Fumigation toxicity of volatile natural and synthetic cyanohydrins to stored-product pests and activity as soil fumigants

Insecticidal fumigation toxicity of natural and synthetic cyanohydrins was evaluated with four stored-product pests: the lesser grain borer, Rhyzopertha dominica (F), the red flour beetle, Tribolium castaneum Herbst, the saw-toothed grain beetle Oryzaephilus surinamensis L, the maize weevil, Sitophilus zeamais (Motsch) and the house fly, Musca domestica L. The fumigation LC50 values were calculated by probit analysis. For house flies, all but one of the cyanohydrins tested were more potent than 1,3-dichloropropene (Telone). Three were as efficacious as chloropicrin. For the lesser grain borer, all cyanohydrins tested were more insecticidal than dichloropropene, and all but one were more potent than chloropicrin. Four were as insecticidal as dichlorvos. The acetate of 1-cyano-1-hydroxy-2-propene (CHP-ace) was also tested in soil for antifungal and antibacterial activity, and inhibition of weed seed germination. CHP-ace reduced the total soil bacterial and fungal counts significantly, and was effective in inhibiting the germination of weed seeds in soil, indicating a broad spectrum of activity as a soil fumigant.     

Composition and biological activity of essential oils from Labiatae against Nezara viridula (Hemiptera: Pentatomidae) soybean pest

BACKGROUND: Plant essential oils have been recognised as an important natural source of insecticide. This study analysed the chemical constituents and bioactivity of essential oils that were isolated via hydrodistillation from Origanum vulgare L. (oregano) and Thymus vulgaris L. (thyme) against eggs, second instar and adults of Nezara viridula (L.). RESULTS: The major component of oregano was p‐cymene, and, for thyme, thymol. The ovicidal activity was tested by topical application; the essential oil from thyme was more effective. The fumigant activity was evaluated in an enclosed chamber; the LC₅₀ values for oregano were 26.8 and 285.6 µg mL^?1 for nymphs and adults respectively; for thyme they were 8.9 µg mL^?1 for nymphs and 219.2 µg mL^?1 for adults. To evaluate contact activity, a glass vial bioassay was used; the LC₅₀ values for oregano were 1.7 and 169.2 µg cm^?2 for nymphs and adults respectively; for thyme they were 3.5 and 48.8 µg cm^?2 respectively. The LT₅₀ analyses for contact and fumigant bioassays indicated that thyme was more toxic for nymphs and adults than oregano. Both oils produced repellency on nymphs and adults. CONCLUSION: These results showed that the essential oils from O. vulgare and T. vulgaris could be applicable to the management of N. viridula. Copyright © 2011 Society of Chemical Industry     

Acaricidal activities of paeonol and benzoic acid from Paeonia suffruticosa root bark and monoterpenoids against Tyrophagus putrescentiae (Acari: Acaridae)

The acaricidal activities of paeonol (2'-hydroxy-4'-methoxyacetophenone) and benzoic acid identified in the root bark of tree peony, Paeonia suffruticosa Andrews, against copra mite, Tyrophagus putrescentiae (Schrank), adults were examined using direct contact and vapour phase toxicity bioassays and compared with those of cinnamyl acetate, cinnamyl alcohol and 37 monoterpenoids as well as the acaricides benzyl benzoate, dibutyl phthalate and N,N-diethyl-m-toluamide (DEET). Based on LD(50) values in fabric piece contact toxicity bioassays, the acaricidal activities of benzoic acid (4.80 microg cm(-2)) and paeonol (5.29 microg cm(-2)) were comparable to that of benzyl benzoate (4.46 microg cm(-2)) but more pronounced than those of DEET (30.03 microg cm(-2)) and dibutyl phthalate (25.23 microg cm(-2)). In vapour phase toxicity bioassays, paeonol and benzoic acid were much more effective in closed containers than in open ones, indicating that the effects of these compounds were largely due to action in the vapour phase. As judged by 24 h LD(50) values, (1S)-(-)-verbenone (7.42 mg per disc) was the most toxic fumigant, followed by (1S)-(-)-camphor, (S)-(+)-carvone, (R)-(-)-linalool and (+/-)-camphor (10.45-18.18 mg). Potent fumigant toxicity was also observed with paeonol, (2S,5R)-(-)-menthone, (+/-)-citronellal, benzoic acid, (1S,4R)-(-)-alpha-thujone and (R)-(+)-pulegone (25.10-34.63 mg). Neither benzyl benzoate, DEET nor dibutyl phthalate caused fumigant toxicity. Paeonia root bark-derived materials, particularly paeonol and benzoic acid, as well as the monoterpenoids described, merit further study as potential acaricides or as leads for the control of T. putrescentiae.     

Insecticidal activity of new fluorinated pyrethroids and their stability toward chemical oxidation and photoreaction

The insecticidal activity of several new fluorinated pyrethroids was measured using houseflies untreated and treated with piperonyl butoxide (PB). 10, 10-Difluorophenothrin and 10, 10-difluoroallethrin, which include fluorine atoms at a position most easily attacked by mixed function oxidases (mfo) in the acid moiety, showed smaller topical LD₅₀ values on the PB-untreated flies than the parent insecticides but rather large values on the PB-treated flies, suggesting that the introduction of fluorine prevents metabolic oxidation, although it has a negative effect on the interaction with a target site. Monofluorinated analogues of phenothrin, in which the structure of chrysanthemic acid was rearranged, still had moderate insecticidal activity, but flies were scarcely killed by 7 fluoroallethrin into which fluorine was introduced at a position most easily oxidized by mfo in the alcohol moiety. Competitive oxidation of the fluorinated derivatives and the parent compounds showed that fluorine at both the 10- and 7′-positions stabilizes the alkenyl side-chains of the pyrethroids against selenium dioxide and m-chloroperoxybenzoic acid. Photochemical studies with 10, 10-difluorophenothrin indicated that the photo-instability of the cyclopropanecarboxylic part could not be improved by this modification.     

Glucosinolate aglucones and analogues: insecticidal properties and a QSAR

Naturally occurring aglucones of three glucosinolates (sinigrin, glucotropaeolin, and epi-progoitrin) were tested for fumigation activity against the house fly, Musca domestica, and the lesser grain borer, Rhizopertha dominica. A total of eight natural aglucones were evaluated in the bioassays. Two aglucones of sinigrin showed efficacy against both species which was comparable with that of a commercial fumigant, chloropicrin. None of the aglucones tested was comparable in activity to dichlorvos. Aglucones of glucotropaeolin were also insecticidal, but not to the same level as the sinigrin aglucones. The aglucones of epi-progoitrin were only slightly effective as fumigants. A quantitative structure–activity relationship (QSAR) was developed for synthetic analogues of the sinigrin and glucotropaeolin aglucones. An electronic parameter, σ*, provided the best predictor of activity in R. dominica, whereas a hydrophobicity parameter, π, best predicted activity in M. domestica. © 1998 Society of Chemical Industry     

Stereochemical basis for the insecticidal activity of carbamoylated and acylated pyrazolines

Methyl 3-(4-chlorophenyl)-1-[N-(4-chlorophenyl)carbamoyl]-4-methyl-2-pyrazoline-4-carboxylate was converted to corresponding (1R)- and (1S)-phenethyl esters via its carboxylic acid and acid chloride at the C-4 atom to separate the diastereomers. Their configurations were confirmed by X-ray analysis. Both isomers of the (1R)methylbenzyl ester were subjected to transesterification with sodium methoxide to obtain enantiomers of the starting methyl ester. Their insecticidal activity was measured against American cockroaches (Periplaneta americana (L.)) by injection and against house flies (Musca domestica L.) by topical application under various synergistic conditions with metabolic inhibitors. The activity values of the four α-methylbenzyl esters and the R-isomer of the starting methyl ester were similar. The S-enantiomer of the methyl ester was about 10 and 100 times more active than the R-isomer against the cockroach and the fly, respectively. Some N-arylacetyl and N-aryloxyacetyl derivatives of the starting N-(4-chlorophenyl)carbamoyl compound gave very low activity. Conformation-energy profiles for some compounds suggested that the conformation of substituents on the N-1 atom in the pyrazoline ring has a specific role for the potential insecticidal effects.     

Insecticidal activity of fatty acid constituents of fixed vegetable oils against Callosobruchus maculatus (F.) on cowpea

The insecticidal activity of lauric, oleic and linoleic acids against Callosobruchus maculatus on cowpea was investigated in laboratory bioassays. In pre-oviposition grain treatments, it was found that, at dosages between 1.96 and 11.59 kg-lauric acid had no effect on progeny development, while the oily oleic and linoleic acids were active in reducing progeny development. The active fatty acids had no effect on oviposition (in no-choice experiments) or on mortality of adults or larvae that successfully penetrated treated cowpea seeds, and their insecticidal activity, like that of fixed vegetable oils, depended mainly on ovicidal action. When applied to cowpeas in a pure state, oleic acid had an LC₅₀ value of 1.64mlkg^?1, which made it approximately 3 and 8 times more toxic against eggs of C. maculatus than groundnut oil and linoleic acid respectively. When the ovicidal activities of the three fatty acids were tested by dipping egg-infested seeds in acetone- based solutions, they were all found to be similarly toxic, lauric, oleic and linoleic acids having LC₅₀, values of 40, 38 and 26 ml litre^?1 respectively (with overlapping 95% C.L.). These values made them 2-4 times more toxic than acetone-based solutions of groundnut and traditional coconut oils. The possibility of employing fatty acids in large-scale and traditional small-scale food storage systems is discussed.     

新型七氟异丙基取代2,2-二氟-1,3-苯并二氧-5-乙酰胺衍生物的合成与杀虫活性

为探索环境友好新型农药先导化合物,通过水相中酰胺缩合反应合成了16个未见文献报道的七氟异丙基苯基取代的2,2-二氟-1,3-苯并二氧-5-乙酰胺类目标化合物。其结构通过核磁共振氢谱、氟谱以及高分辨质谱确认。初步生物活性测定表明,部分目标化合物对蚕豆蚜虫和粘虫表现出良好的杀虫活性,初步构效关系显示苯环上取代基的种类和位置在化合物的杀虫活性中起关键作用。     

Effect of storage on the efficacy of powdered leaves ofAnnona squamosa for the control ofCallosobruchus maculatus on cowpeas(Vigna unguiculata)

Annona squamosa L. is widespread in Sri Lanka and its leaves are collected by some farmers to protect their stored cowpeas from predation by bruchids. Removal of the leaves during the dry season, when the fanners harvest their cowpeas, can decrease the yield ofA. squamosa fruit. This study investigated whether storing the leaves before they are used would reduce the insecticidal activity of the leaves. Overall, acetone and ethanol extracts made from fresh and stored leaves ofA. squamosa decreased the number of adultCallosobruchus maculatus (F.) emerging from cowpeas; however, in some bioassays the extracts from fresh leaves were more active than those from leaves stored for 6 months. Acetone extracts from fresh and stored leaves were toxic to adult beetles, whereas the ethanol extracts were not active. Acetone and ethanol extracts from fresh leaves had potent ovicidal activity when applied to 2-day-old eggs.     

Effects of monoterpenoid insecticides on [H]-TBOB binding in house fly GABA receptor and Cl uptake in American cockroach ventral nerve cord

Monoterpenoids and their derivatives from plant essential oils showed good insecticidal activities in previous studies, but the mechanisms of their action as natural insecticides are not known yet. In the present work, we evaluated the pharmacological action of five monoterpenoids (α-terpineol, carvacrol, linalool, pulegone, and thymol) on native insect GABA receptors from house flies and American cockroaches using radiotracer methods. In the [³H]-TBOB binding assay, carvacrol, pulegone, and thymol all enhanced the [³H]-TBOB binding to membrane preparation of house fly heads with EC₅₀ values of 48 μM, 432 μM, and 6 mM, respectively. Moreover, these three monoterpenoids at concentrations of 500 μM and 1 mM also significantly increased the ³⁶Cl⁻ uptake induced by GABA in membrane microsacs prepared from American cockroach ventral nerve cords. These results revealed that carvacrol, pulegone, and thymol are all positive allosteric modulators at insect GABA receptors. The other two monoterpenoids that were tested, α-terpineol and linalool, showed little or no effect in both the [³H]-TBOB binding and ³⁶Cl⁻ uptake assays.     

Synthesis and bioactivity evaluation of novel spiromesifen derivatives

BACKGROUND: The development of environmentally friendly and novel structural pesticides is now an area of intense research in the agriculture field. Spirocyclic tetronic acids such as spiromesifen are typical compounds of this kind. In order to discover novel compounds with improved and broader-spectrum insecticidal activities, a series of spiromesifen derivatives were synthesised and bioassayed. RESULTS: The derivatives were identified by ¹H NMR and MS. Preliminary bioassays demonstrated that some bioactivities of compounds 5a to 5u were better and had a broader spectrum than the lead compound spiromesifen. Moreover, these compounds showed better insecticidal activities against Mythimna sepatara and Aphis fabae than acaricidal activities against Tetranychus cinnabari. Furthermore, LC₅₀ of 5s against Aphis fabae reached 1.09 mg L⁻¹. At the same time, compounds 5g, 5i, 5k and 5r also warrant further study because of their superior bioactivities to spiromesifen. What is more, suitable carbon chain length in the 4-position ester and the log P value of these spiromesifen derivatives dramatically influenced their insecticidal activities. Butyric or pentanoic ester and a log P value of 4.0–6.0 may be preferred. CONCLUSION: The present work demonstrates that some spiromesifen derivatives can be used as potential lead compounds for developing novel insecticides and acaricides. Copyright © 2011 Society of Chemical Industry     

Behavioural and electrophysiological investigation of 1-(7-ethoxygeranyl)-2-methylbenzimidazole on the house fly Musca domestica

The insecticidal properties of 1-(7-ethoxygeranyl)-2-methylbenzimidazole (EGMB) were investigated on larval and adult house flies. Unsynergised EGMB gave topical LD₅₀ values of 0.53 μg per female fly on NAIDM strain house flies. When flies were pretreated with 5.2 μg piperonyl butoxide, susceptibility was increased (LD₅₀ 0.12 μg per female fly). House fly larvae were less susceptible to EGMB (LD₅₀ 2.2 μg). Poisoning with EGMB resulted in a rapid reduction in locomotor activity of both larval and adult house flies. This reduction in locomotion was progressive and led to complete paralysis. Various parameters of larval nervous system function were investigated in larvae during these early phases of poisoning. As early as 15 min after dosing larvae with LD₉₅ doses of EGMB, sensory nerves were less responsive. Over a somewhat longer time (2–4 h), neurally evoked contractures were adversely affected by EGMB. In some cases, this effect appeared to be due to reduced postsynaptic potential amplitude; in other instances, it appeared to be due to an effect independent of neuromuscular transmission. The close temporal correlation between behavioural and electrophysiological observations suggests that the nervous and muscular systems are important sites of action of EGMB.     

Neurophysiological activity and toxicity of pyrethroids derived by addition of methylene,sulfur or oxygen to the chrysanthemate 2-methyl-1-propenyl substituent

Conversion of chrysanthemates to their cyclopropane, episulfide, and epoxide derivatives by addition of methylene, sulfur, or oxygen, respectively, to the 2-methyl-1-propenyl double bond yields products generally of reduced toxicity but enhanced neurophysiological activity and photostability. The reduced toxicity is established with cis-cyphenothrin derivatives administered intracerebrally to mice and topically to house flies and with cis-phenothrin derivatives applied topically to American cockroaches and house flies, even in the presence of piperonyl butoxide for the house flies. In contrast, cyclopropane, episulfide, and epoxide derivatives of phenothrin are more potent than the parent compound in eliciting repetitive firing following stimulation of a cercal sensory nerve of the American cockroach in vitro. The individual 1′R and 1′S isomers of epoxides derived from (1R,cis,αS)cyphenothrin, (1R,cis)phenothrin, and (1R,trans)tetramethrin differ in potency by up to 20-fold for insecticidal activity, >30-fold for intracerebral toxicity to mice, and ～100,000-fold in the cercal sensory nerve assay. In each case the epoxide isomer of higher R_f is more potent than that of lower R_f when derived from a trans-chrysanthemate and vice versa from a cis-chrysanthemate.     

Toxicity of spray and fumigant products containing cassia oil to Dermatophagoides farinae and Dermatophagoides pteronyssinus (Acari: Pyroglyphidae)

The toxicity of formulations of oil of cassia, Cinnamomum cassia Blume, (20 and 50 g L(-1) sprays and 100% oil-based fumigant) to adult Dermatophagoides farinae Hughes and D. pteronyssinus Trouessart was examined using contact and vapour-phase toxicity bioassays. Results were compared with the lethal activity of three commercial acaricides: benzyl benzoate, dibutyl phthalate and diethyl-m-toluamide (deet). The contact toxicity of cassia oil to both dust mite species was comparable with that of benzyl benzoate but was higher than that of the other two acaricides. Sprays containing 20 and 50 g L(-1) cassia oil were effective against both mite species when applied to fabric, glass, paper, plastic, tin or wood substrates. Applications of the 50 g L(-1) spray to different space volumes and surface areas determined that 50-60 mg of cassia oil was needed to control dust mites in 3.4 m(3) or in 1 m(2). In tests with fumigant devices, toxicity varied according to the thickness of non-woven fabric covering the device, the exposure time, the number of fumigant devices used and the volume of the space sprayed. Fumigant toxicity to adult D. pteronyssinus was more pronounced with devices enclosed in thinner (40 microm) versus thicker (45 or 50 microm) non-woven fabric covers. A single fumigant device with a 40 microm thick non-woven fabric cover resulted in substantial control in a space of 0.05 m(3) but exhibited only moderate to weak control in spaces >or= 0.097 m(3) at 4 days after application. Two fumigant devices gave 88% mortality in a space of 1.73 m(3). Cassia oil applied as sprays or in fumigant devices appears to provide effective protection of humans from house dust mites.     

Insecticidal activity and microsomal metabolism of biooxidizable lindane analogs

The insecticidal activity of lindane analogs, in which some chlorine atoms were replaced by other groups susceptible to microsomal oxidative metabolism, was determined against mosquitos, house flies, and German cockroaches. When tested with a synergist, piperonyl butoxide, one of the methylthio analogs was as active as lindane, whereas several others were also highly active. By examining the ratio of synergized and unsynergized LD₅₀ values (synergistic ratio value), the highly insecticidal methylthio, methoxy, and methyl analogs appear to undergo metabolic detoxication effectively in house flies. By means of in vitro metabolism experiments using microsomal fraction from house fly abdomen, the methoxy, ethoxy, and methylthio analogs were shown to be metabolized rapidly at similar rates. The synergized insecticidal activities of these compounds against various insect species relate linearly with each other, suggesting that the oxidative degradation is inhibited by the synergist to a similar extent and that the transport process to the site of action is not a limiting factor in determining the relative insecticidal activity.     

Distinguishing between carbamate and organophosphate insecticide poisoning in house flies by symptomology

Three criteria, latency to convulsions, still period, and recovery are used to distinguish between carbamate and phosphate insecticide poisoning in house flies, Musca domestica. Because of shorter latencies with carbamate-treated flies, the central nervous system was considered more sensitive to the presence of carbamates than phosphates. Recovery from carbamate-induced tetany was considered correlated with reactivation of carbamylated cholinesterase. There appeared to be a fundamental difference between the insecticidal actions of carbamates and phosphates not wholly explainable by cholinesterase inhibition. Tethered or held house flies were less susceptible to poisoning than unrestrained flies.     

Quantitative structure-activity study of insecticidal 2-methoxy-5-(substituted-phenyl)-1, 3, 2-oxazaphospholidine 2-sulfides against Musca domestica L. by topical application

The quantitative relationship between the structure of 2-methoxy-5-(substituted-phenyl)-1, 3, 2-oxazaphospholidine 2-sulfides (5-PMOS) and their insecticidal activity against the house fly. Musca domestica L., was analyzed using reported physicochemical parameters and regression analysis. The electronic nature of the substituent on the phenyl group of 5-PMOS has the most significant effect on the activity, followed by hydrophobic and steric effects; the optimum value of Σρ is zero and the more hydrophobic the substituents on the phenyl group, the higher the insecticidal activity. The plots of observed pLD₅₀, values against calculated pLD₅₀ values for compounds having substituents in the ortho-position deviated downwards from those of compounds having substituents at the meta and/or para positions. This ortho-effect, which reduces the insecticidal activity of compounds having substituents at the ortho-position, was expressed by a dummy parameter D, which has the value 2 for di-ortho-substituted derivatives, 1 for mono-ortho-substituted derivatives and zero for others. Thus, the highest activity was obtained for 2-methoxy-5-phenyl-1, 3, 2-oxazaphospholidine 2-sulfide, and the activity was decreased by the introduction of any substituents on the phenyl group.     

Effect of fungal metabolites and some derivatives against Tribolium castaneum (Herbst) and Nezara viridula (L.)

Two fungal metabolites, aspyrone (3-(1,2-epoxypropyl)-5-hydroxy-6-methyl-5,6-dihydropyran-2-one) and asperlactone (3-(1,2-epoxypropyl)-5-(1-hydroxyethyl)-5-furan-2-one) were isolated from an Aspergillus ochraceus Wilhelm strain showing IGR activity against Tribolium castaneum (Herbst). Synthetic derivatives of aspyrone were produced using published methods. These derivatives together with aspyrone and asperlactone were tested for insect growth-regulating activity against T. castaneum, and for ovicidal activity against Nezara viridula L. Of the compounds tested asperlactone appeared to be the most active.     

The potential use of allicin as a biopesticide for the control of the house fly,Musca domestica L.

The house fly, Musca domestica L., is a widespread pest of intensively reared livestock, where its presence negatively affects growth and productivity through the irritation their activity causes. Furthermore, adult flies mechanically vector a wide range of animal and human pathogens and, as such, pose a health risk to both livestock and people. The development of resistance in M. domestica populations to most of the insecticides used against them, coupled with diminishing product availability in many regions, means that new fly control methods and materials are constantly required. In the present study, a formulation of allicin, a compound derived from garlic cloves, was evaluated against the eggs, larvae and adults of Musca domestica L.. An in-diet LD₅₀ of 134 ppm against larvae was achieved, whilst marked ovicidal activity was also recorded. Adults were similarly affected when exposed directly and indirectly to surface residues of the compound. The results indicate that allicin exhibits potential to be used against filth flies through incorporation into their developmental substrates and, potentially, for the control of other economically important dipteran pests.     

Purification and characterisation of proteins secreted by the entomopathogenic fungus Metarhizium anisopliae with insecticidal activity against adults of the Mediterranean fruit fly,Ceratitis capitata (Diptera: Tephritidae)

BACKGROUND: The control of the Mediterranean fruit fly (medfly) Ceratitis capitata (Wied) is usually performed with protein bait sprays incorporating chemical insecticides that may have adverse effects on humans, non‐target organisms and the environment. In recent years, scientists have sought more environmentally friendly insecticides for medfly control, such as plant‐ and microorganism‐derived compounds. Among these compounds, entomopathogenic fungi are an unexplored source of natural insecticides. RESULTS: The crude soluble protein extract (CSPE) of the entomopathogenic fungus Metarhizium anisopliae (Mestch.) (strain EAMa 01/58‐Su) shows chronic insecticidal activity when administered per os. Mortality in flies exhibits a dose response. The CSPE produces an antifeedant effect in adult flies, a result probably due to a progressive deterioration of the fly midgut after ingestion of the extract. Protease and temperature treatments show that insecticidal activity against C. capitata is due to proteinaceous compounds that are highly thermostable. Four monomeric proteins from this crude extract have been purified by liquid chromatography and gel electroelution. Although all four monomers seem to be involved in the insecticidal activity of the CSPE, the 15 kDa and the 11 kDa proteins appear to be mainly responsible for the observed insecticidal effect. CONCLUSIONS: Four new fungal proteins with insecticidal activity have been purified and identified. These proteins might be combined with insect baits for C. capitata biocontrol. Copyright © 2009 Society of Chemical Industry