Biomedical subjects

Michael E Scharf

Publications and source records attributed to Michael E Scharf.

At least 19 recordsLinked to original sources

PubMed2007

Hexamerin-based regulation of juvenile hormone-dependent gene expression underlies phenotypic plasticity in a social insect.

Worker termites of the genus Reticulitermes are temporally-arrested juvenile forms that can terminally differentiate into adultsoldier- or reproductive-caste phenotypes. Soldier-caste differentiation is a developmental transition that is induced by high juvenile hormone (JH) titers. Recently, a status quo hexamerin mechanism was identified, which reduces JH efficacy and maximizes colony fitness via the maintenance of high worker-caste proportions. Our goal in these studies was to investigate more thoroughly the influences of the hexamerins on JH-dependent gene expression in termite workers. Our approach involved RNA interference (RNAi), bioassays and quantification of gene expression. We first investigated the expression of 17 morphogenesis-associated genes in response to RNAi-based hexamerin silencing. Hexamerin silencing resulted in significant downstream impacts on 15 out of the 17 genes, suggesting that these genes are members of a JH-responsive genomic network. Next, we compared gene-expression profiles in workers after RNAi-based hexamerin silencing to that of (i) untreated workers that were held away from the colony; and (ii) workers that were also held away from the colony, but with ectopic JH. Here, although there was no correlation between hexamerin silencing and colony-release effects, we observed a significant correlation between hexamerin silencing and JH-treatment effects. These findings provide further evidence supporting the hypothesis that the hexamerins modulate JH availability, thus limiting the impacts of JH on termite caste polyphenism. Results are discussed in a context relative to outstanding questions on termite developmental biology, particularly on regulatory gene networks that respond to JH-, colony- and environmental-cues.

Animals↗

PubMed2006

Social exploitation of hexamerin: RNAi reveals a major caste-regulatory factor in termites.

Lower termites express a unique form of eusocial polyphenism in that totipotent workers can differentiate into either soldier or reproductive caste phenotypes. In this initial effort using RNA interference in termites, we found that two hexamerin genes, Hex-1 and Hex-2, participate in the regulation of caste polyphenism. Our methodology involved a dual gene-silencing approach that used a single short-interfering RNA fragment to silence the two homologous hexamerin genes. We performed validation studies that evaluated effects on nontarget housekeeping genes, silencing of a nonhousekeeping control gene, and effects at the protein level. We found that the two hexamerin proteins, which are inducible by the morphogenetic juvenile hormone and which constitute a significant proportion of total termite protein, suppress juvenile-hormone-dependent worker differentiation to the soldier caste phenotype. This mechanism allows termite colonies to retain high proportions of altruistic worker caste members, thus apparently enhancing colony-inclusive fitness. These findings demonstrate a unique status quo regulatory mechanism for termite worker caste retention and provide an example of previously undescribed preadult developmental/caste-regulatory genes from any social insect.

Amino Acid Sequence↗

PubMed2006

Evaluation of volatile low molecular weight insecticides using Drosophila melanogaster as a model.

Volatile insecticides, otherwise known as fumigants, have numerous uses in pest control and integrated pest management. Fumigants have been broadly applied in the protection of stored agricultural commodities and also in the elimination of structural pest infestations. However, fumigants have so far been mostly overlooked for use in management of public health pests such as flies and mosquitoes. This paper reports information on the development of a volatility bioassay for use in evaluating volatile insecticides against dipteran insects and on the use of this bioassay to compare the relative efficacy of 30 candidate compounds to Drosophila melanogaster Meig. The findings revealed seven highly effective insecticidal compounds, which include three heterobicyclics (menthofuran, thiophene and coumaran) and four formate esters [butyl, hexyl and heptyl formate and ethylene glycol diformate (EGDF)]. Ethyl formate, a compound previously identified as being a highly effective fumigant against coleopteran stored product pests, caused toxicity in Drosophila but was not as effective as other tested formates. Two volatile fumigant insecticides, dichlorvos (DDVP) and methyl isothiocyanate (MITC), were also tested as positive controls. Both of these volatile standards were significantly more toxic than the seven most effective of the novel compounds. Finally, regression analyses revealed that volatility is not entirely predictive of acute toxicity and that other structural features should be considered when designing and synthesizing volatile insecticidal compounds for future study.

Animals↗

PubMed2006

Genetic basis for resistance to gel baits, fipronil, and sugar-based attractants in German cockroaches (Dictyoptera: blattellidae).

A gel bait-resistant Blattella germanica (L.) strain (Cincy) was collected in Cincinnati, OH, in 2003. This strain exhibited strong behavioral resistance to Avert (0.05% abamectin), Maxforce FC (0.01% fipronil), and Pre-Empt (2.15% imidacloprid) gel baits. Reciprocal mass crosses and back crosses between the Cincy strain and a susceptible strain (Jwax) were made and tested for their inheritance of resistance to Avert, Maxforce FC, and Pre-Empt gel baits. Topical assays comparing the parental and reciprocal-heterozygous strains indicated the resistance to fipronil was incompletely recessive. LD50 and LD50 values of the Jwax male x Cincy female strain were not significantly different from he Jwax female x Cincy male strain, suggesting no sex linkage in physiological fipronil resistance. Feeding assays revealed that F1 reciprocal crosses were significantly less responsive to blank Avert and Maxforce FC baits (without active ingredients) than the susceptible strain. The Jwax female x Cincy male strain did not display significantly greater consumption of blank Avert and Maxforce FC baits relative to the Jwax male x Cincy female strain. In feeding assays with agar containing D-fructose, D-galactose, D-glucose, D-lactose, D-maltose, and D-sucrose, the crosses showed an intermediate feeding response to glucose compared with the Cincy and Jwax strains, and a similar response to other sugars compared with the Jwax strain. The Jwax male x Cincy female strain was significantly less responsive to glucose than the Jwax female x Cincy male strain. Mortality induced by Avert, Maxforce FC, and Pre-Empt gel baits against the F6 Jwax male x Cincy femaale strain was 44.2 +/- 6.8, 92.9 +/- 2.1, and 78.7 +/- 5.2%, respectively, indicating the resistance to Avert and Pre-Empt gel baits inherited by Cincy females was extremely stable. The F6 Jwax male x Cincy female strain was significantly more resistant to Avert, Maxforce FC, and Pre-Empt than the F6 Jwax female x Cincy male strain. These findings suggest that behavioral resistance to gel baits has weak sex-linkage, with a greater degree of the resistance trait being inherited by female cockroaches. Alternatively, physiological resistance to fipronil has no sex-linkage, but it is nonetheless important to the complete resistance phenotype.

Animals↗

PubMed2005

Immunological assessment of an insecticide resistance-associated esterase in the Western corn rootworm.

In previous investigations, we have determined that organophosphate resistance in the western corn rootworm, Diabrotica virgifera virgifera, is at least partially attributed to a group of non-specific carboxylesterases referred to as group II. Antiserum raised against a purified 66-kDa group II esterase is specific for the denatured enzyme. This antiserum reacts similarly with both beetle homogenates from resistant and susceptible populations, although there is much higher signal intensity in immunoblots of resistant relative to susceptible beetles. These results suggest that overproduction of group II esterases is the underlying basis of esterase-mediated resistance in D. v. virgifera by demonstrating that (1) group II esterases are immunologically indistinguishable between the resistant and susceptible populations, and (2) the intensity differences are due to increased group II esterase proteins in the resistant population. The diagnostic potential of immunological-based assays was tested with a traditional diagnostic concentration bioassay and a biochemical-based native PAGE assay. Significant correlations were observed among all three diagnostic assays (regression coefficients ranging from 0.95 to 0.96). These results demonstrate the importance of the 66-kDa protein as a resistance-associated biochemical marker, thus emphasizing the potential for 66-kDa protein-targeted immunoassays in resistance monitoring programs.

Animals↗

PubMed2005

Profiling of abundant proteins associated with dichlorodiphenyltrichloroethane resistance in Drosophila melanogaster.

Dichlorodiphenyltrichloroethane (DDT) metabolism-based resistance in Drosophila melanogaster is a complex metabolic system associated with the transcription of detoxification related genes, ion transport, lipid and sugar metabolism pathways. However, little is known about the differences regarding the proteome of field- and laboratory-selected resistant Drosophila genotypes. We investigated the impact of DDT resistance in the abundant proteome of field- and laboratory- selected resistant Drosophila using a two-dimensional gel electrophoresis DDT reference map. Proteomic profiling was performed in two DDT susceptible genotypes (Canton-S and 91-C) and three DDT resistant lines (Rst(2)DDT(91-R), Rst(2)DDT(Wisconsin) and Rst(2)DDT(Hikone-R)). Protein spots were stained with Coomassie blue and compared using PDQuest software. Selected protein spots were cut out and analyzed using matrix assisted laser desorption-time of flight mass spectrometry. Querying the NCBInr. 10.21.2003 database with mass spectrometric data yielded the identity of 21 differentially translated proteins in Rst(2)DDT(91-R), Rst(2)DDT(Wisconsin) and Canton-S representing proteins putatively involved in biochemical pathways such as glycolysis and gluconeogenesis, the pentose phosphate pathway, the Krebs cycle and fatty acid oxidation. We hypothesize that both strategies are aimed to use of the pentose phosphate pathway to increase glucose utilization while Rst(2)DDT(91-R) relies primarily on glycolysis to produce reduced NADP and increase DDT detoxification. DDT exposure in Canton-S induced six proteins, while four proteins were repressed in Rst(2)DDT(Hikone-R). Our data suggest that insecticide resistance appears to impact different metabolic pathways in Drosophila genotypes selected with the same pesticide (DDT).

Animals↗

PubMed2005

Effects of juvenile hormone III on Reticulitermes flavipes: changes in hemolymph protein composition and gene expression.

Termites express polyphenism during caste differentiation that is mostly undefined at the molecular level. Using the eastern subterranean termite, Reticulitermes flavipes Kollar, we wanted (1) to test juvenile hormone (JH) model assays for their ability to induce detectable molecular changes in worker termites and (2) to investigate hemolymph proteins and their corresponding genes during JH-induced soldier caste differentiation. Our results illustrate pronounced changes in two hemolymph proteins after JH treatment, as well as differences among several caste phenotypes. Significant increases in the expression of four genes encoding hemolymph proteins, including two vitellogenins and two hexamerins, were observed after JH exposure. These findings are the first to demonstrate such protein and gene expression changes during termite caste differentiation. These results also validate the utility of JH model assays for inducing detectable molecular changes in worker termites that have begun presoldier differentiation.

Animals↗

PubMed2005

Efficacy of simulated barrier treatments against laboratory colonies of Pharaoh ant.

Five selected insecticides were applied to four substrates and evaluated in laboratory studies for repellency and toxicity against the Pharaoh ant, Monomorium pharaonis (L.). We tested both repellent and nonrepellent formulations on outdoor (concrete and mulch) and indoor (ceramic and vinyl) substrates. Repellency was evaluated using a behavioral bioassay in which colonies were given a choice to leave the treated zone and move into empty nests provided in the untreated zone. We used a novel experimental design whereby ants walked on a Slinky coil suspended from a metal support frame, thus permitting a long foraging distance with a minimum use of space and resources. Cypermethrin, a repellent pyrethroid insecticide, resulted in colony budding, although the response was delayed. Toxicity of insecticides was evaluated as worker, queen, and brood mortality. The most effective treatment was fipronil, which provided 100% reduction in pretreatment activity by 2 d posttreatment on both concrete and mulch. Chlorfenapyr was highly effective on both outdoor and indoor substrates. Significant substrate effects were observed with insecticides applied to nonabsorbent substrates (ceramic tile), which performed better than insecticides applied to absorbent substrates (vinyl tile). Other highly absorbent materials (mulch and concrete), however, did not reduce insecticide efficacy. This is because ants relocated nests into and/or under these attractive nesting materials, thus increasing their exposure to toxic insecticide residues. Our results demonstrate efficacy of nonrepellent liquid insecticides as indoor treatments for the control of Pharaoh ants and possibly as exterior perimeter treatments.

Absorption↗

PubMed2005

Impacts of soil moisture level on consumption and movement of three sympatric subterranean termites (Isoptera: Rhinotermitidae) in a laboratory assay.

Three subterranean termite species, Reticuliternes flavipes (Kollar), Reticulitermes tibialis Banks, and Reticulitermes virginicus (Banks), were collected from locations in northern Indiana and tested under laboratory conditions to determine whether preferential differences exist among species. Foraging behaviors and location of all three species were studied using a linear, three-dimensional assay with a soil moisture gradient (5, 15, 25, 35, 45, and 55% moisture by weight) and quantified by (1) consumption weights and (2) location counts. In a 7-d period, R. flavipes and R. tibialis consumed almost twice as much filter paper as R. virginicus. No significant difference in feeding was attributed to moisture level for R. tibialis, but there were differences for R. flavipes and R. virginicus. In terms of location of harborage, there were clear patterns associated with moisture level, as predicted using a Poisson distribution. Results from consumption and location data show unique patterns among species, and illustrate species-specific variation in feeding location and nesting preference in response to moisture. There are significant differences in movement patterns, consumption, and mortality among Indiana Reticulitermes according to the laboratory assay. These findings contribute to the overall understanding of midwestern Reticulitermes termites.

Animals↗

PubMed2004

Catalytic activity and expression of two flavin-containing monooxygenases from Drosophila melanogaster.

Two flavin-containing monooxygenase genes occur in the Drosophila genome (named DmFMO-1 and DmFMO-2). Differences exist between these two FMOs in: (1) genomic DNA architecture and predicted post-translational modifications; (2) recombinant protein solubility, activity, and absorbance spectra; and (3) subcellular distribution and developmental transcription/translation profiles in wildtype flies. Characteristic FAD absorbance spectra and strong catalytic competence in methimazole sulfoxidation were observed for recombinant DmFMO-2. Alternatively, weak sulfoxidation was observed for DmFMO-1, which correlated with reduced solubility in the recombinant system. Western blot analyses using specific antisera raised to each FMO showed the two FMOs to be immunologically distinct. In addition, Western blot analyses revealed FMO protein expression in both the microsomal and cytosolic sub-cellular fractions. Interestingly, a larger form of DmFMO-1 occurs in the cytosol that is most strongly expressed in the adult head. These findings suggest divergent physiological roles for DmFMO-1 and DmFMO-2. More specifically, it appears that DmFMO-1 has a distinct developmental role, while DmFMO-2 may have a general housekeeping function.

Amino Acid Sequence↗

PubMed2004

Phylogenetic relationships of nearctic Reticulitermes species (Isoptera: Rhinotermitidae) with particular reference to Reticulitermes arenincola Goellner.

DNA sequence comparisons of the mitochondrial COII, 16S, and 12S rRNA genes were used to infer phylogenetic relationships among the six known US Reticulitermes species (Reticulitermes flavipes, Reticulitermes arenincola, Reticulitermes tibialis, Reticulitermes hageni, Reticulitermes virginicus, and Reticulitermes hesperus) and the closely related European species Reticulitermes santonensis. The interspecific pairwise sequence divergence, based on uncorrected "p" distance, varied up to 10% across the COII, 4.9% across the 16S, and 3% across the 12S fragments. Phylogenetic trees were constructed using maximum parsimony, likelihood, and distance methods. The combined results suggest several phylogenetic relationships including: (i) R. flavipes, R. arenincola, and European R. santonensis are possibly conspecific; (ii) R. virginicus and R. hageni are closely related species; and (iii) R. tibialis and R. hesperus are closely related species. Interestingly, while there is apparent synonymity between R. flavipes and R. arenincola by DNA sequence, there are clear morphological differences in the soldier caste. This finding suggests a combination of molecular and morphological approaches are necessary for accurate species identification. These data lend resolution to the complex problem of Reticulitermes systematics, and will assist future efforts directed toward characterizing species distribution and ecology.

Animals↗

PubMed2004

Impacts of residual insecticide barriers on perimeter-invading ants, with particular reference to the odorous house ant, Tapinoma sessile.

Three liquid insecticide formulations were evaluated as barrier treatments against perimeter-invading ants at a multifamily housing complex in West Lafayette, IN. Several ant species were present at the study site, including (in order of abundance) pavement ant, Tetramorium caespitum (L.); honey ant, Prenolepis imparis (Say); odorous house ant, Tapinoma sessile (Say); thief ant, Solenopsis molesta (Say); acrobat ant, Crematogaster ashmeadi (Mayr); crazy ant, Paratrechina longicornis (Latrielle), field ants, Formica spp.; and carpenter ant Camponotus pennsylvanicus (DeGeer). Studies began in May 2001 and concluded 8 wk later in July. Individual replicate treatments were placed 0.61 in (2 feet) up and 0.92 m (3 feet) out from the ends of 46.1 by 10.1-m (151 by 33-foot) apartment buildings. Ant sampling was performed with 10 placements of moist cat food for 1 h within treatment zones, followed by capture and removal of recruited ants for later counting. All treatments led to substantial reductions in ant numbers relative to untreated controls. The most effective treatment was fipronil, where 2% of before-treatment ant numbers were present at 8 wk after treatment. Both imidacloprid and cyfluthrin barrier treatments had efficacy comparative with fipronil, but to 4 and 2 wk, respectively. Odorous house ants were not sampled before treatment. Comparisons of ant species composition between treatments and controls revealed an increase in odorous house ant frequencies at 1-8 wk after treatment in treated locations only. These results demonstrate efficacy for both nonrepellent and repellent liquid insecticides as perimeter treatments for pest ants. In addition, our findings with odorous house ant highlight an apparent invasive-like characteristic of this species that may contribute to its dramatic increase in structural infestation rates in many areas of the United States.

Animals↗

PubMed2004

Behavioral and physiological resistance of the German cockroach to gel baits (Blattodea: Blattellidae).

A gel bait-resistant German cockroach, Blattella germanica (L.), strain Cincy was collected in Cincinnati, OH. This strain exhibited a high level of behavioral resistance to Avert (0.05% abamectin) and Maxforce FC (0.01% fipronil) gel baits. Topical application assays indicated moderate levels of physiological resistance of the Cincy strain to abamectin and fipronil. Resistance ratios (based on LD50 values from topical applications) to abamectin and fipronil were 2.5 and 8.7, respectively. The Cincy strain of had a significantly lower LD50 value to abamectin than a nonaverse field strain (Dorie) and similar LD50 values to fipronil as the Dorie strain. The aversion behavior (avoidance of gel baits) was therefore caused by food ingredients in the gel baits. The Cincy strain showed avoidance of agar containing fructose, glucose, maltose, and sucrose, which are phagostimulants to the laboratory strain. Modifications of the inert ingredients in the Maxforce FC gel bait significantly improved the efficacy against the Cincy strain. The Cincy strain produced significantly smaller oothecae and lower numbers of eggs in each egg capsule than the nonaverse Jwax and Dorie strains of cockroaches, suggesting fitness costs are associated with resistance.

Animals↗

PubMed2004

Monitoring western corn rootworm (Coleoptera: Chrysomelidae) susceptibility to carbaryl and cucurbitacin baits in the areawide management pilot program.

Areawide pest management involves the uniform application of a pest control strategy over wide geographic areas. Therefore, these programs are likely to impose intense selective pressures, and the risk for resistance development among pest species for which areawide management programs are implemented is likely to be high. Pilot studies for areawide management of western corn rootworm, Diabrotica virgifera virgifera LeConte, were conducted from 1996 to 2002 at four different sites across the Corn Belt. This program used cucurbitacin baits to deliver high doses of a traditional neurotoxic insecticide (carbaryl) to individual insects while reducing the overall rate of insecticide use. Because of the concern and potential for resistance evolution, annual assessments of susceptibility to the active ingredient carbaryl were conducted both within the managed area as well as from untreated control areas. Significantly reduced susceptibility to carbaryl based on survival at a diagnostic concentration was detected in three of the four management sites (Kansas, Iowa, and Illinois/Indiana), whereas susceptibility of beetles collected outside the managed areas remained unchanged. Additionally, significantly reduced responsiveness to cucurbitacin baits was observed in beetles collected from the managed area relative to the control area at the same three sites. These results suggest strongly that areawide management has the potential to select for resistance and that a strategy for managing resistance and reducing selective pressure should be proactively implemented.

Animals↗

PubMed2003

Caste- and development-associated gene expression in a lower termite.

BACKGROUND: Social insects such as termites express dramatic polyphenism (the occurrence of multiple forms in a species on the basis of differential gene expression) both in association with caste differentiation and between castes after differentiation. We have used cDNA macroarrays to compare gene expression between polyphenic castes and intermediary developmental stages of the termite Reticulitermes flavipes. RESULTS: We identified differentially expressed genes from nine ontogenic categories. Quantitative PCR was used to quantify precise differences in gene expression between castes and between intermediary developmental stages. We found worker and nymph-biased expression of transcripts encoding termite and endosymbiont cellulases; presoldier-biased expression of transcripts encoding the storage/hormone-binding protein vitellogenin; and soldier-biased expression of gene transcripts encoding two transcription/translation factors, two signal transduction factors and four cytoskeletal/muscle proteins. The two transcription/translation factors showed significant homology to the bicaudal and bric-a-brac developmental genes of Drosophila. CONCLUSIONS: Our results show differential expression of regulatory, structural and enzyme-coding genes in association with termite castes and their developmental precursor stages. They also provide the first glimpse into how insect endosymbiont cellulase gene expression can vary in association with the caste of a host. These findings shed light on molecular processes associated with termite biology, polyphenism, caste differentiation and development and highlight potentially interesting variations in developmental themes between termites, other insects, and higher animals.

Animals↗

PubMed2003

Inheritance of methyl-parathion resistance in Nebraska western corn rootworm populations (Coleoptera: Chrysomelidae).

Field populations of western corn rootworm, Diabrotica virgifera virgifera LeConte, were collected from three different sites (York Co., Phelps Co., and Saunders Co.) in Nebraska during 1996. Adult bioassays of these three populations were conducted with different concentrations of methyl-parathion and at a diagnostic concentration (1.0 microg/ml) to determine resistance levels among these populations. Self and reciprocal crosses were made between the two resistant and one susceptible laboratory-reared populations. Dose-responses and dominance ratios calculated for the four reciprocal crosses indicated that resistance was incompletely dominant in both strains, although in one of the strains there was an indication of sex linkage. However, evaluation of native polyacrylamide gels stained for nonspecific esterases and nonspecific esterase activity of parents and F1 progeny of the crosses suggested that esterase inheritance was completely dominant and autosomal. The results of this study were inconclusive with regard to the precise nature of inheritance, because the bioassays and esterase assays could not discriminate between heterozygotes and homozygotes. However, they do provide insight into the potential for developing simple diagnostic assays to assess resistance frequencies. Based on the inheritance studies described in this investigation, we can begin to generate information on specific genetic factors that dictate the evolutionary divergence of discrete resistant populations and facilitate modeling efforts designed to approximate the movement of genes for resistance among populations.

Animals↗

PubMed2003

Characterization of general esterases from methyl parathion-resistant and -susceptible populations of western corn rootworm (Coleoptera: Chrysomelidae).

A consistent correlation between elevated esterase activity and methyl parathion resistance among Nebraska western corn rootworm, Diabrotica virgifera virgifera LeConte, populations has previously been documented. Characterization of general esterase activity using naphtholic esters as model substrates indicated that differences between resistant and susceptible strains could be maximized by optimizing assay conditions. The optimal conditions identified here were similar to those reported for other insect species. The majority of general esterase activity was found in the cytosolic fractions of resistant populations, whereas the activity was more evenly distributed between cytosolic and mitochondrial/nuclear fractions in the susceptible population. General esterase activity was predominately located in the adult thorax and abdomen. Although there were significant differences in general esterase activities between resistant and susceptible populations, the differences exhibited in single beetle activity assays did not provide sufficient discrimination to identify resistant individuals. In contrast, single larva activity assays provided greater discrimination and could be considered as an alternative to traditional bioassay techniques.

Animals↗

PubMed2002

In vivo and in vitro metabolism of fipronil by larvae of the European corn borer Ostrinia nubilalis.

In vivo and in vitro metabolism of [14C]fipronil was examined in a susceptible European corn borer (Ostrinia nubilalis, Hübner) laboratory strain. [14C]Fipronil penetrated the larval integument slowly, with 71.5% of the applied radioactivity recovered from surface rinses 24 h after topical application. Despite this slow penetration, radioactivity was detected in both the excrement and internal organo-soluble fractions. Radioactivity in the internal aqueous fraction and tissue pellet accounted for less than 0.8% of total radioactivity. The in vivo studies suggest that fipronil oxidation to its sulfone metabolite is the major route of metabolic conversion. In vitro studies were performed using subcellular microsomal fractions isolated from European corn borer larval midguts. Cytochrome P450-dependent monooxygenase activity (methoxyresorufin O-demethylase) was consistently observed in midgut preparations, and formation and detection of the sulfone metabolite in the same midgut preparations was also NADPH-dependent and inhibited by piperonyl butoxide. In vitro metabolism results indicate microsomal monooxygenases are responsible for the conversion of fipronil to its sulfone form in the European corn borer.

Animals↗