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.     

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.     

Stored grain pest prevalence and insecticide resistance in Egyptian populations of the red flour beetle Tribolium castaneum (Herbst) and the rice weevil Sitophilus oryzae (L.)

As a consequence of the widespread use of insecticides against insect pests in grain warehouses and in the food industry, insecticide resistance has greatly increased among these species all over the world. Nonetheless, insecticide resistance in stored grain insects in Egypt was little studied. Therefore, our study aimed to forecast infestation risks and determine the insecticide resistance level in Egyptian populations of the main insect pests of stored grains. To achieve this goal, we surveyed the populations of stored-product insects in wheat in two different sites in the Alexandria governorate (Egypt) between June and August 2017. Moreover, insecticide resistance levels in Egyptian populations of Tribolium castaneum (Herbst) and Sitophilus oryzae (L.) collected from wheat storage facilities (granaries and flour mills) in Alexandria governorate were also determined. Three contact insecticides, namely malathion, pirimiphos-methyl and cypermethrin, were tested. Tarsal contact bioassays on filter paper were carried out on adults following FAO methods and concentration-mortality lines were estimated to determine the resistance ratios for each insecticide and population. The data from the monitoring of insects revealed that T. castaneum and S. oryzae were the most common species infesting wheat in both Alexandria granaries and mills. Populations of S. oryzae were generally more resistant to malathion than the populations of T. castaneum. However, T. castaneum populations were more resistant to pirimiphos-methyl than the S. oryzae populations. Both populations of T. castaneum and S. oryzae were susceptible to cypermethrin. The detected levels of insecticide resistance indicate that this phenomenon takes place and should be a concern in Egyptian populations of T. castaneum and S. oryzae requiring monitoring and design of resistance management practices.     

Food oils as kairomones for trapping Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) adults

Insect infestation in the grain-based food in storage is often reported; Tribolium castaneum is a major pest. Determination of its population size using traps is entangled with the management attempts. Pheromone traps developed for T. castaneum often use kairomones with its aggregation pheromone 4,8-dimethyldecanal (4,8 DMD). However, low trapping efficacy is reported, and the information on promising kairomones is insufficient. The objective of this research was to evaluate the performance of some locally-available food oils as kairomones, alone and in combination with the pheromone for trapping T. castaneum adults. In the first experiment, the attraction of T. castaneum adults towards different food oils, the pheromone or the commercial kairomone was tested. In the second experiment, the attraction of T. castaneum to effective food oils + pheromone was determined under laboratory condition. In the third experiment, the attraction of T. castaneum by effective food oils + pheromone was evaluated under warehouse condition. Under laboratory condition, the highest attraction of T. castaneum adults was demonstrated by mee (Madhuca longifolia) and coconut (Cocos nucifera) oils. Either of these two oils when combined with the pheromone attracted more adults than the pheromone alone. Furthermore, attraction of T. castaneum adults by the two oils separately was similar to the commercially-available combination of pheromone and the kairomone. In contrast, under warehouse condition, the combination of mee oil and pheromone attracted T. castaneum adults similar to the commercially-available combination of pheromone and the kairomone. However, the attraction by the combination of coconut oil and pheromone was lower than that, and similar to the pheromone only. This study emphasizes the potential use of food oils as kairomones to trap T. castaneum adults, and augment the efficiency of pheromone traps available for this species.     

Effectiveness of diatomaceous earth for control of Sitophilus zeamais (Coleoptera: Curculionidae), Tribolium castaneum and Palorus subdepressus (Coleoptera: Tenebrionidae)

The effectiveness of diatomaceous earth (DE) or diatomite has been assessed against three major beetle pests of stored maize: Sitophilus zeamais (the maize weevil), Tribolium castaneum (the red flour beetle) and Palorus subdepressus (the depressed flour beetle). Maize has been treated with four doses of DE (1.5, 3, 4.5 and 6 g/kg) and four doses of Actellic Super™ Dust a chemical insecticide used as a reference (0.25, 0.5, 0.75 and 1 g/kg). The effective mortality was measured for each treatment after 1, 2, 4, 7 and 14 d of exposure. The corrected mortality rates were calculated by considering the mortality in the control group. Diatomaceous earth was as effective as Actellic Super™ Dust but required higher doses. Diatomaceous earth acted faster on S. zeamais and P. subdepressus compared to T. castaneum. The highest dose tested for DE caused the same mortality in T. castaneum as the recommended dose of Actellic Super™ Dust. Diatomaceous earth is a good alternative for the control of these three devastating insect pests of maize stocks and can readily be incorporated into integrated stored products pest management programs.     

Thermal death kinetics of adult red flour beetle Tribolium castaneum (Herbst) in canola seeds during radio frequency heating

Thermal mortalities of adult red flour beetles Tribolium castaneum (Herbst) infesting canola seeds at various moisture contents and volumes were determined after radio frequency (RF) heating (i.e. temperature between 30 and 80°C). The mortality of 92% was achieved at the end temperature of 343 K for small-volume (1.96 × 10^?4 m³, 0.250 kg) seeds, and the mortality of 99% at 333 K for large-volume (1.77 × 10^?3 m³, 2.26 kg) seeds. Regardless of sample volume, the thermal mortalities of the test insects increased significantly after the seed temperature reached 333 K (60°C). The kinetic parameters of the thermal death of the adult T. castaneum were estimated using inverse simulation. The ordinary differential equation-based kinetic model with the Arrhenius temperature-dependent reaction rate constant was solved using the fourth-order Runge–Kutta method. The kinetics followed first-order reaction with the activation energy of 100 kJ/mol. Good agreements were observed between the mortalities predicted using the kinetic model and the experiments (R² = 0.972–0.987) except for the small-volume seeds at 11% MC (11 g/100 g raw materials) (R² = 0.741). The predicted lethal times (s) to achieve 95 and 99% mortalities using the kinetic model agreed well with those determined from the experiments.     

Density-dependent reproductive success in Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Two strains of Tribolium castaneum, one being susceptible to malathion (Asm) and the other malathion-specific resistant (PRm), were used to assess the effect of population density and its interaction with genetic background in reproductive success. A highly significant allometric relationship between female body weight and fecundity (R²=0.413) and another between female body weight and larval survivorship (R²=0.561) were found. Data showed that population density exerted an indirect effect on the reproductive success. The body weight of the Asm female was not affected by variations in population density but the body weight of the PRm female increased with reduced population density.The genetic background (strain) and/or malathion-specific resistance greatly influenced reproductive success. Concerning the percentage survivorship of offspring of the two strains, there was an opposite trend with increased population density: in PRm, survivorship was lower at high density (76.64±13.75; mean±SD) and higher at low density (88.39±7.61), whereas in Asm, survivorship was higher at high density (53.39±15.57) and lower at low density (43.99±20.08). The PRm female laid more eggs than the Asm. Reproductive success was significantly higher in PRm than in Asm. In addition, the genetic background (the strain) and/or the pleiotropic effect of malathion-specific resistance had a significant effect on the fecundity of PRm because the differences in fecundity and reproductive success between Asm and PRm went beyond the body weight of the female and might be explained by their genetic background and/or the pleiotropic effect of malathion-specific resistance.     

TribUTE-F assay: Fluorescence-based rapid quantification of dietary intake in the red flour beetle,Tribolium castaneum (Coleoptera: Tenebrionidae), facilitates evaluation of antifeedant inhibitory effects

Tribolium castaneum (Herbst.) is an important pest of stored grains, nuts, and cereals worldwide. Different methods have been used to estimate dietary intake and feeding preferences of this beetle. A previously described TribUTE (Tribolium Urges To Eat) assay estimates its dietary intake by measuring the amount of gypsum excreta in beetles fed gypsum, a non-digestible and non-toxic compound, using an analytical microbalance. The method revealed the sweet preferences of T. castaneum adults. However, the measurements based on microbalance require individual quantitation of each sample, and the weight of the samples is sometimes below the detection limit of the microbalance. Here, an improved TribUTE assay, designated TribUTE-F assay, that uses gypsum labeled with the fluorescence dye ROX as an endogenous tracer is described. The fluorescence intensity remains constant during the consumption and excretion of the labeled gypsum and it is strongly correlated with the amount of gypsum. This approach was then used to evaluate the inhibitory effect of an antifeedant, mulberry latex, on dietary intake of T. castaneum adults. Compared with microbalance measurements, the new method enables more accurate measurement of near the minimum detectable quantities and is a suitable tool for the discovery of antifeedants.     

甲酸乙酯与氮气混合熏蒸对赤拟谷盗的毒力研究

采用广口瓶密闭熏蒸法,系统研究了氮气浓度、甲酸乙酯浓度、处理时间、温度等影响因子对熏蒸效果的影响.结果表明,氮气浓度的提高可显著增加甲酸乙酯对赤拟谷盗的熏蒸效果(P＜0.05),在12μL/L的甲酸乙酯浓度下,78％的氮气浓度中,赤拟谷盗的校正死亡率为5.6％,而在95％的氮气浓度中,校正死亡率达到91.7％;不同氮气浓度下,甲酸乙酯均显示出良好的速效性,在24 h内即可发挥很好的熏蒸活性;温度对氮气和甲酸乙酯混用的熏蒸效果具有显著的影响,在所有供试温度条件下(15.0～32.5℃),低温下氮气与甲酸乙酯的熏蒸效果显著优于高温(P＜0.05);在25.0℃条件下熏蒸24 h,氮气浓度为78％、87％、90％和95％时,甲酸乙酯对赤拟谷盗的LC50分别为20.72、17.49、14.77、9.00 μL/L.     

Aerosol concentration,deposition, particle size,and exposure interval as mortality factors Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae)

A series of trials was conducted for an experiment. In the first trial, adults of Tribolium confusum Jacquelin du Val, the confused flour beetle, were exposed on concrete arenas and treated with a combination aerosol of pyrethrin + methoprene dispensed for 5, 10, and 20 min at particle sizes of 4, 8, 12, and 16 μm, inside an aerosol exposure chamber. Nearly all adult T. confusum were knocked down when immediately removed from the chamber. Among all the exposure time and particle size combinations, recovery increased as the post-exposure holding period increased from one to seven days and when adults were transferred to untreated dishes with flour. A second experiment evaluated the residual effect of the aerosol on concrete arenas at 1, 3, and 6 weeks using 3-4-week-old larvae of T. confusum. Adult emergence of exposed larvae decreased with increasing particle size and exposure time. A biological index that assessed development of exposed larvae to the pupal and adult stages was also related to particle size and exposure interval, and this index was correlated with adult emergence. A third set of experiments investigated effects of particle size on adult fecundity for the 10-min exposure time. Male and female adults were cross-mated: exposed female with exposed male, exposed female with unexposed male, exposed male with unexposed female, and unexposed female and unexposed male. Progeny production was reduced as particle size increased, and there were indications that females were affected more than males by the aerosol treatment. This research could be used to improve insect pest management programs by adjusting application equipment to dispense aerosols at particle sizes that give optimum control of exposed adults and residual control of immatures and would also benefit pest management programs.     

Laboratory evaluation of development and survival of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) under constant temperatures

The red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) is a serious pest of stored products. The effect of temperature on the development and survival of this species was determined at five constant temperatures (20, 25, 30, 32.5 and 35 °C) in the laboratory. Results showed a temperature-dependent development of T. castaneum. Data were fitted to the nonlinear Briere model, which for the total immature period estimated the lower threshold at 20.2 °C, the upper developmental threshold at 35.3 °C, and the temperature for maximum developmental rate at 31.2 °C. The Ikemoto and Takai linear model indicated that 659.7 degree-days above a threshold of 16.9 °C were needed to complete immature development from egg to adult emergence. Survival of immature stages varied significantly across temperatures and was well described by an extreme-value function. The model indicated that the highest survival (73.0%) was estimated to occur at 27.4 °C. The curve shows a skewed bell shape, indicating that survival decreases at both ends of the temperature range. These results are useful tools for the prediction of T. castaneum phenology, as well as for its management.     

Aggregation pheromone 4,8-dimethyldecanal and kairomone affect the orientation of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) adults

Tribolium castaneum, the red flour beetle, is a major pest of stored products throughout the world. The male T. castaneum adults biosynthesize and release the aggregation pheromone 4,8-dimethyldecanal (4,8 DMD), and the monitoring traps having the synthetic form of this pheromone and kairomone are commercially available. However, certain information available on the response of T. castaneum adults to the strength of pheromone and the nature of air flow is inadequate and thus limits the potential use of this compound. The objectives of this research were to determine if the orientation of adult beetles to the synthetic form of the pheromone 4,8 DMD is affected by the distance from the pheromone, its concentration and air movement. Experimental design was completely randomized design with three replicates. The T. castaneum adults released at different distances from the pheromone placed at varying concentrations tested their orientation to the pheromone with the presence or absence of air flow. The control experiments were conducted without the pheromone. A separate experiment tested if exposure to 4,8 DMD alters the direction of movement in T. castaneum adults. The maximum trap catch (24%) was obtained with 0.5 μL of 4,8 DMD and when the beetles were released at distances up to 60 cm from the pheromone. The percentage of beetles trapped declined when the beetles were released 60–120 cm from the pheromone. The average angles on beetle turning during their orientation were significantly higher in the presence of pheromone than the respective controls. Air movement downstream of the pheromone trap increased the percentage beetles trapped compared to that in the absence of air flow. It is concluded that the orientation of T. castaneum adults is affected by the concentration of 4,8 DMD, distance from the pheromone and the air movement.     

Impact of geographical origin and rearing medium on mating success and lateralization in the rice weevil,Sitophilus oryzae (L.) (Coleoptera: Curculionidae)

Changes in reproductive behavior of mass-reared insects have been investigated in a wide range of species. The geographical origin, as well as different mass rearing practices, may affect the existence and magnitude of lateralization. However, little is known regarding the biotic and abiotic factors affecting lateralization in laboratory-reared insect strains, in terms of rearing media and origin from which the strain had been collected from. Sitophilus oryzae is a destructive beetle species that attacks stored products worldwide. We investigated the impact of geographical origin and rearing media on male mating success and lateralization in three strains of S. oryzae [i.e., a Greek strain reared on wheat (GW), a Greek strain reared on maize (GM) and a Peruvian strain reared on maize (PM)], in order to assess factors that affect mating behavioral trends and the concomitant progeny production. Precopula, copula and whole mating duration were slightly higher in GW males over GM and PM males. Male weevils showed right-biased head-wagging behavior and left-biased copulation attempts, regardless of the tested strains. Male mating success was higher in males performing left-biased copulation attempts followed by right-biased head wagging behavior, without significant differences among the tested strains. Overall, this study adds knowledge to the mating behavior of S. oryzae, highlighting the impact of the geographical origin and the rearing commodity on male mating success and laterality. The quantification of male mating traits may allow comparisons with different strains and/or host cereals, offering reliable evaluations of the impact of different mass rearing procedures.     

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.     

Differential susceptibilities of two closely-related stored product pests,the red flour beetle (Tribolium castaneum) and the confused flour beetle (Tribolium confusum), to five selected insecticides

The red flour beetle (Tribolium castaneum Herbst) and the confused flour beetle (Tribolium confusum Jacquelin du Val) are among the most commonly encountered insects infesting stored food, but their susceptibilities to different insecticides often differ significantly, which complicates efforts to manage populations in milling and processing facilities. In this study, the susceptibilities of T. castaneum and T. confusum late-stage larvae to five selected insecticides, esfenvalerate, pyrethrins, dichlorvos, methoprene and pyriproxyfen, were assessed with and without synergists using topical applications. In four-day bioassays (without flour) with dichlorvos, esfenvalerate and pyrethrins, T. castaneum larvae were less susceptible (low larval mortality) to dichlorvos and esfenvalerate than T. confusum, whereas the reverse was true for treatment with pyrethrins. Pre-treatment with one of three synergists, piperonyl butoxide (PBO, cytochrome P450 monooxygenase inhibitor), S,S,S-tributyl phosphorotrithioate (DEF, esterase inhibitor), or diethyl maleate (DEM, glutathione S-transferase inhibitor), suggested involvement of esterases in the detoxification of dichlorvos and pyrethrins, and cytochrome P450 monooxygenases in the detoxification of esfenvalerate in both species. Interestingly, pre-treatment with some synergists increased the toxicity of insecticides in only one species: DEM and DEF increased the toxicity of dichlorvos to T. castaneum, whereas only DEF increased dichlorvos toxicity to T. confusum. In 28-day bioassays with larvae treated with each of two insect growth regulators (IGRs), methoprene and pyriproxifen, T. confusum was the more tolerant species. All T. castaneum died in either the larval or pupal stages with either IGR. In contrast, only pyriproxyfen caused complete mortality in T. confusum larvae, and even the highest dose of methoprene allowed nearly 70% of T. confusum larvae to pupate, and 4.5% of adults to emerge. Our results show that although these two species are closely related, they display very different susceptibilities to different insecticides, and different metabolic detoxification mechanisms may contribute to their differential insecticide susceptibilities.     

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.