Effect of different droplet size on the knockdown efficacy of directly sprayed insecticides

BACKGROUND: Although insecticidal aerosols have been widely accepted for household use, the discharged amount should be maintained at minimum levels because they contain volatile organic compounds. Hence, it would be valuable to develop a technique whereby insecticide droplets adhere efficiently to an insect's body. The present study was undertaken in order to clarify how differences in the mode of adhesion to the insect body influence the knockdown effect. RESULTS: When the discharged volume of droplets with different diameters was the same, the adhesion volume of larger droplets was twice that of smaller droplets, resulting in a higher insect knockdown. In contrast, when the adhesion volume of the two droplet types was the same, a greater number of smaller droplets than larger droplets adhered, and the smaller droplets caused higher insect knockdown. The knockdown effect of both droplet types was lowered when the mesothoracic spiracles of cockroaches were blocked; however, the effect of larger droplets was lowered to a lesser degree. CONCLUSION: The results suggest that, the probability of adhesion to the more susceptible regions of an insect's body, i.e., areas surrounding the mesothoracic spiracles, was improved when a greater number of smaller droplets were adhered, resulting in higher knockdown. Copyright © 2011 Society of Chemical Industry     

Characteristics and implications of knockdown of the tsetse fly Glossina morsitans morsitans westw. by deltamethrin

Low doses of deltamethrin cause prolonged knockdown of the tsetse fly Glossina morsitans morsitans. Fifty per cent of female flies, treated with the LD₁₅-(48 h) of deltamethrin, failed to regain their capacity for normal flight for 30 h, compared with 6 h for bioresmethrin and 4 h for permethtin at the equivalent dose. Recovery after exposure to tetramethrin occurred within 1 h. The knockdown effect of deltamethrin on males was even more pronounced although, with both sexes, the onset of the effect was delayed for about 3 h. It is suggested that this prolonged knockdown effect of deltamethrin, at extremely low application rates, may make a significant contribution to the effectiveness of the compound against the tsetse fly.     

Quantitative structure-activity studies of substituted benzyl chrysanthemates: 4. Physicochemical properties and the rate of progress of the knockdown symptom induced in house flies

A procedure to evaluate the knockdown activity of pyrethroids against house flies in which metabolic factors could be eliminated as far as possible was established. With piperonyl butoxide and NIA 16388 as the inhibitors of oxidative and hydrolytic metabolism, respectively, the “intrinsic” knockdown potencies of 22 substituted benzyl (1R)-trans-chrysanthemates and related compounds were determined 2.5–3 hr after topical application to house flies. From the intrinsic knockdown potency and the rate of progress of the knockdown symptom from the earliest stage of intoxication, a “penetration” rate constant was estimated by first-order kinetics using a two-compartment model. The rate constant was correlated quantitatively with the hydrophobic parameter of the molecule. The lower the hydrophobicity, the higher the rate constant within the range of compounds used in this study.     

Time-dose-response relationships of pyrethroid insecticides with special reference to knockdown

The relationship between incoordination, knockdown and mortality was investigated by following the course of poisoning in Schistocerca gregaria of two synthetic pyrethroids, bioresmethrin and bioallethrin. Kinetics describing theonset of these responses as a function of dose are interpreted in terms of the dynamics of penetration and detoxication. The possibility of the same site of action for knockdown and kill is briefly discussed.     

Quick knockdown results in high mortality: is this theory correct? A case study with phosphine and the red flour beetle

BACKGROUND

The fumigant phosphine is used all over the world for disinfestation of stored grains and commodities. Adults of 23 different populations of Tribolium castaneum from 10 different countries were evaluated for phosphine resistance using a modification of the Detia Degesch Phosphine Tolerance Test Kit (DDPTTK). Adults were exposed to 3000 ppm and recorded for 5–270 min for their mobility.

RESULTS

Among the tested populations, high levels of phosphine resistance were recorded in populations from Brazil, Serbia, and Spain. No survivals were recorded after 7 days post exposure for eight of 23 in a tested population.

CONCLUSIONS

Our work revealed four scenarios: 1, quick knockdown–low (or no) recovery; 2, Slow knockdown–high recovery; 3, Quick knockdown–high recovery; and 4, Slow knockdown–low recovery. Our data indicate that post exposure period is critical for the evaluation and characterization of phosphine resistance. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Activity of some new pyrethroids against Blattella germanica L.

The activities of natural and synthetic pyrethroids against male German cockroaches (Blattella germanica) were examined by means of dusting and direct spraying techniques. NRDC 107 (5-benzyl-3-furylmethyl (+)-trans-chrysanthemate) was the most active compound in killing cockroaches. Pyrethrins gave the most rapid knockdown and were 60% as active as NRDC 107 (Bioresmethrin) in killing power. Tetramethrin and the corresponding (+)-trans-ester gave rapid knockdown. Only (+)-trans-allethrin [(+)-trans-chrysan-themate of (±)-allethrolone] provided useful knockdown and killing power together. Piperonyl butoxide had a relatively stronger synergistic action with less active killing agents. The rate of knockdown during the first few minutes of exposure was not altered greatly by piperonyl butoxide.     

A new pyrethroid-type ester with strong knockdown activity

Thirteen pyrethroid-type esters of substituted 1(or 3)-hydroxymethylimidazolidine-2, 4-dione were synthesised and their knockdown activities against houseflies, mosquitoes and cockroaches were examined. Knockdown activities of 2,4-dioxo-1-prop-2-ynylimidazolidin-3-ylmethyl esters in oil solutions were higher than those of known knockdown pyrethroids; three of the compounds also possessed strong knockdown and flushing-out activities against cockroaches.     

The activity of some pyrethroids against Periplaneta americana and Blattella germanica

The knockdown and contact killing actions of various pyrethroids were compared using Blattella germanica and Periplaneta americana. A wide range of knockdown activity was found; 5-benzyl-3-furylmethyl (1R)-cis-3-(dihydro-2-oxo-3-thienylidenemethyl)-2,2-dimethylcyclopropanecarboxylate (RU 15525) acted fastest, more rapidly than pyrethrins, against B. germanica as well as having a low LD₅₀ value. Topical application and direct spray tests showed that (S)-α-cyano-3-phenoxybenzyl (1R)-cir-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropanecarboxylate (NRDC 161) was more active as a killing agent, by an order of magnitude, than cismethrin, the next most active compound, and also had considerable knockdown activity. Piperonyl butoxide generally had little synergist effect. Female P. americana were over three times more tolerant than males to a range of insecticides applied topically. Residual knockdown action in the WHO resistance test was observed to provide baseline data. There was little overlap in speed of action between pyrethroids and other insecticides among the compounds tested.     

Factors which influence the knockdown effect of insecticide products

Knockdown in insects following application of an insecticide may be defined as the state of intoxication and partial paralysis which usually precedes death. Pyrethroid insecticides cause knockdown within a few minutes in contrast to the slower action of other groups of compounds. Users throughout the world have varying interpretations of knockdown and may apply different emphasis depending upon the species involved and local application techniques. To obtain valid assessments it is necessary to carry out tests under the most realistic conditions possible and to see that the effects of variations in procedure are taken into full account. Some factors which influence knockdown are: single rapid dosing or continuous pick-up during the observation period; size and distribution of spray-droplets; size of test chamber; interaction in mixtures of synergist and insecticides; use of organic solvents or water-based formulations. Examples of these are given.     

Assessing the performance against houseflies of indoor aerosol space sprays. Part I. Factors examined during tests with houseflies in free flight

The development of a mathematical model which, by quantifying the interaction of a population of houseflies with an ageing spray cloud, is capable of predicting the knockdown and kill performance of insecticidal aerosol formulations shown against houseflies, Musca domestica L., will be presented in a series of four separate papers. In this first paper, measurements were made of insecticide collected by houseflies during free flight using a standard room-spray technique. With pressure-packed aerosol formulations where the solvent is the principal change, it was shown that both knockdown and mortality responses of the insects were directly related to dose collected. The process of droplet collection was most significantly influenced by their size and availability, dependent upon the time after spraying, the position of insect release and the activity of individual adult M. domestica. The knockdown or mortality response of the insect to given amounts of insecticide was largely unaffected by the remaining solvent, although, with mineral oil, some inhibition was noted at low mortality levels. The amount of insecticide accumulated by houseflies in their initial flight was of prime importance in determining the overall effect. Flies remaining not knocked down at the end of the exposure period were shown to be so because they had accumulated less toxicant and not necessarily because they were more tolerant of the insecticide. The establishment of a relationship between the number of flies in flight and time after release has provided a key function for incorporation into the model.     

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 detoxification indicator strains as tools for enhancing chemical discovery screens

BACKGROUND: Insecticide discovery screens carried out on whole organisms screen for potency resulting from chemical activity at the target site. However, many potentially insecticidal compounds are naturally detoxified in vivo and do not make it to the target site. It is hypothesised that insect strains with their xenobiotic detoxification machinery compromised could be used to identify such compounds that normally fail to show up in screens; these compounds could then be more rationally designed to increase their bioavailability. This strategy was tested with transgenic Drosophila lines with altered expression of Cyp6g1 and Dhr96. RESULTS: It was observed that Cyp6g1 knockdown transgenic lines have increased susceptibility to the test compound imidacloprid, while Dhr96 knockdown transgenic lines are resistant. Evidence was found for a systemic response to xenobiotic exposure, uncovered by piperonyl butoxide treatment and by gene expression profiling. Sex-specific gene expression regulated by DHR96 was also observed. CONCLUSION: The results confirm that this approach to chemical discovery could identify compounds that escape traditional screens. The complexity of the system means that a panel of single and multiple gene knockdown transgenic lines may be required. Copyright © 2011 Society of Chemical Industry     

Screening techniques for the evaluation of chemicals with activity as tick repellents

Screening techniques are described for the evaluation of the activity of tick repellents in vitro and in vivo, for the control of ticks of veterinary importance. In addition a modification of the in-vitro technique is described whereby the knockdown activity of chemicals may be assessed. There was a lack of correlation between results obtained in vitro and those obtained in vivo. Butopyranoxyl and N, N-diethyl-m-toluamide, which were highly active in vitro, showed only medium to low activity in vivo. Conversely, benzyl benzoate and dimethyl carbate, which were highly active in vivo, showed only low activity in vitro. Chemical breakdown, volatility, the ability of the chemical to bind to hair and skin, and differences in the behaviour and the morphology and physiology of the sense organs between larval and adult Rhipicephalus evertsi evertsi (Neumann 1897) are suggested as likely explanations for these differences in activity. Of the four synthetic pyrethroids tested, cypermethrin, deltamethrin, permethrin and fenvalerate, only the first three were shown to have good knockdown activity but only two, deltamethrin and permethrin, produced significant mortality of the exposed larvae. Further tests would be required to determine whether there is a correlation between knockdown and mortality.     

10th British Weed Control Conference

The performance of different spray droplet spectra of cypermethrin from cone nozzles applied to brassica leaves was evaluated by bioassay using Plutella xylostella larvae. A spray droplet spectrum containing small droplets (VMD = 119 μm) caused a significantly higher knockdown and mortality compared to a coarser spray (VMD = 210 μm). No significant difference in the responses was observed when cypermethrin was sprayed over the top of the plants compared to plants sprayed from both sides using either nozzle; but the fine spray consistently gave better knockdown and mortality regardless of spray direction. The results indicated that spray effectiveness of cypermethrin could be improved by using a fine spray nozzle.     

Insecticidal properties of some allethrin isomers used in coil formulations against mosquitoes

Previous studies have been made on the relative efficacy of the eight possible stereoisomers of allethrolonyl chrysanthemate. Some of these compounds and their mixtures have been classified according to their knockdown activity against Aedes aegypti. Two techniques were used, the contact method recommended by WHO and the method described by Katsuda and Ogami to study the effect on mosquitoes of the smoke from burning coils. Results show that on Aedes aegypti, the relative knockdown activity of the various stereoisomers of allethrin was about the same with both methods. The d trans chrysanthemate of d allethrolone (S-Bioallethrin) was the most effective.     

Effects of diazepam and chlordimeform analogs on the German and the American cockroaches

Twenty-one diazepam- and chlordimeform (CDM)-related compounds were synthesized by mimicking some parts of the 1,4-benzodiazepine tranquilizing drugs, and were tested for their insecticidal activity against the German cockroach. Some of these compounds showed knockdown effects and some were insecticidal. Against the German cockroach the most toxic CDM analog was N-propargyl CDM (compound 6), and that with a potent knockdown potency was compound 13 which has a structural resemblance to diazepam. Ligand-receptor binding assay was carried out, using [³H]diazepam as a ligand to examine the relation between CDM-related compounds and the 1,4-benzodiazepines. The [³H]diazepam binding to a specific site in the American cockroach brain was inhibited by the insecticidal compounds. Among these compounds a correlation exists between their inhibitory potency on specific [³H]diazepam binding and their insecticidal activity, suggesting a possible significance of such an interaction with the diazepam binding site for the toxicity of these compounds against cockroaches.     

Quantitative structure-activity relationships of pyrethroid insecticides

The structure-activity relationships of two congeneric series of pyrethroid insecticides, the methylbenzyl (1RS)-cis,trans-chrysanthemates tested against Musca domestica (houseflies) and Phaedon cochleariae (mustard beetles), and the (E)-4-aryl-3-chlorobut-2-enyl chrysanthemates and their corresponding 2,2,3,3-tetramethylcyclo-propanecarboxylates tested against M. domestica only, have been examined using multiple regression analyses and substituent constants. With M. domestica, different optimum partition values (π) were indicated for knockdown and toxicity; with P. cochleariae, an optimum π value for toxicity, similar to that for M. domestica, was obtained 24 h after application, but at later times the more lipophilic compounds were more effective. For the methylbenzyl chrysanthemates, a steric constraint associated with 3,5-dimethyl substitution reduced toxicity approximately five-fold. The influence on toxicity of geometrical isomerism and electronic effects are briefly discussed. Differences between the required polarities for knockdown and toxicity are attributed to variations in the binding affinities of pyrethroid molecules at the sites of action.     

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.     

Oil formulation of pyrethroids for contamination of tsetse flies (Glossina spp.) through tarsal contact with treated targets

Mosquito netting side panels of targets used for tsetse control were treated with lambda-cyhalothrin, either dissolved in a mixture of acetone and a chlorohydrocarbon oil, ‘Cereclor’® > (ICI, UK) or as a conventional wettable powder formulation suspended in water. Treated netting samples were weathered under natural conditions in full sun in Zimbabwe. Following brief tarsal contact of test insects (adults of Glossina morsitans morsitans Westw.) with treated netting, the wettable powder induced 100% knockdown for four months after treatment but 24-hour mortality levels were reduced from the third month onwards. The oil formulation induced 100% knockdown for up to ten months following treatment and 100% mortality at 24 hours for up to eight months. Chemical assay showed that after two months there had been a rapid reduction in the amount of active ingredient to only 20% of that applied using the wettable powder, whereas the oil formulation took seven months to fall to this level. Provided that at least 5% of the original amount of pyrethroid remained on the fabric it was quite effective and the superiority of the oil formulation was further enhanced by the observation that the starting concentration was only 25% of that of the wettable powder.