Fuji Jian

Temperature and Geotaxis Preference by Cryptolestes ferrugineus (Coleoptera: Laemophloeidae) Adults in Response to 5°C/m Temperature Gradients at Optimum and Hot Temperatures in Stored Wheat and Their Mortality at High Temperature

Abstract Cryptolestes ferrugineus (Stephens) is often found in abundance in association with heating stored grain. Their mortality at high temperature and their distribution at optimum and hot temperatures are important information for insect control and for models of their distribution in grain bins. The lethal exposure times of the adults were determined at 42 ± 0.2–50 ± 0.2°C and 75 ± 5% RH. Insect mortality increased with increasing temperatures and exposure time. For each temperature, there was a cumulative period of thermal stress, and after the critical exposure time an additional few hours or minutes at that temperature would kill all of the adults. The mortality was 100% at 45°C in 78 h, at 47°C in 18 h, at 49°C in 4.5 h, and at 50°C in 3 h. At 50°C, insect mortality determined at 0 h was significantly different than that determined 12 h later after the insects had been moved to room temperature. A regression equation predicted insect mortality better than published models when temperatures were above 45°C. The net displacement of the adults in both vertical and horizontal directions at 27.5–52.5°C was determined in 100 by 100 by 1,000-mm wheat columns at 14.5 ± 0.3% moisture content with or without a 5°C/m temperature gradient. The adults responded to temperature gradients and the preferred temperature was from 30 to 36.5°C. There was no obvious boundary between preference and nonpreference temperatures for the adults. In horizontal wheat columns without a temperature gradient, the adults moved in both directions, and the distribution pattern gradually became more uniform when temperature increased but was under 42°C. At hot temperatures, adults could locate and move to the cooler area in <12 h; however, the adults could not move at 50°C. Geotaxis, temperature gradient, and the interaction between these two factors affected insect distribution and movement direction; and the geotaxis was more influential than temperature gradient at any condition in the vertical columns. A pattern for adult movement was suggested.

Thermal Imaging of a Stored Grain Silo to Detect a Hot Spot

A hot spot is a localized high temperature zone in a grain bulk and normally spoilage begins in this location. Many sensors need to be installed throughout the bin to detect hot spots by measuring grain temperature. A non-contact method to detect a hot spot in a stored grain silo would be beneficial. The capability of thermal imaging to detect a hot spot in an experimental silo (galvanized steel, 1.5-m diameter and 1.5-m height) filled with barley was studied. An artificial heat source was placed at nine locations inside the grain bulk and set at four temperature levels (30°C, 40°C, 50°C, and 60°C) in each location. The outer surface of the silo wall and the top surface of the grain bulk were thermally imaged up to 48 h at each treatment (n = 3). The temperature of the top surface of the grain bulk was significantly (a = 0.05) higher (0.4°C to 2.6°C) than the atmospheric temperature after 48 h of hot spot establishment. The hot spot was detected from the thermal images of the silo wall and grain bulk (as a high temperature region) when it was located 0.3 m from the silo wall and 0.3 m below the grain surface, respectively. The hot spot was not detected on the thermal images of the silo wall when the wind velocities were 1.0, 1.5 and 2.0 m/s, and immediately after wind (n = 3). Similarly, thermal imaging did not detect the hot spot on the grain bulk when the ambient temperature was 1°C (hot spot = 30°C), and on silo wall when the ambient temperature was -8°C (hot spot = 60°C) (n = 3). The surface temperature of the grain bulk decreased with increasing moisture content. It was 25.8°C, 24.3°C, 23.4°C, 22.8°C, and 22.4°C for the grains with 8%, 12%, 16%, 20%, and 24% moisture content, respectively, when the room temperature was 26°C (n = 20). Thermal imaging can not be used as an independent method to monitor the grain temperature in a silo.

Movement and Distribution of Adult Rusty Grain Beetle, Cryptolestes ferrugineus (Coleoptera: Laemophloeidae), in Stored Wheat in Response to Different Temperature Gradients and Insect Densities

Abstract The movement and distribution of adult Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae) in grain provide important information for detection of insect pests and for simulations of their distribution in grain bins. Adult movement and distribution were determined in 100 by 100 by 1000-mm wheat (14.5 ± 0.2% moisture content) columns at four insect densities, three temperature gradients, and dynamic (changing) temperature conditions. Insect density was a minor factor influencing insect movement and distribution in grain columns with temperature gradients. Dispersal resulted in a uniform distribution at a higher insect density (higher than two adults per kilogram of wheat), and aggregation occurred at a low insect density. Adults wandered in the first 6 h after introduction, and there were fewer adults wandering in the vertical direction than in the horizontal direction. Adults moved faster in the vertical direction than in the horizontal direction, and the maximum speed of the movement was 6 m/d in the horizontal direction, and >10.8 m/d in the vertical direction through wheat. Adults could detect temperature gradients in <1 h and preferred warmer temperatures when they had a choice. Insect distribution in horizontal wheat columns at any temperature gradient was unstable for 24 h. Twenty-four hours after introduction, adults gradually overcame their positive geotactic behavior if the upper temperature was more biologically suitable or was not <27.5°C. Adults responded faster to higher temperature gradients than to lower temperature gradients. There was a similar pattern of adult distribution in 144 h.

Vertical movement of adult rusty grain beetles, Cryptolestes ferrugineus, in stored corn and wheat at uniform moisture content

Abstract Vertical movement and distribution of Cryptolestes ferrugineus (Coleoptera: Laemophloeidae) adults in stored wheat and corn were studied in small (0.1 x 0.1 x 1 m) and large (0.6 m diameter and 1.12 m high) columns. The adults were introduced at the top, middle, and bottom of the small columns with a uniform moisture content (wheat: 14.5 ± 0.1%, corn 13.5 ± 0.1%, 15.5 ± 0.1%, and 17.5 ± 0.1%) at 27.5 ± 0.5°C. When introduced at different locations, adults showed a similar distribution in stored grain bulk with a uniform temperature and moisture content of 14.5% for wheat or 15.5% for corn. Adults showed downward displacement over 24 h when corn moisture was lower than 15.5%, but they did not show downward displacement when moisture content was 17.5%. The upward or downward movement might partially be caused by a drift effect due to beetles sliding between seeds and the displacement of the adults might be the combined effect of walking and falling during their movement. The hydrophilic behavior plus the drift effect explain why the beetles had a faster downward dispersal in the 13.5% corn than in the 15.5% and 17.5% corn and a slight upward displacement in 17.5% corn because they were more active at the lower moisture contents. Adults had a similar movement and distribution in both the small and large wheat columns.

Movement of Adult Cryptolestes ferrugineus (Coleoptera: Laemophloeidae) in Wheat: Response to Temperature Gradients and Gravity

Abstract Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae) is the most prevalent insect species in granaries in western Canada. Their movement and distribution at different environmental conditions provide important information for insect detection and control and for models of their distribution in grain bins. The distribution and wandering movement of C. ferrugineus adults were studied in a 100 by 500 by 500-mm wheat (14.5 ± 0.2% moisture content) chamber with or without a 5°C/m temperature gradient. In the grain chamber at a uniform temperature, adults dispersed homogeneously in each horizontal layer and heterogeneously in the vertical direction when the temperature was 22.5–30°C. Adults moved toward a warmer temperature and in the direction of gravity at the same time in the grain chamber with temperature gradients in the horizontal or/and vertical directions. Adult movement and distribution in the two-dimensional chamber could be represented by published data obtained in one-dimensional columns. The movement and distribution of females (mixed ages) were not significantly different from those of males (mixed ages) in response to temperature gradients and gravity. Wandering movement of adults was restricted by temperature gradients.

The Ecosystem Approach to Grain Storage

The progress in understanding the stored grain ecosystem is reviewed. Succession of insects, insect movement and distribution, interaction among insects and microflora, and the development of hot spots inside stored grain ecosystems are evaluated. Based on these case studies, we examined the understanding of the stored grain ecosystem from the view of ecosystem approach. To understand the storage grain ecosystem, integration of the parts (the collected data under small scale laboratory conditions) into a usable whole (the entire grain storage ecosystem) is required. To verify the synthesised whole, both small and full scale tests are required. To manage the stored grain ecosystem, understanding the ecosystem and application of ecosystem approach are the keys.

Movement of Tribolium castaneum (Coleoptera: Tenebrionidae) Adults in Response to Temperature Gradients in Vertical and Horizontal Wheat and Corn Columns

Abstract The movement and redistribution of adult Tribolium castaneum (Herbst) in stored grain provide important information for detection of insect pests and for simulations of their distribution in grain bins. Movement and redistribution of T. castaneum adults in 1 or 6 d and in wheat or corn were determined in a 100 by 100 by 1000-mm acrylic box with a 10°C/m temperature gradient (from 20 to 30°C) or at a uniform temperature (20, 25, and 30°C). In a vertical corn column with a uniform temperature, ≈15 and 25% of adults moved to the top or bottom section in 6 d, respectively; and <30% of adults were recovered in 1-d movement in the middle two sections where insects were initially introduced. In a horizontal or vertical wheat column, >90% of the adults were recovered in the two middle sections where insects were introduced after 6 d. Adults responded to the temperature gradient and preferred the warmer areas in both wheat and corn. The slower movement in wheat is probably caused by the small granular space in bulk wheat than in bulk corn.

A THREE-DIMENSIONAL, ASYMMETRIC, AND TRANSIENT MODEL TO PREDICT GRAIN TEMPERATURES IN GRAIN STORAGE BINS

A three-dimensional, transient, combined model (headspace model + soil model + conduction model in bulk grain) was developed to predict grain temperatures in a granary. Different meshes (mesh refinement in the whole domain or at the boundary) including linear and hybrid (linear and quadratic) elements were used to simulate grain temperatures. Prediction accuracies of temperatures produced by the different meshes were compared, and the model was validated using measured temperatures in two flat bottom bins (3.76 m diameter and 5.5 m high filled with wheat up to 3 m) located side by side in the north-south orientation near Winnipeg, Manitoba. Grain temperatures predicted by the model were in close agreement with the measured temperatures throughout a 21-month test in the two bins. By using a hybrid element mesh (mesh refinement at the boundary), the mean, standard error, and maximum of the absolute difference between the measured and predicted temperatures in the south bin were 2.2°C, 0.4°C, and 7.0°C, respectively. The mean, standard error, and maximum of the absolute difference predicted by a linear element model (88 linear elements each layer) in the south bin were 2.1°C, 0.3°C, and 6.3°C, respectively. Including a headspace model improved the prediction accuracy of the conduction model at the top of the grain bulk. Mesh refinement only at the boundary produced a homogeneous distribution of errors in the whole domain; however, mesh refinement in the whole domain gave higher errors at the walls than at the center of the bins. Considering the increased computer time and slightly improved accuracy by mesh refinement at the boundary, a uniform mesh with mesh refinement in the whole domain was preferable for predicting grain temperatures in an entire grain bin.

Thermal Conductivity, Bulk Density, and Germination of a Canola Variety with High Oil Content under Different Temperatures, Moisture Contents, and Storage Periods

Thermal conductivity of canola seeds is used as an engineering parameter in the design of processing, storing, drying, and cooling systems. Loose (standard) and compacted bulk densities, germination, and thermal conductivity of 5.5%, 7.5%, 9.5%, 11.5%, 13.5%, and 15.5% moisture content (wet basis) of canola (cultivar NX4-105 RR with 45.4% ±0.4% oil content) seeds stored at 30°C for 0 d, 30 d, and 60 d were measured at -20°C, -10°C, 0°C, 10°C, 20°C, and 30°C. Moisture content of the canola seeds had a larger influence on the value of standard bulk density than temperature. The canola seeds with different storage times could be compacted by 5.1% ±0.6%. The mean of thermal conductivity of the 0 d canola seeds was 0.08684 W m-1 K-1. The thermal conductivity of 0 d canola linearly increased with increasing moisture content or temperature. The thermal conductivity, standard bulk density, and germination of the canola seeds significantly decreased with increasing storage time at 30°C, and a linear relationship was observed between the percentages of decreased standard bulk density, seed germination, and thermal conductivity. There was no significant difference in thermal conductivity of the canola seeds under loose and compacted conditions.

Models to Predict Mortality of Tribolium castaneum (Coleoptera: Tenebrionidae) Exposed to Elevated Temperatures During Structural Heat Treatments

ABSTRACT Novel thermal death models were developed with certain assumptions, and these models were validated by using actual heat treatment data collected under laboratory conditions at constant temperatures over time and in commercial food-processing facilities where temperatures were dynamically changing over time. The predicted mortalities of both young larvae and adults of the red flour beetle, Tribolium castaneum (Herbst), were within 92–99% of actual measured insect mortalities. There was good concordance between predicted and observed mortalities of young larvae and adults of T. castaneum exposed to constant temperatures in laboratory growth chambers and at variable temperatures during structural heat treatments of commercial food-processing facilities. The models developed in this study can be used to determine effectiveness of structural heat treatments in killing young larvae and adults of T. castaneum and for characterizing insect thermotolerance.