Efficacy of the amorphous silica dust, Dryacide, against Tribolium confusum Duv. and Sitophilus granarius (L.) (Coleoptera: Tenebrionidae and Curculionidae)

Amorphous silica dust (Dryacide) was used to treat wheat at concentrations of 0, 250, 500, 750, and 1000 μg silica dust/g wheat. Adult Sitophilus granarius and Tribolium confusum were placed in the grain which was then incubated at 20 or 30°C and 40 or 60% r.h. Mortality counts were taken after 48 and 168 hr. S. granarius was more susceptible to silica dust than T. confusum under the same conditions. At the same temperature, the toxicity of silica dust to both species was more pronounced at 40 than 60% r.h. T. confusum was more tolerant to silica dust at 30 than at 20°C; whereas, S. granarius was more susceptible to it at 30 than 20°C. Silica dust reduced progeny 100% at 40% r.h. in all the concentrations that had been used. Progeny, however, were produced by S. granarius at 30°C and 60% r.h. but with significantly reduced numbers with increasing dosge. Silica dust had no adverse effect on wheat seed germination, wheat flour, and baking quality.     

Mortality of Sitophilus oryzae (L.) and S. granarius (L.) in atmospheres produced by an exothermic inert atmosphere generator

The exposure to atmospheres with low O₂ required to kill 50 and 95% of the developing Sitophilus oryzae (L.) and S. granarius (L.) indicated that the earlier and later stages were more susceptible and the middle stages were less susceptible. At 27°C, the duration of exposure required to produce 95% mortality during the 4th instar through early pupal development was about 10 days for S. oryzae and 6 days for S. granarius. The toxicity of the atmosphere produced by an exothermic inert atmosphere generator to each stage of S. oryzae was higher at 27°C than at 21°C. Larvae and pupae of S. granarius were more susceptible to the atmosphere than corresponding stages of S. oryzae. The type of grain in which the S. oryzae were developing did not significantly alter the mortality due to the generated atmosphere.     

The effect of thermal acclimation and relative humidity on the oxygen consumption of three Sitophilus species

The oxygen consumption of adult Sitophilus oryzae (L.). S. granarius (L.) and S. zeamais Motsch, that were acclimated at 27 or 15°C was measured at constant temperatures of from 10 to 30°C and relative humidities of 94, 70 or 50%. Warm-acclimated weevils that were free to move within the respirometers used significantly more oxygen than cold-acclimated weevils in almost all measurement regimens. In general, oxygen uptake was greatest at 70% r.h., intermediate at 94% and lowest at 50%. High oxygen consumption in certain regimens suggested an interaction between the effects of humidity and measurement temperature in S. oryzae and, to a lesser extent, in S. granarius. An interaction between humidity and acclimation temperature was indicated in S. granarius by the finding that the Q₁₀s of warm-acclimated weevils increased as humidity decreased whereas the Q₁₀s of cold-acclimated weevils did not change. The relationships between the logarithm of oxygen consumption and measurement temperature were described in all three species by quadratic functions. The oxygen consumption of S. oryzae closely restrained within the respirometers was not affected by relative humidity. Such weevils consumed more oxygen at 15 and 20°C when warm-acclimated than they did when cold-acclimated; there was no significant difference, however, between the oxygen consumption of warm- and cold-acclimated weevils at either 25 or 30°C.     

Toxicity and uptake of methyl bromide in hybrid descendants of resistant and susceptible Sitophilus granarius (L.)

Progeny of susceptible Sitophilus granarius repeatedly crossed with individuals from a resistant strain attained resistance to methyl bromide without selection with the fumigant and when this hybrid strain was subsequently subjected to methyl bromide pressure a higher degree of resistance than was present in the resistant parent developed. Resistant insects absorbed slightly less fumigant than susceptible insects in the first few hours of exposure but more in a 24 hr fumigation period. Resistance could not be related to either rate or degree of uptake of fumigant. The quantities of absorbed fumigant required to kill insects from both strains are given.     

Fumigation with carbonyl sulfide: a model for the interaction of concentration, time and temperature

The new fumigant carbonyl sulfide offers an alternative to both methyl bromide and phosphine as a grain fumigant. Separate mathematical models for levels of kill, based on quantitative toxicological studies were developed for adults and eggs of the rice weevil Sitophilus oryzae (L.). These models suggest that fumigation exposure times for carbonyl sulfide will be a compromise between those of methyl bromide (typically 24 h) and phosphine (7–10 d) to achieve a very high kill of all developmental stages. S. oryzae eggs were more difficult to kill with carbonyl sulfide fumigation than the adults. At 30°C, a 25 g m⁻³ fumigation killed 99.9% of adults in less than 1 d, but took 4 d to kill the same percentage of eggs. Models were generated to describe the mortality of adults at 10, 15, 20, 25 and 30°C. From these models it is predicted that fumigation with carbonyl sulfide for 1–2 d at 30 g m⁻³ will kill 99.9% of adults. Furthermore the models illustrate that fumigations with concentrations below 10 g m⁻³ are unlikely to kill all adult S. oryzae. Significant variation was observed in the response of eggs to the fumigant over the temperature range of 10 to 30°C. Models were generated to describe the mortality of eggs at 10, 15, 20, 25 and 30°C. As the temperature was reduced below 25°C, the time taken to achieve an effective fumigation increased. Extrapolating from the models, a 25 g m⁻³ fumigation to control 99.9% of S. oryzae eggs will take 95 h (4 d) at 30°C, 77 h (3.2 d) at 25°C, 120 h (5 d) at 20°C, 174 h (7.5 d) at 15°C and about 290 h (11 d) at 10°C. The role of temperature in the time taken to kill eggs with carbonyl sulfide cannot be ignored. In order to achieve the desired level of kill of all developmental stages, the fumigation rates need to be set according to the most difficult life stage to kill, in this instance, the egg stage.     

The influence of relative humidity and thermal acclimation on the survival of adult grain beetles in cooled grain

The influence of humidity and thermal acclimation on the survival of Cryptolestes ferrugineus, Oryzaephilus surinamensis, Rhyzopertha dominica, Sitophilus granarius, S. oryzae and Tribolium castaneum in cooled wheat or flour at 45 and 70% relative humidity was studied in the laboratory. Young adults were held continuously at 30 or 32°C; cooled gradually to 13.5°C and held at that temperature; cooled gradually to 9°C and held at that temperature; or transferred directly to 9°C.

Survival at low temperatures differed, often considerably, between species, being generally shortest in T. castaneum (0.7–16 weeks) and longest in S. granarius (5–40 weeks). There was considerable interaction between the effects of temperature and humidity, with survival being, to varying degrees, shorter in 45% r.h. than in 70% r.h. At 45% r.h., an equilibrium relative humidity common in Australian storages, all species survived when the grain was cooled to 13.5°C but only S. granarius survived 26 weeks in grain cooled to 9°C.

Chill-coma temperature and acclimation temperature were linearly related in all species at each humidity. Neither the slopes nor intercepts of the relationships were influenced by humidity. There was generally an inverse relationship between survival and chill-coma temperature.

At 45% r.h., the increase in survival at 9°C attributable to acclimation ranged from 2-fold in S. oryzae (0.9 weeks) to 3.5-fold in C. ferrugineus (3.8 weeks). Corresponding values for beetles at 70% r.h. ranged from 2.3-fold in R. dominica (2.4 weeks) to 7.9-fold in C. ferrugineus (6.9 weeks).     

A novel use of modified atmospheres: Storage insect population control

The research described here aimed to establish the feasibility of using modified atmospheres (MA) to protect commodities throughout their storage life by using oxygen (O₂) levels that disrupt the life cycles of the target beetle species. Rather than achieving complete mortality of all stages, the aim was to identify more easily obtainable MAs that would kill the most susceptible stage and prevent population growth. Simulated burner gas and nitrogen (N₂) atmospheres with O₂ contents between 3% and 6%, were tested, along with a N₂-based MA with elevated carbon dioxide (CO₂) (10–20%).

Laboratory tests were carried out on five species of stored-product beetles, Cryptolestes ferrugineus, Oryzaephilus surinamensis, Sitophilus granarius, S. oryzae and Tribolium castaneum. After exposure to the MAs for 28 d an assessment was made of the mortality of adults, the number of adults from progeny produced under the MAs and, for the simulated burner gas, the number of adults from progeny produced in a 28-d period after exposure to the MA. The tests were carried out at 20 and 25 °C with 75% and 85% r.h. at each temperature.

The O₂ content preventing population growth varied with species and temperature. For simulated burner gas or N₂ it was about 4% for O. surinamensis, S. granarius and S. oryzae, and about 3% for C. ferrugineus and T. castaneum at 25 °C. At 20 °C it was about 3% for all species tested. When CO₂ was increased to 10% or 20%, reducing O₂ to 5% was sufficient to eliminate emergence of S. granarius at 20°C, but a few individuals emerged at 25 °C. For C. ferrugineus there was a 95% reduction with 5% O₂ plus 20% CO₂ at 20 °C, but not at 25 °C.     

The toxic action of phosphine in combination with some alkyl halide fumigants and carbon dioxide against the eggs of Tribolium castaneum Herbst (Coleoptera: Tenebrionidae)

The toxicity of phosphine, three alkyl halide fumigants (ethylene dibromide, methyl bromide and methyl iodide), carbon dioxide, mixtures of phosphine + alkyl halide fumigants, and phosphine + carbon dioxide, to 1-, 2-, and 3-day-old eggs of Tribolium castaneum Herbst was studied. Combinations of phosphine and alkyl halide fumigants showed antagonism as evidenced by their joint action ratios at the LD₉₀ (< 1). The mortality data indicated that mixtures of phosphine and carbon dioxide were more effective than either alone. At LD₅₀, the order of toxicity of the individual fumigants for a 24 hr exposure and on a weight basis (mg fumigant/litre of air) was: phosphine > methyl iodide > ethylene dibromide > methyl bromide. A decline in susceptibility of eggs with age for methyl bromide and ethylene dibromide and a peak tolerance at 2 days for carbon dioxide were noted.     

The use of a managed bulk of grain for the evaluation of PC, Pitfall beaker, Insect Probe and WBII Probe traps for monitoring Sitophilus granarius during the winter and summer in the UK

A 100 tonne flat-store of wheat has been used to evaluate PC (surface and buried), pitfall beaker, insect probe and WBII probe traps for monitoring Sitophilus granarius. Trials were conducted over 8-week trapping periods and S. granarius were seeded into the bulk at a density of one per kg. Trials were conducted during the winter/spring and during the spring/summer of the following year in the UK. WBII probe traps were used in the summer trial only. The results show the efficiency of various trap types for trapping S. granarius in a commercial environment at different temperatures. Most S. granarius per trap were caught by the surface PC traps in the winter trial and by WBII probe traps in the summer trial when compared to all other trap types. However, in the winter trial the pitfall beaker traps captured S. granarius more consistently than others while surface PC traps were more consistent in the summer. The results from both trials provide little evidence of a correlation between trap catch increase and increase in grain temperature. This may indicate that trap catch in general shows a delay in response to temperature changes, and that temperature measurement more closely related to individual trap catches may be required to reveal the true extent of any correlation between temperature and trap catch for S. granarius.     

Diflubenzuron as a grain protectant for control of Sitophilus species

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.     

Toxic and antifeedant action of nutmeg oil against Tribolium castaneum (Herbst) and Sitophilus zeamais Motsch

The essential oil extracted from nutmeg seeds using steam distillation was tested against the stored product insect pests, Tribolium castaneum (Herbst) and Sitophilus zeamais Motsch., for contact toxicity, fumigant toxicity and antifeedant activity. Filter paper impregnation was employed for contact and fumigant toxicity studies, whereas a flour disc bioassay was used to investigate antifeedant effects. Adults of S. zeamais were about ten times more susceptible than T. castaneum adults to contact action (LC₅₀ values of 1.7 mg/cm² and 18 mg/cm² respectively). However, S. zeamais adults were only 1.7 times more susceptible than T. castaneum adults to fumigant action (LC₅₀ values of 4.5 mg/cm² and 7.7 mg/cm² respectively). Furthermore, the larvae (10–16 days old) of T. castaneum were more susceptible than the adults, but the susceptibility of the larvae decreased with age. Nutmeg oil also significantly (P < 0.05) affected the hatching of T. castaneum eggs and the subsequent survival of the larvae in the concentration range 1.4–3.2 mg/cm². The production of F1 progeny of both T. castaneum and S. zeamais exposed to media treated with nutmeg oil was significantly (P < 0.05) reduced at all concentrations tested. F1 progeny production was totally suppressed at nutmeg oil concentrations of 1.05 g/100 g rice for T. castaneum and 0.35 g/100 g wheat for S. zeamais. Nutritional studies showed that nutmeg oil significantly (P < 0.05) affected the growth rate and food consumption of both insect species, depending on the concentrations used, but the antifeedant activity was more pronounced against S. zeamaisthan against T. castaneum. At 20 g nutmeg oil/100 ml, the feeding deterrence index of T. castaneum was only about 7%, whereas that of S. zeamaiswas 33%. These results suggest that nutmeg oil may be useful as a grain protectant with contact, fumigant and antifeedant activities against these insects.     

The toxicity of twelve fumigants to three species of mites infesting grain

Eggs of Tyrophagus longior, Acarus siro and Glycyphagus destructor were highly tolerant of each fumigant tested at 10°C while mobile stages were susceptible. Some eggs of T. longior survived the highest test dosages of methyl bromide, phosphine, ethylene oxide, ethyl formate, methallyl chloride and ethyl bromide. The ascending order of toxicity for the other fumigants, as judged by the ct product needed to kill all eggs, was methyl chloroform (MC), carbon tetrachloride (CTC), ethylene dichloride (EDC), methyl formate, ethylene dibromide and acrylonitrile. The toxicity of EDC was generally enhanced by the addition of MC or CTC, though dosages for control were still high, and a single fumigation can only be expected to provide a short-term absence of mobile stages. If complete control is required, this can be achieved by two treatments at a low dose if these are separated by an interval during which the surviving eggs hatch but do not reach the adult stage. The length of this interval depends on temperature and at 10°C is about 7 weeks, at 15°C 3 weeks and at 20°C 2 weeks.     

Factors affecting the resistance of insect eggs to sulphuryl fluoride—II: The distribution of sulphuryl-S fluoride in insect eggs after fumigation

Investigation of the distribution of sulphuryl-³⁵S fluoride in fumigated Schistocerca gregaria (Forsk.) and Tenebrio molitor (L.) eggs showed that labelled sulphur was found predominantly in the chorion and the hydrolysed protein fraction of the resistant S. gregaria eggs. In the more susceptible T. molitor eggs, between 20 and 40 per cent of the labelled sulphur was found in the protein hydrolysate, and up to 75 per cent in the trichloroacetic acid extract. Only a very small amount of the sulphur was found in the ether extracts and the residual materials. It is suggested that resistance is due mainly to the impermeability of the egg shell to the fumigant, most of the fumigant being chemically held by the proteinaceous egg shell and epembryonic membranes.     

The mode of action of fumigants

Studies on the action of the widely used fumigants, hydrogen cyanide, phosphine, methyl bromide, carbon tetrachloride, ethylene dichloride, and ethylene dibromide, are reviewed with a view to establishing some of the biochemical lesions responsible for the toxicity of fumigants to insects. The modes of action of ethylene oxide, carbon disulphide, sulphuryl fluoride, and methyl chloroform are also briefly discussed.     

The synergism of DDT, deutero-DDT, and methoxychlor in a pyrethrin-resistant strain of Sitophilus granarius (L.) (Coleoptera, Curculionidae)

A pyrethrin-resistant strain of Sitophilus granarius was also cross-resistant to DDT and to less easily dehydrochlorinated analogues such as Prolan. Compounds which were known to inhibit the oxidative detoxication of DDT and pyrethroids, synergized DDT against the resistant S. granarius but not against a susceptible strain. The active compounds were: piperonyl butoxide, sesamex, sulfoxide, Piprotal (‘Tropital’), Synepirin 500, and SKF 525A. Of three compounds known to inhibit the detoxication of DDT to DDE in other insects, two, DMC and piperonyl cyclonene, failed to synergize DDT against either strain of S. granarius; however, WARF-antiresistant was an effective DDT synergist in the resistant strain. Very large factors of synergism were obtained with methoxychlor plus sesamex against both resistant and susceptible weevils.     

Susceptibility of local strains of Sitophilus oryzae (L.) and Tribolium castaneum (Herbst) to insecticides

The toxicity of several insecticides to two local strains of S. oryzae and T. castaneum was determined by exposure to treated papers or wheat. Malathion, lindane, dichlorvos and diazinon were more toxic than DDT, carbaryl and pyrethrins. The S. oryzae strain was very susceptible to lindane (0·43×) and malathion (0·26×), but the T. castaneum strain was found to be tolerant to lindane (1·95×) and malathion (7·6×). The T. castaneum was more tolerant to all tested insecticides than the S. oryzae strain.     

Barotolerance of Staphylococcus aureus is increased by incubation at below 0 degrees C prior to hydrostatic pressure treatment

The effect of preincubation under low temperatures on inactivation of Staphylococcus aureus IFO 13276 by hydrostatic pressure treatment (HPT) was investigated. Preincubation before HPT was carried out by submerging cell suspension in an ethylene glycol bath at temperatures from 30 to −20 °C for 15 min. After HPT at the same temperatures, survivors of incubated S. aureus was not significantly (P>0.05) influenced when preincubation took place at temperatures above 0 °C. Survivors of incubated S. aureus, however, were approximately two log cycles higher when preincubation took place at temperatures below 0 °C. This increase in barotolerance of S. aureus was not observed in the presence of 40 μg/ml of chloramphenicol.     

Laboratory evaluation of some additional organophosphorus insecticides against stored-product beetles

The relative susceptibilities of Tribolium confusum Duv. and T. castaneum (Hbst) to seven new organophosphorus insecticides were determined by applying the compounds topically at four dosage rates. SD 8447 (0,0-dimethyl 2-chloro-1-(2,4,5-trichlorophenyl, vinyl phosphate) was more effective than malathion against both species and was evaluated against eight more species of stored-product beetles. It was more toxic than malathion to Rhyzopertha dominica (F.), Lasioderma serricorne (F.), Stegobium paniceum (L.) and Sitophilus zeamais Motsch. but less so against Oryzaephilus surinamensis (L.), O. mercator (Fauv.), Ptinus tectus Boield and Sitophilus granarius (L.). S. zeamais was about eleven times more susceptible to this compound than S. granarius.     

Integrated pest management in stored grain: Combining surface insecticide treatments with aeration

Three aerated, commercial stores of 5000–10,000 t of wheat in England were discovered to have surface infestations of Sitophilus granarius in mid-winter when the grain temperature was 4–9°C. The infestations were monitored using pitfall and probe traps and catches dropped to zero after the application of etrimfos or pirimiphos-methyl 2% dust into the top 0.3 m at 50g/m². The effects of surface treatments in cooled bins were also examined in a farm scale experiment. Six, 20 t bins of wheat, were each aerated at 10 m³/h/t with an 0.02 kW fan and infested with 1/kg each of S. granarius and Oryzaephilus surinamensis and 0.5/kg of Cryptolestes ferrugineus as well as the mites Glycyphagus destructor and Acarus siro. The surface of three bins were treated with 45 g/m² of 2% pirimiphos-methyl dust. Insect numbers, as determined by pitfall traps and probe traps at the surface, 1 and 2 m, fell in all bins during the winter as temperatures fell to 5°C. As the bins warmed up in the spring, numbers of O. surinamenis rose again in the untreated bins. In the second year, S. granarius reached peak numbers in the untreated bins in mid-winter. The much lower numbers of insects trapped in the treated bins were a result of the surface treatment and the few found may have been attributable to migration from the untreated bins. A. siro and G. destructor, together exceeded 1500/kg at the surface of untreated bins, but were less than 10/kg in treated bins. In the second year, few of either species were found and the predatory mite, Cheyletus eruditus, reached 200/kg in all bins, before declining. The experiment showed some of the shortcomings of an integrated pest management system for stored grain, based on cooling, storage at 15% m.c. and monitoring of pest numbers. These were surface populations of mites in the first winter, spring surface re-occurrence of O. surinamensis and surface populations of S. granurius in the second winter. These were overcome by adding surface admixture to the other elements of the IPM system. The IPM programme cost less than half of the cost of admixing the bulk with the cheapest insecticide and used 10% of the insecticide.     

Some effects of the carbon dioxide absorbency of humidity controlling solutions on the results of life history experiments with stored products insects

The longevity of Sitophilus granarius (L), S. zeamais Mots., and Tribolium castaneum (Herbst) and the fecundity and rate of development of T. castaneum were all adversely affected when the insects were kept in desiccators with relative humidity controlling solutions which did not adsorb carbon dioxide. Gas samples taken and analysed every 3–4 days, revealed that the rate of oxygen consumption was higher when carbon dioxide was allowed to accumulate than when it was not. The relevance of the experimental results both to normal storage conditions and to airtight storage is discussed.