Insecticidal efficacy of diatomaceous earth against Sitophilus oryzae (L.) (Coleoptera: Curculionidae) and Tribolium confusum du Val (Coleoptera: Tenebrionidae) on stored wheat: influence of dose rate, temperature and exposure interval

Laboratory experiments were conducted in order to assess the insecticidal effect of a diatomaceous earth formulation (Silicosec^®, Biofa GmbH, Germany) against Sitophilus oryzae and Tribolium confusum on stored wheat. Adults of the two species were exposed on wheat treated with diatomaceous earth at four dose rates: 0.25, 0.5, 1 and 1.5 g/kg of wheat, respectively. For each dose rate, the treated wheat was placed at 22°C, 25°C, 27°C, 30°C and 32°C. Dead adults were counted after 24 and 48 h, 7 and 14 d of exposure. After the 14-d interval, the live adults were removed and placed for 7 d in untreated wheat (in the case of S. oryzae) or untreated flour (in the case of T. confusum), and the production of F₁ was recorded. For both species, dose rate, temperature and exposure interval significantly affected mortality (P<0.001). Mortality was higher at longer exposure intervals. The efficacy of SilicoSec against S. oryzae increased with temperature, but for T. confusum mortality was lower at 32°C, compared to 30°C, for 24 and 48 h exposure intervals. Tribolium confusum proved less susceptible to SilicoSec than S. oryzae. In general, the rates of 1 and 1.5 g/kg of wheat provided a satisfactory level of protection against the two species examined. For S. oryzae, F₁ emerged only at 22°C, in wheat treated with 0.25 or 0.5 g/kg. However, for T. confusum, F₁ were recorded at 22°C for 0.5 g/kg and at 22°C, 25°C, 27°C and 30°C for 0.25 g/kg.     

Survival of Sitophilus oryzae (L.) on wheat treated with diatomaceous earth: impact of biological and environmental parameters on product efficacy

A series of experiments was conducted to evaluate the effects of temperature, relative humidity (r.h.), population density, concentration, exposure interval, and residual aging on susceptibility of Sitophilus oryzae (L.), the rice weevil, to diatomaceous earth (DE). In the first experiment, hard red winter wheat was treated with 300 ppm of the Protect-It™ formulation of DE, and 10, 20, or 30 1-2 week-old mixed-sex adult weevils were exposed on 35 g of wheat for 1 week at combinations of 22°C, 27°C, or 32°C; 40%, 57%, or 75% r.h. No weevils survived when exposed at 40% or 57% r.h., but at 75% r.h. survival was related to both population density and temperature. A higher percentage of adults survived when 30 were exposed compared to 10 and 20, and within each density, survival decreased with increasing temperature. No F₁s were produced at any r.h. on wheat held at 22°C. At 27°C and 32°C, the maximum number of F₁s was produced on wheat held at 75% r.h. In the second experiment, wheat was treated with 25%, 50%, 75%, or 100% of the label rate of 300 ppm, and 10 mixed-sex adult S. oryzae were exposed on 35 g of wheat for either 1, 2, or 3 weeks at 27°C, 57% and 75% r.h. Survival decreased with increasing exposure interval and concentration, but within exposure interval and concentration, survival was usually greater at 75% versus 57% r.h. In the final experiment, wheat was treated with 300 ppm, held at 22°C and 27°C, 57% r.h., and bioassayed at monthly intervals for 3 months by exposing 20 adult mixed-sex S. oryzae on 35 g of wheat for 1 or 2 weeks. At each month, survival of S. oryzae was greater when exposed at 22°C compared to 27°C and when exposed for 1 week compared with 2 weeks. Survival gradually increased with each monthly bioassay, except for those conducted at 3 months. Results of these studies show that S. oryzae is susceptible to DE, but survival of exposed insects will depend in part on the temperature and r.h. humidity (or grain moisture content) at which they are exposed. Survival is directly related to temperature, and as r.h. increases either higher concentrations or longer exposure intervals will be necessary to maintain a certain level of mortality. There may also be a loss of efficacy with residual aging.     

Evaluation of a new insecticide formulation (F2) as a protectant of stored wheat, maize, and rice

A new commercial formulation, F2, was evaluated as a protectant of stored wheat, stored maize, and stored rough (paddy) rice. This formulation comprises the technical active ingredients 0.03% deltamethrin, 0.37% piperonyl butoxide, and 0.95% chlorpyriphos-methyl, plus 10% mineral oil and 88.0% of the diatomaceous earth Protect-It^®. Tests were conducted with dust and slurry formulations at 50 and 100 ppm, 57% and 75% relative humidity, and 22°C, 27°C, and 32°C. On wheat, survival of the lesser grain borer, Rhyzopertha dominica (F.), ranged from 0% to 30.0%, survival of the rice weevil, Sitophilus oryzae (L.), was 0-6.2%, and survival of the red flour beetle, Tribolium castaneum (Herbst), was 0-97.5%. Few F₁ adults of any of the three species were found in the treated samples. Survival of the maize weevil, Sitophilus zeamais (Motschulsky), on treated corn was 0-32.5%, while survival of T. castaneum was 0-88.7% in the 50-ppm dust and slurry treatments, and 0-51.4% in the 100-ppm treatments. Again, few F₁ adults of either species were found in treated maize. Survival of R. dominica on treated rough rice averaged 0-4.1% and survival of S. oryzae on treated rice was 0-48.8%, but the majority of weevils that survived were in one replicate. F₁ adults in the treatments ranged from 0 to 24.4. Results show that the combination insecticidal product F2 was extremely effective on all three commodities at the rate of 100 ppm, as either a dust or slurry, and could be used as a commodity protectant.     

Combined effects of contact insecticides and 50 °C temperature on Sitophilus oryzae (L.) (Coleoptera: Curculionidae) in wheat grain

The effects of the insecticides deltamethrin, bifenthrin, thiamethoxam, spinosad and abamectin were tested in the laboratory in combination with extreme temperature of 50 °C to discover potential improvements of existing pest management programmes for Sitophilus oryzae (L.) control. Adults were released into wheat grain treated with three insecticide doses ranging 0.125–1.0 mg/kg and exposed to 50±1 °C temperature at the intervals of 0, 65, 75 and 85 min, and direct and combined effects were determined after 1, 2, 7 and 14 days of exposure/recovery at 25±1 °C and 60 ± 5% r. h., as well as impact on F₁ progeny production/reduction PR (%) after 8 weeks.The results showed that the mortality of S. oryzae adults increased with exposure/recovery duration more than under the activity of each insecticide alone and its interaction with extreme temperature. After 14 days, all three rates of deltamethrin (0.125–0.5 mg/kg), the two higher rates of bifenthrin (0.25 and 0.5 mg/kg) and the highest rates of abamectin (0.5 mg/kg) and thiamethoxam (1.0 mg/kg) caused maximum adult mortality (100%) and PR (100%) after weevil exposure to 50 °C already after the interval of 65 min, while spinosad had the same effect after 75 and 85 min, which effectiveness was 1.25–20 times higher than the activities of the insecticides and 50 °C temperature alone, considering all trial variants. The lowest rate of bifenthrin (0.125 mg/kg) was found after 65 min activity in combination with exposure to 50 °C, and especially spinosad (0.25 mg/kg) after 65 and 75 min, to have stimulated progeny production 17, 33 and 236%, respectively, while deltametrin showed 100% effectiveness against S. oryzae in all combinations of wheat grain treatment at 50 °C temperature, including the dose 0.125 mg/kg.     

Influence of grain type on the susceptibility of different Sitophilus oryzae (L.) populations, obtained from different rearing media, to three diatomaceous earth formulations

Bioassays were carried out to assess whether the commodity, from which adults of the rice weevil Sitophilus oryzae emerged, influences the insecticidal efficacy of three diatomaceous earth (DE) formulations: Protect-It™, PyriSec^® and DEBBM. Protect-It™ is a DE formulation that contains 10% silica gel, while PyriSec^® and DEBBM are enhanced DEs that contain natural pyrethrum and the plant extract bitterbarkomycin, respectively. The S. oryzae populations tested were reared on wheat, barley or maize and the susceptibility of each to the DE formulations was assessed on all three commodities. The DE application doses were: 500 ppm for Protect-It™ and PyriSec^®; 150 and 75 ppm for DEBBM. Mortality of S. oryzae adults was counted 7 and 14 d after their exposure on the treated commodities. Bioassays were carried out at 25 °C and 55% r.h. Barley-reared S. oryzae were the most tolerant of all formulations and treated commodities, whereas maize-reared were the most susceptible ones. DE effectiveness was always lower in maize than in wheat or barley irrespective of the commodity from which the populations were obtained. Furthermore, Protect-It™ and PyriSec^® were more effective than DEBBM in wheat or barley, but not in maize.     

Effectiveness of spinosad dust against different European populations of the confused flour beetle, Tribolium confusum Jacquelin du Val

Six populations of the confused flour beetle, Tribolium confusum, obtained from Greece, Italy, Portugal, Denmark, Germany and France were tested for their susceptibility to a spinosad dust formulation, containing 0.125% spinosad. For this purpose, adults and larvae of T. confusum were exposed on wheat treated with two dose rates of the dust formulation, 0.06 and 0.19 ppm of a.i. corresponding to 50 and 150 ppm of the formulation, at 25 °C and 65% r.h. Mortality of the exposed individuals was assessed after 7, 14 and 21 days of exposure on the treated substrate. The increase of dose and exposure interval increased mortality, while adults were more tolerant to spinosad than larvae. Significant differences were noted among populations, for both adults and larvae. The most tolerant to spinosad was the strain from Greece, while the least tolerant were the strains from Germany and Denmark. After 7 days of exposure, on wheat treated with 50 ppm, mortalities of adults of the Greek, German and Danish strains were 2%, 25% and 62% respectively, while the respective figures for 150 ppm were 1%, 31% and 81% respectively. In the case of larvae, of the same strains, mortality at 50 ppm was 6%, 27% and 28% and at 150 ppm 11%, 23% and 40%, respectively. The results of the present study suggest that different strains and stages of T. confusum differ widely in their susceptibility to spinosad-treated wheat.     

Efficacy of diflubenzuron plus methoprene against Sitophilus oryzae and Rhyzopertha dominica in stored sorghum

The efficacy of diflubenzuron (1 mg kg⁻¹)+methoprene (1 mg kg⁻¹) against Sitophilus oryzae (L.) and Rhyzopertha dominica (F.) in sorghum was evaluated in a silo-scale trial in southeast Queensland, Australia. Sorghum is normally protected from a wide range of insects by mixtures of grain protectants. The chitin synthesis inhibitor diflubenzuron was evaluated as a potential new protectant for S. oryzae in combination with the juvenile hormone analogue methoprene, which is already registered for control of R. dominica. Sorghum (ca 200 t) was treated after harvest in 2000 and assessed for treatment efficacy and residue decline during 6.5 months storage. The reproductive capacity of S. oryzae and R. dominica was greatly reduced in bioassays of treated sorghum throughout the trial, and efficacy remained relatively stable during the trial. An initial exposure of S. oryzae adults to treated sorghum for 2 weeks reduced F₁ progeny production of all strains by 80.8-98.8%, but a second exposure of 4 weeks reduced F₁ progeny production by 98.5-100%. In addition, the reproductive capacity of any S. oryzae progeny produced was greatly reduced. Exposure of R. dominica adults to treated sorghum for 2 weeks reduced F₁ progeny production of all strains by 99.6-100%, including a methoprene-resistant strain. The results indicate that S. oryzae or R. dominica adults invading sorghum treated with diflubenzuron (1 mg kg⁻¹)+methoprene (1 mg kg⁻¹) would be incapable of producing sustainable populations.     

Laboratory assessment of insecticidal effectiveness of natural zeolite and diatomaceous earth formulations against three stored-product beetle pests

The insecticidal effectiveness of two natural zeolite formulations (Minazel plus and Minazel), applied to wheat at selected rates of 0.25, 0.50 and 0.75 g/kg, and a diatomaceous earth formulation (DE) (Protect-It™), applied at the recommended rates of 0.15 g/kg for Sitophilus oryzae, 0.20 g/kg for Rhyzopertha dominica and 0.30 g/kg for Tribolium castaneum, were tested under laboratory conditions (24 ± 1 °C temperature and 45 ± 5% relative humidity). The highest adult mortality was observed after the longest exposure period of 21 days and 7 days of recovery, when all three zeolite dosage rates and the recommended DE dosage caused 97-100% mortality of S. oryzae and 94-100% of T. castaneum. On the other hand, 100% mortality was not achieved in any test variant involving R. dominica; the highest (about 92%) was detected for DE, while 52% and 79% mortality was achieved with the zeolites at the highest rate of 0.75 g/kg. Progeny reduction by >90% was achieved after 21 days of contact of all three beetle pests with DE-treated wheat, while the same level of reduction was achieved for S. oryzae and T. castaenum only after contact with the highest rate of the zeolite product, Minazel. Thus the two zeolite formulations are comparable to diatomaceous earth in controlling adult S. oryzae, R. dominica and T. castaneum, but only the Minazel formulation could effectively protect wheat from attack by S. oryzae or T. castaneum, and only with a higher rate of application than for the DE formulation.     

Fumigant toxicity of essential oil from Artemisia sieberi Besser against three stored-product insects

Artemisia sieberi is a widely distributed plant in Iran. Because some species of Artemisia are insecticidal, experiments were conducted to investigate fumigant toxicity of the essential oil. Dry ground leaves were subjected to hydrodistillation using a modified Clevenger-type apparatus and the resulting oil contained camphor (54.7%), camphene (11.7%), 1,8-cineol (9.9%), β-thujone (5.6%) and α- pinene (2.5%).The mortality of 7 days old adults of Callosobruchus maculatus, Sitophilus oryzae, and Tribolium castaneum increased with concentration from 37 to 926 μL/L and with exposure time from 3 to 24 h. A concentration of 37 μL/L and an exposure time of 24 h was sufficient to obtain 100% kill of the insects. Callosobruchus maculatus was significantly more susceptible than S. oryzae and T. castaneum; a second more detailed bioassay gave estimates for the LC₅₀ of C. maculatus as 1.45 μL/L, S. oryzae 3.86 μL/L and T. castaneum 16.76 μL/L. These results suggested that A. sieberi oil may have potential as a control agent against C. maculatus, S. oryzae and T. castaneum.     

Influence of grain and relative humidity on the mortality of Sitophilus oryzae (L.) adults exposed to ethyl formate vapour

Ethyl formate (EF) is being investigated as an alternative to phosphine and methyl bromide, for the fumigation of stored products. The compound has been found to have a rapid action against stored-product insects and shows promise as a fast-acting disinfestant.The response of Sitophilus oryzae adults to EF in a sealed system was studied. Insects were exposed to a range of EF doses for 24 h at 25 °C, with a range of grain quantities and relative humidities (r.h.). It was found that rapid mortality of S. oryzae adults in a sealed system was obtained, with a range of applied concentrations required to achieve 99% mortality. Concentrations as low as 11.2 mg L⁻¹, for the exposures without wheat at 97% r.h., achieved 99% mortality, whereas 81.2 mg L⁻¹ EF was required for the exposures carried out on 1500 g wheat in 2.7 L at 60% r.h. Modelling studies of the mortality data revealed that, in general, the presence or absence of grain had the largest influence on mortality, where the larger the grain quantity, the higher the required EF dose to achieve 99% mortality. To a lesser degree, the r.h. also influenced the observed mortality, where the higher the r.h., the lower the required EF dose to achieve 99% mortality. In this experimental system, the factors that determined the level of mortality were a complex interaction of the initial dosage concentration (C₀), concentration×time product (Ct), grain quantity and r.h.     

Toxicity of ethyl formate to adult Sitophilus oryzae (L.), Tribolium castaneum (herbst) and Rhyzopertha dominica (F.)

Fumigations were conducted using a continuous flow-through laboratory process to maintain constant concentrations of ethyl formate and low levels (<0.8%) of respiratory carbon dioxide. The procedure minimised the effects of sorption by exposing test insects without media and minimised the effect of carbon dioxide by use of continuous flow. The concentration×time (Ct) products of ethyl formate for adult Sitophilus oryzae, Tribolium castaneum and Rhyzopertha dominica at 25 °C and 70% relative humidity for the 6 h exposure were, respectively: (1) LD₅₀ 107.8, 108.8 and 72.8 mg h L⁻¹ and (2) LD_99.5 207.4, 167.1 and 122.2 mg h L⁻¹. Endpoint mortality was reached within 24 h of initial exposure.     

Toxic compounds in essential oils of coriander, caraway and basil active against stored rice pests

Essential oils, distilled from seeds of Coriander sativum and Carum carvii and from leaves of five different varieties of Ocimum basilicum, were fractionated by column chromatography and tested in the laboratory for volatile toxicity against three stored rice pests (Sitophilus oryzae, Rhyzopertha dominica and Cryptolestes pusillus). The active fractions were analyzed by GC-MS. Coriander contained linalool (1617 ppm of the oil) as the main product active against the three pests. Camphor-rich fractions (over 400 ppm) were very toxic to R. dominica and C. pusillus. The caraway profile included carvone and limonene as expected but (E)-anethole, generally regarded as a minor product in the essential oil of this species, was also a major component, being present at 365 ppm. Carvone was the most effective (972 ppm) monoterpenoid against S. oryzae. In addition, (E)-anethole at 880 ppm was toxic to R. dominica while vapors of limonene (1416 ppm) and fenchone-rich (554 ppm) fractions killed adults of C. pusillus only. Three major essential oil profiles were present in the five varieties of O. basilicum analyzed: methyl eugenol/estragole, estragole and estragole/linalool chemotypes. The abundance of components had a strong influence on the outcome of the bioassays. Fractions, where combinations of products occurred with or without other minor compounds, were often more toxic than any one compound alone.     

Residual effects of deltamethrin and malathion on different populations of Sitophilus granarius (L.) on treated wheat grains

The impact of 2-, 7-, 14-, 30-, 90-, 150- and 720-day-old deposits of deltamethrin, applied with or without the synergist piperonyl butoxide (PBO), and of malathion, on adults of different populations of granary weevil Sitophilus granarius on wheat was investigated in the laboratory. The insecticides used were commercial formulations and their application rates were as recommended: deltamethrin (dustable powder) 0.5 mg a.i./kg, deltamethrin + PBO (1:10) (emulsifiable concentrate) 0.25 mg a.i./kg, and malathion (dustable powder) 10 mg a.i./kg. The weevil populations examined were: (a) a laboratory population, (b) field populations with different susceptibility to some insecticides as established previously, and (c) populations selected in the laboratory with deltamethrin or pirimiphos-methyl.The 2-day-old deposit of malathion caused complete mortality of all weevil populations after 7 and 14 days. The corresponding deposit of deltamethrin was 100% effective only against the laboratory weevils after 7-14 days, while deltamethrin at the lower level formulated with PBO caused about 90% mortality of laboratory weevils and much lower levels of kill among field and selected weevils.Deposits of deltamethrin and malathion up to 90 days old killed all field weevils after 14 days of exposure. The 150-day-old deposit of deltamethrin was also 100% effective against field weevils exposed for 14 days, while the effectiveness against selected populations was around 50%. Malathion deposits of the same age gave 40-50% mortality of field weevils, and 4-68% mortality of selected weevils. The 720-day-old deposits of malathion were ineffective against all weevil populations, while the mortality of laboratory weevils after 14 days contact with deltamethrin deposits of the same age was 76%, and that of field and selected weevils about 50%.     

Impact of resistance on the efficacy of binary combinations of spinosad, chlorpyrifos-methyl and s-methoprene against five stored-grain beetles

Laboratory experiments were conducted to determine the efficacy of spinosad (a biopesticide), chlorpyrifos-methyl (an organophosphorus compound (OP)) and s-methoprene (a juvenile hormone analogue) applied alone and in binary combinations against five stored-grain beetles in wheat. There were three strains of Rhyzopertha dominica, and one strain each of Sitophilus oryzae, Tribolium castaneum, Oryzaephilus surinamensis and Cryptolestes ferrugineus. These strains were chosen to represent a range of possible resistant genotypes, exhibiting resistance to organophosphates, pyrethroids or methoprene. Treatments were applied at rates that are registered or likely to be registered in Australia. Adults were exposed to freshly treated wheat for 2 weeks, and the effects of treatments on mortality and reproduction were determined. No single protectant or protectant combination controlled all insect strains, based on the criterion of >99% reduction in the number of live F₁ adults relative to the control. The most effective combinations were spinosad at 1 mg kg⁻¹+chlorpyrifos-methyl at 10 mg kg⁻¹ which controlled all strains except for OP-resistant O. surinamensis, and chlorpyrifos-methyl at 10 mg kg⁻¹+s-methoprene at 0.6 mg kg⁻¹ which controlled all strains except for methoprene-resistant R. dominica. The results of this study demonstrate the difficulty in Australia, and potentially other countries which use protectants, of finding protectant treatments to control a broad range of pest species in the face of resistance development.     

Identification and characterization of a novel fermented substance produced by edible Aspergillus oryzae AO-1 that inhibits DPP-IV activity

We identified a novel fermented substance (FKA) produced by the edible Aspergillus oryzae strain AO-1 that inhibited dipeptidyl peptidase IV (DPP-IV) (IC₅₀ = 3.41 mg·mL^− 1). HPLC analysis of FKA showed specific one metabolite (WYK-1), which inhibited DPP-IV (IC₅₀ = 6.98 μM). WYK-1 was identified as a tetrahydroxyisoquinoline derivative. Interestingly, we examined 60 strains of A. oryzae, AO-1 was the only A. oryzae strain that produces WYK-1. This is the first report that an edible A. oryzae strain produces a DPP-IV inhibitor such as WYK-1. This study also suggests that FKA has applications in the development of novel antihyperglycemic therapeutics or functional foods.     

Molecular characteristics of partially hydrolyzed fucoidans from sporophyll of Undaria Pinnatifida and their in vitro anticancer activity

The effects of molecular characteristics on the anticancer activity of fucoidans were investigated after hydrolysis by copper acetate and then fractionation with 30 and 5 kDa membranes, which produced three fucoidan fractions: F_>30 K, F_5–30 K and F_<5 K. The F_>30 K and F_5–30 K consisted of mostly carbohydrate (58.2–61.3%) and sulphate (31.7–35.5%) with small amounts of proteins (1.2–6.4%). However, the major constituents of F_<5 K were sulphate (31.8%) and ash (37.5%) with smaller amounts of carbohydrate (15.5%) and protein (1.2%). The molecular weights (M_w) of F_>30 K, F_5–30 K and F_<5 K, obtained by a light scattering technique, were 262, 5.6 and 1.6 kDa, respectively. The observed anticancer activities were 18.0–28.5% for F_>30 K, 19.2–57.5% for F_5–30 K and 26.5–36.5% for F_<5 K, respectively, in the concentration range of 0.2–0.8 mg/mL. The results suggest that the anticancer activity of fucoidans could be considerably improved by lowering their M_w and by improving the binding properties of sulphate groups possibly through changing the molecular conformation.     

Survival and reproduction of Tribolium castaneum (Herbst), Rhyzopertha dominica (F.) and Sitophilus oryzae (L.) following periods of starvation

This study determined the starvation tolerance of Tribolium castaneum (Herbst), Rhyzopertha dominica (F.) and Sitophilus oryzae (L.) in terms of both adult survival and reproduction, the impact of starvation on reproduction not having been studied before. Experiments were conducted at 30 °C and 55% or 70% r.h. using a laboratory strain and a field strain of each species. The number of progeny was a better indicator of the impact of starvation on a species than adult survival. Tribolium castaneum was the most tolerant species, requiring up to 35 d starvation before no progeny were produced. Rhyzopertha dominica and S. oryzae required up to 8 d starvation before no progeny were produced. The results suggest that hygiene will have a greater impact on populations of S. oryzae and R. dominica than T. castaneum.     

Insect population dynamics in commercial grain elevators

Data were collected in 1998-2002 from wheat stored in commercial grain elevators in south-central Kansas. Bins at these elevators had concrete walls and were typically 6-9 m in diameter and 30-35 m tall. A vacuum-probe sampler was used to collect grain samples in the top 12 m of the wheat in each bin. The primary insect species found in the wheat samples were: Cryptolestes ferrugineus, Rhyzopertha dominica, and Tribolium castaneum. In the top 3.7 m of grain, R. dominica, C. ferrugineus, T. castaneum and Sitophilus oryzae made up 44, 36, 19 and 1% of the insects found in the samples, respectively. From 3.8 to 12.2 m, R. dominica, C. ferrugineus, T. castaneum and S. oryzae were present at 84, 8, 8, and 1%, respectively. The most prevalent species also changed over time. In June, the start of wheat harvesting and storage in Kansas, insect density was low in the bins. At this time, C. ferrugineus was the most common insect, and it was found mostly in the top grain sample (0-1.2 m). In September through November, C. ferrugineus and R. dominica were at similar densities; however, from February to March, R. dominica was more common.Generally, insect density was greatest at the top and decreased with grain depth. Very few insects were found in samples collected from greater than 12 m (most of the bins contained grain to depths of 24-36 m). Insect density for all species increased rapidly from June through October. During this period less than 20% of the bins had economically significant insect densities (>2 insects/kg). From October until February, the average insect density remained fairly constant but it was greatly reduced in April, May, and June. Bins that had insect densities >2 insects/kg tended to be located adjacent to other heavily infested bins.     

The effect of a new chitin synthesis inhibitor, novaluron, on various developmental stages of Tribolium castaneum (Herbst)

Novaluron, a novel chitin synthesis inhibitor (CSI), was tested against the various developmental stages of Tribolium castaneum (Herbst), at concentrations ranging from 0.1 to 100 ppm. It did not kill T. castaneum adults at these concentrations, but at 1.0 ppm it caused total mortality of third-instar larvae. Novaluron did not affect the number of eggs laid by T. castaneum adults that were exposed to treated wheat flour, but it totally inhibited their hatching after the third day of exposure at a concentration of 1 ppm. On the first day after infestation novaluron did not totally prevent hatching, even at the highest tested concentration of 100 ppm. The time needed to restore egg hatchability after adults were transferred to untreated flour depended on the concentration of novaluron used in the treatment. When the adults of T. castaneum were exposed to novaluron-treated whole wheat grains (at 1 ppm), similar effects to those of the treated flour at the same concentration were observed: egg hatching was drastically reduced. The effect of uptake via contact of adults with novaluron-treated surfaces was examined by exposing them to a mixture of untreated flour and 10% novaluron-treated sand at a concentration of 10 ppm, and only 1% of the eggs hatched after 18 days of exposure. When adults were removed from treated surfaces of Petri dishes to untreated flour, the hatching rate was again reduced by 100%. It was concluded that the contact penetration of novaluron into T. castaneum adults prevents the hatching of eggs subsequently laid.     

Quality assessment of wild European eel (Anguilla anguilla) stored in ice

The quality assessment of wild European eel (Anguilla anguilla) stored in ice and in boxes without ice (3 ± 1 °C) was investigated by the sensory analysis, levels of nucleotide breakdown products and biogenic amines for up to 19 days. Sensory analysis was assessed using the Tasmanian Food Research Unit Scheme. K and related values (K_i, G, P, H and F_r) were used as freshness indicators. Linear regressions (r²) obtained from K, K_i, G, P, H and F_r were 0.95, 0.96, 0.83, 0.96, 0.99 and 0.96, respectively, for eel stored in ice whereas, for eel kept in boxes without ice, the values were 0.86, 0.86, 0.96, 0.91, 0.98 and 0.86, respectively. When eel stored in ice and in boxes without ice were considered at the limit of acceptability by assessors at ∼12–14 days and ∼5–7 days, respectively, the average K, K_i and P values were ∼70–85%, H values were ∼60% and F_r values were ∼10% for both storage conditions. The level of histamine exceeded the legal limit (5 mg/100 g fish) in eel stored without ice after 6–7 days and, in ice, after 13–14 days of storage, at which time eels were rejected by the sensory panel. The concentrations of biogenic amines were higher in eel stored in boxes without ice than in eel kept in ice. The levels of histamine in the muscle of eel kept in boxes without ice and in ice increased to the maximum levels of 17.9 mg/100 g on day 12 and 12.6 mg/100 g on day 19, respectively.