Static and dynamic methods to determine adsorption isotherms of hemp seed (Cannabis sativa L.) with different percentages of dockage.

Adsorption and desorption isotherms of hemp seeds with 0%, 5%, 10%, 15%, and 20% of dockage were determined using the salt solution static (SSS) method. The wet hemp seeds with 0% dockage were also dried at 30℃ with 50% RH, 35℃ with 30% and 50% RH, and 40℃ with 30% and 50% RH inside a thin-layer dryer (thin-layer dynamic method). The hemp seeds with different percentages of dockage showed hysteresis, and this hysteresis became more obvious with the decrease of temperature. At the same condition, the equilibrium moisture content of hemp seeds with 0% dockage was approximately 0.5 percent points lower than that of the hemp seeds with dockage. The best equation to fit the equilibrium moisture content data under constant temperature and RH was the modified GAB equation for both adsorption and desorption isotherms. The constant rate period of drying was observed for <0.75 hr when drying air RH was 30% or when drying air temperature was 40℃. The Henderson and Pabis model was the best model to fit the thin-layer drying data. The equilibrium moisture contents measured by the SSS method were lower than those measured by the thin-layer dynamic method when temperature was ≤35℃.

Demography of Rusty Grain Beetle in Stored Bulk Wheat: Part I, Population Dynamics at Different Temperatures and Grain Bulk Sizes.

Population dynamics of rusty grain beetle, Cryptolestes ferrugineus (Stephens; Coleoptera: Cucujidae), was studied using different sizes of grain bulks (patches) at various temperatures. The temperatures were 21, 25, 30, 35°C, T-decrease (30°C in the first 4 wk and then decreased 1°C /wk), and T-increase (21°C in the first 2 wk and then increased 1°C /wk). Number of adults and offspring and infested wheat kernels were counted every 4 wk up to 24 wk (31 wk for the T-decrease). The grain bulk patches used were: small (50 ml inner volume, 0.03 kg wheat), medium (2.6 liters inner volume, 2 kg wheat), and large (18 liters inner volume, 14 kg wheat). All of the correlation coefficients between the insect numbers and kernel infestation percentage were ≥0.63. Two types of the population dynamic curves were observed: insect number or density continually increased with time during the entire experiment, or there was a rise then a fall in insect number or density over time, giving a peak number or density. The peak insect density was approximately 400 to 500 adults/kg of wheat for all patches at 30°C or lower. At 35°C, the peak densities of live adults were 3,956 ± 630, 2,094 ± 34, and 1,003 ± 70 adults/kg of wheat in small, medium, and large patches, respectively. Patch size influenced insect population dynamics at 35°C. Insect number inside large patch was more dependent on the previous insect number than that inside small patches.

Demography of Rusty Grain Beetle in Stored Bulk Wheat: Part II. Mathematical Modeling to Characterize and Predict Population Dynamics.

Data collected in Part I of this study were further analyzed by using mathematical modeling methods. Out of the nine unstructured population models tested, no model could fit the insect numbers under all of the tested conditions. This analysis showed that Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae) inside small patches (50 ml volume) had different characterization of population dynamics from that inside large patches (18 liter volume) and had different population demography when the insect number at the previous time was different. The key factor analysis showed that the first two main factors influencing the population dynamics were the temperature and the previous insect numbers. The total numbers of insects increased with the increase of sum of degree days. However, the degree day model developed based on the constant temperatures could not predict insect numbers under fluctuating temperatures. A newly developed model, which used the result of the unstructured population models, key factor analysis, and the degree day model, could explain about 66% of the insect numbers under fluctuating temperature conditions.

Chill-coma and Minimum Movement Temperatures of Stored-Product Beetles in Stored Wheat.

The minimum temperature at which stored-product insects can move inside stored grain bulks with different grain moisture contents is not known. The movement of adults of four stored-product insects, Cryptolestes ferrugineus (Stephens), Tribolium castaneum (Herbst), Sitophilus oryzae (L.), and Sitophilus zeamais (Motschulsky), at low temperatures inside jars or bulks of wheat with 11.1 or 16.0% moisture content was measured. Spontaneous walking stops (SMh), CCT (no movement after shaken), and minimum movement (TMmin, caught in probe pitfall traps) temperatures were determined at stepped-decrease of temperature. The ranges of SMh, CCT, and TMmin temperatures of the four stored-products beetles were 4.0 to 9.0°C, 2.0 to 8.0°C, and 6.0 to 11.5°C, respectively. The TMmin was ∼3°C higher than the SMh for all the tested beetles. C. ferrugineus had the lowest SMh, CCT, and TMmin temperatures, whereas S. zeamais had the highest values of these determined temperatures. C. ferrugineus under a faster stepped-decrease of temperature had higher SMh, CCT, and TMmin temperatures than that under a slower stepped-decrease of temperature, while adults of T. castaneum were not influenced by the temperature decrease rate. The two species of Sitophilus did not survive to the end of the experiment at the faster stepped-decrease of temperature. Two grain moisture contents did not affect these determined temperatures for all tested species.

Models to predict mortality of Tribolium castaneum (Coleoptera: Tenebrionidae) exposed to elevated temperatures during structural heat treatments.

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.

Three-dimensional temporal and spatial distribution of adult Rhyzopertha dominica in stored wheat and corn under different temperatures, moisture contents, and adult densities.

Three-dimensional temporal and spatial distributions of adult Rhyzopertha dominica (F.) at adult densities of 1.0, 5.0, and 10.0 adults per kg grain and at 20 +/- 1, 25 +/- 1, and 30 +/- 1 degrees C were determined in 1.5 t bins filled with wheat (Triticum aestivum L.) with 11.0 +/- 0.8, 13.0 +/- 0.6, and 15.0 +/- 0.5% moisture content (wet basis) or corn (Zea mays L.) with 13.0 +/- 0.2% moisture content (wet basis). At each of five sampled locations, grain was separated into three 15-kg vertical layers, and adult numbers in each layer were counted. Inside both corn and wheat, adults did not prefer any location in the same layer except at high introduced insect density in wheat. The adults were recovered from any layer of the corn and >12, 65, and 45% of adults were recovered in the bottom layer of the corn at 20, 25, and 30 degrees C; respectively. However, <1% of adults were recovered in the bottom layer of wheat. Numbers of adults correlated with those in adjacent locations in both vertical and horizontal directions, and the temporal continuous property existed in both wheat and corn. Adults had highly clumped distribution at any grain temperature and moisture content. This aggregation behavior decreased with the increase of adult density and redistribution speed. Grain type influenced their redistribution speed, and this resulted in the different redistribution patterns inside wheat and corn bulks. These characterized distribution patterns could be used to develop sampling plans and integrated pest management programs in stored grain bins.

Fabrication and optimization of a conducting polymer sensor array using stored grain model volatiles.

During storage, grain can experience significant degradation in quality due to a variety of physical, chemical, and biological interactions. Most commonly, these losses are associated with insects or fungi. Continuous monitoring and an ability to differentiate between sources of spoilage are critical for rapid and effective intervention to minimize deterioration or losses. Therefore, there is a keen interest in developing a straightforward, cost-effective, and efficient method for monitoring of stored grain. Sensor arrays are currently used for classifying liquors, perfumes, and the quality of food products by mimicking the mammalian olfactory system. The use of this technology for monitoring of stored grain and identification of the source of spoilage is a new application, which has the potential for broad impact. The main focus of the work described herein is on the fabrication and optimization of a carbon black (CB) polymer sensor array to monitor stored grain model volatiles associated with insect secretions (benzene derivatives) and fungi (aliphatic hydrocarbon derivatives). Various methods of statistical analysis (RSD, PCA, LDA, t test) were used to select polymers for the array that were optimum for distinguishing between important compound classes (quinones, alcohols) and to minimize the sensitivity for other parameters such as humidity. The performance of the developed sensor array was satisfactory to demonstrate identification and separation of stored grain model volatiles at ambient conditions.

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

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 degrees 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 Tribolium castaneum (Coleoptera: Tenebrionidae) adults in response to temperature gradients in vertical and horizontal wheat and corn columns.

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 degrees C/m temperature gradient (from 20 to 30 degrees C) or at a uniform temperature (20, 25, and 30 degrees C). In a vertical corn column with a uniform temperature, approximately 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.

Movement and distribution of adult rusty grain beetle, Cryptolestes ferrugineus (Coleoptera: Laemophloeidae), in stored wheat in response to different temperature gradients and insect densities.

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 degrees C. Adults responded faster to higher temperature gradients than to lower temperature gradients. There was a similar pattern of adult distribution in 144 h.

Alternatives to methyl bromide treatments for stored-product and quarantine insects.

Methyl bromide is used to control insects as a space fumigant in flour and feed mills and ship holds, as a product fumigant for some fruit and cereals, and for general quarantine purposes. Methyl bromide acts rapidly, controlling insects in less than 48 h in space fumigations, and it has a wide spectrum of activity, controlling not only insects but also nematodes and plant-pathogenic microbes. This chemical will be banned in 2005 in developed countries, except for exceptional quarantine purposes, because it depletes ozone in the atmosphere. Many alternatives have been tested as replacements for methyl bromide, from physical control methods such as heat, cold, and sanitation to fumigant replacements such as phosphine, sulfuryl fluoride, and carbonyl sulfide, among others. Individual situations will require their own type of pest control techniques, but the most promising include integrated pest management tactics and combinations of treatments such as phosphine, carbon dioxide, and heat.