Disinfestation of red flour beetle (Tribolium castaneum) present in almonds (Prunus dulcis) using microwave heating and evaluation of quality and shelf life of almonds

Almonds (Prunus dulcis) are one of the high-value nuts facing insect pest infestation predicaments during post-harvest operations and subsequent storage. The red flour beetle (Tribolium castaneum) (Coleoptera: Tenebrionidae) is an economically important and notorious insect pest that globally infest almonds thereby resulting in high storage losses. Currently, the fumigants (hydrogen phosphide and propylene oxide) commonly used during almond storage pose a health hazard to the applicator and consumer as well as the environment. Other disadvantages of chemical methods include chemical residue, high exposure time (2–4 days), pest resistance, the demise of beneficial insects and incomplete disinfestation of the egg stage of the target pest. Among other physical disinfestation methods, the use of microwave as a disinfestation technique offer advantages of less processing time, lower energy consumption, clean technology, and no residues. Therefore to test the efficacy of microwave in pest control of stored almonds, we exposed life stages of T. castaneum to microwave irradiation at different power levels (120–600 W) and durations (30–90 s). Hundred percent mortality of all selected life stages was achieved at 480 and 600 W when infested almonds exposed for 90 and 60 s respectively. The quality attributes of treated almonds such as color difference, water activity, hardness, peroxide value, free fatty acid, and iodine value were measured and found to be acceptable. The fatty acid composition and sensory analysis demonstrated no significant difference (p > 0.05) in control and microwave treated almonds. The storage studies revealed that microwave treated almonds were free from infestation and rancidity for up to 12 months, whereas untreated almonds were spoiled within 3 months.     

Physical and chemical properties of flour products affect the development of Tribolium castaneum

The rust-red flour beetle, Tribolium castaneum, is a polyphagous pest of cereal grains and many other stored products. The presence of this pest causes contamination and economic losses by reducing the quality and quantity of commodities in storage. This research was aimed to study the development of T. castaneum on different flour products and investigate the factors affecting the survivorship and development time of T. castaneum. We used 16 flour products differentiated by production process (commercial vs. non-commercial) and commodity types. We conducted experiments on the development of T. castaneum in the laboratory by placing 15 mating pairs of T. castaneum into a treatment jar and allowing them to feed on different flour products. The results showed that T. castaneum adults laid eggs in all flour products. The larvae could live and survive, although the population density was found to be significantly lower in the commercial products. The pupae and adult (F₁ progeny) were only found in all non-commercial products and three commercial products. In addition, the total development time of T. castaneum was shown to be significantly faster in commercial products and did not differ among commodity types. We found that particle size variation and protein content of flour products affected the survivorship and development time of T. castaneum. In conclusion, understanding the particle size and chemical composition of flour products is a pivotal step in developing a pest management strategy for T. castaneum.     

Fumigant toxicity of allyl isothiocyanate to populations of the red flour beetle Tribolium castaneum

The phasing out of methyl bromide as a fumigant, the phosphine resistance problems in stored product insect-pests, and the ever-growing concerns with human health and environmental safety have been guiding the search of alternative fumigants. Allyl isothiocyanate (AITC) is the main component of mustard oil with reported pesticide activity and potential as a fumigant of stored foodstuffs. The fumigant toxicity of AITC was assessed in adults of 18 populations of the red flour beetle Tribolium castaneum (Coleoptera: Tenebronidae). These populations were all susceptible to AITC with negligible variation among them. Two of these populations were further used to test the AITC susceptibility of eggs, larvae (early and late instars), and pupae of T. castaneum. All of the developmental stages of both populations were similarly susceptible to AITC. No cross-resistance between phosphine and AITC was observed. Despite the significant variation in body mass, respiration rate, and fitness among the populations of T. castaneum, they were not correlated with AITC susceptibility. Larvae and adult malformations were observed when larvae and pupae were exposed to AITC. These results show the potential of AICT as an alternative fumigant against stored product insects.     

Low and high temperatures for the control of cowpea beetle, callosobruchus maculatus (F.) (coleoptera: Bruchidae) in chickpeas

Chickpea (Cicer arietinum L.; Leguminasae) is an important pulse crop grown, around the world. The whole grain of chickpea is damaged by the cowpea seed beetle, Callosobruchus maculatus (Coleoptera: Bruchidae), which is the most important field-carry-over storage pest of pulses. The management of this insect in storage using chemicals leads to insecticide residues in grains and insecticide resistance development in insects. Thermal disinfestation is one of the means of physical insect control. Eggs, larvae, pupae and adults were held at 42 or 0 °C for varying durations. Pupae and adults were equally heat tolerant. The lethal time to reduce survival by 50% (LT₅₀) at 42 °C for eggs, larvae, pupae and adults were 18, 57, 78 and 71 h, respectively. Pupa was the most cold-tolerant stage. The LT₅₀ at 0 °C for eggs, larvae, pupae and adults were 3, 8, 10 and 4 d, respectively. The LT₅₀ for pupae were 4907, 4262, 336, 36 and 13 min at the grain temperature of 42, 45, 50, 55 and 60 °C, respectively. The LT₅₀ of pupae at 0,−5,−10 and −15 °C were 274, 122, 7 and 2 h, respectively.     

Growth and development of Tribolium castaneum (Herbst) on rice flour and brown rice as affected by time and temperature

Tribolium castaneum (Herbst), the red flour beetle, is a cosmopolitan stored product insect that infests a variety of raw grains and processed grain products. Although this pest is prevalent in rice mills, there is a comparative lack of data on growth and development on rice by-products and fractions compared to other grains. In this study, ten mixed-sex adults were exposed on 200 g of either rice flour or brown rice, and populations were assessed after 2, 4, 6, 8, and 10 months at 22, 27, or 32 °C. At 22 °C, the number of adults, pupae and larvae on rice flour and brown rice remained low throughout the 12-month storage period. At 27 °C, the number of adults on rice flour increased to a maximum at 8 months, while adult populations on brown rice remained relatively constant from 2 to 10 months, with few pupae or larvae in the samples. At 32 °C, adult populations on rice flour and brown rice were constant after month 2, with low numbers of pupae and larvae. Adult predation could have accounted for low numbers of pupae and larvae. Using the original 10-month data, populations were projected for an additional 14 months to predict population patterns. Adult numbers showed an increase over time at all temperatures on rice flour and brown rice at 22 °C but numbers seemed to stabilize at 27 and 32 °C. For both diets at 27 and 32 °C, projected pupae and larvae numbers remained steady but low compared to adults. However, populations would not be expected to increase indefinitely because at some point the resources would become limited and populations would crash or decline. Results show T. castaneum can deplete fixed resources such as bags of rice flour or brown rice when temperatures equal or exceed 27 °C.     

Effects of gamma radiation on the Mediterranean flour moth,Ephestia kuehniella Zeller,mature larvae and acceptability of irradiated larvae by Bracon hebetor say females

Mediterranean flour moth, Ephestia kuehniella Zeller, mature 5th instars were exposed to gamma radiation dosages ranging from 50 to 350 Gy at 50 Gy increments and the effects on pupation, adult emergence and sex ratio were investigated. In addition, effects of irradiation on the rate of development to pupae and adults and the acceptance of irradiated larvae by Bracon hebetor Say females were examined. Results showed that the radio-sensitivity of E. kuehniella larvae increased with increasing dose. Pupation was significantly affected at 100 Gy and completely prevented at 350 Gy. Adult emergence was only slightly different from pupation; emergence was significantly affected at 100 Gy and completely prevented at 300 Gy. Irradiation also negatively affected the rate of development of larvae to pupae and adults. In addition, irradiation significantly affected male: female ratio; sex ratio was skewed in favour of males, and at 250 Gy all emerged moths were males. Furthermore, irradiation had no adverse effect on the degree of acceptance of mature larvae to parasitization; irradiated insects were as acceptable to B. hebetor females as nonirradiated ones.     

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.     

Repellency and some biological effects of different ultrasonic waves on Mediterranean flour moth,Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae)

Ephestia kuhniella is one of the most important stored pests in the world. Repellency and biological effects of various ultrasonic signals with different frequencies and wave shapes on adult, larvae and pupae of the pest were studied in laboratory conditions. Choice and non-choice tests was performed by an invented signal generator device. In choice tests, different ultrasonic frequencies, and for each frequency, four different waveforms were emitted by the device and numbers of repelled moths were separately calculated. Dispersion patterns, weight and survival of the pest treated by the ultrasound were compared with control in non-choice tests. The choice tests indicated that shape and frequency of ultrasound significantly affected evasive behavior of the moths by the waves. The highest repellency effects of ultrasound were observed at frequencies of 43–45 kHz and wave shapes of Sin (x) and Cos (x). Male moths significantly were more affected by the ultrasound. In non-choice test, weights of the pest larvae and pupae and the larvae survival were significantly reduced when they treated by ultrasound with frequency 40–45 kHz and Sin (x) wave shape that emitted by specific pattern. Also, our findings showed that the larvae and adults considerably tend to avoid from the ultrasound source. Results of the study can be applied for control of the pest in store locations or silage.     

Feasibility of detection of infested rice using an electronic nose

Electronic nose (E-nose) technology has a potential to be used for detecting insects in stored rice. It may provide a new method to detect the insect activity by providing smell prints for the headspace volatiles in rice mass. The objective of this research was to study the feasibility of using E-nose to detect infested rice during the storage process. An E-nose instrument (Cyranose 320) consisting of 32 sensors for detecting the volatile components produced in infested rice was used for this study. Storage rice with moisture content of 11.8 ± 0.3% was used for conducting the tests. The rice samples were infested with different numbers of adult insects, including rice weevil (Sitophilus oryzae), lesser grain borer (Rhyzopertha dominica) and red flour beetle (Tribolium castaneum), in containers containing 1 kg of rice. The samples were stored at temperatures of 15 °C and 30 °C for four weeks. Air samples in the containers were taken for measurements every five days. The data were analyzed using the principal component analysis (PCA) method. The results revealed that the E-nose was not able to distinguish the clean rice and infested rice with lesser grain borer. While the E-nose had high response ability to the volatile components produced by rice weevil and red flour beetle after four weeks of storage. Consequently, the E-nose could discriminate the clean and infested rice with above insects after four weeks of storage at temperature of 30 °C. Additionally, under the aforementioned conditions, the E-nose could not distinguish the clean and infested rice during the first, second and third weeks of storage. The classification accuracy of E-nose for clean and infested rice was low at storage temperature of 15 °C for the tested insets. It can be concluded that the E-nose has the capability to detect infested rice after four weeks of storage.     

Movement of Cryptolestes ferrugineus out of wheat kernels and their mortalities under elevated temperatures

The rusty grain beetle, Cryptolestes ferrugineus (Coleoptera: Laemophloeidae), is a common pest in stored grain. The present study examined the time taken for larvae of C. ferrugineus to exit wheat kernels at 40–55 °C, stage-specific mortality at 40–60 °C, and whether a combination of heat and shaking could be used to control this pest. The average time larvae took to leave wheat kernels ranged from 130 min at 40 °C to 6 min at 55 °C. At 55 °C and 6 min exposure, 81 ± 2% of larvae exited the kernels, 10 ± 1% of larvae were alive inside kernels and 9 ± 2% were dead inside kernels. Under constant temperature of 55 °C, less than 5% of the larvae escaped in 2 min, but under the rising temperature of 40, 45, 50 and then to 55 °C, over 50% of the larvae escaped in 2 min at 55 °C. The time taken to reach 50 and 95% mortality was similar for all stages. Higher temperatures resulted in higher mortality in a shorter exposure time. The longest LT₉₅ for pupae was 6480, 293, 50 and 3.7 min at 45, 50, 55 and 60 °C, respectively. At 55 °C for 88 min, combined with shaking gave 88% control in a 100-g wheat bulk. Time needed to kill eggs and pupae were much longer than the time needed to force larvae out of kernels. Therefore, the combination of heat and shaking would only provide partial disinfestation of C. ferrugineus.     

Microwaves to control Callosobruchus maculatus in stored mung bean (Vigna radiata)

Disinfestation of stored grains using microwaves can be an alternative to chemical methods for controlling insects in grains and pulses. Mung bean of 12% moisture content (m.c.) was infested with different life stages of the cowpea weevil (Callosobruchus maculatus) and exposed to 200, 300 or 400 W microwave power levels for 14, 28 and 42 s. One hundred percent insect mortality for all life stages (egg, young larva, old larva, pupa and adult) was achieved with exposure to 400 W power level for 28 s, which caused a surface temperature of mung bean of 68.1 °C. Eggs were the most susceptible and adults were the least susceptible life stages to microwave treatments. No significant difference was observed between mortality of larvae and pupae stages and their mortality was between eggs and adults. Mung bean temperatures increased and germination decreased with increased power level or exposure time.     

The effect of modified atmospheres,an alternative to methyl bromide,on the susceptibility of immature stages of angoumois grain moth Sitotroga cerealella (Olivier) (Lepidoptera: Gelechiidae)

The angoumois grain moth, Sitotroga cerealella is recognized as a common pest of grains world-wide. This investigation aimed at determining the most effective CO₂ concentration in air against the immature stages of the pest in laboratory tests. The sensitivity of newly-laid eggs (<24 h old), 4th instar larvae and 3-day-old pupae to 4 modified atmospheres (MAs) containing 30%, 45%, 65% and 75% CO₂ in air was investigated at 27 °C and exposure periods between 2 h and 264 h. The percentage mortality of the newly-laid eggs, as well as the reduction of adult emergence from 4th instar larvae and 3-day-old pupae tended to increase with the increase of CO₂ concentrations in air and exposure period. According to LT₉₅ values, the order of sensitivity of the three developmental stages of S. cerealella to the four MAs tested was as follows: eggs > pupae > larvae.     

Alpha-amylase inhibitor from local common bean selection: Effect on growth and development of Corcyra cephalonica

Cultivars of common bean (Phaseolus vulgaris L.) from the Kalpa valley of the Kinnaur district were screened for alpha-amylase inhibitor activity against porcine pancreatic α-amylase and significant differences were found amongst them. The inhibitor protein was partially purified from Triloki cultivar by ammonium sulphate precipitation and Sephadex G-100 gel filtration chromatography. Inhibitor protein was non-competitive, heat labile and retained 55.51 per cent activity at 70 °C. It had two pH optima of 5.0 and 7.6. Inhibitor protein inhibited amylases of 3rd -4th instar larval extracts of Corcyra cephalonica Stainton, the rice moth. C. cephalonica larvae (3rd -4th instar) were fed on wheat flour mixed with 0.013 percent (w/w) of partially purified α-amylase inhibitor protein. The growth of larvae in the treatment was significantly reduced. Treated larvae showed 100 percent mortality after 11 days. In the untreated control, no larval mortality was observed and adults emerged after 45 days. The inhibitor protein was effective at very low concentrations and could be exploited for control of this grain storage pest.     

Microwave radiation for control of Tribolium confusum in wheat and flour

The susceptibility of Tribolium confusum Jacquelin du Val to microwave energy was determined by irradiating vials of infested wheat or flour near the aperture of an optimum gain horn coupled through a waveguide to a magnetron operating at 8·5 GHz and 30 W average output at a pulse repetition frequency of 4000 Hz. Mortality was a function of exposure time and wheat moisture content. Adult mortality was higher in insulated samples of wheat than in non-insulated samples. Susceptivility of stages to radiation at 60°C was: eggs > pupae > adults > larvae. Survival of pupae near the surface of wheat indicated that heat was distributed non-uniformly. Mortality was higher in wheat than in white flour. Adults from 1·5 to 7 months old were equally susceptible to radiation.     

Influence of temperature and artificially-created physical barriers on the efficacy of synergized pyrethrin aerosol

The dispersal of aerosol insecticides within a flour mill may be hampered by barriers created from machinery and other equipment that block dispersion. Additionally, seasonal temperature variations may influence aerosol dispersion and subsequent effectiveness against stored product insects. The influence of barriers and temperatures on the efficacy of synergized pyrethrin aerosol against adults and pupae of the confused flour beetle, Tribolium confusum (Jacquelin du Val), was evaluated in experimental sheds. Insects were exposed to the aerosol at target temperatures of 22, 27, and 32 °C. Wooden boxes 1 m in length, 20 cm in width, and 5, 10, or 20 cm in height were used for creating different open and concealed areas for exposing insects. Results showed that exposing adults of T. confusum in open areas produced more moribund adults (those knocked down and unable to move except for reflex twitching or unable to respond when touched with a probe) at all temperatures, while survival increased with increasing distance from the front to the back of the boxes. Given the decreased survival, it would appear that more aerosol dispersed under the box height of 20 cm compared to 5 and 10 cm box heights because survival was generally less under the 20 cm box compared to the other two. Less than 2% of the pupae exposed in the open emerged as adults, but as the distance increased from the front to the back of the box adult emergence from these exposed pupae increased. Synergized pyrethrin aerosol can provide good control of T. confusum pupae and adults and may not be affected by seasonal temperature variations, but aerosol dispersion into obstructed or concealed areas may affect control.     

Assessment of eight rice cultivars flour for feeding resistance to Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) is an important pest of processed stored grains worldwide. Study of life history, feeding efficiency and digestive function of an insect on different host cultivars can indicate their resistance for the insect's population increase. Due to the economic importance of T. castaneum on stored rice flour, this research was aimed to investigate the life history, feeding indices and digestive enzymatic activity of T. castaneum on flour of eight rice cultivars (Ali-Kazemi, Dom-Siah, Fajr, Gilaneh, Gohar, Hashemi, Khazar, and Neda). A delay in the developmental time of T. castaneum was detected on cultivar Gohar. The lowest fecundity and egg fertility were observed on cultivar Gohar. Feeding indices of fourth instar larvae were the lowest on cultivars Gohar and Neda. The amylolytic activity of fourth instar larvae was the highest on cultivars Hashemi, Dom-Siah, Ali-Kazemi and Gilaneh, and the lowest on cultivar Gohar. Also, the highest and lowest proteolytic activities of fourth instar larvae were on cultivars Khazar and Hashemi, respectively. Significant correlations were detected between tested parameters of T. castaneum with starch and protein value of examined cultivars flour. The results of cluster analysis indicate that Dom-Siah, Hashemi and Ali-Kazemi are relatively susceptible cultivars, and other tested cultivars, especially Gohar, are relatively resistant cultivars for feeding of T. castaneum. The resistant rice cultivars could be further evaluated to identify secondary biochemicals that contribute to T. castaneum resistance.     

Comparative performance of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) across populations,resource types and structural forms of those resources

The significance of Tribolium castaneum (Herbst) as a pest of stored grains will likely be influenced by the relative availability of different resources regionally and the beetles’ ability to utilize each of them. Therefore the performance across the life cycle of laboratory and field populations of T. castaneum on commonly available structural forms of wheat and sorghum, as conventional resources, was quantified and compared to that on cotton seed. The latter is not usually associated with T. castaneum, but large beetle infestations have been recorded commonly in cotton gins in Australia. The highest number of individuals of each stage (from a given number of eggs) developed on wheat and sorghum flour and kibbled seeds. Cotton seed did not support the development of laboratory population beetles and all neonate larvae died before pupation. In contrast, some of the field population larvae did develop on cotton flour, but their number was significantly lower in comparison to development on wheat and sorghum. Field population beetles produced significantly more eggs than did laboratory population beetles, on both the whole seed and flour. Field population females had a consistently higher fecundity (～78% more eggs) than the laboratory population females, at least over the first three weeks of adult life. These results suggest that field populations of T. castaneum should be used in experiments if we are to develop a more realistic understanding of the field ecology of this species. The relative rate at which these insects infest available resources in the field also warrants further investigation.     

基于图像处理的储粮低密度虫害监测系统的设计与验证

为解决高害虫密度储粮处理成本昂贵和现有监测系统实时性和移动性不足等问题,采用Web技术,结合自主设计的粮虫诱捕器,建立了储粮低密度虫害实时监测系统。树莓派控制诱捕器采集害虫图像并进行图像处理得到图像中害虫的数量,再将数据传至云端服务器,用户通过Web客户端获取历史以及实时的害虫图像和害虫数量。在实验室用该系统监测了赤拟谷盗密度为0.5、1、2、3、4、5头/kg的稻谷,通过系统捕获第一只害虫的时间来评价其灵敏度,24 h内对害虫的捕捉率验证系统用于低密度虫害监测的可行性,并以人工直接计数结果为参考计算了系统计数的准确率,结果表明：系统灵敏度高,在低密度害虫条件下对害虫的捕捉率高于61.98%且诱捕器捕捉的害虫数与稻谷中的害虫总数存在显著线性关系,系统计数准确率为90.26%。因此,该系统可用于低密度虫害的实时监测。     

Effect of heat treatment of sorghum grains on storage stability of flour

Sorghum flour is susceptible to rancidity and develops off-flavor within a short duration when stored. Heat treatment on the development of rancidity after long-term storage of flour was studied. Heat treatment varying in severity was applied to the whole grains of different varieties of sorghum viz., CSH-9, CSH-5, M35-1 and a local variety varying in their morphological features. A trend was seen that when the thermal duration was for a shorter time, the shorter was the storage duration in certain varieties. Exposure of grains to moist heat for 15 min retarded hydrolytic rancidity significantly (p < 0.05) in CSH-5 until 6 months of storage and in the remaining varieties until 8 months of storage, Heat application for 15 min retarded the development of rancidity irrespective of the morphological variations and the oil content. Lipase activity varied among the varieties with CSH-5 recording higher activity when compared to the other varieties. No major differences in the physicochemical properties were observed in flours from 15 min heat-processed grains when compared to flours from unprocessed grains.     

Triple-bagging of cowpeas within high density polyethylene bags to control the cowpea beetle Callosobruchus maculatus F. (Coleoptera: Bruchidae)

Laboratory and on-farm trials were carried out to determine the effectiveness of cowpeas triple-bagging with heavy-grade polyethylene to control the cowpea weevil, Callosobruchus maculatus (F.), the main storage pest of cowpea, Vigna unguiculata, Walp, in West Africa. In the laboratory bruchids numbers and seed damage were significantly reduced when storing cowpeas within 2 layers High Density Polyethylene (HDPE) bags of at least 80 μm wall thicknesses. This thickness considerably reduced oxygen concentration in the bag after 5 days of storage and inhibited insect development. However late instar larvae and pupae were less affected by low oxygen concentration. On-farm storage trials with 2 layers HDPE 50 kg capacity bags tightly sealed and placed in an additional woven nylon bag (triple bag) was effective in controlling the bruchids for 7 months. Moreover, seed damage (<7%) and grain germination were not significantly affected (>89%). These findings allow optimizing the triple-bagging technology with readily local manufactured and affordable bags for long duration cowpea storage.