Investigation of sodium monofluoroacetate (1080) bait shyness in wild brushtail possum (Trichosurus vulpecula) populations

Bait shyness is a significant threat to the sustainable control of vertebrate pests. New Zealand's foremost vertebrate pest is the introduced brushtail possum (Trichosurus vulpecula). Bait shyness was identified in two wild possum populations by comparing the consumption of two non-toxic bait types before and after each population was presented with one of the bait types containing the toxin sodium monofluoroacetate (1080). Before poisoning, approximately 60% of total bait consumption was of the type which 1080 was later presented in, whereas after poisoning this bait type made up only 2-4% of total consumption. This shyness persisted for at least 11 weeks in one of the populations. No individual component (bait base, cinnamon lure or green dye) of the toxic bait could be isolated as the primary cue eliciting bait shyness as the response. Possible means of overcoming bait shyness are discussed in light of these findings.     

Bait aggregation to reduce cost and toxin use in aerial 1080 baiting of small mammal pests in New Zealand

BACKGROUND: The metabolic toxin sodium fluoroacetate (‘compound 1080’) is widely used for controlling introduced mammalian pests in New Zealand. For large-scale operations, 1080 is distributed aerially in bait to kill brushtail possums (Trichosurus vulpecula Kerr) and ship rats (Rattus rattus L.). While usually successful in reducing pest populations by > 80%, widespread distribution of toxic bait is relatively expensive and raises concerns from some members of the public. Here, trials with spatial aggregation of baits in forested habitats were conducted to determine whether this can reduce toxin usage while maintaining operational efficacy. RESULTS: When 1080 baits were aggregated into clusters (by hand sowing) or into strips (by precision aerial deployment), indices of possum relative abundance were reduced by 92–100%, compared with 73–100% reductions using conventional aerial broadcasting, while all methods reduced relative abundance indices of rats by 88% or greater. Radio tracking indicated a kill rate of > 90% against possums, regardless of bait distribution method. CONCLUSIONS: Simply by modifying bait distribution patterns, spatial aggregation can be used to maintain the high encounter rate of pests with 1080 bait that is necessary for operational efficacy, while reducing current toxin usage by up to 80%. Aggregated bait delivery could have relevance for other mammalian pest control scenarios internationally. Copyright © 2012 Society of Chemical Industry     

The effect of dextromethorphan in preventing cholecalciferol-induced poison shyness and sickness-induced anorexia in the laboratory Norway rat

BACKGROUND: Overcoming bait and poison shyness is critical to the success of pest control operations against rats and other rodents. The authors hypothesized that the N-methyl-D-aspartate receptor blocker, dextromethorphan, could prevent the acquired memory of sickness and sickness-induced anorexia resulting from rodents eating poisoned bait. RESULTS: Cholecalciferol (1/4 LD(50)) was mixed with dextromethorphan and fed to rats on two 2 day sessions, with an 18 day break in between. Dextromethorphan did not prevent poison shyness; during the second poisoning period, both the cholecalciferol only and the cholecalciferol plus dextromethorphan groups had lower intakes of the bait compared with the control and dextromethorphan only groups. In addition to the previously recorded symptoms of cholecalciferol poisoning, the rats in this trial were observed to have nose bleeds, weepy eyes, laboured breathing and, in the case of the cholecalciferol only treated group, a period of decreased water intake followed by a period of increased water intake. There was also a period of increased water intake in the cholecalciferol plus dextromethorphan group.CONCLUSION: Dextromethorphan failed to prevent poison shyness and the anorectic effect of cholecalciferol. However, it did reduce anorexia from 17 days in the cholecaliferol group to 8 days in the cholecalciferol plus dextromethorphan group.     

Reducing sodium fluoroacetate and fluoroacetamide concentrations in field rodent baits

Laboratory trials were carried out in order to establish the minimum active ingredient (a.i.) concentration of sodium fluoroacetate (1080) and of fluoroacetamide (1081) in wheat baits employed againstMicrotus guentheri, the Levant vole, andMeriones tristrami, Tristram’s jird, without interfering with the toxicants’ efficacy. Using a mixture of treated and untreated grain enabled a greater reduction in the a.i. concentration compared with that which could be achieved whenall the grains offered contained a lower a.i. concentration of the toxicants. ForM. tristrami the lowest efficient final a.i. concentration in the bait was 0.0125% for 1080 mixed bait (1:4 mixture of 0.05% poison grains with filler grains) and 0.01% for 1081 mixed bait (1:10 mixture of 0.1% poison grains with filler grains); and forM. guentheri — 0.005% mixed bait of 1080 or 1081 (1:10 mixture of 0.05% poison grains with filler grains). This leads to a reduction of the hazards involved in the use of prepared baits of these toxicants in the field.     

An efficacy test of cholecalciferol plus diphacinone rodenticide baits for California voles (Microtus californicus Peale) to replace ineffective chlorophacinone baits

California voles cause damage to pastures and rangelands, orchards and nurseries, and a wide variety of field crops, including artichokes. The anticoagulant rodenticides (chlorophacinone and diphacinone) typically used for voles are becoming less effective in controlling their populations. Consequently, there is a need to identify new rodenticides that will have a high efficacy on California voles so that agricultural production losses to rodents can be substantially reduced. We tested a new formulation containing two active ingredients (cholecalciferol and diphacinone) as a control method for California voles. Both a pelleted bait and an oil-coated artichoke bract bait were very palatable and efficacious against wild-caught, captive California voles. Efficacy levels of 70%–80% were achieved in the two-choice feeding trials. Additionally, the days-to-death (5–6 days) were less than the time-to-death with anticoagulant only baits. We recommend that a field efficacy study be conducted with cholecalciferol plus diphacinone bait formulations to determine their field performance in the reduction of agricultural damage by California voles.     

The toxicity of brodifacoum wheat bait to the field rodents Microtus guentheri and Meriones tristrami

The toxicity of the anticoagulant brodifacoum to the field rodent species Microtus guentheri (Danford & Alston) and Meriones tristrami Thomas was tested in the laboratory. Brodifacoum 0.05 g kg^?1 whole-wheat bait was offered to the animals without additional food. The LD₅₀ calculated for M. guentheri was 2.28 mg kg^?1 body weight. Brodifacoum was found to be more toxic to M. tristrami; the LD₅₀ was c. 0.8–0.9 mg kg^?1 body weight. The toxicity data served to plan the doses of bait to be broadcast in the field.     

Biomanagement of Fusarium wilt of tomato by the soil application of certain phosphatesolubilizing microorganisms

Abstract

We tested whether a new automated bait dispenser, the Scentinel®, could be programmed to deliver non-toxic bait selectively only to animals of specified dimensions (>400 g body weight and <110 mm body diameter, the size of a ferret or a mink). We tested whether wild ferrets would discriminate between two types of bait (egg/oil and homogenised brain tissue). We set 24 Scentinels in 12 randomised pairs for 11 weeks on a 2400-ha area of pastoral farmland in New Zealand. Of 1559 visits by small animals, 198 were by ferrets (c. 28 individuals). The Scentinels correctly delivered 895 baits to visitors weighing >400 g, and no baits to 543 visitors of <400 g. The mean body weight of live ferrets recorded by Scentinels was not significantly different from that of 34 carcasses collected from the same area by professional trappers. Of the 145 baits dispensed to ferrets, egg/oil bait was significantly more often eaten. We conclude that the Scentinel can reliably deliver bait to specified sizes of animals and deny it to others. It can also facilitate extensive bait preference tests on unrestrained wild pests.     

Rodent behaviour in relation to baiting techniques1

The use of poison baits is still the most important control method against commensal as well as field rodents. The baiting techniques used must be adapted to the ecology and behaviour of the target species. The various aspects of rodent behaviour influencing the effect of a control operation are discussed with emphasis on feeding behaviour, exploratory behaviour, neophobia, bait shyness, transporting, hoarding and territoriality. Advantages and disadvantages of sustained versus pulsed baiting techniques are discussed from a behavioural point of view.     

Laboratory Evaluation of Zinc Phosphide as a Rodenticide against Bandicota bengalensis

Abstract

The toxicity and efficacy of the acute rodenticide zinc phosphide (Zn₃P₂) was evaluated in the laboratory against the lesser bandicoot rat (Bandicota bengalensis), from Rangoon, Burma. The acute LD50 and LD95 doses of orally-administered zinc phosphide for B. bengalensis were found to be 25.0 mg/kg and 113.0 mg/kg of body weight respectively. When caged bandicoots were given a choice between plain and poison baits, the optimum rodenticidal concentrations in the bait was found to be 2.5%. Symptoms of poisoning appear from 32 minutes to 3 hours after feeding starts, giving individual animals time to consume from 10 to over 27 LD50 doses of 25% zinc phosphide before feeding stops. Death occurred in a minimum of 4 to 5 hours following either oral dosing or free choice feeding. There appears to be aversion to the poison at higher concentrations in food baits. The relative merits of zinc phosphide and pyriminyl as rodenticides against the lesser bandicoot in Rangoon will have to be determined in a series of comparative field trials.     

Neophobia in wild rats is elicited by using bait stations but not bait trays

Brown rats (Rattus norvegicus) are among the most common vertebrates often becoming a major pest in urban environments. Managing rat populations is difficult, given the complex behaviours these murids can display. To help improve local control, we studied the response of wild rats to bait stations comparing baits placed on three different kinds of surfaces (on the ground, on trays and in bait stations) near burrows. We show that rats neither avoided nor preferred any tray type in particular – the latency to pick up the food pellet from the ground did not differ from the latency to pick it up from trays. However, the latency to pick the food pellet was significantly higher when food was placed in bait stations. We conclude that for effective administration of toxic baits, common bait stations are not the most effective method and should be used only in cases when placing baits directly on the ground or on a tray poses a threat to other animals and humans.     

Methods of Laboratory Toxicological Investigations on the Common Vole (Microtus arvalis [Pallas])1

This paper reports on some laboratory methods for evaluating the toxicity of rodenticides to the common vole. Test conditions including the experimental animals used, their housing, feeding and handling (measuring body weight, marking of the individuals, route of administering the toxicant), test materials and observations are presented. New toxicants were screened simultaneously on white rats and on voles. For each compound, the following data were determined: a) the acute (single dose) approximate LD₅₀ (= ALD₅₀), b) the acute (single dose) LD₅₀, as well as the multiple dose toxicity for anticoagulants, c) the approximate 5-day LD₅₀ and d) the 5-day LD₅₀. For the determination of a) and c), about 6 animals were used. The LD₅₀ values were determined by giving 6–8 doses to each of 10 rats and 4 doses to each of 4–6 voles. A brief report is given on the determination of the joint toxic action of the 2 chemicals. Rodenticidal formulations were tested on voles in various no-choice and choice feeding tests. No-choice tests with compounds having an acute toxicity were carried out for 24 h, those with anticoagulants for 5 × 24 h and those with narcotics for 2 × 24 h. The corresponding periods for choice tests were 2 × 24 h, 5 × 24 h and 4 × 24 h, respectively. Preference and repellency tests were also carried out. The stability of a rodenticide in baits exposed to weather, as well as the effectiveness of fumigants on solid carriers were investigated under simulated environmental conditions.     

An index technique to monitor broadcast calibration and bait pick up, plus rodent and avian sign under arid conditions

As part of product-performance and wildlife-hazards studies of 2% zinc phosphide (Zn3P2) steam-rolled-oat baits (11.2 kg ha-1) to reduce vole populations (Microtus spp) in alfalfa (Medicago sativa), we used randomly located, brushed-dirt plots (eight approximately 930-cm2 plots per 0.2-ha enclosure) to monitor bait-broadcast and -removal patterns, as well as to index vole and avian sign. Research was conducted in 18 x 0.2-ha enclosures containing 2.5-year-old stands of alfalfa; a 2-day pre-bait (placebo baits broadcast in all enclosures) period followed by a 14-day test-bait period (placebo and 2% Zn3P2 baits in nine enclosures each) characterized the bait exposures. Baits were broadcast manually by two certified pesticide applicators (CPAs) using Spyker Model-75 spreaders. Baits that fell onto plots were counted < 30 min later to assess the uniformity of bait distribution. The main statistical design was a 2 (placebo or Zn3P2 baits) x 3 (vole-only, vole-pheasant, vole-quail exposures) x 14 (days) factorial, with days considered repeated measurements. In the six vole-only enclosures, baits were removed from the brushed-dirt plots and replaced with four 0% or 2% Zn3P2 baits (one per 232.6-cm2 quadrant; 32 per enclosure); these 'placed' baits were then monitored daily for removal, while the surfaces of all plots were monitored daily for the presence:absence of animal/bird sign. Key results were: (a) 3.51 (+/- 2.66) and 3.39 (+/- 3.52) mean (+/- SD) baits were found on plots after pre-bait and test-bait broadcasts, respectively--less than the predicted 4.52 particles per 930-cm2 plot; (b) baits 'placed' on plots in placebo-baited enclosures were removed earlier than those in Zn3P2-baited enclosures--data in agreement with observed vole mortality; and (c) species x bait interactions occurred for both the vole- and pheasant-sign counts, but not quail-sign counts--data also indirectly confirming Zn3P2-induced mortality effects on voles and pheasants. This technique has utility for a variety of wildlife biology and chemical registration studies; although limited to arid conditions, the technique affords useful indices of broadcast calibration, bait pick-up, as well as target and non-target species mortality.     

The toxicity of phosphine,methyl bromide, 1,1,1-trichloroethane and carbon dioxide alone and as mixtures to the pupae of red flour beetle,Tribolium castaneum herbst

The toxicity of phosphine, methyl bromide, 1,1,1-trichloroethane (methyl chloroform) and carbon dioxide and mixtures of phosphine + methyl bromide, methyl bromide + methyl chloroform, phosphine + carbon dioxide, and methyl bromide + carbon dioxide to one- to two-day-old pupae of Tribolium castaneum Herbst was studied. Joint action ratios estimated at LD₅₀ and LD₉₀ for a 24-h exposure indicated no enhancement of toxicity for mixtures of phosphine and methyl bromide, or methyl chloroform and methyl bromide on the pupae. Carbon dioxide up to 40% in air enhanced the toxic action of phosphine as well as of methyl bromide. Higher levels of carbon dioxide, however, failed to improve the toxicity of phosphine or methyl bromide proportionately. Carbon dioxide used alone produced a maximum of 11% mortality of the pupae exposed to 10–70% levels for 24 h. The order of toxicity of the fumigants both at LD₅₀ and LD₉₀ was phosphine > methyl bromide > methyl chloroform.     

Tenth international congress of plant protection,Brighton, November 1983

Abstract

Field trials were conducted to control rodent pests of wheat crop by improving bait acceptability through taste enhancers (additives). Egg shell, egg yolk, yeast, minced meat, sheep blood and chicken blood were mixed 2% by weight individually in a bait base of broken rice and wheat flour. Brodifacoum and bromadiolone bait with egg shell additive ranked first, and egg yolk second, in preference over other additive poison baits and poison bait without additive. Poison baiting yielded 93.3% and 86.7% reduction in rodent population with brodifacoum and bromadiolone (0.005% each), respectively. Three baitings, at tillering, flowering and maturity stage of the crop, gave 91.0% tiller damage reduction with brodifacoum and 86.0% with bromadiolone as compared to control (untreated). It is concluded that three poison baitings containing egg shell additive should be initiated at tillering stage followed by flowering and maturity of the wheat crop for increased yield.     

Attraction of Chrysoperla carnea complex and Chrysopa spp. lacewings (Neuroptera: Chrysopidae) to aphid sex pheromone components and a synthetic blend of floral compounds in Hungary

BACKGROUND: The deployment of synthetic attractants for the manipulation of lacewing populations as aphid predators is currently used in integrated pest management. This study investigates a synthetic bait comprising floral compounds previously found to attract the Chrysoperla carnea complex, and, for the first time, the aphid sex pheromone components (1R,4aS,7S,7aR)‐nepetalactol and (4aS,7S,7aR)‐nepetalactone, in field experiments in Hungary, for their ability to manipulate lacewing populations. RESULTS: The synthetic floral bait attracted both sexes of the Chrysoperla carnea complex, and Chrysopa formosa Brauer showed minimal attraction. The aphid sex pheromone compounds alone attracted males of C. formosa and C. pallens (Rambur). When the two baits were combined, Chrysopa catches were similar to those with aphid sex pheromone baits alone, but carnea complex catches decreased significantly (by 85–88%). CONCLUSION: As the floral bait alone attracted both sexes of the carnea complex, it showed potential to manipulate the location of larval density via altering the site of oviposition. Aphid sex pheromone compounds alone attracted predatory males of Chrysopa spp. and can potentially be used to enhance biological control of aphids. For the carnea complex, however, a combination of both baits is not advantageous because of the decrease in adults attracted. Assumptions of intraguild avoidance underlying this phenomenon are discussed. Copyright © 2010 Society of Chemical Industry     

Termite cuticular extracts improve acceptance of bait for controlling invasive Asian needle ants,Brachyponera chinensis

BACKGROUND

The Asian needle ant, Brachyponera chinensis, is an invasive ant currently spreading in urban and natural habitats throughout the eastern United States. Recent studies have documented the negative impact of B. chinensis on native ecosystems and human health, yet effective control strategies are lacking. Control difficulties are, in part, due to the unique biology of B. chinensis, which is a predatory ant and a termite specialist. Given that subterranean termites are an important nutritional resource for B. chinensis, the current study evaluated the potential of termite cuticular extract to improve the target-specificity and efficacy of commercial bait used for B. chinensis control.

RESULTS

The efficacy of bait augmented with termite cuticular extracts was evaluated in laboratory and field trials. In laboratory assays, B. chinensis colonies were offered granular bait treated with termite cuticular extract. Results demonstrated that the acceptance of commercial bait is significantly increased by the addition of termite cuticular extract or synthetic (Z)-9-pentacosene, a major component of termite cuticular extract. Foraging activity of Asian needle ants was significantly greater on baits augmented with termite cuticular extract or (Z)-9-pentacosene relative to standard bait. Furthermore, bait augmented with termite cuticular extract worked substantially faster relative to standard bait. To evaluate population effects, field studies were conducted in forested areas invaded by B. chinensis. Bait treated with termite cuticular extract scattered on the forest floor provided rapid control of B. chinensis and ant densities throughout the treated plots declined by 98% within 14 days.

CONCLUSION

The incorporation of termite cuticular extracts and individual cuticular hydrocarbons such as (Z)-9-pentacosene into traditional baits used for B. chinensis control may offer a novel tool to manage this increasingly problematic invasive ant. © 2023 The Author. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Comparative toxicology of AC 217,300 in various species of insects

AC 217,300 was highly toxic by topical application to adult Musca domestica and Blattella germanica, and larvae of Spodoptera eridania, with LD₅₀ values in μg/g of 20, 19, and 61, respectively. It was relatively nontoxic to Diabrotica undecimpunctata howardi beetles and Heliothis virescens larvae with LD₅₀ values of 165 and >883. When incorporated into baits, AC 217,300 was still highly toxic to M. domestica, B. germanica, and S. eridania. A significant increase in toxicity to H. virescens was observed although the percentage mortality was only 45%. AC 217,300 was not effective against D. undecimpunctata with either mode of application. A comparison of toxicity with tissue residues indicated that AC 217,300 was highly toxic to M. domestica, B. germanica, H. virescens, and S. eridania if it was absorbed. However, D. undecimpunctata appeared to be much less sensitive to AC 217,300, as only 18% mortality was observed with corresponding tissue concentrations two to six times those producing 95–100% mortality in M. domestica and S. eridania. Exposure of M. domestica to an AC 217,300-treated bait for 3–6 hr was sufficient to cause 50–100% mortality after 2 days and 95–100% mortality by 7 days. With B. germanica, a 1- to 3-day exposure resulted in 75–90% control within 7 days, while exposure for 3–7 days gave 90–100% control. Environmental temperature had a pronounced effect on the toxicity of AC 217,300 to both M. domestica and B. germanica. A 20-fold increase in toxicity was observed when the environmental temperature was raised from 21 to 32°C. This observation, in concert with the symptoms of intoxication, support the hypothesis that AC 217,300 is an inhibitor of energy production. Approximately 85 and 87% of the total residue of AC 217,300 extracted from treated M. domestica and B. germanica, respectively, was parent material. Six minor metabolites were detectable, of which three were tentatively identified by cochromatography with authentic standards. None of the identified metabolites had any insecticidal activity in vivo, suggesting that AC 217,300 is the actual toxicant.     

The influence of bait presentation on bait uptake by mice (Mus domesticus) in infested urban domestic dwellings

Several researchers have established a link between the presence of house mouse (Mus domesticus) infestations and detrimental effects on human health. Controlling mouse infestations therefore requires methods that are quick, safe and effective. A tamper-resistant bait station with a wax block which is manufactured to fit within it so that it cannot be shaken out is considered the safest way to present the bait. However, some authors have expressed concern about the efficacy of this method. Research to examine the effects of bait stations on the feeding of mice infesting domestic dwellings was undertaken in the city of Manchester, UK. Working in conjunction with Manchester City Council, suitable sites were found. A balanced Latin Square experimental design was employed to overcome any operational biases that could have occurred. Non-toxic baits were presented in one of four ways: whole wheat in a cardboard box; whole wheat in a open tray; whole wheat in a tamper-resistant box; and a non-toxic wax block in a tamper-resistant box. Baits were placed in four different locations within dwellings and during the feeding trial; the bait stations were rotated, so that each bait type was presented in each location. The bait take from 12 dwellings within 3 housing blocks was recorded. Three-quarters of the bait consumed during the trial was taken from the cardboard box. No bait was taken from the tamper-resistant box containing the wax block.

Risk assessments should drive the approach adopted in presenting rodenticide. Dwellings where vulnerable adults/children/pets are present may represent a risk of accidental poisoning may require a regime with tamper-resistant bait boxes containing wax blocks, to prevent baits being accessed. However, a balance between the safest and the most effective presentation of bait is needed and in areas where there is unlikely to be any access to baits (e.g. behind kitchen kickboards), use of alternatives must remain to ensure the shift resolution of infestations. Where bait can be placed safely and there are no children or pets present, cardboard boxes provide an effective means of ensuring that bait is consumed by the mice infesting domestic dwellings.     

Insecticidal compounds from the essential oil of Chinese medicinal herb Atractylodes chinensis

BACKGROUND: In a screening programme for new agrochemicals from Chinese medicinal herbs, the essential oil of Atractylodes chinensis (DC.) Koidz was found to possess strong insecticidal activity against the common vinegar fly, Drosophila melanogaster L. The essential oil was extracted via hydrodistillation, and its constituents were determined by GC‐MS analysis. RESULTS: The main components of A. chinensis essential oil were β‐eudesmol (21.05%), β‐selinene (11.75%), γ‐elemene (7.16%) and isopetasam (5.36%). Bioactivity‐directed chromatographic separation on repeated silica gel columns led to the isolation of five compounds, namely atractylon, α‐elemol, β‐eudesmol, hinesol and β‐selinene. β‐Selinene, α‐elemol and hinesol showed pronounced contact toxicity against D. melanogaster adults, with LD₅₀ values of 0.55, 0.65 and 0.71 µg adult^?1 respectively. Atractylon and β‐eudesmol were also toxic to the fruit flies (LD₅₀ = 1.63 and 2.65 µg adult^?1 respectively), while the crude oil had an LD₅₀ value of 2.44 µg adult^?1. CONCLUSION: The findings suggested that the essential oil of Atractylodes chinensis and its active constituents may be explored as natural potential insecticides. Copyright © 2011 Society of Chemical Industry     

Time,concentration and temperature relationships for phosphine activity in tests on diapausing larvae of Ephestia elutella (Hübner) (Lepidoptera: Pyralidae)

The activity of phosphine against diapausing larvae of Ephestia elutella was shown to depend on several different interactions of duration of exposure, temperature and gas concentration. Using the model proposed by Knight, (C? C₀) × (t? t₀) = k, a constant for mortality, the minimum effective concentration C₀ was raised and the minimum effective exposure t₀ extended as temperatures were increased. The effect of temperature on these thresholds was reduced at higher mortality levels. A range of concentration levels, influenced by temperature, elicited an increase in tolerance at the LD₉₉ level over that evident at higher or lower concentrations. These concentration ranges were 0.9–2-1 mg litre-¹at 25°C,0.7–2.3 mg litre-¹ at 20°C and 0.1–1.5 mg litre-¹ at 15°C. A mathematical model was fitted to relate concentration and time thresholds, mortality and temperature. At the LD₅₀ level, values for t₀ ranged from 2.5 h at 15°C to 5.0 h at 25°C. C₀ values increased from about 0.6 to 7.0 μg litre-¹ over this temperature range. At the LD₉₉ level, t₀ values ranged from 21 to 28 h and C₀ values from 11 to 19 μg litre-¹. Phosphine appeared most effective at each temperature at concentrations from about 40 to 60–100 μg litre-¹.