Population growth and development of the psocid Liposcelis obscura (Psocodea: Liposcelididae) at constant temperatures and relative humidities

The effects of nine temperatures (22.5, 25.0, 27.5, 30.0, 32.5, 35.0, 37.5, 40.0, and 42.5 °C) and four relative humidities (RHs; 43, 55, 63, and 75%) on the population growth and development of the parthenogenetic Liposcelis obscura Broadhead (Psocodea: Liposcelididae) were investigated in laboratory studies. Results showed that L. obscura did not survive at 43% RH at all temperatures tested. At 55% RH, L. obscura survived at 22.5, 25, and 27.5 °C; none survived at 42.5 °C and ≤63% RH. Population growth was highest at 40.0 °C and 75% RH, where population increase was 216-fold from an initial population of five adult females. Liposcelis obscura has three-to-five nymphal instars, and the percentages of individuals with three, four, and five instars were 52, 41, and 7%, respectively. Temperature-dependent developmental equations were developed for L. obscura eggs, individual nymphal, combined nymphal, and combined immature stages. Liposcelis obscura populations grew much faster at 30–42.5 °C and 75% RH. Based on the equation for total developmental time, the predicted optimal development temperature is 39.2 °C and development was completed in 14.0 d. The upper developmental threshold was estimated as 47.1 °C. The lower developmental threshold was estimated as 14.7 °C. These data provide a better understanding of L. obscura population dynamics and can be used to develop effective management strategies for this psocid.     

Development and validation of a model for predicting survival of young larvae of Tribolium castaneum exposed to elevated temperatures during heat treatment of grain-processing facilities

Heat treatment involves raising the ambient temperature of grain-processing facilities to 50–60 °C for at least 24 h to manage stored-product insects. The young larvae (first instars) of the red flour beetle, Tribolium castaneum (Herbst), are the most heat tolerant stage at temperatures of 50–60 °C when compared to eggs, old larvae, pupae, and adults. A thermal death kinetic model was developed to predict survival of T. castaneum young larvae exposed to six constant elevated temperatures between 42 and 60 °C. The model was based on two non-linear relationships: 1) logarithmic decrease in survival of larvae as a function of time, and 2) logarithmic decrease in larval survival as a function of temperature. The model was validated with 12 time-dependent temperature datasets collected during actual heat treatments of pilot-scale flour and feed mills and a commercial grain-processing facility. The observed survival of larvae in plastic boxes/vials with flour was used to validate model predictions. The heating rate to reach 50 °C from the ambient temperature, among the 12 datasets ranged from 0.9 to 7.8 °C/h. The mean absolute deviation between observed and predicted larval survival for 10 of the 12 datasets ranged from 2.1 to 11.4%; for the other two datasets it was 16.2 and 18.3%. These results show that the thermal death kinetic model can be used to predict survival of young larvae of T. castaneum based on time-dependent temperature profile obtained at any given location during heat treatment of grain-processing facilities.     

Effects of temperature on development of the azuki bean weevil,Callosobruchus chinensis (Coleoptera: Bruchidae) on two leguminous seeds

The azuki bean weevil, Callosobruchus chinensis L., is one of the most serious stored product pests in the world. The temperature driven stage-specific development of C. chinensis was examined at eight constant temperatures of 15.97, 18.31, 22.09, 26.15, 30.50, 34.39, 38.00, and 40.00 °C on azuki bean (Vigna angularis [Wild.] Ohwi & Ohashi) and cowpea (Vigna unguiculata L.) seeds. Parameters for stage-specific development such as threshold temperatures and thermal constants were determined by linear and nonlinear models. The total developmental time (egg - adult) decreased with increasing temperature from 14 to 38 °C on both seeds. However, total developmental time varied from 127.93 to 122.25 days at 15.97 °C to 19.31 and 19.17 days at 38.00 °C on azuki bean and cowpea seeds, respectively. The nonlinear Logan-6 and Performance models estimated optimal temperatures as 37.3, 37.0, 36.5 and 37.1 °C on azuki bean, and as 36.7, 36.4, 34.5 and 36.6 °C on cowpea for egg, larva, pupa and egg to adult, respectively. The linear model estimated the lower temperature thresholds (T_min) of egg, larva, pupa and egg to adult as 16.97, 10.47, 1.36, and 10.28 °C on azuki bean, respectively, and 16.84, 10.33, 10.92, and 9.83 °C on cowpea, respectively. The thermal constants (K) for each stage completion was 35.13, 255.21, 233.11, and 503.41° days (DD) for egg, larva, pupa, and egg to adult on azuki bean, respectively and 32.45, 246.50, 107.04, and 490.02 DD for egg, larva, pupa, and egg to adult on cowpea, respectively. Temperature also influenced the adult longevity. These findings on thermal requirements and temperature thresholds can be used to predict the occurrence, number of generations and population dynamics of C. chinensis.     

The effect of temperature and relative humidity on the development of Tribolium freemani Hinton (Coleoptera: Tenebrionidae)

The effects of various combinations of temperature, ranging from 12.5 to 40.0°C, and relative humidity, between 0 and 85.0% r.h., on the developmental rates and mortalities of Tribolium freemani Hinton on wheat feed were studied. Eggs did not hatch at 40.0 or 12.5°C. The egg period was shortest, 3.2 days, at 35.0°C and lengthened progressively at lower temperatures to 34.6 days at 15.0°C. Relative humidity did not affect markedly either the egg period or hatchability. Larval-pupal development was completed at temperatures between 20.0 and 35.0°C, at all the relative humidities investigated (0–85.0%). The shortest median larval-pupal developmental period was 25.7 days at 32.5°C and 84.0% r.h. and the highest adult emergence rate was 98.8% at 27.5°C and 84.7% r.h. Pupae could develop between 17.5 and 35.0°C. The shortest pupal period was 5.3 days at 35.0°C and the longest 27.1 days at 17.5°C. Relative humidity of pupal stage had little effect on either developmental period or mortality of pupal stage. The estimated threshold temperatures of development were 14.6 ± 0.74°C, 19.4 ± 0.93°C, 15.6 ± 0.34°C and 19.1 ± 0.92°C for egg, larval, and pupal stages and for total development, respectively. The thermal constants for egg, larval, and pupal stages and for total development were 66.1 ± 3.98, 303.2 ± 34.92, 101.7 ± 2.73, and 434.2 ± 48.07 degree-days, respectively. T. freemani needed more degree-days to complete development than Tribolium castaneum, T. confusum, or T. madens.     

Life history studies of externally feeding pests of stored sorghum: Corcyra cephalonica (Staint.) and Tribolium castaneum (Hbst)

A laboratory study of the ecology of single-species populations of C. cephalonica (Staint.) and T. castaneum (Hbst) was made on sorghum at three temperatures (25, 30 and 35°C) and three relative humidities (60, 70 and 80% r.h.). The effects of two lower humidities (40 and 50% r.h.) on both species were also studied at 30°C. The optimal conditions for multiplication of C. cephalonica were found to be 30°C and 60–80% r.h., while for T. castaneum the optimal temperature was 35°C at the same range of humidity. Lower humidities (40 and 50% r.h.) had a small adverse effect on both species. The results are compared with those of other workers and discussed in relation to the distribution of the two species in Sudan. It is concluded that the pest potential of C. cephalonica has been underestimated in the past.     

Development of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) on sorghum milling fractions

A series of tests was conducted to determine if Tribolium castaneum (Herbst), the red flour beetle, could survive on six milled sorghum fractions: Bran, Coarse Grits, Fine Grits, Flour, Red Dogs, and Shorts. In the first test, parental adults were exposed on the fractions, removed, and then the fractions were held for six-seven weeks at 27 °C. Late instar larvae and progeny adults were present in all fractions. In the second test, at least 80% of single neonates (1-2-day-old larvae) held on 1 g of a fraction at 27 °C for seven weeks were able to complete development to the adult stage. In the final test, individual neonates were held on 1 g of a fraction at 37 °C, 32 °C, 27 °C, or 22 °C. Time to adult emergence at each temperature ranged from 17 to 23 days, 21–27 days, 28–50 days, and 67–113 days, respectively, depending on the specific fraction. Logistic functions were compared for mean developmental times for each temperature-fraction combination. The six fractions were also analyzed for ash, fat, fiber, moisture, protein, and starch content. The fractions varied with respect to these chemical constituents; fat and moisture content were negatively correlated with development in some comparisons, though overall there was no correlation between these chemical components and neonate development on the fractions. Temperature had an obvious effect on neonate development, which has implications for assessing risk of pest infestations inside sorghum mills during warmer months of the calendar year. In addition, T. castaneum will reproduce and develop on all of the sorghum fractions included in this study, which are commonly generated during the sorghum milling process. Sanitation and removal of residual materials such as the measured fractions could also help with overall pest management of T. castaneum.     

Influence of temperature and application rate on efficacy of a diatomaceous earth formulation against Tribolium castaneum adults

Unsanitary storage bins can harbor grain-infesting insects, including the red flour beetle, Tribolium castaneum (Herbst). In a previous study involving heat treatment of empty bins, temperatures in the range of 50–55 °C for 2–4 h were effective in completely killing stored-product insects. Previous research in flour mills showed improved efficacy in killing stored-product insects by using diatomaceous earth (DE) dusts at temperatures below 50 °C. In the current study, the efficacy of a diatomaceous earth formulation (DiaFil^® 610) applied to concrete arenas, to simulate floor of empty bins, was examined at three application rates (0, 2.5 and 5.0 g/m²) to control T. castaneum adults at five constant temperatures (28, 36, 42, 44, and 46 °C). Ten adults of T. castaneum were placed on individual untreated and DE-treated concrete arenas for 4, 8, 12, and 24 h at each of the five temperatures. The efficacy of DE against T. castaneum adults increased with an increase in temperature and exposure time. Generally more adults died at 5.0 g/m² when compared with 2.5 g/m². In 2.5 and 5.0 g/m² DE treatments, exposure for 12 h at a temperature of 42 °C resulted in 73–77% mortality of adults with 100% mortality observed after 24 h. At 44 and 46 °C, 100% mortality of adults was observed after 24 h of exposure at both DE rates. At these two temperatures, the high mortality in untreated arenas (controls) at 8, 12, and 24 h exposures ranged from 27 to 100% confounding the true effects of DE. Our results suggest that combined use of DE and temperatures below 50 °C can be used as an integrated approach for controlling insects in empty bins prior to storage of newly-harvested grain.     

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.     

Population dynamics of red flour beetle (Tribolium castaneum (Herbst)) under different temperatures and patch sizes

Population dynamics of red flour beetles, Tribolium castaneum (Herbst), was determined using three different sizes of grain patch (bulk) at different temperature profiles. Grain patches were 0.03 kg, 2 kg, and 14 kg of wheat with 14.5% moisture content (wb). The temperature profiles tested were constant temperatures of 21, 25, 30, 35 °C, and incrementally decreased or increased temperatures (T-decrease (Td) and T-increase (Ti)). Every 28 d up to 168 d, the live and dead adults were separated from the wheat and their numbers counted. At Td, adults were separated and counted every 28 d during the first 140 d, then one last time 70 d later. After separating and counting, these adults were discarded and the wheat, which contained immature stages, was incubated at 30 °C. Four weeks later the emerged adults (referred to as “offspring”) were counted. The number of both adults and offspring showed great variation among temperatures at the same storage time and the same patch size. The peak number and density of insects also showed variation among different temperatures and patch sizes. Peak live adult density was the highest in the small patches. The peak live adult densities were 300 ± 50 at 21 °C, 673 ± 118 at 25 °C, 689 ± 48 at 30 °C, 1100 ± 150 at 35 °C, 1150 ± 150 at Td, and 1133 ± 94 adults/kg at Ti. The offspring density at 35 °C was higher than that at other temperatures in the small patches. Even though many factors and their interaction influenced population dynamics of T. castaneum, the number of insects was mainly influenced by temperature at the same patch size, while large patch size could provide more room for insects to multiply.     

Cold hardiness of immature and adult stages of the Mediterranean flour moth,Ephestia kuehniella

The cold hardiness profile of immature and adult stages of the Mediterranean flour moth, Ephestia kuehniella was investigated in the laboratory. Supercooling point (SCP) of early instars, late instars, pupae and adults of E. kuehniella was determined using a circulating bath with a cooling rate of 1 °C/min. Mean SCP of pupae was significantly lower (−23.3 °C) than that for early and late instars (−16.1 and −19.5 °C, respectively), but did not differ significantly from that for adults (−21.6 °C). Moreover, mortality at sub-zero temperature was estimated by cooling eggs, early instars, late instars, pupae and adults to −5, −7.5, −10 and −12.5 °C for 30, 60, 90 and 120 min. Main effects of temperature, exposure time and developmental stage on mortality proved to be significant. Two-way interactions as well as the three-way interaction between all tested factors also proved to be significant in most cases. Generally, pupae and adults were the most cold-tolerant, followed in decreasing order by late instars, early instars and eggs. However, when exposure temperature declined to −12.5 °C, no significant differences were observed between the developmental stages in any exposure, suggesting that temperatures as low as −12.5 °C are equally detrimental to all developmental stages. Complete mortality was observed only when early instars, late instars and adults were exposed to −12.5 °C for 120 min. In all tested temperature regimes mean lethal time (LTime₅₀) of pupae was higher compared to the other developmental stages. Similarly, in all exposure times mean lethal temperature (LTemp₅₀) of pupae was lower in relation to the other stages. Non-freezing injury above the SCP was well documented for all stages of E. kuehniella indicating a pre-freeze mortality. The potential of using low temperatures to control E. kuehniella is discussed.     

Orientation of Tribolium castaneum (Coleoptera: Tenebrionidae) adults to 4,8-dimethyldecanal,kairomone and botanical oils following ambient,low, or high temperature exposure

The aggregation pheromone 4,8-dimethyldecanal (4,8 DMD) used alone or with kairomone-baited traps generally is used for monitoringTribolium castaneum (Herbst) but low efficiency is reported. Furthermore, insect orientation to pheromones and kairomones following low or high temperature exposure is not yet understood. This research evaluated the orientation of T. castaneum adults to 4,8 DMD and common kairomones following exposure to ambient, low or high temperatures. Fifty adults were introduced to the middle of rectangular glass chamber, and movement to the treatment or control was determined after 1 h. In experiment 1, insects reared at 30°C were used. Experiments 2 and 3 used insects exposed to 10°C for 4 days (cold temperature) and 42°C for 12 h (brief high temperature), respectively at 2–8 h following cold or heat exposure. The highest trapping occurred when 4,8DMD was combined with neem oil whereas the lowest was in coconut oil alone. Neem oil alone demonstrated repellent action. Prior exposure to cold or heat initially reduced taxis of T. castaneum adults to traps. The attraction for adults exposed to cold and heat was restored after 6–8 h when traps contained pheromone + neem or coconut oil. This study marks the first to experimentally test how exposure to high or low temperatures, two key IPM tactics in the post-harvest supply chain, affects the behavioral response of an important stored-product species to pheromone- and kairomones-baited traps.     

Temperature-dependent development and reproduction of the cowpea weevil,Callosobruchus maculatus F., in mungbean: Estimating a target temperature for its control using aeration cooling

The bruchid, Callosobruchus maculatus F., commonly known as the cowpea weevil, infests stored mungbean and other legumes. Aeration cooling has potential as a non-chemical means of managing this species in stored legumes. Population growth of C. maculatus in mungbean was investigated at nine constant temperatures (15, 17.5, 20, 22.5, 25, 27.5, 30, 32.5 and 35 °C) at 60% RH so that a target temperature for cooling could be estimated. We used two laboratory strains: Strain 1 and Strain 2 that had been in culture for 16–17 years and 1–2 years respectively. The results for the two strains were very similar. Egg to adult development occurred between 20 and 35 °C for Strain 1 and 17.5 and 35 °C for Strain 2. The optimal temperature for population growth was estimated to be 32.2 and 33.7 °C for Strains 1 and 2, respectively. The estimated lower threshold for population growth, i.e. the temperature at which population growth is zero, was 17.5 °C for Strain 1 compared with 17.1 °C for Strain 2. Based on our results, we recommend a target temperature of 17 °C for aeration cooling to manage C. maculatus infestations in mungbean during storage.     

The survival of immature grain beetles at low temperatures

A laboratory study was made of the survival of the immature stages of Cryptolestes ferrugineus, Oryzaephilus surinamensis, Rhyzopertha dominica, Sitophilus granarius, Sitophilus oryzae and Tribolium castaneum in gradually cooled wheat or flour of ca 11% moisture content (m.c.) that was held at either 13.5 or 9°C for 13, 26, 39 or 52 weeks and then transferred to 30 or 32°C for incubation.In a high density experiment, no C. ferrugineus and 0.5% or less T. castaneum survived cold treatment. The proportion of R. dominica, S. granarius and S. oryzae that survived decreased from 33–59% or 4–16% for 13 week exposures to 13.5 or 9°C respectively, to 2.4% or less for exposures of 52 weeks. Although 8.7% of O. surinamensis survived exposure to 13.5°C for 52 weeks none did so after exposure to 9°C for 39 weeks or longer.In a low density experiment designed to obviate possible culture heating, 0.5% or less of T. castaneum and 1.1% or less of O. surinamensis completed development after exposure to either 13.5 or 9°C for any of the periods used. The proportion of R. dominica surviving cold treatment for 13 and 26 weeks was greater than in the high density experiment whereas the proportion of S. granarius and S. oryzae was sometimes less and sometimes greater. With these three species, survival after exposures of 39 or 52 weeks was generally zero.The results are discussed in terms of other studies on cold tolerance in grain beetles and the likely efficacy of refrigerated aeration in Australia.     

Development of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) on rice milling components and by-products: Effects of diet and temperature

Development of Tribolium castaneum (Herbst), the red flour beetle, was assessed on different rice components and their various by-products (i.e., diets) commonly found in rice mills, in two separate experiments. In the first experiment, eggs did not develop through to the adult stage on rough rice hulls, paddy rice dust, and milled rice dust, while eggs developed to the adult stage to some extent on rice flour, milled whole kernels, brown rice, milled broken kernels, and bran. For the diets where development occurred, the lowest percentage was on brown rice, and adults that emerged on brown rice had smaller elytra compared to adults emerging on the other diets. In the second experiment, 1–2-day old neonates were exposed on the diets listed above and held at 22, 27, 32, and 37 °C. At all temperatures, development to the pupal and adult stages was slowest on rice flour. At 22 °C, development to those stages took about twice as long compared to development at 27 °C. As temperature increased developmental times were reduced. Even though neonates developed slowest on rice flour adult emergence rates were not affected. Predictive models were used to estimate potential population development on the diets. At 22 and 27 °C, adult size as measured by elytra length was greatest when they developed on bran, while body weight was generally lowest for adults that developed on brown rice. Results show that T. castaneum can utilize rice components and by-products produced during the rice milling process, although not all components or by-products were optimal for development, and emphasis should be placed on cleaning and sanitation to remove food sources to limit infestations. Mill managers can use these results to show the importance of sanitation, and potentially improve overall pest management programs inside the mill.     

Estimating economic damage to cocoa bean production with changes in the spatial distribution of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) in response to climate change

Cocoa is a crop that serves as a major source of income in some countries, but its production has been affected by red flour beetles, Tribolium castaneum (Herbst). In this study, we aimed to predict the global potential distribution of T. castaneum under the current climate and in response to climate change (2050 and 2100). In addition, we attempted to use the results for estimating damage and economic losses in the major cocoa beans-producing countries. The CLIMEX model was used to evaluate the climatic suitability of regions for T. castaneum, and the economic damage was estimated by incorporating a series of published models and published data. The results showed that the potential distribution of T. castaneum was consistent with that of cocoa beans-producing countries, and as expected, at the local-level, T. castaneum was concentrated in cocoa cultivation areas. It was estimated that up to 50% damage to cocoa beans and economic loss of 3.16 billion US dollars due to production loss could occur. This study is the first attempt to estimate the economic damage to cocoa bean production by predicting the potential distribution of T. castaneum. Further, this study not only provides insight to combine the potential distribution of a species and an estimation of the related economics, but also provides basic data for establishing an effective monitoring/controlling strategy for preventing damage by T. castaneum.     

Feeding substrate and temperature interplay determining infestations and losses by the sawtoothed grain beetle (Oryzaephilus surinamensis)

Sawtoothed grain beetle, Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae), is a secondary pest of stored products and one of the serious insect pests of cereal grains, commodities and packaged food throughout the world. However, this species is a concern beyond cereal grains, what may be differentially affected by temperature. Therefore, insect developmental time, larva and pupa survival, and adult emergence of O. surinamensis were assessed on different substrates (rice, sesame and date palm) at different temperatures (20, 25, 30 and 35 °C and 65% r.h). The substrate loss incurred by this insect infestation was also recorded. The larval stage was the main determinant for the overall developmental time of the sawtoothed grain beetle, regardless of the substrate and temperature tested. Adult emergence was affected by substrate (F_2,48 = 4.50, P = 0.02) and particularly temperature (F_3,48 = 24.94, P < 0.001), but not their interaction (F_6,48 = 0.40, P = 0.87), exhibiting little variation until reaching 30 °C, but with a quick decline at 35 °C. The performance of the insects in rice was better, and worse in dry date. Furthermore, the survival was inversely related to substrate loss, regardless of the substrate used for rearing the sawtoothed grain beetle. Thus, substrate and temperature range are major determinants of sawtoothed grain beetle infestation with consequences for this species management.     

The toxicity of methyl chloroform to stored product insects

The susceptibility to methyl chloroform of all developmental stages of Cryptolestes ferrugineus, Ephestia kuehniella, Oryzaephilus surinamensis, Rhyzopertha dominica, Sitotroga cerealella, Sitophilus granarius, S. oryzae and Tribolium confusum, diapausing larvae of Ephestia elutella, E. cautella, Plodia interpunctella and Trogoderma granarium and adults of Tribolium castaneum, was studied. Tests were conducted at 15, 20 and 25°C, 55–75% r.h. with concentrations ranging from 25 to 200 mg/l and exposure times from 8 h to 16 days. The toxicity of methyl chloroform was in general similar to that of carbon tetrachloride. Immature stages of R. dominica, S. cerealella and Sitophilus spp, and diapausing larvae of T. granarium, showed the highest levels of tolerance. Methyl chloroform was more effective at the higher temperatures but a concentration of 50 mg/l was below the threshold level for full toxicity against 5 species at 25°C. Depending on the species concerned, the concentration × time (CT) product required for control varied from 3,700 mgh/l at 25°C to 60,000 mgh/l or more at 20°C. At 15°C fewer species were tested but five out of nine survived CT products in the region of 30,000 mgh/l. There was no appreciable difference between the susceptibility of the immature stages of malathion-resistant and susceptible strains of O. surinamensis. Neither were any consistent differences observed between adults of normal susceptibility and those resistant to methyl bromide or phosphine.     

Effect of chemical and physical properties of Dried Distillers Grains with solubles (DDGS) on Tribolium castaneum (Herbst) development

Dried Distillers Grains with Solubles (DDGS) has been used as a grain-based supplement in animal feed. The focus of this study was to investigate the effects of chemical and physical characteristics that may affect DDGS susceptibility to Tribolium castaneum (Herbst) infestation. Multiple regression-based models were built to determine if the diet’s chemical and physical characteristics affect T. castaneum development. Based on the regression models, diet particle size was the most influential factor in larval development. Larval weight increased more rapidly on T. castaneum normal laboratory diet, 90% flour/10% brewer’s yeast (F/Y), followed by ground DDGS, compared to raw DDGS with different particle sizes. To determine the effect of diet particle size on larval development, experiments were conducted to increase particle size by pelletizing F/Y using a rotary drum granulation apparatus. T. castaneum larval stage lasted significantly longer on F/Y granules with a particle size of 1.4 mm or larger. Although the chemical properties of DDGS (protein, fat, fiber and ash content) were not significant predictors of T. castaneum larval development, larval developmental time and weight gain on ground DDGS was significantly slower than on F/Y, highlighting the potential importance of nutritional factors not accounted for in our analysis. Our results conclude that storing DDGS as raw ingredient and in the granule or pellet form with large particle size may help limit T. castaneum infestations. Although granulation or pelletization may not be economically feasible for small manufacturing plants, larger producers may benefit from the reduced risk of insect contamination associated with secondary feeders such as T. castaneum.     

Prediction of insect mortality in cooled stored grain

Grain aeration with ambient air is the primary method used in France to prevent and control insect infestations. French grain storage operators consider that complete total mortality of insects can be achieved by maintaining grain temperature at 5 °C for 3 months. A predictive model on insect survival at low temperature was developed, using data from literature to test this hypothesis on Sitophilus oryzae, Sitophilus granarius, Rhyzopertha dominica, Cryptolestes ferrugineus, Oryzaephilus surinamensis, Tribolium castaneum and Tribolium confusum. A Cox proportional hazard regression, belonging to survival analysis, was associated to a Receiver Operator Analysis to evaluate the model and to predict durations of cold exposure required to obtain a total mortality for each species at different developmental stages and temperatures. The model described well the data since occurrence or not of a total mortality was correctly described in 77.2% of all cases. Computed predictions highlighted the facts that species cold-tolerance ranking varied depending on the temperature levels and that difference of cold tolerance between adult and immature stages depended greatly on species. A temperature of 0 °C is sufficient to kill all insect populations within 3 months, except Cryptolestes ferrugineus ones. However, a temperature of 5 °C is highly insufficient to achieve a total mortality. Practical implementations of this work are discussed.