The effect of carbon dioxide gas alone or in combinations on the mortality of Tribolium castaneum (Herbst) and T. confusum du Val (Coleoptera, Tenebrionidae)

Adults of Tribolium castaneum (Herbst) and T. confusum du Val exposed to various mixtures of N₂ or He and O₂ were killed when the O₂ concentration reached to 1·7% or below, whereas the adults exposed to CO₂ : O₂ mixtures were killed mostly due to the deleterious effects of CO₂ itself. At 26·7°C and 38 ± 6%r.h., 95 per cent mortality of T. confusum adults was obtained by an exposure of 271 hr to 45% CO₂ : 55% air mixture; 58 hr to 62% CO₂ : 38% air mixture; and 47·5 hr to 80% CO₂ : 20% air mixture, while for T. castaneum adults 95 per cent mortality required 192, 60, and 44 hr respectively. Data obtained by exposing mature and immature stages of both species to 100% CO₂ suggest that adults were the most susceptible, followed by larvae, eggs and pupae. Generally speaking, inactive stages (egg and pupal) were more tolerant to CO₂ than active stages (larval and adult). Increasing the temperature from 15·6° to 26·7°C resulted in increased insect mortalities; the degree of response varying in different stages. Increasing r.h. decreased the susceptibility of adult insects to 100% CO₂.

Under airtight conditions 200 adult T. castaneum with 8 g of food medium sealed in 1·2 1. glass flasks depleted the O₂ supply from 20·9% to a critical 1·7% level in 7 days, and adults of T. confusum depleted to the 1·6% level in 5 days of airtightness, and both species produced about 20% of carbon dioxide gas.     

Susceptibility of stored-product beetles on wheat and maize treated with thiamethoxam: effects of concentration, exposure interval, and temperature

Sitophilus zeamais Motschulsky, the maize weevil, Oryzaephilus surinamensis (L.), the saw-toothed grain beetle, and Tribolium castaneum (Herbst), the red flour beetle, were exposed for 1, 2, 3, and 6 d at 22°C, 27°C, and 32°C on maize treated with 0, 0.5, 1.0, 2.0, or 4.0 ppm thiamethoxam, a new-generation neonicotenoid insecticide. A second series of tests was conducted on hard winter wheat using S. oryzae (L.), the rice weevil, Rhyzopertha dominica (F.), the lesser grain borer, and T. castaneum. Mortality of all species on both commodities generally increased with insecticide concentration, exposure interval, and temperature, and data were described by linear and non-linear regressions with concentration as the independent variable. Mortality of S. zeamais ranged from 58% to 90% on maize treated with 0.5 ppm thiamethoxam, and approached 95–100% as concentration increased to 4 ppm. Oryzaephilus surinamensis appeared to be slightly less susceptible than S. zeamais; mortality ranged from about 18% to 80% at 5 ppm and there was a more gradual increase in mortality as concentration increased. Mortality of T. castaneum generally did not exceed 40% at any concentration unless the beetles were exposed for 6 d. Mortality of R. dominica and S. oryzae was less than 60% when exposed on treated wheat for 1 and 2 d, but increased to nearly 100% when exposed for 6 d at 27°C and 32°C. Mortality of T. castaneum did not exceed 20% at the 1- and 2-d exposures, and approached 100% only when beetles were exposed for 6 d at 32°C. Few F₁ adults of any species were found in treated maize or in treated wheat but the number of F₁ T. castaneum in untreated maize and untreated wheat was very low compared with the other species. Results show that thiamethoxam would be an effective protectant of stored maize seed and stored wheat seed.     

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).     

Centralised bulk pre-packaging of fresh pork retail cuts in various gas atmospheres

A centralised bulk pre-packaging technique (laboratory method), utilising various gas mixtures (c. 100% CO₂; c. 75% CO₂:25% N₂; c. 80% O₂: 20% CO₂ and c. 25% CO₂:50% N₂:25% O₂), was evaluated in terms of quality attributes such as microbiology, colour, odour and consumer acceptability. According to the bacterial counts recorded, all four packaging treatments were successful in prolonging the storage life (21 days c. 0°C) of centralised bulk pre-packaged pork retail cuts, while still ensuring a subsequent shelf life of at least 3 days (c. 0°C). The gas mixture comprising c. 25% CO₂:50% N₂:25% O₂ was the most successful treatment in terms of acceptability and colour scores.     

Repellent effect of pea (Pisum sativum) fractions against stored-product insects

Peas (Pisum sativum) are toxic to some stored-product insects. The repellent effect of fractions of pea seed to stored-product insects was evaluated in multiple-choice tests in which wheat kernels were dusted with fractions rich in either protein, fibre or starch at 0.001 to 10% (wt:wt). There was a negative correlation between pea protein concentration and the number of adults found in grain for Cryptolestes ferrugineus and Sitophilus oryzae, but not for Tribolium castaneum. Pea fibre repelled C. ferrugineus adults but not S. oryzae and T. castaneum. Pea starch did not repel any of the insects. One-week old and 6-week old C. ferrugineus were equally repelled by pea protein. Repellency was detectable 1 h after exposure. Cryptolestes ferrugineus and S. oryzae did not become habituated to the repellent action of pea protein even after 4 weeks of exposure. Habituation was observed, however, when C. ferrugineus was exposed to pea fibre for 4 weeks. In a two-choice bioassay (0 vs. 0.1% and 0 vs. 1% pea protein), the pea-protein-treated grain had significantly fewer insects (C. ferrugineus, S. oryzae, Sitophilus zeamais, T. castaneum, and Tribolium confusum) than untreated grain. The properties of the pea protein fractions seem well suited for developing a natural stored grain protectant.     

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.     

Unbaited probe traps and grain trier: a comparison of the two methods for sampling Coleoptera in stored barley

Inside a Central Greece storeroom containing 80 metric tons of barley, 10 unbaited probe traps were placed at a depth of 80 cm from January 1997 to January 1998. The traps were inspected every 20 days. Additionally, during the same period, samples were taken every 20 days using a non-partitioned grain trier. More adults were found in the traps than in the grain trier, especially during the warm months. Twenty-one species were found. Cryptolestes ferrugineus, Alphitobius diaperinus, Oryzaephilus surinamensis, Ahasverus advena, Tribolium castaneum and Rhyzopertha dominica were the most abundant species in the traps, whereas Sitophius oryzae and Oryzaephilus surinamensis were the most abundant in the grain trier samples. Probe traps were more sensitive in detection of adults, with the exception of S. oryzae and S. granarius. Iwao’s regression analysis indicated repulsion among individuals in both techniques. Furthermore, all species (except for C. ferrugineus in grain trier samples) showed an aggregated distribution among sampling units. For Iwao’s model, the greatest r² values were those for the species C. ferrugineus and A. diaperinus in the traps, while the values for the same species in the grain trier samples were the lowest.     

Display life of sheep meats retail packaged under atmospheres of various volumes and compositions

Longissmus dorsi loins were removed from Suffolk cross-breed lambs (4–9 months) and hoggets (15–20 months). The effect of package gas composition was investigated by packaging loins with gas mixtures containing 80:20:0, 60:20:20 and 60:40:0/O₂:CO₂:N₂ with a 2:1 headspace to meat volume ratio. The most effective gas mixture for prolonging shelf-life was used to study the effect of different headspace to meat volume ratios. Loins were packaged with a headspace to meat volume ratio of 2:1, 1.5:1 or 1:1. All modified atmosphere (MA) packs were held under refrigerated display conditions (4 °C, 616 lx) for 12 days. Loins were assessed for microbial, oxidative and colour stability and headspace composition every 3 days. The 80:20:0/O₂:CO₂:N₂ gas composition and the 2:1 headspace to meat volume ratio was the most effective packaging combination at maintaining and prolonging the attractive red colour of MA packaged lamb and hogget meat. 80:20:0/O₂:CO₂:N₂ resulted in significantly (p<0.01) higher Hunter a values in lamb. The 2:1 ratio gave higher visual assessment values in lamb and higher Hunter ‘a' values for hogget meat throughout the trial. The 2:1 ratio was the most effective at decreasing Pseudomonas and increasing the numbers of lactic acid bacteria in the total microbial load in both lamb and hogget meat. Lipid oxidation in lamb and hogget meat occurred at a slower comparative rate than discolouration or microbial growth and was not the major determinant of shelf-life. The 2:1 headspace to meat volume ratio was most effective at maintaining the initial gas mix in both lamb and hogget MA packs.     

The effects of residual oxygen concentration and temperature on the degradation of the colour of beef packaged under oxygen-depleted atmospheres

Samples of beef longissimus dorsi (LD), approximately 5 × 5 × 1 cm, were packaged in pairs under 10 litre volumes of N₂ or CO₂ containing O₂ at concentrations between 100 and 1000 ppm. The packaged samples were stored at temperatures of 5, 1, 0 or −1·5°C, for times between 4 and 48 h. Samples of beef psoas major (PM) were packaged under N₂ or CO₂ containing O₂ at between 100 and 600 ppm, and stored at −1·5°C for 24 or 48 h. After storage, each sample was assessed for colour deterioration and discoloration, and for the fraction of metmyoglobin in the surface pigment.

The results obtained with N₂ and CO₂ atmospheres were similar. The colours of all LD samples had deteriorated after 4 h storage at 5 or 1°C, although the degree of deterioration increased with increasing O₂ concentration. All LD samples stored for 12 h at 5 or 1°C were extensively discoloured, with metmyoglobin fractions generally exceeding 60%, but those stored at −1·5°C for 48 h or less, under O₂ concentrations ≤ 400 ppm had undergraded colours. The colours of some LD samples stored at −1·5°C under about 600 ppm of O₂ were also undergraded, but the colours of samples stored under 800 or 1000 ppm had deteriorated by 24 h. The colours of LD samples stored at 0°C under > 200 ppm had deteriorated after 24 h storage, and the colours of samples stored under 100 ppm O₂ had deteriorated after 48 h storage. All PM samples were wholly discoloured after storage at −1·5°C. Evidently, the colour of beef muscle of high colour stability is resistant to degradation by atmospheres containing < 600 ppm of O₂ when the meat is stored at sub-zero temperatures, but not when the storage temperature is at or above 0°C. Beef muscle of low colour stability, such as the PM, will discolour at all low concentrations of O₂ irrespective of the storage temperature.     

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.     

A practical trial of pyrethrins-in-oil surface sprays for the protection of bagged grain against infestation by Cadra cautella (Wlk.) (Lepidoptera, Phycitidae) in Kenya

Two formulations of synergized pyrethrins in technical white oil were tested as monthly protective sprays on stacks of fumigated bagged wheat, primarily against Cadra cautella (Wlk.) but also against Sitophilus oryzae (L) and Tribolium castaneum (Hbst.), under warm-temperate storage conditions in up-country Kenya. The formulations were: 0·4% pyrethrins with 2·0% piperonyl butoxide, applied at 50 ml/m², and 0·4% pyrethrins with 0·4% piperonyl butoxide at 20 ml/m².

Results were assessed by recording infestation in samples taken from each stack after 18 weeks storage and five spray applications.

Both treatments gave reasonably good protection against C. cautella but were not satisfactory against S. oryzae or T. castaneum. There was no evidence of any taint in bread made from the treated grain, but the higher application rate caused excessive staining of the bags.

It is concluded that satisfactory control of reinfestation by C. cautella can be expected in practice using 0·4% pyrethrins in oil with only a minimal quantity of added piperonyl butoxide, and that 20 ml/m² is a suitable rate for application to bagged produce.     

Beef shelf life in low O(2) and high CO(2) atmospheres containing different low CO concentrations

The use of atmospheres with low concentrations of CO (0.1 to 1%), in combination with O₂ (24%), high CO₂ (50%) and N₂ (25 to 25.9%), for preserving chilled beef steaks was investigated. The atmosphere used as reference contained 70% O₂+20% CO₂+10% N₂. Bacterial counts showed that all atmospheres containing CO greatly reduced total aerobic population numbers, including Brochothrix thermosphacta. Lactic acid bacteria, however, were not affected. CO concentrations of 0.5–0.75% were able to extend shelf life by 5–10 days at 1±1°C, as demonstrated by delayed metmyoglobin formation (less than 40% of total myoglobin after 29 days of storage), stabilisation of red colour (no change of CIE a* and hue angle after 23 days), maintenance of fresh meat odour (no variation of sensory score after 24 days) and significant (P<0.01) slowing of oxidative reactions (TBARS).     

Observations on the susceptibility of compressed dried grass and legume to infestation by some storage insects

Under conditions controlled at 25°C and 70% r.h. and under outdoor conditions in southern England, the storage insect pests Sitophilus granarius (L.), Oryzaephilus surinamensis (L.), Cryptolestes ferrugineus (Steph.) and Ephestia elutella (Hueb.) were unable to breed or to survive for long on blocks of compressed, dried forage (grass or legume). The beetles Ptinus tectus Boield. and Trigonogenius globulus Sol. were able to breed on this material under both sets of conditions, but Stegobium paniceum (L.) only at 25°C. At the higher relative humidities associated with outdoor conditions the moths Hofmannophila pseudospretella (Staint.) and Endrosis sarcitrella L. produced thriving cultures. The damage caused by S. paniceum and the moths was severe; in particular, H. pseudospretella completely destroyed the foodstuff during 1 yr of storage at ambient outdoor shade temperatures in Britain.     

Laboratory evaluation of three novel insecticides inhibiting cuticle formation against some susceptible and resistant stored products beetles

The insecticidal activity of three 1-(2.6-disubstituted-benzoyl)-3-phenylureas was evaluated against a number of susceptible and resistant stored products beetles. The compounds were DU 19111 (1-(2,6-dichlorobenzoyl)-3-(3,4-dichlorophenyl)-urea), PH60-38 (1-(2,6-dichlorobenzoyl)-3-(4-chlorophenyl)-urea), and PH60-40 (1-chlorophenyl)-3-(2,6-difluorobenzoyl)-urea).

PH60-40 was found to be the most effective compound against susceptible strains of Sitophilus granarius, Sitophilus oryzae, Tribolium castaneum and Lasioderma serricorne. All three compounds were ineffective against Stegobium paniceum. A strain of T. castaneum (Kuala Lumpur strain) showing malathion-specific resistance was found to be more susceptible to PH60-40 than its “susceptible” strain. A non-specific resistant strain of T. castaneum (CTC12 strain) showed approximately two times tolerance to PH60-40 compared with the “susceptible” strain.

PH60-40 was shown to have ovicidal properties and also killed young larvae of T. castaneum after short exposure periods. Oviposition was not affected.

Wheat sprayed with an emulsifiable formulation of PH60-40 at 2, 5 or 10 ppm was found to be protected against susceptible T. castaneum, S. granarius and Oryzaephilus surinamensis and against resistant S. oryzae and T. castaneum (Kuala Lumpur strain) following 40 weeks storage at 20°C and 44 weeks storage at 35°C.

Preliminary toxicological data indicates that PH60-40 is of a sufficient order of safety for consideration for grain admixture. The compound is therefore of potential interest as a replacement for the more conventional grain protectants especially in situations where resistance is producing increasing control problems.     

The display life of retail-packaged beef steaks after their storage in master packs under various atmospheres

Beef strip loins were divided into four portions. One portion of each loin was vacuum-packaged and then stored at −1·5°C. The other portions were each divided into three steaks, which were retail-packaged. The retail packs were master-packaged under atmospheres of N₂, CO₂, or O₂ + CO₂ (2 : 1, v/v) and then stored at 2°C. Product was assessed after storage times of up to 60 days. At each assessment, a vacuum pack and a master pack of each type, each containing product from the same loin, were withdrawn from storage. The vacuum-packaged product was cut into three steaks, which were retail-packaged. The newly prepared retail packs and those from the master packs were displayed in a retail cabinet, at air temperatures that averaged between 3 and 5·7°C, and were assessed twice daily until the product was judged to be unacceptable. When first assessed, steaks cut from vacuum-packaged product were generally considered desirable, with little metmyoglobin in the surface pigment, although the edges of same steaks were discoloured. Steaks stored under N₂ or CO₂ for 4 days or less were only slightly desirable at best, with metmyoglobin forming relatively large fractions of the surface pigment. However, after storage under N₂ or CO₂ for 6 days or more, metmyoglobin fractions were low, and the steaks bloomed to a desirable red colour. Steaks stored under O₂ + CO₂ had lower metmyoglobin fractions, and were desirable after storage for up to 8 days. However, the fractions of metmyoglobin increased, and steaks were judged to be less desirable after longer storage times. Steaks stored under O₂ + CO₂ for 20 days were unacceptable. After storage, the numbers of bacteria on steaks from vacuum packs and N₂, CO₂, and O₂ + CO₂ atmospheres were, respectively, <10⁴, <10⁶, <10⁵, and <10⁴ CFU/cm². The flora from steaks stored under CO₂ were composed wholly of lactic acid bacteria. Other flora were dominated by lactic acid bacteria, but contained fractions of enterobacteria and/or Brochothrix thermosphacta.

The appearance of product from vacuum packs generally was unacceptable after 72 h of display. The display life of steaks stored under N₂ or CO₂ was shorter than that of the product from vacuum packs when product was stored for 2 days or less, or 46 days or more. After other storage times, the product from vacuum packs or master packs with N₂ or CO₂ atmospheres had a similar display life. The display life of product stored under O₂ + CO₂ was similar to that of product from vacuum packs or CO₂ or O₂ + CO₂ was similar to that of product from vacuum packs after storage times of 8 days or less but was shorter after storage times of 12 or 16 days. The flora on displayed product from vacuum packs or CO₂ or O₂ + CO₂. atmospheres did not attain the maximum number of 10⁷ CFU/cm². and the product did not develop off-odours of microbial origin. However, numbers of 10⁷ CFU/cm² were approached or attained during display of product stored under N₂ for 28 days or longer, and some of that product developed moderate off-odours. It then appears that, under temperature regimes that are common in commercial practice, retail-packaged strip-loin steaks with a display life of 2 days or longer can be obtained from master packs after storage periods of up to about 2, 4, or 7 weeks, respectively, with master-pack atmospheres of O₂ + COPin2 (2 : 1, v/v), N₂, or CO₂.     

Mortality of adult Cryptolestes ferrugineus (Stephens) exposed to changing CO2 concentrations

The concentration of carbon dioxide (CO₂) in a grain bin declines during a fumigation due to leakage, but mortalities of adult Cryptolestes ferrugineus (Stephens) have been obtained and reported at constant CO₂ concentrations. A procedure for predicting the mortality of adult C. ferrugineus exposed to conditions of changing CO₂ concentration was developed. Based on published data, a regression equation was obtained for mortality of adult C. ferrugineus exposed to elevated CO₂ concentrations at a temperature of 25°C. The regression equation was used to calculate a cumulative lethality index. Complete mortality should occur when the cumulative lethality index equals one. Agreement between the observed insect mortality and the corresponding cumulative lethality index was good in five experimental fumigations conducted in sealed, welded-steel hopper bins, but the cumulative lethality index over-predicted the insect mortality in the sixth experimental fumigation.     

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.     

Evaluation of two new diatomaceous earth formulations, enhanced with abamectin and bitterbarkomycin, against four stored-grain beetle species

Two new natural diatomaceous earth (DE) formulations, enhanced with abamectin (DEA-P/WP), or bitterbarkomycin (DEBBM-P/WP), were tested under laboratory conditions against adults of the rice weevil, Sitophilus oryzae, the lesser grain borer, Rhyzopertha dominica, the red flour beetle, Tribolium castaneum and the rusty grain beetle, Cryptolestes ferrugineus. The bioassays were carried out on wheat, at 30±1 °C and 70±5% r.h. The two enhanced DEs were applied either as dusts (P) or as wettable powders (WP) at the dose rates of 75, 100 125 and 150 ppm. Adult mortality was assessed after 14 and 21 d of exposure on the treated substrate. After this interval, the treated wheat was retained for an additional period of 49 d in the case of S. oryzae and 63 d in the case of the other three species, in order to evaluate progeny production. Generally, for all species tested, mortality was higher on wheat treated with powders in comparison with wettable solutions. After 14 d of exposure, all adult rice weevils were dead even at the lowest dose rate of DEA-P, while 100% mortality was noted at doses 125 ppm of DEBBM-P. For the other species, mortality was 100% on wheat treated with 75 ppm of DEBBM-P, with the exception of T. castaneum for which all adults were dead at doses 100 ppm. Progeny production was low, and no progeny were produced in the cases of R. dominica and C. ferrugineus, for both DEs. However, for S. oryzae, progeny production was high on wheat treated with WP formulations, at dose rates 100 ppm. Similar trends were noted for T. castaneum, at 100 ppm of DEBBM-WP. The results of the present study indicate that both DEA-P/WP and DEBBM-P/WP are more effective against the four beetle species examined in comparison with the currently commercially available DE formulations.     

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.     

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.