Comparative observations on the activity of purethroids against some susceptible and resistant stored products beetles

The activity of six synthetic pyrethroids, allethrin, bioallethrin, resmethrin, bioresmethrin, cismethrin, tetramethrin and also natural pyrethrins, fenitrothion and malathion was examined against susceptible and resistant adult beetles infesting stored products. Cismethrin applied topically was the most active material, alone or synergized, against susceptible Tribolium castaneum, Lasioderma serricorne or Stegobium paniceum.

Solutions in odourless kerosene applied as direct sprays were an average of 6·9 times more active against susceptible T. castaneum than solutions in mineral oil of pyrethrins, bioresmethrin or cismethrin with or without piperonyl butoxide. The factor of synergism was greater when using mineral oil solutions than when using kerosene solutions. It was thought that the more viscous oil slowed penetration of the insecticide giving longer for detoxification, this being inhibited when the synergist was present.

Applied as a dust on wheat, bioresmethrin plus piperonyl butoxide was more active than malathion and less active than fenitrothion against Oryzaephilus surinamensis or susceptible and malathion resistant T. castaneum. Against Sitophilus granarius and susceptible or malathion resistant S. oryzae, synergized bioresmethrin and cismethrin were more active than either malathion or fenitrothion. Malathion resistant S. oryzae was more easily killed by pyrethroids than the susceptible strain. Synergized bioresmethrin was concluded to be the most suitable pyrethroid for controlling stored products beetles, except Lasioderma serricorne and Stegobium paniceum, and was of value against organophosphorus-resistant strains.     

Synergized bioresmethrin as a potential grain protectant

Results of grain protectant trials comparing 4 ppm bioresmethrin + 20 ppm piperonyl butoxide with 12 ppm malathion are presented. The trials utilised commercial welded-steel silos of 5 tonne capacity as commonly used for grain storage on farms and were undertaken during 1967–69 and 1973–74. Treated wheat, in 5-tonne lots, was sampled at monthly intervals and subjected to bioassays of 7, 14 and 28 days duration, F₁ and sometimes F₂ generation counts were also made.

The best overall treatment was 4 ppm bioresmethrin plus 20 ppm piperonyl butoxide. After 12 months, the treated grain controlled Rhyzopertha dominica, 2 susceptible and 1 resistant strain; Sitophilus granarius, 1 resistant strain; S. oryzae, 2 susceptible and 1 resistant strains: Oryzaephilus surinamensis; Plodia interpunctella and Ephestia cautella. A much lower efficiency was observed in the control of adult Tribolium confusum, however, there was complete suppression of the F₁ generation. Poor adult control in the 14-day bioassays contrasted with excellent control in the 28-day bioassay and the F₁ and F₂ bioassays of T. castaneum.

In Australia R. dominica resistant to organo-phosphorus insecticides poses a severe threat to the grain handling industry. Synergised bioresmethrin should be able to restore broad spectrum control, the probable exception being Tribolium species. Bioresmethrin is less toxic to mammals than pyrethrins for which there is an established tolerance of 3 ppm and 20 ppm for piperonyl butoxide on grain.     

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.     

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.     

Evaluation of extracts of neem (Azadirachta indica A. Juss) for the control of some stored product pests

Laboratory investigations on the activity of neem leaf and seed extracts in water or methylated spirit on Callosobruchus maculatus, Sitophilus oryzae and Cylas puncticollis were made at 27 ± 2°C and 65 ± 5% r.h.. Field trials were conducted to determine their effectiveness as protectants of cowpeas and maize in storage at 28 ± 4°C and 82 ± 7% r.h for 5 months.

The results showed that the effectiveness of neem is affected by differences in insect behaviour. The extracts were more active as suppressants of C. maculatus than Sitophilus spp; there was no effect on C. puncticollis. All of the extracts tested resulted in a significant reduction in oviposition, % egg hatch and % adult emergence in C. maculatus and in adult emergence of Sitophilus.

Field trials showed that the extracts mostly gave good protection to cowpea against C. maculatus for 5 months, but only moderate protection to maize against S. zeamais. Seed extracts were more effective than leaf extracts.     

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).     

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.     

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.     

Toxicity of three organophosphorus compounds and pyrethrins to malathion-resistant Tribolium castaneum (Herbst) (Coleoptera, Tenebrionidae)

Malathion-resistant red flour beetles, Tribolium castaneum (Herbst), were tested for susceptibility to Bay 77488 (o,o-diethyl phosphorothioate o-ester with phenylglyoxylonitrile oxime), Bay 78182 (o,o-diethyl phosphorothioate o-ester with (o-chlorophenyl)glyoxylonitrile oxime), diazinon, and pyrethrins by topical applications. The malathion-resistant beetles showed 13·3-fold resistance to pyrethrins, 19·7-fold resistance to Bay 78182, 7·7- and 10·7-fold resistance to diazinon, and only 4·5- and 9·5-fold resistance to Bay 77488. Only about one-quarter as much Bay 77488 as malathion was required for the ₅₀ in the resistant beetles. About one-third as much Bay 78182 as malathion was required. Diazinon and pyrethrins were less toxic than malathion to the resistant insects.     

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.     

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.     

Efficacy of chlorfenapyr against Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae) adults exposed on concrete, vinyl tile, and plywood surfaces

The insecticidal pyrrole chlorfenapyr was applied to concrete, vinyl tile, and plywood surfaces, at an application rate of 1.1 g AI m⁻². Adult Tribolium castaneum (Herbst), the red flour beetle, and adult Tribolium confusum (Du Val), the confused flour beetle, were exposed for 2 and 4 h, removed, and held without food for 7 d post-exposure. All beetles survived the initial exposures, but survival of both species decreased during the 7-d holding period, with T. confusum being the more susceptible species. Survival was generally lower on concrete than on tile or plywood, and was greatly reduced on all three surfaces after 4 h of exposure compared to 2 h. Survival of T. castaneum after 2 h of exposure on concrete, tile, and plywood was 2.5±2.5%, 25.5±15.4%, and 40.0±7.1%, respectively, after 7 d. In contrast, all T. confusum exposed on concrete and tile were dead after 4 and 5 d, respectively, while survival on plywood after 7 d was 20.0±16.8%. After 4 h of exposure, all T. castaneum and T. confusum exposed on concrete and tile were dead after 2–4 d post-exposure, while survival on plywood after 7 d was 41.5±6.4% and 0 for each species, respectively. Non-linear and linear regressions were fit to the data for both species. Results show exposure to chlorfenapyr is effective against T. castaneum and T. confusum, but efficacy will vary depending on the surface substrate.     

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.     

Purification and characterization of a glucoamylase from Rhizopus oryzae

Glucoamylase (EC 3.2.1.3) of Rhizopus oryzae NRRL 395 was purified approximately sevenfold by sequential ammonium sulfate fractionation, Biogel P-100 gel filtration, Q-Sepharose anion exchange and S-Sepharose cation exchange. The pH and temperature optima were 4·8 and 60°C, respectively. Enzyme was stable at temperatures up to 40°C and pH values between 3 and 8. The molecular weight was 67 000 daltons as determined by sodium dodecylsulfate-polyacrylamide gel electrophoresis, and the pI was 8·7 as determined by chromatofocusing. The K_m for amylopectin and soluble starch were 0·98 and 1·34 mg/ml, respectively. The V_max for amylopectin and soluble starch were 782 and 136 μmoles of glucose produced per mg of protein per min, respectively. The enzyme activity was inhibited by Hg²⁺, Pb²⁺ and Cd²⁺, but not by EDTA.     

Potential for autumn aeration of stored rough rice and the potential number of generations of Sitophilus zeamais Motschulsky in milled rice in Japan

Historical weather data from 84 sites in Japan were used to estimate the number of hours 15°C from 1 September to 31 October, based on the individual years from 1994 to1999, to evaluate the potential for using aeration at a threshold level of 15°C to cool rough rice stored during autumn. The number of hours 15°C in September and October ranged from 68±21 in Kyushu to 1067±27 h in northern Hokkaido. At an airflow rate of 0.0013 m³/s/m³, the time required to cool a storage silo containing rough rice to 15°C ranged from 85 days in southern Japan to 5 days in northern Japan. Weather data for the same sites were also used to estimate the number of hours below 15°C from 1 May to 30 September, to evaluate the potential of Sitophilus zeamais Motschulsky, the maize weevil, to infest bagged milled rice at ambient or uncontrolled temperatures. The number of hours 15°C from 1 May to 30 September ranged from 33±15 h in Kyushu to 2392±130 h on the northeastern coast of Hokkaido. As temperature decreased, there was a predicted increase in the number of days required to complete a generation, and as relative humidity increased, a predicted increase in the number of generations that could be produced. These simulation studies show how historical weather data can be used to develop risk management models for storage of bulk rough rice and bagged milled rice in Japan. Aeration during autumn could be used to cool large-bulk storage silos containing rough rice, while the simulations for development of Sitophilus zeamais populations on bagged milled rice emphasize the importance of insect management strategies for value-added products.     

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.     

Toxicity of naturally occurring compounds of Lamiaceae and Lauraceae to three stored-product insects

The compounds 1,8-cineole, camphor, eugenol, linalool, carvacrol, thymol, borneol, bornyl acetate and linalyl acetate occur naturally in the essential oils of the aromatic plants Lavandula angustifolia, Rosmarinus officinalis, Thymus vulgaris and Laurus nobilis. These compounds were evaluated for fumigant activity against adults of Sitophilus oryzae, Rhyzopertha dominica and Tribolium castaneum. The insecticidal activities varied with insect species, compound and the exposure time. The most sensitive species was S. oryzae, followed by Rhyzopertha dominica. Tribolium castaneum was highly tolerant of the tested compounds. 1,8-Cineole, borneol and thymol were highly effective against S. oryzae when applied for 24 h at the lowest dose (0.1 μl/720 ml volume). For Rhyzopertha dominica camphor and linalool were highly effective and produced 100% mortality in the same conditions. Against Tribolium castaneum no oil compounds achieved more than 20% mortality after exposure for 24 h, even with the highest dose (100 μl/720 ml volume). However, after 7 days exposure 1,8-cineole produced 92.5% mortality, followed by camphor (77.5%) and linalool (70.0%). These compounds may be suitable as fumigants because of their high volatility, effectiveness, and their safety.     

Clostridium perfringens and its toxins in minced meat from Kars, Turkey

The aim of this study was to determine the prevalence of Clostridium perfringens and its toxins in minced meat. A total of 96 minced meat samples were collected from local markets (16) and small butcher's shops (80) in Kars (Turkey). Samples were analysed for the presence of C. perfringens and its toxins using a commercially available ELISA kit. A total of 31 (32%) Clostridium spp. strains were isolated and 17 (55%) of these isolates were identified as C. perfringens. Four (25%) of the samples from local markets and 27 (34%) from small butcher's shops were contaminated with Clostridium spp. Furthermore, C. perfringens was isolated from two (12%) and 15 (19%) samples from local markets and small butcher's shops, respectively. Mean counts of Clostridium spp. were 2.2 ± 0.83 × 10² CFU g^-1 for local markets and 4.35 ± 8.53 × 10² CFU g^-1 for small butcher's shops; mean counts for C. porringers were 2.75 ± 0.21 × 10² and 6.82 ± 10.96 × 10² CFU g^-1 from markets and butcher's shops, respectively. The number of samples contaminated with both Clostridium spp. and C. perfringens was higher in small butcher's shops than in local markets. Moreover, higher numbers of Clostridium spp. and C. perfringens were isolated in samples from small butcher's shops than from local markets. A total of 13 (13%) samples were also positive for toxins produced by the organism, as detected by ELISA. Eleven samples from small butcher's shops and two samples from local markets were positive for the C. perfringens toxins tested. Moreover, two (12%), one (1%), four (4%) and two (2%) samples were contaminated with C. perfringens types A, B, C and D, respectively. In conclusion, some meat samples collected from local markets and small butcher's shops contained C. perfringens and its toxins and, therefore, present a potential risk of food poisoning.     

Persistence and activity of permethrin in stored wheat and its residues in wheat milling fractions

The pyrethroid insecticide permethrin was applied at 2 or 8 mg a.i./kg to wheat, or at 2 mg a.i. permethrin plus 10 mg a.i. piperonyl butoxide/kg to wheat, and the wheat seeds were stored for 20 months under ambient conditions (17–32°C and 40–60% r.h.). Bioassays conducted with adults of Sitophilus oryzae (L) placed on treated wheat samples indicated that all treatments were effective in controlling S. oryzae during storage for at least 20 months. The residues of permethrin and its cis/trans isomers were determined in ground whole wheat and its milling fractions, and the time periods for the initial residue levels to be reduced by half, were evaluated. These ranged from 178 to 200, 217 to 231, and 255 days, in the ground whole grain, bran and flour, respectively. The residues of permethrin in whole ground grain ranged from 1.378 ± 0.190 (day 1) to 0.247 ± 0.026 mg/kg (day 427) in the wheat treated at 2 mg a.i. permethrin/kg, and from 7.400 ± 0.234 (day 1) to 1.294 ± 0.017 mg/kg (day 427) in the wheat treated at 8 mg a.i. permethrin/kg. There was no indication of any effect of piperonyl butoxide on permethrin residue levels. After 35 days of storage 75–80% of permethrin residues were found in the bran portions of seeds subjected to each of the three treatments, while after 427 days of wheat storage at ambient conditions no detectable levels of permethrin residues were found in flour from wheat treated at the rate of 2 mg a.i./kg of wheat.     

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.