James M. Desmarchelier

Selective treatments, including combinations of pyrethroid and organophosphorus insecticides. For control of stored product Coleoptera at two temperatures

Abstract Selective treatments, appropriate to simulated storage conditions, reinfestation pressures and species or strains of insects present in the wheat, required less insecticide than any “blanket” or all-purpose treatment. In particular, the pyrethroids bioresmethrin, synergized bioresmethrin or synergized pyrethrins were especially effective where Rhyzopertha dominica and especially a strain resistant to organophosphorus insecticides, was the only species present. Conversly, the organophosphorus insecticides dichlorvos, malathion, fenitrothion and pirimiphos-methyl were especially effective against Tribolium and Sitophilus species. There was no antagonism between any of the pyrethroids and any of the organophosphorus insecticides when they were applied in combination, in that the period of protection given by combinations was the period of protection given by the pyrethroid component against R. dominica and the organophosphorus component against Tribolium and Sitophilus species. As an example of the data required for selective treatments, bioassays were conducted at 20 and 30°C and it was found that the net effect of the lower temperature in reducing toxicity but increasing persistence was to increase the period of protection given by insecticides in cooled storages. It is suggested that the amounts of insecticides applied to grain could be considerably reduced if more consideration was given to grain conditions, if reinfestation pressures were more carefully examined and if less attention were given to surviving adults under conditions where progeny do not develop.

Determination of pyrethroid residues on paddy rice by reversed-phase high-performance liquid chromatography.

Several synthetic pyrethroids and the synergist piperonyl butoxide have been determined as aged residues on paddy rice by reversed-phase high-performance liquid chromatography with detection at 225 nm. These compounds are commonly used as protectants for stored grains. Studies on the comparative rates of extraction of both the pesticides and interfering material from the grain were conducted with acetone, methanol, and hexane as extracting solvents. Acetone was the best of these solvents because it provided quantitative extraction of the pesticides over a 48-h period, and did not give high levels of ballast material. Pyrethroids present in the extract at levels in excess of 0.5 microgram/ml could be determined by direct injection, but at lower concentrations, clean-up and preconcentration were required. Clean-up of acetone extracts was accomplished with either Florisil or alumina pre-columns, and up to a tenfold preconcentration was achieved by adsorption of the pesticide on a C18 pre-column, or by concentrating the extract through evaporation of the solvent. These approaches gave good recoveries and linear calibration plots. Detection limits were of the order of 0.05 microgram/ml.

The relationship between wet-bulb temperature and the intrinsic rate of increase of eight species of stored-product Coleoptera

Abstract Intrinsic rates of increase, r , of eight species of stored-product Coleoptera were shown to be linearly related to wet-bulb grain temperature, T WB , by the equation r = k ( T − T 0 ) WB , for r max > r > 0 where T 0 is the wet-bulb temperature at which r = 0, and r max is the maximum rate of development under any conditions. The species for which this relationship was verified were Sitophilus oryzae (L.), Sitophilus granarius (L.), Sitophilus zeamais Motschulsky, Oryzaephilus surinamensis (L.), Oryzaephilus mercator (Fauvel), Rhyzopertha dominica (F.), Lasioderma serricorne (F.) and Tribolium castaneum (Herbst). From the linear relationship between rate of increase and wet-bulb temperature it is possible to deduce an ideal cooling strategy, which is based on minimizing the time ( t ) multiplied by the temperature at which the wet-bulb temperature exceeds T 0 , i.e. the summation Σ ( T − T 0 ) · t .

The effects of the temperature-toxicity relationships of certain pesticides upon the population growth of Sitophilus oryzae (L.) (Coleoptera: Curculionidae)

Abstract An experiment to assess the effects of temperature upon the toxicity of two pesticides to Sitophilus oryzae is described. The pesticides used, pirimiphos-methyl and deltamethrin, were shown to have opposite relationships with temperature. The consequences of these relationships are discussed in relation to the population growth of S. oryzae and, in particular, to the use of cooling in combination with low levels of pesticide as an integrated control measure for this and other pest species.

Diflubenzuron as a grain protectant for control of Sitophilus species

Abstract Diflubenzuron, applied to wheat at low doses (0.2–0.6 mg kg −1 ), prevents development of first generation (F1) progeny of Sitophilus oryzae and S. granarius species except those developing from a short period of oviposition (1–2 weeks) immediately after application. These F1 progeny fail to produce F2 progeny when transferred to wheat dosed with diflubenzuron, and produce very few progeny when transferred to untreated wheat suggesting an effect on fertility in the adult insect. At 30°C, a dose of 0.4 mg kg −1 is adequate to control S. oryzae and S. granarius , although a dose of 0.6 mg kg −1 is required at 20°C. Strategies for use of diflubenzuron are discussed.

Ethyl formate, formic acid and ethanol in air, wheat, barley and sultanas: analysis of natural levels and fumigant residues

Ethyl formate and ethanol in air, eg in fumigant studies, were readily detected by gas chromatography (GC) (flame ionisation). Residues in wheat, barley and sultanas were analysed by GC, after extraction in polar solvents (eg methanol, aqueous propanol). Both natural levels and levels resulting from fumigation with ethyl formate were measured. Formic acid was extracted from commodities with polar solvents (eg methanol, water) and analysed by GC after esterification. Solvent extracts of commodities were concentrated after addition of disodium hydrogen orthophosphate, and an aliquot added to acidified alcohols (several combinations of acids and alcohols were tested) in a sealed container. Formic acid esters were determined by GC, from headspace sampling over the esterification solvent. Esterification was faster with strong acids than with boric acid. However, esterification with boric acid/butanol gave the least interference of all tested methods. Product identity was confirmed by GC/mass spectrometry. High natural levels of formic acid, and low natural levels of ethyl formate and ethanol, presented problems in identifying residues arising from fumigation. These natural levels are relevant to food regulations for ethyl formate, especially those based on ‘total formic acid, free and combined’. Polar columns (eg FFAP, carbowax) were useful for measurement of formic acid esters, which eluted before the alcohols used for esterification or extraction, whereas elution followed the molecular mass on non-polar columns, such as GS-Q or DB-624. © 1999 Society of Chemical Industry

Aeration according to seed wet-bulb temperature

Abstract The rate of insect population growth in stored seed is strongly influenced by both the seed temperature and moisture content so both need to be taken into account when using aeration to control insect populations. This paper explains how to do this by using Seed Wet-Bulb Temperature (SWBT). Strategies for, and benefits of, using SWBT to manage aeration systems are explained, including: the use of SWBT to predict the rate of insect population growth, how to select a target SWBT for controlling insect populations, and how to select an aeration controller setting that will achieve the target SWBT. It is shown that SWBT control of aeration systems has particular benefit in warm temperate climates and the implications for moisture migration are analyzed. Essential data needed for using SWBT to manage aeration systems are provided including figures that give SWBT data and limiting conditions for mould growth, for nine types of seed. The methods used for determining SWBT and for determining the conditions that promote growth of moulds are detailed.

Statistical analysis of decay of organophosphorus and pyrethroid insecticides and carbaryl on paddy rice, maize, sunflowers and field peas

A model is developed to describe the decay of seven insecticides on stored paddy rice, maize, sunflowers and peas, and is shown to be more precise than each of six literature models on pesticide decay. It relates residues (R), as a ratio of applied concentration (R(0)), to time after insecticide application (t), modifying the usual first-order kinetics equation lnR=lnR(0)-kt by assuming that the rate constant k has a mixture of values according to a gamma distribution with mean K. The resulting equation is lnR=lnR(0)-Kcln(1+t/c), where c is a constant determined empirically. For large c, this model reduces to the first-order model with K=k. The parameter K is further modelled as linear in temperature for maize and rice. The rate of loss of protectants was found not to be seriously affected by co-application with other insecticides, and this is a useful finding for future studies on rates of loss of grain protectants. The apparent rate of loss was also not seriously affected by the method of analysis, whether by gas chromatography or high-performance liquid chromatography, and this finding supports previous validation of the methods.

Mathematical examination of availability to insects of aged insecticide deposits on wheat

Abstract The toxic effect of an insecticide deposit on wheat depends not only on the amount of insecticide present but also on the age of the deposit. Decay of deposit and loss of toxic effect were measured chemically and biologically, respectively. As such processes were kinetically first order with respect to amount of insecticide, it was possible to derive linear equations relating mortality in probits and age of deposit. Use of such equations, similar in form to those expressing concentration-mortality relationships, permits a quantitative comparison of results from field trials or period of protection studies in which aging reduces the amount of insecticide available from, and thus the toxicity of, insecticide deposits.

Improved methodology for studying diffusion, sorption and desorption in timber fumigation

Methods to study movement of fumigant through timber were improved, and procedures were developed that obviated the need for sampling lines. Movement for two fumigants (methyl bromide and carbonyl sulphide) through, and sorption on, heartwood of softwood and hardwood were studied. Each fumigant was sorbed less on softwood than on hardwood and penetrated softwood better than hardwood. Neither fumigant penetrated across the grain. Carbonyl sulphide penetrated timber better than did methyl bromide, and was less sorbed on timber. A rapid method of solvent extraction was developed to enable rapid estimation of the amount of intact fumigant sorbed in wood. This procedure enabled excellent recovery of methyl bromide as either intact fumigant or as bromide ion.