Efficacy of the insect growth regulators methoprene, fenoxycarb and diflubenzuron against Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) on maize and paddy rice

The activity of fresh deposits of methoprene, fenoxycarb and diflubenzuron against F₁ progeny of Rhyzopertha dominica on maize and paddy was compared with that on wheat, at two equilibrium relative humidities. There were differences between slopes of log concentration-probit (lc-p) lines for different compounds, and for the same compound on different grains. Judging by values of the IC_99.9, i.e. the concentration which inhibited progeny production by 99.9%, the order of activity against F₁ progeny on different grains was: methoprene, wheat and paddy > maize; fenoxycarb, wheat > paddy > maize; diflubenzuron, wheat and maize > paddy. Equilibrium relative humidity (e.r.h.) had no consistent effect on activity—at 90% e.r.h., the IC₅₀ of fenoxycarb on wheat was reduced and the IC₅₀ of diflubenzuron on maize was increased compared with 70% e.r.h., and other treatments were unaffected.

The efficacy of these compounds on maize and paddy against F₁ and F₂ progeny was evaluated during 48 weeks storage at 30°C, 70% r.h. The resolved S isomer of methoprene was also included. Slopes of lc-p lines were greater against the F₂ than against the F₁, particularly using diflubenzuron on paddy, with corresponding smaller values of the IC_99.9. Equally effective concentrations did not decline systematically over 48 weeks. Minimum effective application rates were judged as the concentrations that prevented living F₂ progeny in at least 2 of 3 replicates. Estimates for 48 weeks protection on maize were: methoprene, 2 mg kg⁻¹; S-methoprene, 1 mg kg⁻¹; fenoxycarb, 10 mg kg⁻¹; and diflubenzuron, 5 mg kg⁻¹. Corresponding estimates on paddy were 0.15 mg kg⁻¹, 0.05 mg kg⁻¹, 5 mg kg⁻¹, and 5 mg kg⁻¹.     

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 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 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.     

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.     

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.     

A comparison of the toxicity of pirimiphos-methyl and malathion to Typhaea stercorea (L.) when applied to stored maize

The toxicity of freshly applied and aged residues of pirimiphos-methyl and malathion were assessed against adult Typhaea stercorea (L.). Maize was treated with each pesticide at doses of 2, 4, 6, and 8 mg kg⁻¹ and stored at a constant 25 °C and 70% r.h. for 12 weeks. All fresh deposits of pirimiphos-methyl produced 100% mortality as did malathion at 4, 6 and 8 mg kg⁻¹. After four weeks storage pirimiphos-methyl still gave 100% mortality at 6 and 8 mg kg⁻¹ but this dropped to 96% at 4 mg kg⁻¹ and 60% at 2 mg kg⁻¹, while mortality for malathion was less than 31% even at 8 mg kg⁻¹. After 12 weeks storage only pirimiphos-methyl gave effective control with 78% mortality at the highest dose of 8 mg kg⁻¹, while control by malathion had completely broken down. The effect of exposure time on T. stercorea for both pesticides at a single dose of 4 mg kg⁻¹ was also assessed. Beetles were left in contact with treated maize for 2, 4, 6, 8 and 10 d. Fresh and four-week-old pirimiphos-methyl residues produced over 98% mortality at all exposure periods but on 12-week-old residues mortality had dropped and was only 61% following 10 d exposure. Only freshly applied malathion gave 100% mortality and even the maximum exposure of 10 d only produced 51% mortality of T. stercorea at four weeks and 39% at 12 weeks.     

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.     

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.     

The effect of ractopamine on myofibre distribution and morphology and their relation to meat quality in swine

One hundred and twenty-eight purebred Lacombe pigs (equal number of barrows and gilts) were assigned to one of four treatments at 64 kg and fed a commercial grower-finisher diet ad libitum to which ractopamine (RAC) was incorporated (0, 10, 15 or 20 mg kg⁻¹). Pigs were slaughtered at 100 kg. Histological samples were collected from the semimembranosus (SM) and the psoas major (PM) muscles from the 0 and 20 mg kg⁻¹ RAC groups. Meat quality and muscle composition data were collected for all pigs. A significant 3-way interaction for muscle weight involving treatment, muscle and gender (P = 0·01) indicated that for the SM, gilts appeared to respond to RAC at a lower level of incorporation (10 mg kg⁻¹) than barrows. Despite these differences in response at the gross muscle level, responses were similar at the cellular level for both muscles. The proportion of red fibres did not change (P = 0·21), the proportion of intermediate fibres decreased (P = 0·01) and the proportion of white muscle fibres increased (P = 0·02) in the mg kg⁻¹ RAC group compared to the controls. In addition, when compared to controls, average fibre diameters in the 20 mg kg⁻¹ RAC group remained constant in the red fibres, and increased significantly in both the intermediate and white fibres (P = 0·01 and 0·02, respectively). Over both muscles Kramer Press values were significantly higher (P = 0·030 in the RAC-fed pigs than in the controls. Incorporation of RAC into the diet did not result in any changes to crude protein or total and soluble hydroxyproline levels. Crude fat tended to increase in the 15 mg kg⁻¹ RAC treatment in the SM and decreased in the 20 mg kg⁻¹ RAC treatment in the PM. The shift in fibre type, and the associated changes in fibre size, may contribute to the increased shear values found in RAC-fed pigs.     

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.     

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.     

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.     

The efficacy of linalool, a major component of freshly-milled Ocimum canum Sims (Lamiaceae), for protection against postharvest damage by certain stored product Coleoptera

Linalool was present at 8.6 ± 0.9 mg/g in the dried leaves of Ocimum canum Sims, an annual mint used in Rwanda to protect against postharvest insect damage. Direct exposure of adults of Zabrotes subfasciatus (Bohem.) to milled, dried O. canum leaves resulted in 100% mortality of males and 50% mortality of females after 48 hr. Dose-response curves for linalool were completed with adult Z. subfasciatus, Acanthoscelides obtectus (Say), Rhyzopertha dominica (F.), and Sitophilus oryzae (L.) using a filter paper bioassay. The LC₅₀ values were: 428 μg/cm² for Z. subfasciatus; 405 μg/cm² for A. obtectus; 428 μg/cm² for R. dominica; 427 μg/cm² for S. oryzae. Knockdown was occasionally followed by recovery at doses less than the LC₅₀ for all species. There are significant differences in the LC₅₀ and LT₅₀ values for male and female Z. subfasciatus. At the lower dosages hyperactivity rarely preceded moribundity and mortality where these occurred, while at higher dosages hyperactivity occurred soon after initial exposure and preceded imminent death. A concentration increase from 250 to 750 μg/cm², representing a tripling of dosage, spanned th 10–100% response mortality for all species at 24 hr. Air-exposure of linalool-treated papers (500 μg/cm²) for up to 24 hr significantly decreased toxicity to both sexes of Z. subfasciatus. Quantitative analysis showed the only significant decrease in the amount of linalool to occur after 0.25 hr, and this did not fully correlate with the resulting decrease in efficacy against both sexes of Z. subfasciatus. The results are discussed in terms of the efficacy of using O. canum for the protection against loss due to insects in the traditional food storage systems of Rwanda.     

Sorption of chloroanisole vapors by raisin packaging material

The behavior and concentration of 2,4,6-trichloroanisole (TCA) vapors migrating into low-density polyethylene film (PE) of 0.39 μm at various temperatures and desorption of TCA from PE were determined. After 12 h exposure, 1642 μg g⁻¹ TCA was sorbed at 30 °C compared with 675 μg g⁻¹ at 20 °C. For PE to reach equilibrium of 4200 μg g⁻¹ at 30 °C took 48 h, but 120 h at 20 °C. The transmission of TCA through PE occurred after 12 h at 30 °C (8.9 μg kg⁻¹ m⁻² h⁻¹) and after 36 h at 20 °C (5.0 μg kg⁻¹ m⁻² h⁻¹). Desorption of TCA from PE increased with temperature. At 80 °C, 99% TCA was desorbed in 1 h compared to 51% at 40 °C, 31% at 30 °C and 17% at 20 °C. The rate of sorption, desorption and transmission of TCA vapors by PE is highly temperature-dependent.     

Life history studies of internally feeding pests of stored sorghum: Sitotroga cerealella (Ol.) and Sitophilus oryzae (L.)

A laboratory study of the ecology of single species populations of Sitotroga cerealella (Olivier) and Sitophilus oryzae (L.) was made at 3 temperatures (25, 30 and 35°C) and 3 relative humidities (60, 70 and 80% r.h.). The effects of 2 lower humidities (40 and 50% r.h.) on both species were also studied at 30°C. The optimum conditions for multiplication of S. cerealella were found to be 25–30°C and 60–80% r.h. while for S. oryzae the optimum was more clearly defined (30°C and 80% r.h.). However S. cerealella could tolerate a higher temperature (35°C) and lower humidities (40 and 50% r.h. at 30°C) than S. oryzae. The results are compared with those of other workers on sorghum and other cereals, and discussed in relation to the distribution of the two species in Sudan.     

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.     

Biologically active polyamines in pig kidneys and spleen: Content after slaughter and changes during cold storage and cooking

Polyamines putrescine, spermidine (SPD) and spermine (SPM) were determined as dansyl derivatives using an HPLC method. Distribution of SPD and SPM in pair kidneys was homogenous. The mean SPD and SPM contents in pig kidneys 24 h after slaughter were 9.39 ± 3.35 and 53.1 ± 14.0 mg kg⁻¹, respectively with no significant differences between barrows and gilts. Putrescine content was below the detection limit of 1.2 mg kg⁻¹. In kidneys stored aerobically or vacuum-packaged at 2–3 °C for 7 and 21 days, respectively, SPD and SPM decreased significantly. Stewing decreased both polyamines more extensively in kidneys processed on day-1 after slaughter than on day-7 after storage at 2–3 °C. The mean SPD and SPM in 10 spleens 24 h after slaughter were 36.7 ± 5.70 and 34.0 ± 7.64 mg kg⁻¹, respectively. Thus, both pork kidney and spleen are foods with a high level of SPM and SPD.     

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.