Toxicity Of Fipronil Research Articles

Toxicity and hazard assessment of fipronil to Daphnia pulex

Hazard assessments based on two measures of toxicity were conducted for the water flea, Daphnia pulex (Leydig) exposed to the insecticide, fipronil. The measures of toxicity obtained were 48 h acute lethal concentration estimates, and a direct measure of population growth rate, the 10-day instantaneous rate of increase ( r i). Additionally, life tables were developed after exposure to several concentrations to tease out the apparent sublethal effects of this insecticide to D. pulex. The acute LC 50 was estimated to be 0.0156 (0.0088–0.083) mg/L. In the 10-day population growth rate study, extinction of D. pulex populations occurred after exposure to 0.08 mg/L of fipronil, which was equivalent to the 48 h acute LC 75. The NOEC and LOEC for population size after a 10-day exposure to fipronil were 0.03 and 0.05 mg/L, respectively. An expected environmental concentration (EEC) in freshwater lakes/ponds based on an application rate of 250 mg ai/ha (recommended rate for use in Tephritid fruit fly control programs) was estimated to be 0.00017 mg/L. Hazard assessments were developed by dividing the EEC by the LC 50 and NOEC for population size. The assessments based on the LC 50 and NOEC for population size were 0.011 and 0.0057, respectively, indicating that fipronil does not pose a hazard to D. pulex when applied at the rates recommended for control of Tephritid fruit flies. Life tables were developed after exposure to two insecticide concentrations and a control. Exposure to 0.015 mg/L, the approximate 48 h acute LC 50, resulted in only a slight decrease in the net reproductive rate ( R o), birth rate ( b), and intrinsic rate of increase ( r m) and an increase in generation time ( T), death rate ( d), and doubling time (DT) compared to the control. Exposure to 0.03 mg/L, the approximate 48 h acute LC 60, and NOEC in the 10-day study, resulted in a 57% decline in the net reproductive rate, a 1.45-fold decrease in birth rate, a 1.5-fold decrease in the intrinsic rate of increase, a 6-day increase in generation time, a 4-fold increase in death rate, and a 1.5-fold increase in doubling time. The stable age distribution (after 60 days) of D. pulex changed after exposure to fipronil. Increasing concentrations of fipronil resulted in a decrease in the percentage of individuals in the first, second, third, and fourth juvenile stages, an increase in the adult stage, and no change in the adolescent stage. These results indicate that certain concentrations of fipronil approaching the LC 50 can negatively affect population parameters of D. pulex, but that EECs, at least for fruit fly control, should be lower than the concentration necessary to cause damage.

Cross-resistance potential of fipronil in Musca domestica.

The toxicity of fipronil to insecticide-susceptible houseflies and the cross-resistance potential of fipronil were determined for six insecticide-resistant laboratory housefly strains by topical application and feeding bioassay. The insecticide-resistant strains represented different levels and patterns of resistance to pyrethroids, organophosphates, carbamates and organochlorines. Five strains were almost susceptible to fipronil in feeding bioassay with resistance factors at LC50 between 0.36 and 3.0. Four of these strains were almost susceptible to topically applied fipronil (resistance factors at LD50 were 0.55, 0.83, 3.3 and 2.5, respectively), whereas one strain was 13-fold resistant to topically applied fipronil. A highly gamma-HCH-resistant strain, 17e, was 430-fold resistant to fipronil in topical application bioassay and 23-fold resistant in feeding bioassay at LD50/LC50. We also tested the toxicity of fipronil in a feeding bioassay and gamma-HCH in topical application bioassay on thirteen housefly field populations. Eleven of the field populations had resistance factors for fipronil ranging from 0.98 to 2.4 at LC50, whereas two populations were 4.0- and 4.6-fold resistant to fipronil. The resistance level to gamma-HCH at LD50 in the field populations ranged from 1.8- to 8.1-fold. The two strains showing fipronil resistance were 3.4- and 8.1-fold resistant to gamma-HCH. Fipronil and gamma-HCH toxicities were positively correlated in the field populations. Biochemical assays of esterase, glutathione S-transferase and cytochrome P450 monooxygenase indicated that the low fipronil resistance observed in laboratory and field strains could be caused by elevated detoxification or be due to a target-site resistance mechanism with cross-resistance to gamma-HCH.

Fipronil effects on estuarine copepod (Amphiascus tenuiremis) development, fertility, and reproduction: a rapid life-cycle assay in 96-well microplate format.

Fipronil is a novel gamma-aminobutyric acid receptor-specific phenylpyrazole insecticide commonly used near estuarine environments for rice production, turf-grass management, and residential insect control. In this study, we evaluated the acute, developmental, and reproductive toxicity of fipronil to the estuarine harpacticoid copepod Amphiascus tenuiremis. Fipronil was highly toxic to A. tenuiremis (adult 96-h median lethal concentration [LC50] = 6.8 microg/L) and was more toxic to male copepods (96-h LC50 = 3.5 microg/L) than to nongravid female copepods (96-h LC50 = 13.0 microg/L). By using a newly developed 96-well microplate-based life-cycle toxicity test, we successfully reared single individuals of A. tenuiremis to adulthood in 200-microl microwells and concurrently assessed developmental and reproductive effects (after paired virginal matings) of environmentally relevant aqueous fipronil concentrations (0.16, 0.22, and 0.42 microg/L measured). Throughout the entire life cycle, copepod survival in all treatments was >90%. However, fipronil at 0.22 microg/L and higher significantly delayed male and female development from stage 1 copepodite to adult by approximately 2 d. More importantly, fipronil significantly halted female egg extrusion by 71% in the 0.22-microg/L fipronil treatment, and nearly eliminated reproduction (94% failure) in the 0.42-microg/L fipronil treatment. A three-generation Leslie matrix-based population growth model of fipronil reproductive and life-cycle impacts predicted a 62% decline in population size of A. tenuiremis relative to controls at only 0.16 microg/L.

Toxicity and pathogenicity of Metarhizium anisopliae var. acridum (Deuteromycotina, Hyphomycetes) and fipronil to the fringe‐toed lizard Acanthodactylus dumerili (Squamata: Lacertidae)

Reptiles in arid and semiarid zones are frequently exposed to insecticides sprayed to control locusts and grasshoppers. We evaluated the toxicity and pathogenicity of new biological and chemical control agents to the fringe-toed lizard Acanthodactylus dumerili in Mauritania, West Africa. A mycoinsecticide based on spores of the entomopathogenic fungus Metarhizium anisopliae var. acridum (isolate IMI 330189, Green Muscle) was tested at high challenge concentrations, using three exposure routes. Thirty-minute inhalation exposure to 3.9 x 10(8) viable conidia/L had no adverse effect. Locomotor activity, feeding activity, food consumption, body weight, and liver-to-body weight ratio were similar among treatments. Gross necropsy revealed no pulmonary lesions, hyphal mats, clumps of spores, or other abnormalities associated with fungal infections. Oral exposure to an oil-miscible flowable concentrate administered at approximately 10(7) viable conidia/g body weight had no effect on locomotor activity, food consumption, and body weight of survivors. However, two of the treated lizards died within one week of exposure. Feeding activity (sexes pooled) and relative liver mass of female survivors were significantly reduced. This was also observed in lizards treated with deactivated (nonviable) conidia, indicating an inherent toxicity of the formulation. Limited necropsy examination at four weeks posttreatment revealed that one lizard treated with viable spores had developed a pulmonary mycetoma that contained a clump of viable spores and fungal mycelium. The toxicity of mycotoxins was tested by feeding mycosed nymphs of desert locust Schistocerca gregaria to lizards. An average consumption of 231 mg (females) or 260 mg (males) nymphs/g body weight showed no adverse effect for any of the endpoints. No risk due to the pathogen is anticipated at recommended field application rates. The second agent tested was fipronil (Adonis), a phenylpyrazole insecticide. A single dose of 30 microg fipronil/g body weight was administered via contaminated prey or stomach instillation. The percentage of dead or moribund lizards at four weeks posttreatment was 62.5% in animals fed contaminated prey and 42.0% in gavaged animals. In both tests, survivors showed significantly reduced feeding activity, food consumption, body weight, and organ-to-body-weight ratios (liver and/or fat body). The high toxicity of fipronil to lizards was not previously known, suggesting that follow-up studies (e.g., subacute dietary tests) are needed to provide adequate data for risk assessment.

Toxicity, Repellency, and Horizontal Transmission of Fipronil in the Formosan Subterranean Termite (Isoptera: Rhinotermitidae)

Toxicity of fipronil was evaluated against field-collected Coptoteres formosanus Shiraki. In topical application assays, fipronil was highly effective against both workers and soldiers at very low doses. Acute toxicity after 24 h was significantly greater in workers than in soldiers. The LD50s were 2.59- and 2.91-fold greater with soldiers than with workers from the two tested colonies. The LD50s of fipronil at 72 h after treatment were <2.0 ng/insect, with no significant differences regarding the tested workers/soldiers or colonies. Treated soldiers placed with untreated workers significantly increased worker mortality. However, there was no significant horizontal transmission of fipronil from treated workers to untreated soldiers. Fipronil at rates of 0.063% or less showed no repellency, whereas sand treatments of 0.125% fipronil were repellent to termite workers.

Toxicity, Repellency, and Horizontal Transmission of Fipronil in the Formosan Subterranean Termite (Isoptera: Rhinotermitidae)

Toxicity, Repellency, and Horizontal Transmission of Fipronil in the Formosan Subterranean Termite (Isoptera: Rhinotermitidae)

Fipronil: environmental fate, ecotoxicology, and human health concerns.

Fipronil is a highly effective, broad-spectrum insecticide with potential value for the control of a wide range of crop, public hygiene, amenity, and veterinary pests. It can generally be applied at low to very low dose rates to achieve effective pest control. Application rates vary between 0.6 and 200 g a.i./ha, depending on the target pest and formulation. It belongs to the phenyl pyrazole or fiprole group of chemicals and is a potent disrupter of the insect central nervous system via interference with the gamma-aminobutyric acid (GABA-) regulated chloride channel. Fipronil degrades slowly on vegetation and relatively slowly in soil and in water, with a half-life ranging between 36 hr and 7.3 mon depending on substrate and conditions. It is relatively immobile in soil and has low potential to leach into groundwater. One of its main degradation products, fipronil desulfinyl, is generally more toxic than the parent compound and is very persistent. There is evidence that fipronil and some of its degradates may bioaccumulate, particularly in fish. Further investigation on bioaccumulation is warranted, especially for the desulfinyl degradate. The suitability of fipronil for use in IPM must be evaluated on a case-by-case basis. In certain situations, fipronil may disrupt natural enemy populations, depending on the groups and species involved and the timing of application. The indications are that fipronil may be incompatible with locust IPM; hence, this possibility requires further urgent investigation. It is very highly toxic to termites and has severe and long-lasting negative impacts on termite populations. It thus presents a long-term risk to nutrient cycling and soil fertility where termites are "beneficial" key species in these ecological processes. Its toxicity to termites also increases the risk to the ecology of habitats in which termites are a dominant group, due to their importance as a food source to many higher animals. This risk has been demonstrated in Madagascar, where two endemic species of lizard and an endemic mammal decline in abundance because of their food chain link to termites. Fipronil is highly toxic to bees (LD50 = 0.004 microgram/bee), lizards [LD50 for Acanthodactylus dumerili (Lacertidae) is 30 micrograms a.i./g bw], and gallinaceous birds (LD50 = 11.3 mg/kg for Northern bobwhite quail), but shows low toxicity to waterfowl (LD50 > 2150 mg/kg for mallard duck). It is moderately toxic to laboratory mammals by oral exposure (LD50 = 97 mg/kg for rats; LD50 = 91 mg/kg for mice). Technical fipronil is in toxicity categories II and III, depending on route of administration, and is classed as a nonsensitizer. There are indications of carcinogenic action in rats at 300 ppm, but it is not carcinogenic to female mice at doses of 30 ppm. The acute toxicity of fipronil varies widely even in animals within the same taxonomic groups. Thus, toxicological findings from results on standard test animals are not necessarily applicable to animals in the wild. Testing on local species seems particularly important in determining the suitability of fipronil-based products for registration in different countries or habitats and the potential associated risk to nontarget wildlife. Risk assessment predictions have shown that some fipronil formulations present a risk to endangered bird, fish, and aquatic and marine invertebrates. Great care should thus be taken in using these formulations where they may impact any of these endangered wildlife groups. Work in Madagascar has highlighted field evidence of this risk. The dose levels at which fipronil produces thyroid cancer in rats are very high and are unlikely to occur under normal conditions of use. There is also dispute as to whether this is relevant to human health risk. However, as fipronil is a relatively new insecticide that has not been in use for long enough to evaluate the risk it may pose to human health, from data on human exposure to the product, a precautionary approach may be warranted. The use of some fipronil-based products on domestic animals is not recommended where handlers spend significant amounts of time grooming or handling treated animals. In general, it would appear unwise to use fipronil-based insecticides without accompanying environmental and human health monitoring, in situations, regions, or countries where it has not been used before, and where its use may lead to its introduction into the wider environment or bring it into contact with people. Further work is needed on the impacts of fipronil on nontarget vertebrate fauna (amphibians, reptiles, birds, and mammals) in the field before the risk to wildlife from this insecticide can be adequately validated. Further field study of the effects of fipronil on the nutrient cycling and soil water-infiltration activities of beneficial termites is required to assess the ecological impacts of the known toxicity of fipronil to these insects.

Toxicity and Bioaccumulation of Fipronil in the Nontarget Arthropodan Fauna Associated with Subalpine Mosquito Breeding Sites

In order to examine ecological impact of fipronil use for larval culicine control in natural hydrosystems, toxicity and bioaccumulation of this new insecticide were analyzed on aquatic species representative of the nontarget arthropodan fauna (nonculicine larval Diptera: Chaoboridae, Chironomidae; planktonic Crustacea: Cladocera, Copepoda, Ostracoda) associated with target larval mosquito populations in the subalpine breeding sites. Standard toxicological bioassays using fipronil aqueous solutions from 1 to 2000 nM indicated different sensitivity levels among species. Insecticide bioaccumulation analyses, using [14C]fipronil solutions in simplified laboratory ecosystem, also indicated large differences among species. These differences may come from biological parameters characteristic of each species. Taking into account these nontarget effects of fipronil, a possible strategy of use of this insecticide for integrated mosquito control management was proposed, which is based upon selective dietary absorption of the insecticide by larval Culicidae.

Toxicity of fipronil and its degradation products to Procambarus sp.: field and laboratory studies.

Fipronil is a phenylpyrazole insecticide that is the active ingredient in the pesticide Icon 6.2 FS which is applied to rice seeds targeting the rice water weevil. An arthropod-selective insecticide, fipronil blocks the GABA-gated chloride channel and is unique in that several of its degradation products have been indicated to be equal or more potent than fipronil. After application of rice seeds (2-3 days postplant) to flooded rice fields, water is typically pumped from the rice fields and can be used for the culture of crayfish (Procambarus sp.). Because fipronil is selective for arthropods, is transported via organic sediment, and crayfish consume organic sediment, 96-h LC(50) experiments were conducted with fipronil and three of its environmental derivatives in crayfish under conditions without carrier solvents in water of similar pH, alkalinity, and hardness as observed in south Louisiana crayfish culture ponds. Measured LC(50)s for fipronil to red swamp (Procambarus clarkii) and white river (Procambarus zonangulus) crayfish were 14.3 (95% CI; 5.1-23.4) and 19.5 (95% CI; 11.1-27.9) microg/L, respectively. LC(50)s of fipronil sulfone (11.2; 9.2-13.2 microg/L), fipronil sulfide (15.5; 13-18 microg/L); and the photoproduct, desulfinyl fipronil (68.6; 46-95.2 microg/L) displayed very high toxicity in crayfish. In situ toxicity studies using caged crayfish in culturing ponds receiving effluent from drained rice fields indicated that effluent from rice fields planted with Icon-treated seed was significantly more toxic compared to untreated surface water (40% survival compared to 83% survival). Hazard quotient comparisons using measured water concentrations in the field and laboratory-based LC(50)s indicated that fipronil and its metabolites in water resulting from Icon-treated rice seed planting poses a significant risk to crayfish survival.

Toxicity and Neurophysiological Effects of Fipronil and Its Oxidative Sulfone Metabolite on European Corn Borer Larvae (Lepidoptera: Crambidae)

The phenylpyrazole insecticide fipronil is the first compound of its class to be registered for commercial use. The mode of action of this class of insecticides involves antagonism of the inhibitory neurotransmitter, γ-aminobutyric acid (GABA). The sulfone metabolite of fipronil has been reported to be similar in toxicity to the parent compound. In this study, the toxicity and neurophysiological effects of fipronil and the sulfone metabolite were determined for European corn borer larvae. Fipronil was very toxic to neonate European corn borer larvae in feeding bioassays (LC50 = 3.34 ng a.i./cm2 of treated diet) and to fifth instars in topical bioassays (LD50 = 18.78 ng/insect). The sulfone metabolite was slightly more toxic to neonate larvae (LC50 = 1.44 ng a.i./cm2) and equally toxic to fifth instar larvae (LD50 = 19.54 ng/insect) compared with the parent compound. Neonate larvae preexposed to piperonyl butoxide (PBO) residues coated on the inside of glass scintillation vials for 6 h at 100 μg/vial resulted in significant antagonism of fipronil toxicity (LC50 = 4.39 ng a.i./cm2), whereas preexposure to PBO at 1 μg/vial had no effect (LC50 = 2.91 ng a.i./cm2). Fifth instars topically treated with 10 μg of PBO caused significant antagonism of fipronil toxicity (LD50 = 34.41 ng/insect). Electrophysiological recordings of spontaneous electrical activity were conducted on isolated ventral nerve cords from fifth instar larvae. Results from these experiments indicate that fipronil and its sulfone metabolite both reverse the inhibitory effect of GABA on spontaneous electrical activity. Fipronil, however, caused an increase in spontaneous electrical activity relative to that of the sulfone metabolite.

Palatability and toxicity of fipronil as a systemic insecticide in a bromadiolone rodenticide bait for rat and flea control.

Vector control in plague-infested areas requires a simultaneous killing of rodents and their fleas. We investigated the efficacy of a combination of a systemic insecticide, fipronil, in a rodenticide bait formulation under laboratory conditions. Four different concentrations of fipronil (0.05%, 0.005%, 0.0005% with acetone as a solvent, and 0.05% with propylene glycol as a solvent) and two controls (solvents only) were combined with the rodenticide bait (crushed organically grown wheat with 0.005% bromadiolone). Each concentration was offered together with an untreated non-poisonous challenge bait to 10 singly caged Rattus rattus L., each with 100 rat fleas Xenopsylla cheopis Rothschild (Siphonaptera: Pulicidae) in the nest. Treated bait consumption was relatively low and an unsatisfactory rat mortality of around 50% only was obtained in all tests. The palatability of the bait, however, was not affected by the fipronil concentration. Even at the lowest fipronil concentration, average flea mortality was still above 95%, and doses of more than I mg fipronil per kg rat body weight gave a nearly complete kill of fleas. Fipronil can be highly effective as a systemic insecticide to for flea control, provided that a more attractive bait base for roof rats is used.

The Toxicological Effects and Bioaccumulation of Fipronil in Larvae of the Mosquito Aedes aegypti in Aqueous Medium

The toxicity and bioaccumulation kinetics of fipronil were analyzed on fourth instar larvae of an Aedes aegypti laboratory strain in order to investigate the possible use of this new phenylpyrazole insecticide in the aquatic medium. Standard bioassays indicate that larvae fed with maize flour on which the fipronil has accumulated are about three times more susceptible to fipronil than unfed larvae because fed larvae ingest considerably more fipronil than unfed larvae. Bioaccumulation kinetic analysis, comparatively performed in simplified experimental microcosms, using [14C]fipronil solutions against dead larvae and living unfed larvae treated or not by Triton X-100, suggests that the insecticide penetrates mainly through the integument but also through the gut. This digestive route of fipronil accumulation is enhanced by feeding, suggesting that ingestion be the main and most selective way of insecticide administration to mosquito larvae. These biological effects of fipronil may offer a possible strategy of use of this insecticide in larval mosquito control.

Oral Toxicity of Abamectin, Boric Acid, Fipronil, and Hydramethylnon to Laboratory Colonies of Argentine Ants (Hymenoptera: Formicidae)

Comprehensive laboratory baiting studies with the 4 insecticides abamectin, boric acid, fipronil, and hydramethylnon were conducted against Argentine ant, Linepithema humile (Mayr). Serial dilutions of each insecticide prepared in a 25% sucrose solution were provided for 24 h or 14 d to groups of workers and queens. Sucrose-water baits containing 1 x 10(-5)% fipronil and 0.1% hydramethylnon provided complete mortality of L. humile workers baited for 24 h. Baits containing 1 x 10(-4) and 1 x 10(-5)% fipronil provided 100% kill of queens. In the continuous baiting, 0.5% boric acid, 1 x 10(-6)% fipronil, and 0.025% hydramethylnon provided 100% mortality of workers. The queens and workers provided baits containing 1 x 10(-5)% fipronil and 0.5% boric acid all died within 14 d. Low concentrations of fipronil and boric acid in sucrose may be promising candidates for Argentine ant control.

Fipronil metabolism, oxidative sulfone formation and toxicity among organophosphate- and carbamate-resistant and susceptible western corn rootworm populations

Fipronil toxicity and metabolism were studied in two insecticide-resistant, and one susceptible western corn rootworm (Diabrotica virgifera virgifera, LeConte) populations. Toxicity was evaluated by exposure to surface residues and by topical application. Surface residue bioassays indicated no differences in fipronil susceptibility among the three populations. Topical bioassays were used to study the relative toxicity of fipronil, fipronil + the mono-oxygenase inhibitor piperonyl butoxide, and fipronil's oxidative sulfone metabolite in two populations (one resistant with elevated mono-oxygenase activity). Fipronil and fipronil-sulfone exhibited similar toxicity and application of piperonyl butoxide prior to fipronil resulted in marginal effects on toxicity. Metabolism of [14C]fipronil was evaluated in vivo and in vitro in the three rootworm populations. In vivo studies indicated the dominant pathway in all populations to be formation of the oxidative sulfone metabolite. Much lower quantities of polar metabolites were also identified. In vitro studies were performed using sub-cellular protein fractions (microsomal and cytosolic), and glutathione-agarose purified glutathione-S-transferase. Oxidative sulfone formation occurred almost exclusively in in vitro microsomal reactions and was increased in the resistant populations. Highly polar metabolites were formed exclusively in in vitro cytosolic reactions. In vitro reactions performed with purified, cytosolic glutathione-S-transferase (MW = 27 kDa) did not result in sulfone formation, although three additional polar metabolites not initially detectable in crude cytosolic reactions were detected. Metabolism results indicate both cytochromes P450 and glutathione-S-transferases are important to fipronil metabolism in the western corn rootworm and that toxic sulfone formation by P450 does not affect net toxicity. © 2000 Society of Chemical Industry

Secondary transmission of fipronil toxicity between Oriental cockroachesBlatta orientalis L in arenas

Mixed colonies of adult male and female Oriental cockroaches were conditioned to a 12:12 h photocycle in arenas (0.23 m2) with a harbourage, food and water and then exposed to deposits (30 mg or 2 × 30 mg) of 0.5 g kg−1 fipronil gel bait at the beginning of a dark phase. The bait was rapidly consumed by the first sub-group of insects to emerge from the harbourage; any residual bait was removed from the arenas 4 h into the following light phase. Third-instar nymphs were then introduced and mortality was monitored over the subsequent 14 days with all cadavers left in situ. Death of cockroaches under these conditions was due to direct poisoning of the sub-group of the adults that consumed the bait and to secondary transfer of toxicity to the remainder of the adult and to the nymphal populations. Mean mortality in the adult populations increased to > 96% (females) and > 53% (males) with consistently higher mortality of females than males; that in the third-instar nymph (unexposed) populations increased to 25–50%. Some cadavers were wholly or partially eaten by other cockroaches during this period, and this was interpreted as the major mechanism of secondary transfer of toxicity. Individual adult females were fed weighed bait deposits (10 mg) and, following death (24 h), the cadavers were transferred to closed containers held at 33%, 52% or 76% relative humidity /28 °C for periods of up to 7 weeks. They were then added individually to groups of five adult females provided with water but no alternative food source. Mean mortalities (>64% at 1 week and > 96% at 7 weeks) were not significantly lower than mean mortalities produced by freshly poisoned cockroaches, showing that no loss in the insecticidal activity of the cadavers occurred under these storage conditions. The potential of necrophagy to supplement the primary action of fipronil bait treatment of Oriental cockroach infestations by inhibiting colony redevelopment is discussed. © 2000 Society of Chemical Industry

Efficacy and Degradation of Fipronil Applied to Cotton for Control of Anthonomus grandis grandis (Coleoptera: Curculionidae)

Fipronil was applied to cotton by ground sprayer at ultralow volume and conventional spray rates. Boll weevil mortality and residue analysis of fipronil and its metabolites at 0,1, 2, 3, and 6 d after application were used to evaluate treatments. An evaluation of the toxicity of fipronil and metabolites to boll weevils also was conducted. The order of toxicity (LD 50 ) of fipronil metabolites at 48 h was sulfide > fipronil > sulfone > desulfinyl. Differences in percentage of mortality between treatments did not occur until 3 d after application when the ultralow volume application had higher mortality (98%) than the conventional (85%) spray rate. There were no differences in mortality between treatments at 6 d after application. Fipronil residues were present on the leaf surface longer and in higher amounts when applied in cottonseed oil at 1.17 liter/ha than when applied in water as a conventional application at 97 liter/ha.

Genetic and biochemical mechanisms limiting fipronil toxicity in the LPR strain of house fly,Musca domestica

Genetic and biochemical mechanisms limiting fipronil toxicity in the LPR strain of house fly,Musca domestica

Genetic and biochemical mechanisms limiting fipronil toxicity in the LPR strain of house fly, Musca domestica

Genetic and biochemical mechanisms limiting fipronil toxicity in the LPR strain of house fly, Musca domestica

Field and laboratory tests of the effects of fipronil on adult female bees of Apis mellifera, Megachile rotundata and Nomia melanderi

SUMMARYThe toxicity of fipronil (5-amino-1[2,6-dichloro- 4(trifluoromethyl)phenyl-4(trifluorormethyl) sulfinyl]-1H-pyrazola-3-carbonitrate), to adult female bees was least to the alkali bee, Nomia melanderi, (LD50 = 1.130 pg/bee), intermediate to the honey bee, Apis mellifera, (0.013 μg/bee) and greatest to the alfalfa leafcutter bee, Megachile rotundata, (0.004 pg/bee), both in topical tests and tests involving fipronil residues on alfalfa (Medicago sativa) foliage. Adding an adjuvant to fipronil sprays changed the toxicity of fipronil to bees in residue bioassay studies with varying results with adjuvant and species of bee. Fipronil at 100 ppm and 500 ppm in feeders containing a sucrose/honey syrup caused a significant reduction in honey bee visitation. Spraying fipronil at 0.014 or 0.028 kg a.i./ha on flowering canola (Brassica napus cv. Legend) did not cause significant mortality of adult honey bees or reduce bee visitation.

Toxicity and neurophysiological effects of fipronil and fipronil sulfone on the western corn rootworm (Coleoptera: Chrysomelidae)

Fipronil is a member of the relatively new phenylpyrazole insecticide class that is active at the neuro-inhibitory gamma amino butyric acid (GABA)-gated chloride channel/ionopore complex. The toxicity and neurophysiological effects of fipronil and its oxidative sulfone metabolite [5-amino-1-(2,6-dichloro-4-trifluoromethylphenyl)-3-cyano-4-trifluoromethylsulfonylpyrazole] were investigated by using an insecticide-susceptible western corn rootworm population. In topical bioassays using adult rootworms, fipronil was toxic at very low doses (LD50 = 0.07; LD90 = 0.33 ng/mg). At the LD90, pre-treatment with the cytochrome P450 monooxygenase inhibitor piperonyl butoxide led to mild antagonism of fipronil toxicity (LD90 = 0.42 ng/mg), while the sulfone analog had greater toxicity (LD90 = 0.22 ng/mg). In neurophysiological studies of spontaneous electrical activity, adult and larval rootworms were equally affected by fipronil and the sulfone analog at 10 μM (in the presence of 5 mM GABA) in comparison to GABA-treated baselines. Using larval rootworms, insensitivity of the GABA receptor to binding by picrotoxinin or dieldrin (10 μM ) was not apparent in the presence of 5 mM GABA. Further neurophysiological investigation using a range of concentrations (0.625–20.0 μM) on larval rootworms indicated concentration-dependent effects on bursting activity for both fipronil and the sulfone analog; however, subtle differences were observed between these two compounds. Results indicate that both fipronil and its oxidative sulfone metabolite have similar toxicological and neurological effects on rootworms. Arch. Insect Biochem. Physiol. 40:150–156, 1999. © 1999 Wiley-Liss, Inc.