Plant essential oils synergize various pyrethroid insecticides and antagonize malathion in Aedes aegypti.

Pyrethroid resistance is a significant threat to agricultural, urban and public health pest control activities. Because economic incentives for the production of novel active ingredients for the control of public health pests are lacking, this field is particularly affected by the potential failure of pyrethroid-based insecticides brought about by increasing pyrethroid resistance. As a result, innovative approaches are desperately needed to overcome insecticide resistance, particularly in mosquitoes that transmit deadly and debilitating pathogens. Numerous studies have demonstrated the potential of plant essential oils to enhance the efficacy of pyrethroids. The toxicity of pyrethroids combined with plant oils is significantly greater than the baseline toxicity of either oils or pyrethroids applied alone, which suggests there are synergistic interactions between components of these mixtures. The present study examined the potential of eight plant essential oils applied in one of two concentrations (1% and 5%) to enhance the toxicity of various pyrethroids (permethrin, natural pyrethrins, deltamethrin and ß-cyfluthrin). The various plant essential oils enhanced the pyrethroids to differing degrees. The levels of enhancement provided by combinations of plant essential oils and pyrethroids in comparison with pyrethroids alone were calculated and synergistic outcomes characterized. Numerous plant essential oils significantly synergized a variety of pyrethroids; type I pyrethroids were synergized to a greater degree than type II pyrethroids. Eight plant essential oils significantly enhanced 24-h mortality rates provided by permethrin and six plant essential oils enhanced 24-h mortality rates obtained with natural pyrethrins. By contrast, only three plant essential plants significantly enhanced the toxicity of deltamethrin and ß-cyfluthrin. Of the plant essential oils that enhanced the toxicity of these pyrethroids, some produced varying levels of synergism and antagonism. Geranium, patchouli and Texas cedarwood oils produced the highest levels of synergism, displaying co-toxicity factors of > 100 in some combinations. To assess the levels of enhancement and synergism of other classes of insecticide, malathion was also applied in combination with the plant oils. Significant antagonism was provided by a majority of the plant essential oils applied in combination with this insecticide, which suggests that plant essential oils may act to inhibit the oxidative activation processes within exposed adult mosquitoes.

Essential oils enhance the toxicity of permethrin against Aedes aegypti and Anopheles gambiae.

Insecticide resistance and growing public concern over the safety and environmental impacts of some conventional insecticides have resulted in the need to discover alternative control tools. Naturally occurring botanically-based compounds are of increased interest to aid in the management of mosquitoes. Susceptible strains of Aedes aegypti (Linnaeus) (Diptera: Culicidae) and Anopheles gambiae (Meigen) (Diptera: Culicidae) were treated with permethrin, a common type-I synthetic pyrethroid, using a discriminate dose that resulted in less than 50% mortality. Piperonyl butoxide (PBO) and 35 essential oils were co-delivered with permethrin at two doses (2 and 10 µg) to determine if they could enhance the 1-h knockdown and the 24-h mortality of permethrin. Several of the tested essential oils enhanced the efficacy of permethrin equally and more effectively than piperonyl butoxide PBO, which is the commercial standard to synergize chemical insecticide like pyrethroids. PBO had a strikingly negative effect on the 1-h knockdown of permethrin against Ae. aegypti, which was not observed in An. gambiae. Botanical essential oils have the capability of increasing the efficacy of permethrin allowing for a natural alternative to classic chemical synergists, like PBO.

Acute Toxicity and Sublethal Effects of Terpenoids and Essential Oils on the Predator Chrysoperla externa (Neuroptera: Chrysopidae).

The search for new safer insecticides has increased in recent agriculture. Botanical compounds such as terpenoids and plant essential oils with insecticidal activity could represent important tools in pest management, and their risk assessment against non-target organisms is necessary since they may serve as a precursor for the synthesis of new insecticide active ingredients. For this study, the acute toxicity and sublethal effects of seven terpenoids and three essential oils with recognized insecticidal activity were evaluated on the predator Chrysoperla externa (Hagen) (Neuroptera: Chrysopidae) in laboratory bioassays. Results indicate that these compounds feature relative selectivity to the predator C. externa; however, sublethal effects on reproduction were recorded for some compounds. The phenolic monoterpenoids carvacrol and thymol were more acutely toxic than other terpenoids screened, with LD50 <20,000 µg/g; however, they were less toxic than natural pyrethrins (toxicity standard) in these bioassays. Sublethal effects on fecundity and fertility were observed for R-(+)-limonene, while oregano oil only affected fecundity. The compounds evaluated here have potential to be used as insecticides and can serve as backbone for future synthesis of selective active ingredients; however, a complete risk assessment to C. externa and other non-target organisms is necessary for their incorporation in future crop protection paradigms.

Mechanisms of toxic action and structure-activity relationships for organochlorine and synthetic pyrethroid insecticides.

The mechanisms and sites of action of organochlorine (DDT-types and chlorinated alicyclics) and synthetic pyrethroid insecticides are presented with discussion of symptoms, physiological effects, and selectivity. The structural requirements for toxicity are assessed, and structure-activity relationships are considered for each subclass. Lipophilicity is important for all the groups because it facilitates delivery of these neurotoxicants to the site of action in the nerve. Steric factors including molecular volume, shape, and isomeric configuration greatly influence toxicity. Electronic parameters also have been demonstrated to affect biological activity in some of the groups of insecticides, e.g., Hammett's sigma and Taft's sigma * as indicators of electronegativity. New synthetic pyrethroids continue to be developed, with varied structures and different physicochemical and biological properties.

Model ecosystem evaluation of the environmental impacts of the veterinary drugs phenothiazine, sulfamethazine, clopidol, and diethylstilbestrol.

Four veterinary drugs of dissimilar chemical structures were evaluated for environmental stability and penchant for bioaccumulation. The techniques used were (1) a model aquatic ecosystem (3 days) and (2) a model feedlot ecosystem (33 days) in which the drugs were introduced via the excreta of chicks or mice. The model feedlot ecosystem was supported by metabolism cage studies to determine the amount and the form of the drug excreted by the chicks or mice. Considerable quantities of all the drugs were excreted intact or as environmentally short-lived conjugates. Diethylstilbestrol (DES) and Clopidol were the most persistent molecules, but only DES bioaccumulated to any appreciable degree. Phenothiazine was very biodegradable; sulfamethazine was relatively biodegradable and only accumulated in the organisms to very low levels. Data from the aquatic model ecosystem demonstrated a good correlation between the partition coefficients of the drugs and their accumulation in the fish.

Comparative toxicology of the pyrethroid insecticides.

The toxic effects elicited by synthetic pyrethroids in animals are varied in degree and nature. Their relative safety to birds and mammals contrasts sharply with their acute effects on fish and arthropods. Explantation of their differences in toxicity depends on examination of all factors of their comparative toxicology. Routes of exposure are important, as are metabolism and elimination rates, especially for mammals and birds with their considerable capabilities for biotransformation. Significant differences in sensitivity at the sites of toxic action may also play a role in differential responses to these insecticides. Finally, physical properties that influence the environmental disposition and subsequently affect bioavailability of the compounds in water, soil, air, produce, and nontarget species are also instrumental in determining the impact of current and future synthetic pyrethroid insecticides.

The interaction of chlorinated alicyclic insecticides with brain GABA(A) receptors in channel catfish (Ictalurus punctatus).

Chlorinated alicyclic insecticides are believed to antagonize the action of the neurotransmitter gamma-aminobutyric acid (GABA) at its receptor in vertebrates. Binding of the specific GABA(A) receptor ligand [35S]-t-butylbicyclophosphorothionate (TBPS) to channel catfish brain P2 membranes suggested a single population of receptors with a Kd (56.6+/-2.6 nM) and Bmax (2435+/-276 fmol/mg protein) that are similar to published values for other fish species. The competition of several chlorinated compounds for TBPS binding was investigated. The most potent inhibitors of TBPS binding were 12-ketoendrin, photoheptachlor epoxide, photoheptachlor, telodrin, and endrin, respectively, with IC50s of 20-90 nM. Photooxychlordane, photo alpha-chlordane, and oxychlordane were intermediate in potency (122-219 nM), as were isodrin, dihydroisodrin, heptachlor epoxide, and alpha-chlordane, which were similar in potency (311-397 nM). Dieldrin, lindane, and dihydroaldrin were much less potent (592-1103 nM). Heptachlor, aldrin, and gamma-chlordane were weak inhibitors of TBPS binding (2073-2738 nM). Chlordene and chlordecone had the lowest potency of all compounds studied (10,201-21,178 nM) with the exception of mirex, which did not inhibit binding at a concentration of 50 microM. There is a good correlation between binding potency and the available toxicity data for several of these compounds in channel catfish. There is also a good correlation between the inhibitory potency in channel catfish by these types of compounds with that in rats.

Evaluation of a liquid chromatographic method for the determination of fumonisins in corn, poultry feed, and Fusarium culture material.

The performance of a liquid chromatographic method for determining fumonisins in corn, animal feeds, and culture material was evaluated. Efficiencies of extractions with the following solvent systems were determined: acetonitrile-water (50 + 50, v/v), methanol-water (75 + 25, v/v), and 100% water. The acetonitrile solvent gave both higher extraction efficiencies and faster extraction times than the other 2 solvents. Extraction was followed by C18 solid-phase extraction column cleanup. Fumonisin B1 (FB1), fumonisin B2 (FB2), and fumonisin B3 (FB3) were measured by precolumn derivatization with o-phthalaldehyde followed by isocratic separation on a C18 reversed-phase column with a mobile phase of 50 mM potassium dihydrogen phosphate (pH 3.3)-acetonitrile (60 + 40). Commercially prepared poultry feed, corn, and Fusarium spp. corn cultures were analyzed at the following levels: FB1, 1.5 to 15,000 micrograms/g; FB2, 0.5 to 4000 micrograms/g; FB3, and 0.17 to 1,500 micrograms/g. Recoveries were 91-94%, 90-100%, and 81-93% for FB1, FB2, and FB3, respectively. Precision (coefficient of variation) was determined with pooled field samples and ranged from 2% at 19 micrograms/g for FB1 to 9% at 0.17 microgram/g for FB3. Time and pH studies of the formation of the fluorescent derivative and its stability were conducted. Complete reaction occurred at pHs above 7.9, with optimal pH for chromatography between 8.0 and 8.5. No statistically significant response differences were detected for reaction times ranging from 4 to 40 min; however, the detector signal was significantly reduced when reaction times were shorter than 4 min. Chromatograms of samples were free of interferences for all feeds, corn, and culture material tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of four monoterpenoids on growth and reproduction of the German cockroach (Blattodea: Blattellidae).

The effects of the monoterpenoids d-limonene, linalool, beta-myrcene, and alpha-terpineol on the growth and development of the German cockroach Blattella germanica (L.) were examined. We evaluated the chemicals' attractiveness in cockroach diet, quantified growth effects induced by monoterpenoids, examined embryotoxic properties of the compounds, and examined their effects on reproduction when administered by oral, topical, and vapor routes of entry. Untreated diet was significantly preferred compared with diet treated with high levels of d-limonene, linalool, and alpha-terpineol. The threshold for acceptance was between 1 and 10% (AI). All four monoterpenoids significantly influenced the days required by nymphs to reach the adult stage; in general, higher monoterpenoid concentrations in the diet were associated with a reduction in the days required by nymphs to mature. Application of high doses of d-limonene or linalool to oothecae of gravid female cockroaches significantly decreased the probability of young emerging from them but did not affect female mortality. Feeding on diet treated with monoterpenoids during nymphal development and through the early, premating period of the adult stage did not significantly influence numbers of broods produced per pair, numbers of offspring per brood, days required to produce a brood, total offspring produced by a pair, or female life span. Topical applications of linalool, beta-myrcene, or alpha-terpineol at near lethal rates to adult cockroaches before they mated had no significant influence on the reproductive parameters examined. A single exposure to sublethal levels of monoterpenoid vapors before mating had no significant influence on any reproductive parameters examined.

Insecticidal properties of several monoterpenoids to the house fly (Diptera: Muscidae), red flour beetle (Coleoptera: Tenebrionidae), and southern corn rootworm (Coleoptera: Chrysomelidae).

House flies, Musca domestica (L.), and their eggs were treated with 22 monoterpenoids to determine the topical, fumigant, and ovicidal activity of each compound. Fumigant activity of 14 monoterpenoids were examined further using red flour beetles, Tribolium castaneum (Herbst). Third-instar southern corn rootworm, Diabrotica undecimpunctata howardi Barber, were treated with carvacrol, citral, citronellal, menthol, pulegone, verbenol, and verbenone to determine their activity on larvae. Structure-activity relationships were evaluated with the toxicity data. We made comparisons between monocyclic aromatic, acyclic aliphatic, monocyclic aliphatic, and bicyclic aliphatic alcohols, ketones, aldehydes, and acids to determine toxicity differences involving the skeletal structure, amount of saturation, and associated functional groups of monoterapenoids. Ketones were more effective than alcohols in the topical, fumigant (T. castaneum), and ovicidal bioassays and less toxic than an analogous aldehyde in the topical, fumigant (M. domestica), and ovicidal bioassays. Aldehydes were more toxic than alcohols in the topical and fumigant (M. domestica) bioassays. In the topical and ovicidal bioassays, aromatic or acyclic alcohols, or both, were more effective than monocyclic and bicyclic alcohols. Vapors of bicyclic ketones were more toxic than monocyclic ketones to adult M. domestica. Monoterpenoid alcohols containing three carbon-carbon double bonds were more effective than saturated alcohols in the topical and larval bioassays. A mono-unsaturated ketone was more toxic than a structurally similar saturated ketone and two di-unsaturated ketones when it was applied topically to adult M. domestica. A saturated monocyclic ketone inhibited egg hatch more effectively than unsaturated monocyclic ketones.

Insecticidal activity of monoterpenoids to western corn rootworm (Coleoptera: Chrysomelidae), twospotted spider mite (Acari: Tetranychidae), and house fly (Diptera: Muscidae).

Acute toxicities of 34 naturally occurring monoterpenoids were evaluated against 3 important arthropod pest species; the larva of the western corn rootworm, Diabrotica virgifera virgifera LeConte; the adult of the twospotted spider mite. Tetranychus urticae Koch; and the adult house fly. Musca domestica L. Potential larvicidal or acaricidal activities of each monoterpenoid were determined by topical application, leaf-dip method, soil bioassay, and greenhouse pot tests. Phytotoxicity was also tested on a corn plant. Citronellic acid and thymol were the most topically toxic against the house fly, and citronellol and thujone were the most effective on the western corn rootworm. Most of the monoterpenoids were lethal to the twospotted spider mite at high concentrations; carvomenthenol and terpinen-4-ol were especially effective. A wide range of monoterpenoids showed some larvicidal activity against the western corn rootworm in the soil bioassay. Perillaldehyde, the most toxic (LC50 = 3 micrograms/g) in soil, was only 1/3 as toxic as carbofuran, a commercial soil insecticide (LC50 = 1 microgram/g). Selected monoterpenoids also effectively protected corn roots from attack by the western corn rootworm larvae under greenhouse conditions. alpha-Terpineol was the best monoterpenoid in the greenhouse pot test. The acute toxicity of monoterpenoids was low relative to conventional insecticides. Some monoterpenoids were phytotoxic to corn roots and leaves. l-Carvone was the most phytotoxic, whereas pulegone was the safest. The results with thymyl ethyl ether, one of the synthetic derivatives of thymol, showed a potential of derivatization to reduce monoterpenoid phytotoxicity.

Heartworm infection in cats: 50 cases (1985-1997).

OBJECTIVE: To characterize risk factors, clinical findings, usefulness of diagnostic tests, and prognosis in cats with naturally occurring heartworm infection (HWI). DESIGN: Retrospective study. ANIMALS: 50 cats with Dirofilaria immitis infection. PROCEDURE: Medical records, thoracic radiographs, and echocardiograms were reviewed and findings compared with appropriate reference populations. RESULTS: Findings suggested that male cats were not predisposed to HWI, domestic shorthair cats were at increased risk, and indoor housing was only partially protective. Fewer cases of HWI were identified in the final quarter of the year, compared with other periods, and prevalence is not apparently increasing. Signs of respiratory tract disease were most common, followed by vomiting. Infection was diagnosed incidentally in > 25% of cats; conversely, 10% of infected cats died suddenly without other clinical signs. Serologic tests were most useful for diagnosis, followed by radiography and echocardiography. Eosinophilia supported the diagnosis. Overall median survival time was 1.5 years but exceeded 4 years in cats surviving beyond the day of diagnosis. CONCLUSIONS AND CLINICAL RELEVANCE: Sex does not appear to be a risk factor for HWI in cats, and indoor housing provides only incomplete protection. Signs of respiratory tract disease (dyspnea and cough) are the strongest indicators of HWI in cats, and some radiographic evidence of infection is detected in most cases. Antibody screening for HWI in cats is efficacious, and antigen testing and echocardiography are most useful for making a definitive antemortem diagnosis.

Degradation of [14C]isofenphos in soil in the laboratory under different soil pH's, temperatures, and moistures.

The effects of three soil pH's, three soil temperatures, and three soil moistures on [14C]isofenphos degradation were investigated. All three factors interacted strongly and significantly affected the persistence of isofenphos as well as the formation of the degradation products (p less than 1%). Isofenphos degradation was greatest at the higher temperatures 35 degrees C greater than 25 degrees C greater than 15 degrees C (except under alkaline pH's), medium moisture 25% greater than 30% greater than 15%, and in both alkaline (pH = 8) and acidic soils (pH = 6) compared with neutral soil (pH = 7). Isofenphos oxon formation was greatest at higher temperatures 35 degrees C compared with 25 degrees C and 15 degrees C, in acidic soil greater than neutral soil greater than alkaline soil, and under high moisture (30%) compared with the 15% and 22.5% moistures. The formation of soil-bound residues was greatest at higher temperatures 35 degrees C greater than 25 degrees C greater than 15 degrees C, higher moisture 30% compared with 15% and 22.5%, and in alkaline soil compared with neutral and acidic soils.

Toxicity of fenvalerate to bobwhite quail (Colinus virginianus) including brain and liver residues associated with mortality.

The toxicity of the synthetic pyrethroid fenvalerate to bobwhite quail (Colinus virginianus) was examined. The acute oral LD50 to adult (19-wk-old) male and female birds was in excess of 4000 mg/kg. The LD50 to immature (5-wk-old) birds was 1785 mg/kg. Dietary toxicity testing with 2-wk-old chicks indicated an 8-d LC50 in excess of 15,000 ppm. Observed signs of intoxication included hyperactivity, irregular locomotion, ataxia, spastic muscle contraction, and, preceding death, sternal recumbency with muscle flaccidity. Significant weight loss (adult birds) or reduction in rate of weight gain (immature birds and chicks) was note generally at all dose levels in the acute testing, but only at the highest level in the dietary test. Brain residue levels associated with mortality increased with the dose (means of 0.10-1.26 ppm), whereas liver residues remained constant (overall mean of 0.74 ppm).