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.     

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.     

Effect of different temperatures and storage atmospheres on Coratina olive oil quality

Olives (Olea europaea cv. Coratina) used for oil production were stored for 30 days at three different temperatures and under different atmospheres (ambient temperature, 5 °C with a flux of humidified air, 5 °C with a flux of 3%O₂ + 5%CO₂). The olives were kept in jars used for fruit storage, each with a capacity for 1.5 kg of olives.     

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.     

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.     

Inactivation kinetics of Bacillus spores in batch- and continuous-heating systems

Kinetic parameters for the thermal inactivation of Geobacillus stearothermophilus ATCC 7953 and Bacillus flexus 1316 spores were determined for temperatures ranging from 100 to 130 °C and 100 to 125 °C, respectively. Ringer's solution (pH = 7.1) was used as the heating medium. A batch-heating system, in which the samples are kept in small tubes that are heated with steam, and a continuous-heating system, which is based upon a heat exchanger and enables high temperature short time heating, were used. Experiments were conducted in both systems and the heat resistances of the two species were determined. Additionally, a comparison of the two heating systems was carried out. The reaction rate constant at the reference temperature, k_ref, the activation energy, E_a, the D-value and the z-value were calculated for the two species. The D-values at 121 °C for G. stearothermophilus and for B. flexus in the batch-heating system were found to be 42 and 4.2 s, respectively. The z-values were calculated as 13 K for G. stearothermophilus and 16 K for B. flexus in the batch-heating system. The results from both systems differed significantly, wherein the continuous-heating system had been more lethal than the batch-heating system.     

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.     

Effects of cold storage, rearing temperature, parasitoid age and irradiation on the performance of Trichogramma evanescens Westwood (Hymenoptera: Trichogrammatidae)

In this study, the effects of cold storage, rearing temperature, parasitoid age, and irradiation on the performance of the egg parasitoid Trichogramma evanescens were investigated. Pupae of T. evanescens can be stored at 4 °C for up to 3 weeks without much loss of performance. The longevity and walking speed of adults emerging from chilled pupae significantly decreased after longer storage periods. The F₁ generation of adults which emerged from pupae stored up to 3 weeks was able to parasitize as well as the control. The parasitization rate was similar at 24, 27, and 30 °C, but significantly decreased at 33 and 36 °C. Although T. evanescens developed to the pupal stage at 36 °C, no adult emergence was observed at this temperature. Developmental periods were longer at 24 °C than at higher temperatures. The optimum age for T. evanescens to successfully parasitize host eggs ranged from 24 to 90 h. The parasitization frequency of the 56-78 h aged females was higher than for the other age groups. The daily egg laying pattern of female T. evanescens adults was similar when they were reared on Ephestia kuehniella or Plodia interpunctella eggs. Gamma- or ultraviolet-irradiated and unirradiated host eggs were equally preferred by adult females.     

Spoilage characteristics of Brochothrix thermosphacta and campestris in chilled vacuum packaged lamb,and their detection and identification by real time PCR

The spoilage potential of Brochothrix campestris and Brochothrix thermosphacta was investigated in vacuum-packed lamb. Striploins (n = 338) were inoculated and stored for twelve weeks at temperatures − 1.5, 0, 2 and 7 °C. Growth around 5–6 log₁₀ CFU/cm² was recorded after six weeks at 0, 2 and 7 °C, and ~ 3 log₁₀ CFU/cm² after nine weeks at − 1.5 °C. B. campestris was shown to cause spoilage by nine weeks at temperatures above 0 °C by the presence of green drip and unacceptable odours. Molecular based assays for the detection and differentiation of B. thermosphacta and B. campestris were developed and validated. A TaqMan assay was designed to target a unique single-nucleotide polymorphism in the Brochothrix 16 s rRNA gene with a sensitivity of < 7 CFU per reaction. Secondly a specific PCR was designed for B. campestris targeting the structural genes, brcA and brcB. These testing regimes offer a rapid and cost effective method for the detection and screening of Brochothrix species in meat products and processing environments.     

Development and survival of the cheese mites, Acarus farris and Tyrophagus neiswanderi (Acari: Acaridae), at constant temperatures and 90% relative humidity

Two species of acarid mites, Acarus farris and Tyrophagus neiswanderi, have been identified infesting Cabrales cheese in an Asturian maturing cave, the former being the prevalent species. The developmental rate and survival of immature stages of these mites were examined at constant temperatures, ranging from 7 to 29.7 °C for A. farris, and 10 to 31 °C for T. neiswanderi, and a relative humidity (r.h.) of 90±5%. The larval stage of A. farris was particularly susceptible to low and high temperatures with 81.7% and 95.2% mortality at 7 and 29.7 °C, respectively. Tyrophagus neiswanderi larvae also showed the greatest mortality at extreme temperatures among immature stages, though at a lower level than for A. farris (8.6% and 25.6% at 10 and 31 °C, respectively). The optimal temperature for development appeared to be 27-28 °C for both species and the developmental rates were higher for A. farris than T. neiswanderi within the range of the cooler temperatures prevalent in the cheese-maturing caves. The nonlinear Logan type-III model provided the best fit for the relationship between developmental rates and temperature (R_a²>0.99) for all immature stages of A. farris, whereas the development of T. neiswanderi was better described by the Lactin model (R_a²>0.97). The lower and upper developmental threshold temperatures predicted for each stage of A. farris were 3-4 °C lower than those predicted for T. neiswanderi. The differential temperature-development rate for each species might explain the greater abundance of A. farris compared to T. neiswanderi. Furthermore, manipulation of temperature based on modeling predictions may well be used to control mite populations during the cheese maturing process.     

Effect of relative humidity on the susceptibility of Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae) to two modified atmospheres

It is known that modified atmospheres (MA) created in a storage environment, involving high carbon dioxide (CO₂) levels (hypercarbia) or low oxygen (O₂) levels (anoxia) are detrimental to bruchid pests of grain legumes. The possibility of enhancing MA action by increasing or decreasing the relative humidity (r.h.) conditions in storage at 25±2°C was investigated against Callosobruchus maculatus (F.), a major bruchid pest of stored cowpea seeds. Mortality of eggs and adults of the bruchid in 70% CO₂ in air and 1.0% O₂ in nitrogen (N₂) was higher at 10±3% and 34±2% than at 70±2% and 90±3% r.h. Mortality of larvae and pupae of the bruchid in the atmospheres was not affected by the r.h. in storage. Development period was longer for adults emerging from bruchid eggs exposed for 12 h to these atmospheres at the lower r.h. Freshly emerged adult bruchids from treated eggs also laid fewer eggs after 12 h of exposure to these atmospheres at the lower r.h.     

Combining ultraviolet light and mild temperatures for the inactivation of Escherichia coli in orange juice

It is difficult to guarantee the effectiveness of UV technology to reach 5 Log₁₀ cycles of inactivation of Escherichia coli in a large amount of fruit juices with high absorption coefficients and turbidities, such as orange juice. The aim of this work was to overcome this limitation by combining UV light and mild temperatures. UV treatments were carried out in an equipment with eight individual annular thin film flow-through reactors connected sequentially and submerged in a thermostatic water bath. A treatment of 13.55 J/mL reached 0.25 ± 0.04, 0.41 ± 0.13, 0.84 ± 0.32, 0.96 ± 0.12, 2.57 ± 0.05, 5.41 ± 0.23, and more than 6 Log₁₀ cycles of inactivation of E. coli STCC 4201 suspended in commercial sterilized orange juice at 25.0, 40.0, 50.0, 52.5, 55.0, 57.5, and 60.0 °C, respectively. The comparison of UV resistance at 25 °C with heat resistance at mild temperatures demonstrated a synergistic effect of both technologies applied simultaneously. The maximum synergistic lethal effect was reached at 55 °C (68.03%).     

Respiration of Rhyzopertha dominica (F.) at reduced oxygen concentrations

Developmental stages of Rhyzopertha dominica were exposed to atmospheres containing 1%, 2%, 3%, 5%, 10% or 15% oxygen (O₂) in nitrogen at 30°C and 70% r.h. Respiration rates were determined with a gas chromatograph. The O₂ intake and carbon dioxide (CO₂) output by insects were expressed in μl/insect h or μl/mg h. Respiration of eggs, young and old larvae, pupae, and adults at normal atmospheric air were at rates of 0.0029, 0.41, 2.52, 0.82, and 2.86 μl CO₂/insect h, respectively. Respiration rates of the same stages in terms of insect weight were 0.14, 4.83, 1.98, 0.64 and, 2.58 μl CO₂/mg h, respectively. At reduced O₂ levels respiration rates of eggs, larvae and pupae were proportional to the O₂ levels. Adult respiration rates were high at 3% and 5% O₂ levels almost reaching that of normal atmospheric air, and were 2.56 and 2.85 μl CO₂/insect h, respectively. In adults, respiration quotient values for the same O₂ levels were higher than at normal atmospheric O₂ and were 1.5 and 1.02, respectively.Respiration of adults in normal air between 20°C and 35°C increased with temperature and gas values varied between 0.89 and 6.82 μl CO₂/insect h, respectively, or 0.93 and 5.63 μl O₂/insect h, respectively.     

The spoilage characteristics of Brochothrix thermosphacta and two psychrotolerant Enterobacteriacae in vacuum packed lamb and the comparison between high and low pH cuts

The spoilage potential of Brochothrix thermosphacta, Serratia proteamaculans and Rahnella aquatilis was investigated in vacuum packaged high (5.9 to 6.4) and low (5.4 to 5.8) pH lamb. Vacuum packaged fore shank (m. extensor carpi radialis) and striploins (m. longissimus dorsi) (n = 306) inoculated with ~ 100 CFU of individual bacteria were stored for twelve weeks at temperatures − 1.5, 0, 2 and 7 °C. Spoilage characteristics and bacterial numbers were recorded and analysed in comparison to un-inoculated control samples. All three bacterial species were shown to grow in vacuum packaged lamb of pH values between 5.4 and 6.4, when stored at chilled temperatures (− 1.5 to 7 °C) for up to 84 days. B. thermosphacta and S. proteamaculans caused spoilage to the meat under these conditions whilst R. aquatilis spoiled high pH meat at 7 °C. These results go against previous beef models stipulating that Brochothrix and Enterobacteriacae species cannot grow on or cause spoilage of low pH meat in the absence of oxygen.     

Characterisation of esterolytic activity from two wild mushroom species, Amanita vaginata var. vaginata and Tricholoma terreum

Characterisation of esterase activities from the edible mushroom species, Amanita vaginata var. vaginata and Tricholoma terreum, were investigated. Native electrophoresis of the crude extracts prepared from both mushroom samples showed the presence of esterolytic activities. The extracts had the greatest activity in the presence of p-nitrophenyl butyrate (pNPB) as a substrate. pH and temperature optima were found to be 8.0 and 30 °C for both enzymes, respectively. V_max and K_m values were determined as 14.2 U/l and 71 μM for A. vaginata var. vaginata and 34.6 U/l and 9.6 μM for T. terreum, respectively. The pH-stability profile showed a stationary line between 3.0 and 10.0 for both enzymes. The esterolytic activities from the extracts were maintained between 10 and 40 °C for 4 h and started to decrease at 50 °C. The effects of EDTA, NaN₃, DTT and PMSF on the enzyme activity were also investigated.     

Initial and delayed mortality of late-instar larvae, pupae, and adults of Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae) exposed at variable temperatures and time intervals

Late-instar larvae, pupae, and adults of Tribolium castaneum (Herbst), the red flour beetle, or Tribolium confusum (DuVal), the confused flour beetle, were exposed for variable durations at 36-54 °C. Beetles were placed in laboratory ovens set at a baseline of 27 °C, the temperature was increased by 0.1 °C per minute until the target temperature was achieved, and beetles were then held for specified exposure durations. There was no mortality after initial exposure or after a 1-week holding period of any life stage of T. castaneum or T. confusum exposed for 32 h to 36, 39, or 42 °C. At 45 °C, there was no initial mortality of either species exposed for different time intervals except for those exposed for 28 h. However, there was a significant increase in mortality after the 1-week holding period of those beetles exposed initially for at least 16 h to 45 °C. There was a sharp increase in mortality after the initial exposures of 4 h at 48 °C; mortality of T. confusum larvae was 90.0±5.7% but was only 10.0±10.0% for larvae of T. castaneum, and no pupae of either species were dead. All life stages of both species were killed after the initial exposure of 12 h, and 1-week mortality of beetles exposed for 4 and 8 h was generally greater than initial mortality. At 51 and 54 °C, 2- and 1-h exposures, respectively, killed all life stages of each species. Mortality in conditions of gradual temperature increase was less than previous studies with sudden temperature increases.     

Partial purification and characterisation of endoglucanase from an edible mushroom, Lepista flaccida

A crude extract was prepared from the fruiting body of Lepista flaccida, an edible mushroom and endoglucanase activity of the extract was increased 14-fold with ammonium sulphate precipitation. Maximum enzyme activity was seen at pH 4.0 and 50 °C when carboxymethylcellulose was used as a substrate. K_0.5 and V_max values of the partially purified endoglucanase were 7.7 mg/ml and 25 ± 0.9 U/mg protein, respectively. The enzyme was quite stable over a broad range of pH (2.0–9.0) at 4 °C. When it was incubated at temperatures between 20 °C and 60 °C for 12 h, it conserved much of its original activity (over 40%). The activity of the enzyme increased by 234 ± 3.6% in the presence of 1 mM Mn²⁺. The endoglucanase was inhibited by EDTA, PMSF, β-ME and DDT. In conclusion, pH and thermal stability of the L. flaccida endoglucanase could make it useful for industrial purposes.     

Heat resistance of Listeria species to liquid whole egg ultrapasteurization treatment

The lethality of ultrapasteurization treatments (70 °C/1.5 min.) applied at constant temperature (isothermal condition) and at a constantly raising temperature of 2 °C/min (non-isothermal condition) in liquid whole egg (LWE) against two strains of Listeria monocytogenes (STCC 5672 and 4032) and one of Listeria innocua has been investigated. Isothermal survival curves up to 71 °C were obtained, which followed first-order inactivation kinetics. The obtained D_t values indicated that L. innocua was significantly (p < 0.05) more heat resistant than L. monocytogenes strains. Non-significant (p > 0.05) differences were observed among z values (12.4 ± 0.4 °C, 13.1 ± 0.4 °C and 12.2 ± 0.7 °C for L. innocua and L. monocytogenes 5672 and 4032, respectively). Based on obtained D_t and z values, isothermal ultrapasteurization treatment (70 °C/1.5 min.) would provide 3.5-, 5.0-, and 6.5-Log₁₀ cycles of L. innocua and L. monocytogenes 5672 and 4032, respectively. Non-isothermal heating lag phase increased the thermotolerance of Listeria species in LWE. The simulated industrial pasteurization treatment for LWE (heating-up phase from 25 to 70 °C followed by 1.5 min. at 70 °C) would attain 5-Log₁₀ reductions of L. monocytogenes 5672 and 4032, and 3.7-Log₁₀ reductions of L. innocua. Therefore, the safety level of industrial ultrapasteurization concerning L. monocytogenes could be lower than that estimated with data obtained under isothermal conditions.     

Fate of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella on fresh-cut celery

Illnesses from Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella have been associated with the consumption of numerous produce items. Little is known about the effect of consumer handling practices on the fate of these pathogens on celery. The objective of this study was to determine pathogen behavior at different temperatures under different storage conditions. Commercial fresh-cut celery was inoculated at ca. 3 log CFU/g onto either freshly cut or outer uncut surfaces and stored in either sealed polyethylene bags or closed containers. Samples were enumerated following storage for 0, 1, 3, 5, and 7 days when held at 4 °C or 12 °C, and after 0, 8, and 17 h, and 1, and 2 days when held at 22 °C. At 4 °C, all populations declined by 0.5–1.0 log CFU/g over 7 days. At 12 °C, E. coli O157:H7 and Salmonella populations did not change, while L. monocytogenes populations increased by ca. 0.5 log CFU/g over 7 days. At 22 °C, E. coli O157:H7, Salmonella, and L. monocytogenes populations increased by ca. 1, 2, or 0.3 log CFU/g, respectively, with the majority of growth occurring during the first 17 h. On occasion, populations on cut surfaces were significantly higher than those on uncut surfaces. Results indicate that populations are reduced under refrigeration, but survive and may grow at elevated temperatures.     

Drying kinetics of nopal (Opuntia ficus-indica) using three different methods and their effect on their mechanical properties

Nopal (Opuntia ficus-indica) is an endemic plant of the arid and semiarid lands of America. Preservation problems are associated with nopal utilization and processing, so a practical alternative is dehydration. This work deals with the drying of nopal correlated with the textural properties of the dried product. Convective drying studies were performed and the most representative experimental results at two air flow rates (3 and 5 m/s) and two air temperatures (45 and 65 °C) are displayed here. Experiments of osmotic drying with glucose at 40 and 60 °Brix, and drying temperatures of 25 and 45 °C were tested. A combination of both drying processes was also performed. Results have shown forced convection drying with a mostly decreasing trend at the constant rate period. In the osmotic drying, moisture loss was associated to glucose concentration. Texture profile analysis of dehydrated nopal suggested that samples undergoing convective drying have more cohesiveness than samples treated solely by osmotic drying. On the other hand, samples treated by osmotic drying became more elastic. Between the two drying methods studied, the convective drying has shown the best results at the experimental conditions assayed.