclo[2.2.1]heptan-2-one isolated from Artemisia iwayomogi and its structural analogues were evaluated against Dermatophagoides farinae and D. pteronyssinus, and their effects were compared with that of the commercial acaricide benzyl benzoate. Based on the 50 % lethal dose (LD50) values against D. farinae, 1,7,7-trimethylbicyclo[2.2.1]heptan-2-one (0.82 μg/cm(2)) was 9.71 times more effective than benzyl benzoate (7.96 μg/cm(2)), followed by (1R)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-one (1.03 μg/cm(2)), (1S)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-one (1.58 μg/cm(2)), and (1R)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-one oxime (3.05 μg/cm(2)) in a filter paper bioassay. The acaricidal activities of 1,7,7-trimethylbicyclo[2.2.1]heptan-2-one and its structural analogues against D. pteronyssinus were similar to those against D. farinae. These results demonstrate that naturally occurring A. iwayomogi-isolated 1,7,7-trimethylbicyclo[2.2.1]heptan-2-one and its structural analogues are suitable for the production of natural acaricides against house dust mites.

Innovative Sugar-Insecticide Feeding Bioassay for Adult Female Anopheles gambiae (Diptera: Culicidae)

The primary malaria vector in sub-Saharan Africa, Anopheles gambiae Giles (Diptera: Culicidae), is an anthropophagic and endophilic mosquito targeted for control with insecticides applied to interior resting surfaces and impregnated onto bed net materials. Effective malaria vector management involves monitoring the insecticide susceptibility of mosquito populations. Contemporary bioassays are based on mosquito contact with insecticide residues. We developed an innovative insecticide bioassay system that involves mosquito ingestion of a sugar-insecticide solution. The sucrose-permethrin solution in our bioassay system contained Trypan blue dye, creating a visual marker of insecticide ingestion in the mosquito's abdomen. Blue fecal spots deposited in the bioassay container provided further evidence of mosquito feeding. We used our bioassay to characterize the permethrin susceptibility of adult females of two strains of A. gambiae, one of which was susceptible and the other exhibited reduced susceptibility to permethrin. We compared the dose-response of both strains to permethrin in a forced-contact filter paper bioassay. Both assay approaches produced similar dose-dependent mortality, indicating that the feeding bioassay had appropriately characterized permethrin susceptibility for both mosquito strains.

Bioactivity-Guided Investigation of Geranium Essential Oils as Natural Tick Repellents

The evaluation of 10 essential oils of geranium, Pelargonium graveolens (Geraniaceae), were all shown to have repellent activity against nymphs of the medically important lone star tick, Amblyomma americanum (L.). The biological tests were carried out using a vertical filter paper bioassay, where ticks must cross an area of the paper treated with repellent to approach host stimuli. One of the essential oil samples that repelled >90% of the ticks at 0.103 mg/cm(2) was selected for further fractionation studies. The sesquiterpene alcohol, (-)-10-epi-γ-eudesmol, was isolated and identified by spectral methods. (-)-10-epi-γ-Eudesmol at 0.103 and 0.052 mg of compound/cm(2) of filter paper repelled 90 and 73.3% of the ticks, respectively. (-)-10-epi-γ-Eudesmol exhibited similar repellency to the reference standard N,N-diethyl-meta-toluamide (DEET) at concentrations of ≥0.052 mg of compound/cm(2) of filter paper, with (-)-10-epi-γ-eudesmol losing much of its repellency at 0.026 mg of compound/cm(2) and DEET at 0.013 mg of compound/cm(2). Isomenthone and linalool did not repel ticks at the concentrations tested. Most repellents are marketed with much higher concentrations of active ingredient than the concentrations of the natural repellents tested herein; therefore, effective compounds, such as (-)-10-epi-γ-eudesmol, found in geranium oil, have the potential for commercial development.

Mechanisms of pyrethroid resistance inHaematobia irritans (Muscidae) from Mato Grosso do Sul state, Brazil

Horn fly resistance to pyrethroid insecticides occurs throughout Brazil, but knowledge about the involved mechanisms is still in an incipient stage. This survey was aimed to identify the mechanisms of horn fly resistance to cypermethrin in Mato Grosso do Sul state, Brazil. Impregnated filter paper bioassays using cypermethrin, synergized or not with piperonyl butoxide (PBO) and triphenyl phosphate (TPP), were conducted from March 2004 to June 2005 in horn fly populations (n = 33) from all over the state. All populations were highly resistant to cypermethrin, with resistance factors (RF) ranging from 89.4 to 1,020.6. Polymerase chain reaction (PCR) assays to detect the knockdown resistance (kdr) mutation also were performed in 16 samples. The kdr mutation was found in 75% of the tested populations, mostly with relatively low frequencies (<20%), and was absent in some highly resistant populations. Addition of TPP did not significantly reduce the LC50 in any population. However, PBO reduced LC50s above 40-fold in all tested populations, resulting in RFs ≤ 10 in most cases. Horn fly resistance to cypermethrin is widespread in the state, being primarily caused by an enhanced activity of P450 mono-oxygenases and secondarily by reduced target site sensitivity.

Control of the Mupli Beetle,Luprops tristis(Coleoptera: Tenebrionidae), and Dormancy Phase-related Variation in Insecticide Susceptibility1

Massive home invasions by the Mupli beetle, Luprops tristis F. (Coleoptera: Tenebrionidae), with the onset of monsoon rains, aggregation in a prolonged state of dormancy at specific locations, and repeated selection of the same locations for years provides an excellent opportunity to control the beetles employing suitable insecticides. The weak physical stature of the surviving beetles during the last phase of dormancy lead to the proposition that there were differences in insecticide susceptibility during the early- and late-dormancy phases. Hence, efficacy of three pyrethroid insecticides were tested with filter-paper bioassays to determine LC99 and KC99 values in the early and late phases of dormancy and to analyse whether the efficacy of the compounds vary between the early and late phases. During the late-dormancy phase, these compounds caused immediate knockdown but not immediate mortality at the lowest application rates. However, because the beetles have to be controlled during the early phase of dormancy when home invasions occur, the best control strategy for this nuisance pest is to knockdown the beetles and physically remove them instead of direct mortality.

Acaricidal activities of materials derived from Pyrus ussuriensis fruits against stored food mites.

The acaricidal activities of materials derived from Pyrus ussuriensis fruits were evaluated against Tyrophagus putrescentiae and compared with that of commercial acaricide (benzyl benzoate). On the basis of the 50 % lethal dose (LD(50)) values, the ethyl acetate fraction of the fractions obtained from an aqueous extract of P. ussuriensis fruits had the highest acaricidal activity (16.32 μg/cm(2)) against T. putrescentiae. The acaricidal constituent of P. ussuriensis fruits was isolated by chromatographic techniques and identified as 1,4-benzoquinone. On the basis of the LD(50) values, 1,4-benzoquinone (1.98 μg/cm(2)) was 5.9 times more toxic than benzyl benzoate (11.69 μg/cm(2)), followed by 2-isopropyl-5-methyl-1,4-benzoquinone (3.29 μg/cm(2)), and 2,3-dimethoxy-5-methyl-1,4-benzoquinone (5.03 μg/cm(2)) against T. putrescentiae in the fumigant bioassay. In a filter paper bioassay, the acaricidal activity of 1,4-benzoquinone (0.07 μg/cm(2)) was 120.1 times more effective than that of benzyl benzoate (8.41 μg/cm(2)), followed by 2-isopropyl-5-methyl-1,4-benzoquinone (0.11 μg/cm(2)) and 2,3-dimethoxy-5-methyl-1,4-benzoquinone (0.30 μg/cm(2)) against T. putrescentiae. These results demonstrate that P. ussuriensis fruit-derived material and its derivatives have potential as new preventive agents for the control of stored food mites.

Soil microorganisms alleviate the allelochemical effects of a thyme monoterpene on the performance of an associated grass species.

BackgroundPlant allelochemicals released into the soil can significantly impact the performance of associated plant species thereby affecting their competitive ability. Soil microbes can potentially affect the interaction between plant and plant chemicals by degrading the allelochemicals. However, most often plant-plant chemical interactions are studied using filter paper bioassays examining the pair-wise interaction between a plant and a plant chemical, not taking into account the potential role of soil microorganisms.Methodology/Principal findingsTo explore if the allelopathic effects on a grass by the common thyme monoterpene “carvacrol” are affected by soil microorganisms. Seedlings of the grass Agrostis capillaris originating from 3 different thyme sites were raised in the greenhouse. Seedlings were grown under four different soil treatments in a 2*2 fully factorial experiment. The monoterpene carvacrol was either added to standard greenhouse soil or left out, and soil was either sterilized (no soil microorganisms) or not (soil microorganisms present in soil). The presence of carvacrol in the soil strongly increased mortality of Agrostis plants, and this increase was highest on sterile soil. Plant biomass was reduced on soil amended with carvacrol, but only when the soil was also sterilized. Plants originating from sites where thyme produces essential oils containing mostly carvacrol had higher survival on soil treated with that monoterpene than plants originating from a site where thyme produced different types of terpenes, suggesting an adaptive response to the locally occurring terpene.Conclusions/SignificanceThe study shows that presence of soil microorganisms can alleviate the negative effect of a common thyme monoterpene on the performance of an associated plant species, emphasizing the role of soil microbes in modulating plant-plant chemical interactions.

Acaricidal activities of the active component of Lycopus lucidus oil and its derivatives against house dust and stored food mites (Arachnida: Acari)

Recent studies have focused on materials derived from plant extracts as mite control products against house dust and stored food mites because repeated use of synthetic acaricides had led to resistance and unwanted activities on non-target organisms. The aim of this study was to evaluate the acaricidal activity of materials derived from Lycopus lucidus against Dermatophagoides farinae, D. pteronyssinus and Tyrophagus putrescentiae. The LD50 values of L. lucidus oil were 2.19, 2.25 and 8.45 µg cm(-2) against D. farinae, D. pteronyssinus and T. putrescentiae. The acaricidal constituent of L. lucidus was isolated by chromatographic techniques and identified as 1-octen-3-ol. In a fumigant method against D. farinae, the acaricidal activity of 1-octen-3-ol (0.25 µg cm(-2)) was more toxic than N,N-diethyl-m-toluamide (DEET) (36.84 µg cm(-2)), followed by 3,7-dimethyl-1-octen-3-ol (0.29 µg cm(-2)), 1-octen-3-yl butyrate (2.32 µg cm(-2)), 1-octen-3-yl acetate (2.42 µg cm(-2)), 3,7-dimethyl-1-octene (9.34 µg cm(-2)) and benzyl benzoate (10.02 µg cm(-2)). In a filter paper bioassay against D. farinae, 1-octen-3-ol (0.63 µg cm(-2)) was more effective than DEET (20.64 µg cm(-2)), followed by 3,7-dimethyl-1-octen-3-ol (1.09 µg cm(-2)). 1-Octen-3-ol and 3,7-dimethyl-1-octen-3-ol could be useful as natural agents for the management of three mite species.

Long-term pre-exposure of the pest mite Tyrophagus putrescentiae to sub-lethal residues of bifenthrin on rapeseed did not affect its susceptibility to bifenthrin

Tyrophagus putrescentiae on rapeseed was exposed to a sub-lethal residue of 0.15 μg of bifenthrin per 100 g of rapeseed over 147 days, i.e. 14 generations. Every 21 days, samples of mites were collected and mortality was evaluated using a bifenthrin-treated filter paper bioassay. The sampled mites were also introduced onto newly-treated seeds. The susceptibility of the mites to bifenthrin remained similar after pre-exposure for all intervals from 21 to 147 days. The, LD 50 ranged from 0.16 to 1.14 μg of bifenthrin per cm 2 of filter paper. After 147 days, the rates of population increase and respiration of mites pre-exposed to the sub-lethal dose of bifenthrin were evaluated on bifenthrin treated (sub-lethal dose) and untreated rapeseed. Pre-exposure to bifenthrin had no significant effect on respiration, but influenced the rate of increase of mites on rapeseed: The mites pre-exposed to the sub-lethal dose of exhibited a higher rate of increase on the bifenthrin-treated rapeseed than on untreated rapeseed. Thus a decrease in the susceptibility of T. putrescentiae to bifenthrin with selection on a sub-lethal bifenthrin dose on rapeseed during up to 147 days of exposure during which the mite completed approximately 14 generations was not observed. However, the sub-lethal doses of bifenthrin stimulated the population growth and metabolic activity of the mites. Under such conditions, the production of hazardous proteins will probably be higher than on untreated rapeseed.

In vitro and field studies on the contact and fumigant toxicity of a neem-product (Mite-Stop®) against the developmental stages of the poultry red mite Dermanyssus gallinae

The acaricidal activity of the neem product MiteStop was investigated for its potential use as a botanical acaricide for the control of the poultry red mite Dermanyssus gallinae. This neem product is a special formulation of an extract of the seeds of the neem tree Azadirachta indica A. Juss. The efficacy was tested under laboratory conditions as well as in poultry houses. Four different methods of application were used in a filter paper bioassay to evaluate contact and vapour phase toxicity tests. The neem product proved to be already active in very small doses. In order to investigate the efficacy under field conditions, a poultry house was sprayed twice within a 7-day period using 1:33 and 1:50 diluted MiteStop. Cardboard traps were used to assess the mite population before, during and after the treatment. The mite population could be reduced by 89%. In a second poultry house, the spraying of defined areas with a 1:30, 1:33 or 1:50 dilution of the acaricide proved to be highly efficacious against all mite stages. Three other field trials proved that MiteStop is highly active against the red poultry mite. The most efficient dilution is 1:33 with tap water and spraying two or three times at intervals of 7 days.

Acaricidal Effects of Thymus vulgaris Leaf-derived Materials and Monoterpene Alcohols against Dermatophagoides spp.

Acaricidal activities of Thymus vulgaris leaf-derived materials were examined using a fumigant and filter paper bioassay and compared to those of monoterpene alcohols and the synthetic acaricide, benzyl benzoate. In the fumigant bioassay, the LD50 value of the T. vulgaris oil was 3.1 and 3.7 μg/cm2 against Dermatophagoides farinae and D. pteronyssinus, respectively. Active constituent of T. vulgaris leaves was purified by various chromatographies and identified as carvacrol by various spectra. When the relative toxicity against Dermatophagoides spp. was measured using a fumigant and filter paper bioassay, carvacrol was 4.1 to 8.0-fold more toxic than benzyl benzoate, but less toxic than β-citronellol. Specifically, in case of acaricidal activity of β-citronellol was 32.2 to 63.1-fold higher than that of benzyl benzoate against Dermatophagoides spp. Taken as a whole, the filter paper bioassay with all tested compounds leading to more effective acaricidal activity than the fumigant bioassay. In addition, the results of this study revealed that carvacrol and the two monoterpene alcohols (β-citronellol and borneol) were generally higher than those of commercial acaricides such as benzyl benzoate against the two mite species. These results indicate that carvacrol, β-citronellol, and borneol could be useful as a new preventive agent against damage caused by arthropod pests.

Toxicity of Kaempferia galanga rhizome-derived extract and steam distillate to Meloidogyne incognita juveniles and eggs, and their effects on Lycopersicon esculentum germination and growth

Abstract The toxicity of Kaempferia galanga rhizome-derived methanol extract (RME), powder (RP) and steam distillate (RSD) to Meloidogyne incognita second-stage juveniles (J2) and eggs, and their effects on Lycopersicon esculentum germination and growth were examined in vitro and in pot experiments. Results were compared with those of three nematicides: carbofuran, fosthiazate and metam sodium. In contact + fumigant bioassays with J2, RME applied at 1, 0.5 and 0.25 mg (g soil)–1 resulted in 92, 88 and 73% mortality, respectively. The lethality of RME was almost the same as carbofuran but lower than that of either fosthiazate or metam sodium. RSD and RP were less active than RME. In vapour-phase mortality bioassays with J2, the test materials were more effective in a closed container than in an open one, indicating that mode of delivery was, in part, a result of vapour action. In direct-contact mortality bioassays with M. incognita eggs, RME, RSD and fosthiazate treatments resulted in 91, 100 and 95% inhibition of hatch at 250 μg ml–1 and 82, 88 and 81% inhibition of hatch at 100 μg ml–1, respectively. In filter paper bioassays with L. esculentum seed, 8.8 μg cm–2 RME and RP did not cause germination inhibition, while RSD and fosthiazate treatments resulted in 84 and 13% germination inhibition. In pot tests, RME and RSD applied at 8 mg (g soil)–1 reduced galling caused by M. incognita significantly, and fosthiazate at 0.02 mg (g soil)–1 stopped galling completely. Kaempferia galanga rhizome-derived materials, particularly a methanol extract, merit further study as potential nematicides and hatching inhibitors for the control of M. incognita as fumigants with contact action.

Studies of Precocene I, Precocene II and Biogenic Amines on Formosan Subterranean Termite (Isoptera: Rhinotermitidae) Presoldier/Soldier Formation

The regulation of the soldier caste in termites involves a self-regulatory mechanism of negative feedback once a specific proportion is achieved. In this process, juvenile hormone (JH) plays an important role. Two groups of compounds with known JH regulatory functions in insects were tested for their effects on Coptotermes formosanus Shiraki soldier caste formation. One group was the antijuvenile hormone agents precocene I and precocene II. The other group was biogenic amines including dopamine, octopamine, serotonin and tyramine. Filter paper bioassays in Petri dishes showed that precocene I at 100 μg/dish significantly delayed the formation of the first presoldier and the first soldier. Additionally, precocene I significantly reduced the soldier proportion at 40 d after treatment as compared with controls. Precocene II had no effect. We also found no biogenic amine effect on termite soldier formation. These results may reflect the importance of precocene I in caste control and a reduced importance in bi...

Repellent activity of DEET against Amblyomma cajennense (Acari: Ixodidae) nymphs submitted to diferent laboratory bioassays

This study was developed to evaluate the repellent activity of N,N-diethyl-3-methylbenzamide (DEET) against Amblyomma cajennense nymphs. Two repellent bioassays were compared and the effective concentration and repellent time were calculated. The fingertip test was accomplished to evaluate in vivo four concentrations of the compound (0.200; 0.100; 0.050 and 0.025 mg.cm⁻²) and the filter-paper bioassay to evaluate in vitro the two highest concentrations.The compound provided repellence higher than 90% in all concentrations and at least 95% repellency in the highest concentration over 5 hours. The effective concentration against 50% of tested nymphs (EC50) was 0.006 mg.cm⁻² and the EC99 was 0.036 mg.cm⁻². Those concentrations were lower than the ones obtained against other tick species, denoting the effectiveness of DEET against A. cajennense. The repellency time against 50% of the ticks (RT50) was 4.8 hours and the RT90 was 2.7 hours. Both bioassays were adequate to evaluate A. cajennense repellency and provided similar results; however the in vivo test is more appropriate to estimate the effective concentration and repellency time.

Dynamics and mechanisms of permethrin resistance in a field population of the horn fly, Haematobia irritans irritans

AbstractA study was conducted at the Pressler ranch, near Kerrville, Texas, USA between 2002 and 2006 to determine the dynamics and mechanisms of resistance to permethrin in a field population of the horn fly, Haematobia irritans irritans (L.). Changes of resistance to pyrethroid insecticide associated with use of a pour‐on formulation of cyfluthrin in 2002 and use of diazinon ear tags in subsequent years were studied using a filter paper bioassay technique and a polymerase chain reaction assay that detects two sodium channel mutations, kdr and super‐kdr resistance alleles. A maximum of 294‐fold resistance to permethrin was observed in the summer of 2002. A significant decrease in the resistance level was observed in spring 2003, and resistance continued to decline after animals were treated with diazinon ear tags. In response to pyrethroid treatments, the allelic kdr and super‐kdr frequency increased from 56.3% to 93.8% and from 7.5% to 43.8%, respectively in 2002, and decreased significantly in 2003 when the pyrethroid insecticide was no longer used to treat animals. Females were found to have a higher allelic super‐kdr frequency than males in 2002, while no difference was detected between males and females in the allelic kdr frequency. There was a significant positive correlation between frequencies of the sodium channel mutations and levels of permethrin resistance, suggesting that the sodium channel mutations, kdr and super‐kdr, are the major mechanisms of resistance to pyrethroids in this horn fly population. Results of synergist bioassays also indicated possible contributions of two metabolic detoxification mechanisms, the mixed function oxidases (MFO) and glutathione S‐transferases (GST). Compared to a horn fly infestation of an untreated herd, treatments with the pyrethroid pour‐on formulation failed to control horn flies at the Pressler ranch in 2002. Sustained control of horn flies was achieved with the use of diazinon ear tags in 2003 and subsequent years.

Acaricidal properties of piperazine and its derivatives against house‐dust and stored‐food mites

Piperazine derivatives possess pharmacological properties, yet the acaricidal activity of these compounds has not been investigated. This study was conducted to evaluate the colour alteration and acaricidal activity of piperazine derivatives against Dermatophagoides spp. and Tyrophagus putrescentiae (Schrank) using filter paper and fumigant methods. In a fumigant bioassay, 1-phenylpiperazine (7.83 microg cm(-2)) against D. farinae (Hughes) was found to be 4.7 times more toxic than DEET (36.84 microg cm(-2)), followed by benzyl benzoate (9.72 microg cm(-2)), piperazine (11.41 microg cm(-2)), 1-ethoxycarbonylpiperazine (20.14 microg cm(-2)) and 1-(2-methoxyphenyl)piperazine (22.14 microg cm(-2)). In a filter paper bioassay, 1-(2-methoxyphenyl)piperazine (3.65 microg cm(-2)) was 5.7 times more toxic than DEET (20.64 microg cm(-2)), followed by 1-ethoxycarbonylpiperazine (4.02 microg cm(-2)), 1-phenylpiperazine (4.75 microg cm(-2)), benzyl benzoate (7.83 microg cm(-2)) and piperazine (10.59 microg cm(-2)). Similar results have been exhibited with piperazine derivatives against D. pteronyssinus (Troussart). However, no activity against T. putrescentiae was observed for piperazine derivatives, except for piperazine. These results indicate that piperazine derivatives may be suitable as vapour-phase acaricide fumigants owing to their high volatility, acaricidal activity and safety. 1-Phenylpiperazine was found to be an excellent mite indicator based on the colour change it induced. Taken together, these findings indicate that piperazine derivatives may be used to replace existing problematical acaricides owing to their activity and ability to act as a mite indicator.