Brief exposure of Blattella germanica (Blattodea) to insecticides formulated in various microcapsule sizes and applied on porous and non-porous surfaces

BACKGROUND: The authors explored how microcapsule size and brief exposure affected the bioavailability of five microencapsulated insecticide formulations, chlorpyrifos 23.1 g L(-1) CS (Detmol-PRO), chlorpyrifos 20 g L(-1) CS (Empire 20), fenitrothion 20 g L(-1) CS (Detmol-Mic), cyphenothrin 10 g L(-1) CS (Detmol-CAP) and diazinon 30 g L(-1) CS (Diacap), to Blattella germanica L. on porous and non-porous surfaces. The hypothesis was tested that microencapsulated (CS) insecticides comprising larger microcapsules show higher efficacy on porous surfaces than formulations with smaller microcapsules. RESULTS: Brief exposure was accomplished by allowing B. germanica to cross a 0.3 m insecticide barrier in 30 s (1.01 cm s(-1)). Such short exposure did not lead to 100% mortality in any formulation or surface tested. Significant differences in bioavailability on the porous and the non-porous surfaces were found: the largest difference was observed in Empire 20 and Detmol CAP, while bioavailability of Detmol MIC did not differ on porous and non-porous surfaces. Comparison of their microcapsule size spectra revealed that formulations containing larger microcapsules had higher efficacy on porous surfaces than formulations with smaller microcapsules. In order to explain the difference in efficacy, the variance of microcapsule sizes was regressed on the efficacy ratio on porous versus non-porous surfaces. Although negative correlation was evident between size of capsules and the efficacy ratio on porous and non-porous surfaces, the difference in the slope parameter was not statistically significant. CONCLUSION: Brief contact of B. germanica with insecticide spray residues, which is common in barrier treatment, may lead to low efficacy, especially on porous surfaces. The latter should be preferably treated with CS insecticides containing a fraction with large capsules. In addition to the size of the microcapsules, the role of other factors, such as wall capsule thickness and chemical composition, on CS insecticide activity on various surfaces should be examined in future work.     

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.     

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     

Evaluation of oil formulations of deltamethrin for use on cotton targets for tsetse fly control

A range of formulations of deltamethrin were prepared, some containing an ultraviolet (UV) absorber compound or a combination of the UV absorber and an oil, and applied to blue cotton tsetse fly target samples which were then exposed to the effect of simulated sunlight and water in the laboratory. The residue of insecticide remaining on the targets and the activity of the latter against tsetse flies was determined. Formulations containing the UV absorber and coconut oil or silicone oil remained the most effective against tsetse flies. A coconut oil formulation of the insecticide was selected for field evaluation in comparison with a commercial deltamethrin formulation, Glossinex 200′ S.C., which contains 10% UV absorber. Target samples treated with these formulations were exposed to natural tsetse fly habitat in Ghana for a period of five months and evaluated for deltamethrin residues and activity against four species of tsetse fly. After five months, 4–13 times more deltamethrin remained on the targets treated with the coconut oil formulation than on those treated with ‘Glossinex’, and consequently the former were more active against tsetse flies than the latter. Target samples sequentially dipped in the coconut oil formulation resulted in uniform insecticide concentration on the targets, whereas those dipped in ‘Glossinex’ contained gradually decreasing deltamethrin concentrations.     

Thermal behaviour and biological activity against Aedes aegypti (Diptera: Culicidae) of permethrin and pyriproxyfen in a smoke‐generating formulation

BACKGROUND: The most common ways to control dengue vector Aedes aegypti (L.) are larval source reduction in domestic habitats and ground application of small quantities of aerosol insecticide (ultralow volume). Nevertheless, these actions have been shown repeatedly to be ineffective in controlling Ae. aegypti populations. RESULTS: The efficacy of a new smoke‐generating formulation containing pyriproxyfen and permethrin was evaluated in the laboratory. Smoke‐generating tablets containing each insecticide individually or combined were prepared, and the recovery of the insecticides from the smoke was determined. Recovery values of over 90% were obtained for pyriproxyfen, and around 50% for permethrin. The biological efficacy of pyriproxyfen released in the smoke was evaluated in the laboratory, on late third‐instar or early fourth‐instar Ae. aegypti larvae, using different concentrations of pyriproxyfen and exposure times. Adult emergence inhibition (EI) values of 100% were obtained at 30 min, and a dose‐dependent effect was observed at 5 min. The effect of pyriproxyfen released in the smoke was due to direct contact with the larvicide in the water rather than by inhalation of the fumes. The efficacy of permethrin released in the fumes was also evaluated as knockdown effect (KT₅₀) on adults for a tablet containing permethrin alone or permethrin plus pyriproxyfen. There was no significant difference in KT₅₀ values obtained for permethrin (KT₅₀ = 19.9 min) and permethrin plus pyriproxyfen (KT₅₀ = 19.4 min). CONCLUSION: The excellent laboratory performance of this new formulation on immature stages and adults indicates that a smoke‐generating tablet containing pyriproxyfen and permethrin could be a new tool for controlling mosquitoes. Copyright © 2009 Society of Chemical Industry     

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.     

A push–pull strategy to suppress stable fly (Diptera: Muscidae) attacks on pasture cattle via a coconut oil fatty acid repellent formulation and traps with m-cresol lures

BACKGROUND

Stable flies [Stomoxys calcitrans (L.)] are economically important pests of cattle and other livestock. As an alternative to conventional insecticides, we tested a push–pull management strategy using a coconut oil fatty acid repellent formulation and an attractant-added stable fly trap.

RESULTS

In our field trials we found that weekly applications of a push–pull strategy can reduce stable fly populations on cattle as well as a standard insecticide (permethrin). We also found that the efficacy periods of the push–pull and permethrin treatments following on-animal application were equivalent. Traps with an attractant lure used as the pull component of the push–pull strategy captured sufficient numbers of stable flies to reduce on-animal numbers by an estimated 17–21%.

CONCLUSIONS

This is the first proof-of-concept field trial demonstrating the effectiveness of a push–pull strategy using a coconut oil fatty acid-based repellent formulation and traps with an attractant lure to manage stable flies on pasture cattle. Also notable is that the push–pull strategy had an efficacy period equivalent to that of a standard, conventional insecticide under field conditions. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

The influence of spray droplet characteristics on the efficacy of permethrin against the diamondback moth Plutella xylostella: The effect of drop size and concentration on the potency of ulv- and ec-based residual deposits

The effect of droplet diameter (36-274 μm) and concentration (10-400 g litre^?1) of permethrin on the knockdown and mortality of 2nd-instar Plutella xylostella larvae was investigated. Larvae were placed on brussels sprout leaf discs treated with residual deposits of permethrin applied as ULV or emulsion formulations. The LD₅₀ of permethrin decreased with droplet size at all concentrations tested. This effect could not be accounted for solely by increased drop numbers per unit area of leaf, suggesting that for both formulations transfer of permethrin to larvae is more efficient for deposits composed of small drops. The concentration of permethrin in the ULV formulation could be reduced to approach a minimum quantity of toxicant per unit area to maintain 50 per cent mortality. The approach to the minimum dose varied with drop size and drop number per unit leaf area. The ULV formulation was approximately 2.7 times more effective at killing larvae than the emulsion, presumably as a result of greater availability of toxicant and transfer to larvae.     

Susceptibility of house flies (Diptera: Muscidae) exposed to commercial insecticides on painted and unpainted plywood panels

House flies were collected from dairies in New York state and the levels of resistance to commercially available insecticide formulations were measured on painted and unpainted plywood panels. Dimethoate was ineffective on all surfaces. The wettable powder permethrin formulation was more toxic than the emulsifiable concentrate formulation. The wettable powder cyfluthrin formulation was also more toxic than the recently developed liquid formulation. In general, the best house fly control was obtained on flat latex painted plywood panels and the poorest control on gloss latex painted panels. It is highly unlikely that producers obtain adequate control with dimethoate and permethrin.     

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     

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.     

Development of a waste brewery yeast larval diet for rearing Bactrocera zonata for use in SIT

In Mauritius, the sterile insect technique (SIT) is being developed to manage the Peach fruit fly, Bactrocera zonata (Saunders) (Diptera: Tephritidae). Novel and economical larval diets are needed to produce millions of artificially reared sterile flies needed to ensure the success of this programme. We assessed the efficacy of conventional (solid) and gel diets with formulations containing modified waste brewery yeast (WBY), an alternative low cost protein source. The WBY is obtained freely from the manufacturing plant located at the Entomology Division of the Ministry of Agro Industry & Food Security, Réduit, Mauritius. Its chemical composition is highly comparable to those of the imported commercial yeast. Formulations of both diet types varied in the ratio of WBY (%) to commercial yeast (CY) (%) (Control: 0:100, A: 25:75, B: 30:70; C: 40:60; D: 50:50). The quality parameters of flies reared on the modified gel larval diets i.e. volume of pupae, pupal weight, pupal recovery, percentage adult emergence and percentage fliers were comparatively better on the gel diet formulations B, C and D, while no significant difference in percentage egg hatch was observed between the conventional diet and the gel diet. The optimum egg seeding rate (larval density) for selected gel diets B, C and D was determined. Formulation C using 0.15 ml of eggs/100 g of diet resulted in the highest pupal recovery, pupal weight, emergence and flight ability. A five-year cost benefit analysis revealed a net cost saving of 38% (US$ 53 418.20) by using the gel diet with WBY instead of the solid diet. The cost for the production for one million flies is US$ 310.67. Our results demonstrate that the selected gel diet formulation in which commercial yeast is partially replaced by waste brewery yeast is a viable alternative to the conventional solid diet for rearing of B. zonata. There are also the added benefits in terms of reduced cost with respect to storage and disposal, due to the elimination of bulking agents.

     

Incorporation and stability of chlorfenvinphos,chlorpyrifos, diazinon and phorate in peat blocks

Factors likely to influence the uniformity of treatment and the stability of the insecticides incorporated into peat blocks were investigated. When an Adelphi horizontal mixer was used, 90% of the blocks contained the mean dose (±10%) after dry-mixing the diazinon granules for 3 min. Treatment was slightly less uniform using a concrete mixer or a spade. Between-block variability was greatest when diazinon was applied to the wet surfaces of prepared blocks; in this process, sprinkling granules by hand was less erratic than spraying a liquid formulation. When granular, wettable powder, or emulsifiable concentrate formulations of diazinon were incorporated using the Adelphi mixer, neither the between-block variability nor the subsequent stability of the insecticide were significantly influenced by the formulation used. Insecticide stability was studied by incorporating chlorfenvinphos, chlorpyrifos, diazinon and phorate at 10 mg a.i. per block in January, March, May and July. The relative order of persistence was chlorfenvinphosChlorpyrifos > phorate≫diazinon. There was little loss of insecticide ( < 10%) from the blocks treated with chlorfenvinphos or chlorpyrifos, and the stability of the insecticides was unaffected by seasonal temperature changes, but the rate of loss of diazinon increased markedly from January to July. The rate of oxidation of phorate to its sulphoxide and sulphone analogues increased gradually from January to May but was much slower than in the field after a bow-wave application. With all insecticides, there was no significant difference in loss rates at 25 and 10 mg a.i. per block. After incorporation into three moss peats and two proprietary blocking composts, there was no consistent difference in the rates of loss of either diazinon or of total phorate residues, although the rates of oxidation of phorate and its sulphoxide were not similar in all the peats and composts. It was concluded that, despite the substantial water content and high insecticide concentrations, the principal factor determining insecticide behaviour in the blocks was the adsorptive capacity of the peat.     

Systemic effects of thiamethoxam and chlorantraniliprole seed treatments on adult Lissorhoptrus oryzophilus (Coleoptera: Curculionidae) in rice

BACKGROUND: Feeding assays using adult rice water weevils and foliage of plants treated as seeds with chlorantraniliprole and thiamethoxam at different rates were conducted to evaluate the systemic adulticidal and feeding effects. Dose–mortality relationships were determined for thiamethoxam seed treatments by combining leaf area lost due to feeding and insecticide residues analyzed by LC/MS/MS. Changes in adulticidal activity of thiamethoxam were also investigated by contrasting adult mortalities at the 5–6‐leaf and tillering stages of rice. RESULTS: Adult weevil mortalities and leaf consumption rates on foliage were affected in thiamethoxam but not in chlorantraniliprole treatments when rice was at the 6–7‐leaf stage. The LD₅₀ for weevils feeding on thiamethoxam‐treated rice at the 2–3‐leaf stage was 447 pg insecticide weevil^?1 (95% CL: 25–830 pg weevil^?1) but was lower (142 pg weevil^?1; 95% CL: 102–180 pg weevil^?1) in experiments with 3–4‐leaf‐stage plants. Mortalities on leaves from 5–6‐leaf‐stage plants were consistently higher than on leaves from tillering plants. Thiamethoxam residues measured by ELISA increased with seed treatment rate and differed between plant stages. CONCLUSION: The LD₅₀ values developed in this study are the first values for leaf‐feeding insects on foliage of plants treated as seeds with thiamethoxam. The attrition of adulticidal activity of thiamethoxam in foliage of older plants may help to explain the reduced effectiveness of seed treatments against rice water larvae that is seen at later stages of rice growth in field studies. The differential activity of these two seed treatments on adults suggests that adult mortality contributes to the field efficacy of thiamethoxam but not to that of chlorantraniliprole. Copyright © 2012 Society of Chemical Industry     

Surfaces and other factors modifying the effectiveness of pyrethroids against insects in public health

Features of the evolution of synthetic pyrethroid insecticides are reviewed and related to the target function in control. The factors affecting residual activity are discussed and related to the surfaces to which different formulations are applied. Many insecticide/formulation/surface combinations lose effectiveness rapidly. The consequence of this in relation to the recovery of cockroach populations are discussed using mathematical models and field observations.     

Is attract‐and‐kill technology potent against insecticide‐resistant Lepidoptera?

Attract-and-kill techniques, associating an attractant and a contact insecticide in a sticky formulation, are a new way of controlling Lepidopteran pests. Insecticide resistance may, however, limit the effectiveness and even the attractiveness of such formulations where resistance pleiotropic effects influence pheromone perception. We have tested this hypothesis on resistant codling moths Cydia pomonella (L) using a commercial formulation containing (E,E)-8,10-dodecadien-1-ol (codlemone), the major component of the sex pheromone, as an attractant and permethrin as toxicant. We first compared the attractiveness of codlemone in a wind tunnel and the contact toxicity of pyrethroids on males of one susceptible and of three strains selected for resistance to diflubenzuron, deltamethrin and azinphos-methyl. The dose-response relationships of males of susceptible and resistant strains to codlemone did not differ significantly. The deltamethrin-selected strain was the most resistant to pyrethroids, exhibiting 138-, 25- and 18-fold resistance ratios to deltamethrin, cypermethrin and permethrin, respectively. The efficiency of the attracticide formulation, applied successively on filter paper support, glass support and wood support, was estimated by recording the mortality delay of males after natural contact with the formulation in the wind tunnel. The deltamethrin- and diflubenzuron-resistant strains were significantly less affected than the susceptible strain by contact with the attracticide on the wooden support, exhibiting 58- and 2.3-fold greater LT50 ratios, respectively. Mortality of deltamethrin-resistant moths did not exceed 40% after 48 h. The LT50 value was significantly greater on filter paper support than on the two other supports. Surprisingly, the LT50 ratio of the deltamethrin-resistant strain was markedly higher on filter paper support (1021-fold), which was more absorbent, than on the glass support (31-fold). No sublethal effects in terms of pheromone response, mating or fecundity occurred in moths surviving contact with the attracticide. Choice of insecticides in attracticide formulations will be influenced by the resistance background of the target pests. Principles of insecticide resistance management may also be applied to attract-and-kill technology by alternating with other insecticides or control methods.     

The interactions between routes of exposure and physicochemical properties of four water-dilutable permethrin formulations in relation to their activities against Trichoplusia ni (Hubner)

A series of laboratory experiments were undertaken to compare the activities of four water-dilutable permethrin formulations against the cabbage looper Trichoplusia ni (Hubner). The formulations used were “Pounce 3.2 EC”, “Ambush 2.0 EC” and two novel formulations (containing evaporation retardants) supplied, for comparison, by Roussel Uclaf Environmental Health Ltd, Berkhamsted, UK (formerly Wellcome Environmental Health Ltd). Bioassays were developed to investigate the activity of the insecticides via topical, residual and residual/dietary routes of exposure. The test insects were exposed to insecticide droplets, of 200 μm diameter, either directly or indirectly (on cabbage leaves or parafilm) using an on-demand droplet generator. Following exposure to insecticide, the test species were confined in petri dishes and mortality assessments were made at 24 h after treatment. The results were analyzed using probits. The results indicated that up to 15-fold differences in activity between formulations may occur when exposure is via residual contact on an artificial waxy surface (parafilm). The novel formulations were found to be far more active than the standard EC formulations. These differences in activity were significantly correlated with the dynamic surface tension and droplet spread upon cabbage leaves of the formulations. The results are discussed in terms of the bioavailability of pyrethroids upon waxy surfaces and also in terms of the potential for manipulating the pick-up of pesticides from plant surfaces.     

Some experiments with different formulations of organophosphorus insecticides as seed dressings to control wheat bulb fly (Leptohylemyia coarctata)

Experiments on the control of wheat bulb fly larvae by seed dressings compared four organophosphorus compounds in standard siliceous earth formulations with special formulations of the same compounds in polyvinyl acetate, polypropylene or wax. The special formulations allowed more insecticide to be placed on the seeds without affecting germination. Counting shoots damaged by wheat bulb fly larvae showed that: siliceous earth formulations of diazinon gave good control which was not improved by special formulations; control with siliceous earth formulations of dimethoate was poor and was improved only little by the special formulations; and control with siliceous earth formulations of parathion and dichlofenthion was moderate and was improved by special formulations, especially polyvinyl acetate and polypropylene. The results suggest that special formulations are of most value with compounds that are moderately effective but where the amount of insecticide in standard seed dressings cannot be increased without damaging the plants.     

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.     

Mobility and persistence of isazofos in granular and microencapsulated formulations in two soils,using field lysimeters

Field lysimeters were used to assess the mobility and persistence of microencapsulated and granular formulations of the soil insecticide, isazofos, in Plainfield sand, and the microencapsulated formulation in Vittoria loam soil, using two moisture regimes, rainfall and supplementary watering. Mobility and persistence comparisons were made with an earlier lysimeter study which used emulsifiable concentrate (EC) and granular formulations of isazofos in Plainfield sand. Isazofos mobility in Plainfield sand increased in the following order for the tested formulations: microencapsulated < granular ≦ EC. Atrazine, which was applied as a suspension concentrate to all lysimeters as an internal reference, appeared to exhibit retarded disappearance rates during initial stages of the study when in the presence of granular isazofos in the rainfall treatment. The degradation of isazofos was faster in Vittoria loam than in Plainfield sand for the microencapsulated formulation in the field lysimeters (only formulation tested), and for all three formulations in a laboratory study.