Enhanced efficiency of electrostatically charged insecticide aerosols

The bioefficacy of a standard domestic aerosol insecticide has been compared with that of a similar spray in which the droplets were electrostatically charged. The aerosol was charged without the need for an external power supply, by enhancing natural charge separation processes that occur during atomisation. The charge-to-mass ratio achieved was 1.1 x 10(-4) C kg-1, compared with 2.2 x 10(-5) C kg-1 for the standard aerosol. Efficiency was assessed for insects in free flight. A direct space-spray application method was used to study the bioefficacy of these aerosols on houseflies, Musca domestica, and an indirect space-spray method on houseflies and mosquitoes, Culex quinquefasciatus. Two levels of concentration of active ingredients were compared. At low concentrations of 1.57 g kg-1 of bioallethrin and 0.29 g kg-1 of bioresmethrin, the charged aerosol achieved a significant reduction in KDT50 (time at which 50% of the flies were knocked down), compared with the standard aerosol. In the direct spray application to houseflies, the KDT50 was reduced by 50%, while in the indirect spray the KDT50 was reduced by 40%. In the indirect spray of mosquitoes, the KDT50 was reduced by 22%. With higher active ingredient concentrations of 2.09 g kg-1 for bioallethrin and 0.39 g kg-1 for bioresmethrin, the charged aerosol also demonstrated faster knockdown than the standard, but the improvement was less marked. In the direct spray application to houseflies, the KDT50 was reduced by 21% compared with the standard aerosol, while in the indirect spray the KDT50 was reduced by 16%. In the indirect spray of mosquitoes, the KDT50 was reduced by 24%. The percentage mortality after 24 h was also increased with the charged aerosol. Charge carried by the droplets results in increased interception of the insecticide, as the droplets are attracted to the insects in flight and space charge effects within the aerosol could cause improved dispersion in the test chamber.     

Evaluation of semiochemical toxicity to houseflies and stable flies (Diptera: Muscidae)

BACKGROUND: The housefly, Musca domestica L., and stable fly, Stomoxys calcitrans (L.) are cosmopolitan pests of both farm and home environments. Houseflies have been shown to be resistant to a variety of insecticides, and new chemistries are slow to emerge on the market. Toxicities of selected semiochemicals with molecular structures indicative of insecticidal activity were determined against adults from an insecticide‐susceptible laboratory strain of houseflies. The three most active semiochemicals were also evaluated against recently colonized housefly and stable fly strains. RESULTS: Nineteen semiochemicals classified as aliphatic alcohols, terpenoids, ketones and carboxylic esters showed toxicity to houseflies and stable flies. Rosalva (LC₅₀ = 25.98 µg cm^?2) followed by geranyl acetone and citronellol (LC₅₀ = 49.97 and 50.02 µg cm^?2) were identified as the most toxic compounds to houseflies. Permethrin was up to 144‐fold more toxic than rosalva on the susceptible strain. However, it was only 35‐fold more toxic to the insecticide‐tolerant field strain. The compounds generated high toxicity to stable flies, with LC₅₀ values ranging from 16.30 to 40.41 µg cm^?2. CONCLUSION: Quantification of LC₅₀ values of rosalva, citronellol and geranyl acetone against susceptible housefly and field‐collected housefly and stable fly strains showed that semiochemicals could serve as potent insecticides for fly control programs. Copyright © 2010 Society of Chemical Industry     

Investigating the potential of selected natural compounds to increase the potency of pyrethrum against houseflies Muscadomestica (Diptera: Muscidae)

BACKGROUND: A study was undertaken to determine the efficacy of seven natural compounds compared with piperonyl butoxide (PBO) in synergising pyrethrum, with the intention of formulating an effective natural synergist with pyrethrum for use in the organic crop market. RESULTS: Discriminating dose bioassays showed PBO to be significantly more effective at synergising pyrethrum in houseflies than the seven natural compounds tested, causing 100% mortality in insecticide‐susceptible WHO and resistant 381zb strains of housefly. The most effective natural synergists against WHO houseflies were dillapiole oil, grapefruit oil and parsley seed oil, with 59, 50 and 41% mortality respectively, compared with 18% mortality with unsynergised pyrethrum. Against 381zb houseflies, the most effective natural synergists were parsley seed oil and dillapiole oil. Esterase inhibition by the natural compounds and PBO in vitro showed no correlation with pyrethrum synergism in vivo, whereas the inhibition of oxidases in vitro more closely correlated with pyrethrum synergism in vivo. CONCLUSION: Dillapiole oil and parsley seed oil showed the greatest potential as pyrethrum synergists. PBO remained the most effective synergist, possibly owing to its surfactant properties, enhancing penetration of pyrethrins. The results suggest the involvement of oxidases in pyrethroid resistance in houseflies, with the efficacy of synergists showing a high correlation with inhibition of oxidases. Copyright © 2011 Society of Chemical Industry     

Evaluation of chlorfenapyr for control of the bed bug,Cimex lectularius L.

BACKGROUND: The presence of bed bug populations resistant to pyrethroids demands the development of new control tactics, including the use of insecticides with new modes of action. Insecticides that disrupt oxidative phosphorylation in insect mitochondria can be an option. Laboratory assays were used to measure the toxicity of chlorfenapyr to susceptible strains and two strains highly resistant to pyrethroids. The effectiveness of two chlorfenapyr‐based formulations was compared, and behavioral responses of bed bugs to dry residues of aerosol sprays were evaluated. RESULTS: Chlorfenapyr was effective against all bed bug strains, killing them at a similar rate, regardless of their susceptibility status to pyrethroids. Dry residues aged for 4 months were as toxic as fresh dry residues. The aerosol formulation had contact activity and caused faster mortality than a water‐based formulation. Bed bugs did not avoid resting on surfaces treated with aerosol. CONCLUSION: Chlorfenapyr is an option for controlling pyrethroid‐resistant bed bugs. While it does not cause quick knockdown, its long residual activity and no avoidance behavior of bed bugs to dry residues appear to make this insecticide suitable for bed bug control. A faster insecticidal effect is obtained with the aerosol formulation, suggesting greater bioavailablity of the toxicant. Copyright © 2010 Society of Chemical Industry     

Insecticidal activity of the pyrethrins and related compounds V. toxicity of the methylbenzyl chrysanthemates to houseflies (Musca domestica) and mustard beetles (Phaedon cochleariae)

The insecticidal activities to houseflies and to mustard beetles of the 19 methylbenzyl (±)-cis-trans-chrysanthemates were measured to establish the patterns of substitution that produce the greatest toxicities to these insects. The two species of insect differ in their responses to the various compounds in the series. The most active compounds to houseflies and mustard beetles are, respectively, 2,4,6-and 2,3,6-trimethylbenzyl (±)-cis-trans-chrysanthemates.     

Laboratory assessment of different methods of applying a commercial granular bait formulation of methomyl to control adult houseflies (Musca domestica l.) in intensive animal units

Female houseflies (Musca dornestica L.) from a susceptible and a multiinsecticide-resistant strain were used to evaluate the toxicity of a granular insecticide bait formulation of the carbamate insecticide methomyl. The bait was either applied to a polystyrene bait target, or scattered over the floor of the fly treatment cages. Targets were treated with methomyl granules dissolved in water with and without apaste carrier or the granules were applied directly to the target using an adhesive. Scattered methomyl granules proved the most effective of the various treatments assessed. Based on the KT₉₀ values, the most effective suspended bait treatments against susceptible or resistant flies were water as a carrier, and egg or ‘Lap’ wallpaper paste as adhesives; the least effective were ‘Polycell’ regular wallpaper paste as an adhesive and carboxymethylcellulose as a carrier. A proportion of flies from both the susceptible and the resistant strain recovered from knockdown; most of these lost their ability to fly (‘hoppers’) and subsequently survived the treatments. When bait targets treated with methomyl granules were fixed at right angles to the wall/floor junction of the treatment cages most of the recovered flies fed again on the bait and received a lethal dose. The mortality of flies exposed to suspended bait targets was influenced by the level of light. For both strains of fly, mortality decreased as the light intensity was lowered; this effect was more pronounced with the resistant strain. The implication of these results for the application of methomyl bait is discussed.     

The requirement for the inclusion of formulation efficacy trials in pesticide preregistration evaluations

BACKGROUND: Optimization of biocide use could serve to reduce the risks of biocides on human health. To optimize the risk/benefit ratio, it is important to develop procedures for evaluating the efficacy of biocide formulations. The authors examined the effectiveness of ten pyrethroid insecticide aerosol formulations registered for the household control of flies. Tests were performed using adult Musca domestica L. Knockdown effects and mortality were measured in a test chamber using the manufacturer's recommended discharge time. RESULTS: The knockdown effect varied greatly between aerosols of similar composition. The knockdown 15 min post-treatment was 66-98% for flies placed 120 cm above floor level and 53-96% for flies placed at a height of 180 cm. The KDT(50) values ranged from 2.5 to 9.2 min for flies placed at 120 cm and from 3.2 to 12 min for flies placed at 180 cm. The highest rates of mortality were obtained for a formulation containing S-bioallethrin, permethrin and piperonyl butoxide (81% at 120 cm and 79% at 180 cm). CONCLUSION: Formulations similar in insecticide composition exhibit significant differences in efficacy. Consequently, insecticidal efficacy preregistration evaluations should address not only the efficacy of the active ingredient but also the effectiveness of the formulation.     

Insecticide resistance in houseflies from the middle east and North Africa with notes on the use of various bioassay techniques

The susceptibility to pyrethroid, organochlorine, organophosphorus and carbamate insecticides, of 20 strains of houseflies (Musca domestica L.) collected in the Middle East and North Africa, was assessed by topical application. No resistance to pyrethroids was found but most flies were resistant to DDT, gamma-HCH, organophosphorus and carbamate insecticides. Numerical factors of resistance for a susceptible and two different resistant strains, obtained using different bioassay techniques, were compared. High mortality (≥95%) was achieved with ‘resisted’ insecticides in tests with space sprays, but only low, variable mortality resulted from deposit tests. If this occurs under practical field conditions, moderately resistant populations of flies could be controlled by using space sprays containing comparatively high concentrations of active ingredient, but increased levels of deposit would be ineffective.     

Knockdown by pyrethroids: Its role in the intoxication process

Using techniques for treating the insects unanaesthetised, knockdown of aduit Musca domestica by pyrethrin I applied topically to or injected into the thorax was assessed by measuring the ED₅₀s on 13 occasions 1 min-48 h after treatment. From 1 min to approximately 1 h after treatment, ED₅₀s for topical application decreased quickly with increasing time. During this “knockdown phase” ED₅₀ values were probably determined mainly by rate of penetration of the insecticide into the insect, but the rate of elimination of the insecticide probably determined the increasing ED₅₀ values during the “recovery phase” which followed. ED₅₀s for injected pyrethrin I were initially much smaller than after topical application but increased continuously until 24 h after treatment. From 100 min onwards ED₅₀s by topical application and injection were similar. These results indicate (1) that the site affected during knockdown is within the insect rather than superficial, and (2) that detoxication and excretion processes determine the ultimate toxicity of the insecticide apparently independently of the method of treatment. Additional tests with a strain of flies having the penetration delaying factor and with the cockroach Periplaneta americana L. supported these conclusions. Speed of knockdown after topical treatment was also affected by the site of application and the solvent in which pyrethrin I was applied. Bioresmethrin was about as effective as pyrethrin I in knocking down flies when applied topically or when injected, but because the ED₅₀ increased very little during the recovery phase it was ultimately much more toxic.     

The kinetics of insecticide action. Part II: The relationship between the pharmacokinetics of substituted benzyl (1RS)-cis,trans-chrysanthemates and their relative toxicities to mustard beetles (Phaedon cochleariae fab.)

A mathematical model describing insect pharmacokinetics has been applied to data describing the penetration and elimination of a series of pyrethroid analogues [the methylbenzyl (1 RS)-cis, trans-chrysanthemates], applied to mustard beetles. The three parameters of the model (k_p, k_e and λ) have been estimated for each compound. The influence of chemical structure on pharmacokinetics, investigated using canonical correlation analysis, is discussed in relation to relative toxicity and knockdown action. In general, physicochemical properties which result in a slow flow of insecticide through the insect are associated with high toxicity. A large proportion (84%) of the variation in relative toxicity has been explained by resistance to elimination (1/k_e), implying that exposure of the site of action to insecticide is related to the total integral IM₂ for material (M₂) inside the insect. The remaining variation has been attributed to differences in behaviour at receptor sites. An optimum partition value (Δπ₀ ≈ 1.6) seems necessary for maximum pharmacodynamic activity in this series of compounds.     

Interaction between the factor delaying penetration of insecticides and the desethylation mechanism of resistance in organophosphorus-resistant houseflies

The desethylation (gene a) and penetration delaying (pen) factors of resistance to organophosphorus insecticides isolated by genetical methods from the diazinon-selected SKA strain of houseflies (Musca domestica L.) were inbred into a strain whose resistance was compared with that of flies with single factors of resistance and the SKA strain. Pen alone decreases kill marginally, and gene a alone raises LD₅₀ to 1·4–48 times that of susceptible flies, depending on the insecticide. The two factors together increase resistance greatly to many organophosphorus insecticides (up to 5–10 times or more to diazinon, malathion-ethyl and chlorthion-ethyl than of flies with gene a only) indicating that the two factors interact. Interaction is greater against the thionates than the corresponding phosphates, probably because pen delays entry of thionates more than of the corresponding phosphates. The role in resistance of each factor when hetero-and homo-zygous, and the reasons for interaction, are discussed.     

The Experimental Application of Insecticides from a Helicopter for the Control of Riverine Populations of Glossina tachinoides in West Africa. IV. Evaluation of Insecticides Applied as Aerosols

Abstract

The effects of aerosol dosages of different categories of insecticide were tested against Glossina tachinoides when applied by helicopter to riverine forest habitats of the River Komoe, Upper Volta, West Africa. The method of application, droplet characteristics of the aerosols and meteorological conditions are described in accompanying papers. Comparative trials based on field dosages calculated initially from dosage mortality curves obtained from topical application studies in the laboratory were carried out. Endosulfan applied at 5.4 g a.i./ha and 9.0 g a.i./ha reduced G. tachinoides populations (determined by Challier/Laveissière traps) by more than 90% in all age and sex categories and evidence is presented which indicates a residual effect at the higher of these dosages. Good results were also obtained with the synthetic pyrethroid decamethrin at a dosage of 0.36 g a.i./ha; another synthetic pyrethroid, permethrin, gave promising results at a dosage of 1.9 g a.i./ha. At the higher dosage of 4.3 g a.i./ha disappointing results were obtained, which were considered to be more attributable to a weakness in the application technique under challenging field conditions, than to a limitation of the insecticide. The organophosphate compounds tested, fenthion, azamethiphos and tetrachlorvinphos although known from laboratory tests to be appreciably toxic to G. tachinoides, performed poorly under field conditions. This was thought to be due to the formulations employed and the authors feel that further small-scale field testing of different formulations of these compounds is warranted. The compounds considered most worthy of larger scale field evaluation were endosulfan and permethrin. Although decamethrin was also very toxic to G. tachinoides it was considered inadvisable to field test this compound on a larger scale, until more information was available on its impact on aquatic food chains. The trials demonstrated that it is not always possible to extrapolate from laboratory-obtained comparative dosage/mortality data (in ng/fly) the field dosages of insecticides (in g a.i./ha) required to produce a certain level of mortality in target populations of G. tachinoides.     

Droplet size and efficacy of an adulticide-larvicide ultralow-volume formulation on Aedes aegypti using different solvents and spray application methods

BACKGROUND: When cases of dengue are reported or the density of adult Aedes aegypti (L.) becomes too high, ultralow-volume (ULV) application of insecticides is the recommended control method. The droplet size of an aerosol insecticide influences its efficiency in killing adult mosquitoes. Many studies have been carried out to determine the optimum droplet size that maximises vector control efforts, but only a few have determined droplet-size spectra for specific equipment using different solvents and comparing thermal and non-thermal aerosols. RESULTS: The present study showed that the droplet size for a water-based adulticide–larvicide formulation was larger than for the same formulation diluted in gasoil or biodiesel. No significant differences in adult mortality were observed between sprayers and solvents, but efficacy decreased with distance from the sprayer nozzle. Adult emergence inhibition was more than 90% when using water as a solvent for both thermal and cold foggers, and the efficacy did not decrease with distance from the sprayer nozzle. On the other hand, oil-based solvents became less effective with distance. CONCLUSION: The use of water as a solvent with both thermal and cold foggers improves the efficacy of the studied formulation containing permethrin as adulticide and pyriproxyfen as larvicide in scaled-up assays. Moreover, it reduces the environmental impact and costs of spraying by comparison with formulations using oil solvents. Copyright © 2011 Society of Chemical Industry     

Genetics of resistance of pyrethroid-selected houseflies,Musca domestica L.

Four resistance factors were isolated genetically from the NPR strain of houseflies (Musca domestica L.), which resists natural pyrethrins, and were characterised toxicologically. The four factors were : pen, which reduces the rate of penetration of insecticides through the cuticle; kdr-NPR, a general pyrethroid resistance mechanism unaffected by the synergist sesamex; py-ses, a mechanism of resistance to natural pyrethrins that can be suppressed by sesamex; and py-ex, a factor that gives strong resistance to synergised natural pyrethrins and to the new synthetic esters, e.g. resmethrin, but little or none to natural pyrethrins alone.     

The insecticidal action of some components of wood preservatives

The use of liquid insecticide formulations for prevention and eradication of attack by common wood-boring insects is discussed and some methods of testing and assessing effectiveness described. Gamma-BHC and dieldrin prevent attack when present at 20 g/m³ of softwood while a number of stomach poisons are effective at from 1 to 10 kg/m³. The important part played by the organic solvent in an eradicant formulation is considered. Anobium punctatum in confined spaces can also be controlled by annual use of plastic strips emitting dichlorvos vapour. At 0.015 to 0.05 μg/l in air, dichlorvos virtually prevents initiation or spread of attack by this insect.     

Metabolism of 2-[methoxy(methylthio)phosphinylimino]-3-ethyl-5-methyl-1,3-oxazolidine in the cotton plant and houseflies

The metabolism of 2-[methoxy(methylthio)phosphinylimino]-3-ethyl-5-methyl-1,3-oxazolidine (Stauffer R-16,661), a new experimental insecticide, was investigated in the cotton plant, houseflies, and in in vitro enzymatic and model oxidation systems. The principal metabolite isolated both in vivo and in vitro proved to be the 4-keto derivative of R-16,661. The structure of this metabolite was confirmed by PMR and mass spectral analysis. Toxicological examination showed that the 4-keto metabolite was approximately equal to R-16,661 in toxicity to the white mouse but was substantially less toxic to the housefly.     

Factors affecting the sequential acquisition by Danish houseflies (musca domestica L.) of resistance to organophosphorus insecticides

The prolonged use of dimethoate, introduced into Denmark to control houseflies (Musca domestica L.) that had become resistant to parathion and diazinon, resulted ultimately in dimethoate resistance. Selection with dimethoate led to the disappearance of the hydrolytic phosphatase, a major mechanism of resistance to parathion and diazinon, and its replacement by the acetylcholinesterase AChER with somewhat decreased sensitivity to inhibition by organophosphorus (OP) insecticides. The hydrolytic phosphatase probably disappeared because low substrate turn-over made it ineffective against dimethoxon (O, O-dimethyl S-methylcarbamoylmethyl phosphorothioate, also known as omethoate). which accumulates at higher concentrations than paraoxon (diethyl4-nitrophenyl phosphate) in the haemolymph. Dimethoate selected AChER preferentially because it improved the chances of houseflies surviving against the relatively poor AChE inhibitor dimethoxon, whereas its relatively small insensitivity to OP insecticides, unimportant against good inhibitors such as paraoxon, prevented its selection by parathion.     

Low expression of nicotinic acetylcholine receptor subunit Mdα2 in neonicotinoid‐resistant strains of Musca domestica L.

BACKGROUND: Neonicotinoid action as well as resistance involves interaction with nicotinic acetylcholine receptors (nAChRs). In the housefly, neonicotinoid resistance also involves cytochrome P450, as indicated by bioassay with synergist as well as altered expression. In bioassay, synergism was only partial and indicated possible target‐site resistance. The nAChR α2 subunit is important in neonicotinoid toxicity to insects, and gene expression of the Mdα2 subunit was investigated in field populations and laboratory strains of neonicotinoid‐resistant and insecticide‐susceptible houseflies, Musca domestica L. The genomic sequence covering exon III–VII of Mdα2 was analysed for mutations. RESULTS: Gene expression profiling of Mdα2 revealed notable differences between neonicotinoid‐resistant and insecticide‐susceptible houseflies. On average, the neonicotinoid‐resistant field population 766b and the imidacloprid selected strain 791imi had 60% lower copy numbers of Mdα2 compared with the susceptible reference strain. Sequencing of exon III–VII of the Mdα2, encoding acetylcholine binding‐site regions and three out of four transmembrane domains, did not reveal any mutations explaining the increased neonicotinoid tolerance in the strains examined. CONCLUSION: Previous discoveries and the results of this study suggest that the neonicotinoid resistance mechanism in Danish houseflies involves both cytochrome P450 monooxygenase‐mediated detoxification and reduced expression of the nAChR subunit α2. Copyright © 2010 Society of Chemical Industry     

Insecticide Resistance in the Western Flower Thrips, Frankliniella occidentalis

The western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae) is a serious pest on a wide range of crops throughout the world. F. occidentalis is difficult to control with insecticides because of its thigmokinetic behaviour and resistance to insecticides. Pesticide resistance can have a negative impact on integrated pest management programmes with chemical control as one of the components. Resistance to a number of different insecticides has been shown in many populations of F. occidentalis. This flower thrips has the potential of fast development of resistance owing to the short generation time, high fecundity, and a haplodiploid breeding system. The mechanisms conferring insecticide resistance in insects can be divided into four levels. First, an altered behaviour can aid the insect to avoid coming into contact with the insecticide. Second, a delayed penetration through the integument will reduce the effect of the insecticide at the target site. Third, inside the insect, detoxification enzymes may metabolise and thereby inactivate the insecticide. Fourth, the last level of resistance mechanisms is alterations at the target site for the insecticide. Knowledge of resistance mechanisms can give information and tools to be used in management of the resistance problem. Recently, studies have been carried out to investigate the underlying mechanisms conferring resistance in F. occidentalis. It appears that resistance in F. occidentalis is polyfactorial; different mechanisms can confer resistance in different populations and different mechanisms may coexist in the same population. Possible resistance mechanisms in F. occidentalis include: reduced penetration, detoxification by P450-monooxygenases, esterases and glutathione S-transferases, and alterations of acetylcholinesterase, the target site for organophosphate and carbamate insecticides. Target site resistance to pyrethroids (knockdown resistance) may also be a resistance mechanism in F. occidentalis.     

Environmental degradation of the insect growth regulator methoprene: V. Metabolism by houseflies and mosquitoes

The metabolism of methoprene (I, isopropyl (2E,4E)-11-methoxy-3,7,11-trimethyl-2,4-dodecadienoate, trademark Altosid) was investigated in larval mosquitoes and houseflies. The most abundant primary metabolite in third- and fourth-instar Aedes and fourth-instar Culex larvae was the hydroxy ester while the hydroxy acid predominated in third-instar Musca larvae. Biological isomerization of the double bond at C-2 in I (i.e., conversion of (E) to (Z)) was an effective mode of insect detoxication, but these dipterans apparently cannot isomerize the (2Z) isomer of I to methoprene. In general, piperonyl butoxide and triorthocresyl phosphate slightly increased the morphogenetic activity of I in these insects.