Behavioural responses of Oryzaephilus surinamensis, Tribolium castaneum and Tribolium confusum to naturally and artificially damaged durum wheat kernels

Observations on behavioural activity involved in the host selection by secondary pests of stored grains, Oryzaephilus surinamensis (Linnaeus), Tribolium castaneum (Herbst) and Tribolium confusum J. du Val, with respect to intact and mechanically or naturally damaged kernels are reported. Our results indicate that the attraction of secondary pests is facilitated by broken grain kernels, which resulted from either mechanical damage during harvesting and/or binning procedures, or the feeding activity of primary insect pests. Insect damaged kernels were more attractive to O. surinamensis, T. castaneum and T. confusum than whole kernels; in addition insect damaged kernels elicit more attractiveness than mechanically split kernels. The damage caused by primary pests, such as Rhyzopertha dominica (Fabricius) and Sitophilus oryzae (Linnaeus), on whole kernels may facilitate colonization by secondary pests, which continue damaging the cereals. O. surinamensis, T. castaneum and T. confusum utilize the grain volatile odours to distinguish whether the grain kernels of the stored cereals are damaged mechanically or by insects.     

Susceptibility of different European populations of Tribolium confusum (coleoptera: Tenebrionidae) to five diatomaceous earth formulations

Laboratory bioassays were conducted to evaluate the susceptibility of seven populations (strains) of the confused flour beetle, Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae), to five commercially available diatomaceous earth (DE) formulations: Insecto, Protect-It, Protector, PyriSec, and SilicoSec. These DEs were applied on wheat, Triticum durum Desf., at two dose rates, 500 and 1000 ppm. The six beetle strains were obtained from Denmark, United Kingdom, Greece, Germany, Italy, and Portugal, whereas a seventh strain came from the Greek strain after laboratory selection with SilicoSec-treated wheat for six generations. Adults of the above-mentioned strains were exposed for 7 d to wheat treated with each DE formulation, and mortality was assessed after exposure. For all DE-dose combinations, significant differences were noted in mortality levels among strains. Generally, the strains from Denmark, United Kingdom, and Germany were the most susceptible to the DEs used, whereas the strain from Portugal was the least susceptible. No significant differences were noted in susceptibility level between the initial Greek strain and the laboratory-selected Greek strain, with the exception of Protector, where the selected strain was significantly more tolerant than the initial strain for both dose rates tested.     

Tribolium confusum responses to blends of cereal kernels and plant volatiles

In this study, we report on the behavioural responses of the Tribolium confusum to 6 blends of cereal volatiles. There were tested four doses (1 ng/min, 10 ng/min, 100 ng/min and 1000 ng/min in 50 μl of hexane applied on filter paper). A Y‐tube experiment revealed that T. confusum females and males were attracted to the blend 1, 4 and 5 at the concentrations between 1 and 10 ng/min. Confused T. confusum females and males were not attracted to any concentration of blend 2 and 3. Yet the beetle females and males were repelled by the highest concentrations (1000 ng/min) for all the blends tested and also by the concentration 100 ng/min of all the blends tested, except for blend 1 and 4. Females and males were also repelled by the three blend 6 concentrations tested (10, 100 and 1000 ng/min).     

Pyrimidines and the X-ray response of Tribolium confusum Duval

Radiosensitizing effects of incorporation into DNA of the halogenated pyrimidines 5-bromouracil or 5-iodouracil, or their nucleosides (BUdR and IUdR), have been demonstrated in a variety of cell types. The results indicate that these antimetabolites influence lethality in x-irradiated adult Tribolium. At relatively low concentrations in the medium, BUdR and IUdR exhibit toxicity 3 to 5 weeks after transfer of beetles to analog-containing medium. Toxicity of IUdR on nonirradiated adults is less pronounced than that of BUdR and is slower to develop. Analog-treated Tribolium exposed to 7 kR, which is sublethal for adults in normal medium, die much earlier than those treated with analog alone or with lethal doses of x-rays alone. Transfer of beetles to normal medium after 3 weeks or less in the presence of analog virtually eliminates lethality attributable to the analog. X-irradiation at the time of transfer, however, leads to high mortality, and the amount of mortality appears to be a function of the duration of analog treatment. Insects grown in medium containing uracil or thymine exhibit the same survival as those reared in unsupplemented medium. Two weeks after 7 kR of irradiation a sharp decline in survival is seen in both uracil- and thymine-treated groups.     

Relative susceptibility of Tribolium confusum life stages exposed to elevated temperatures

Methyl bromide, a space fumigant used in food-processing facilities, may be phased out in the United States by 2005. The use of elevated temperatures or heat treatment is gaining popularity as a methyl bromide alternative. During heat treatment, the temperature of the whole food-processing facility, or a portion of it, is raised and held between 50 and 60 degrees C for 24-36 h to kill stored-product insects. We determined time-mortality responses of the confused flour beetle, Tribolium confusum (Jacquelin du Val), eggs, young larvae, old larvae, pupae, and adults exposed to six constant temperatures between 46 and 60 degrees C. Responses of all five insect stages also were measured using exposure times of 160, 40, and 12 min at 46, 50, and 60 degrees C, respectively. Time-mortality responses of all T. confusum life stages increased with an increase in exposure time and temperature. Both time-mortality and fixed time responses showed eggs and young larvae to be most susceptible at elevated temperatures and old larvae to be least susceptible. Our results suggest that old larvae should be used as test insects to gauge heat treatment effectiveness, because heat treatment aimed at controlling old larvae should be able to control all other T. confusum life stages. Besides providing baseline data for successful use of heat treatments, time-mortality data collected at the six temperatures can be used for developing thermal death kinetic models for this species to predict mortality during actual facility heat treatments.     

Sensitivity to gamma radiation of Tribolium confusum eggs at various developmental stages

Eggs of six different age classes were exposed to gamma rays up to 9.000 rads. As regards the effect on hatchability, the eggs can be divided into two groups. The first group—eggs more than 4 days old—is not influenced by treatment, whereas the second group—younger eggs—is highly susceptible to radiation. As regards the post-embryonic development, relative numbers of the post-embryonic stages 40 days after egg-laying and the post-embryonic mortality are recorded.

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Résumé Des oeufs de Tribolium confusum agés de 1 à 6 jours ont été irradiés à l'aide de rayons gamma. Les doses employécs variaient de 1,500 à 9,000 rad. L'éclosion des oeufs n'est pas ou est fortement influencée suivant que l'irradiation a lieu après ou avant le quatrième jour. Par contre le développement post-embryonnaire se différencie plus fortement en fonction des doses appliquées. On observe un certain retard dans l'évolution des descendants et une mortalité post-embryonnaire variant non seulement suivant l'âge des oeufs mais également suivant les doses appliquées. Ces arrière-effets sont donnés au diagramme I.

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Research supported by the Institute for the Encouragement of Scientific Research in Industry and Agriculture (I.W.O.N.L.).     

Genetic variability in esterases and the insecticide resistance in brazilian strains of Oryzaephilus mercator and Oryzaephilus surinamensis (Coleoptera: Silvanidae)

Oryzaephilus mercator and O. surinamensis are stored grains and processed food pests, the latter being responsible for major economical losses. Polyacrylamide gel electrophoresis was used to analyse esterase patterns during insect development. Seven esterases, three cholinesterases, two carboxylesterases and two acetylesterases, were identified in O. mercator, one of which was proper to adults. Five esterases, of which four were cholinesterases, occurred in O. surinamensis. Strains of O. mercator and O. surinamensis were also exposed to malathion and chlorpyrifos-methyl. According to the LC50 estimates, OmLC-M and OmLA strains of O. mercator and OsLB strain of O. surinamensis were the most resistant to both insecticides. However, higher sensitivity to malathion and chlorpyrifos-methyl has also been verified in some of its esterases. Cholinesterases OmEST-1 and OsEST-5 seem to be involved in this resistance. These results suggest that organophosphate tolerance may be related to genetic variability in esterase isoenzymes.     

Cytological lesions in the midgut of Tribolium confusum larvae exposed to gamma radiation

The major cytological lesions in Tribolium confusum after irradiation were displayed by the midgut epithelium. At 24 hr following exposure to 5.3 kR, the regenerative cells called nidi appeared numerous. They gradually disappeared with increases in dosage and time in accordance with Arndt-Schulze's Law. The columnar epithelial cells and their nuclei appeared swollen and vacuolated on the fifth and twelfth day following exposure to 5.3 kR. They appeared disorganized and shed into the lumen of the midgut on the twelfth and fifth day following 50- and 70-kR irradiation, respectively. The basement membrane and the muscularis appeared loose on the fifth and twelfth day following 70-kR irradiation. It was observed that once the catabolic activity, i.e., histolysis, was initiated in the midgut, it continued to accelerate with increasing dose and time. Thus, the late effects at low doses, 5.3 and 10 kR, appeared as immediate effects at high doses, 50 and 70 kR. The differentiated cells, i.e., columnar epithelial cells, appeared radioresistant as compared to undifferentiated cells, i.e., regenerative cells, which appeared radiosensitive in accordance with the principle of Bergonie and Tribondeau.     

Analysis of orientation behaviour of Tribolium castaneum and T. confusum to synthetic aggregation pheromone

Adult male T. castaneum (Herbst) and T. confusum (du Val) secretes an aggregation pheromone that is attractive to both sexes. Orientation behaviour of the two Tribolium species responding to different concentrations of synthetic aggregation pheromone in still and moving air was studied in an 2.5 m×0.4 m olfactometer. Analysis of Tribolium tracks indicated that the aggregation pheromone stimulated the beetles to walk faster at higher concentrations to increase the frequency and magnitude of turning and to decrease track reversal distances and distances between turns. The mean walking speed of both species was lowest at the highest air speed. The behavioural responses of the beetles to the pheromone in still and moving air were similar, indicating chemotaxis as the major orientation mechanism used by both species to locate an odour source. The beetles showed greater orientation efficiency within a discrete pheromone plume than a diffuse plume.     

Quantitative requirements of the saw-toothed grain beetle,Oryzaephilus surinamensis,for dietary l-isoleucine and l-valine

Larvae of the saw-toothed grain beetle, Oryzaephilus surinamensis, were reared individually on meridic diets from hatching to adult emergence at 32±0·25°C and 75±5% r.h. On diets devoid of l-isoleucine or of l-valine, these larvae developed little, if at all, and died before reaching the larval-pupal ecdysial stage. Graded concentrations of l-isoleucine up to 6·0 mg/g or of l-valine up to 5·0 mg/g increased the rate of development and survival of this insect. Concentrations of either amino acid beyond these levels was neither beneficial nor harmful to O. surinamensis, in terms of rate of development or survival.     

Factors affecting the antennal and behavioural responses of the saw-toothed grain beetle Oryzaephilus surinamensis to food odour and aggregation pheromone

ABSTRACT. The effects of insect age, sex, mated state and culture density on the attraction of adult saw-toothed grain beetles, Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae), to sources of food odour and synthetic aggregation pheromone were investigated. In single-insect behavioural assays, insect age affected the attraction to the food odour, but not to the synthetic aggregation pheromone. Conversely, there were sexual differences in the attraction to the aggregation pheromone, but not to the food odour. The effects of the same factors on the antennal response to food odour and synthetic pheromone were also investigated, using the electroantennogram (EAG) technique. Insect age affected the EAG response to food odour, but not to the synthetic pheromone. There were no sexual differences in the EAG responses to either food odour or synthetic pheromone.
The correlation of factors affecting both behavioural and antennal responses, and the possible role of changes in peripheral olfactory receptor sensitivity in the modulation of behaviour are discussed.     

Competition and overlap of Oryzaephilus surinamensis and Plodia interpunctella populations under condition of stored date fruits

Plodia interpunctella and Oryzaephilus surinamensis are found in food storehouses including dates and palm storages. The current study aimed to determine competition and overlap potentials of the two pests of date fruits. Time series models were used to study two species populations and logistic growth model to estimate the effect of density of the species. The results revealed the environmental capacities of O. surinamensis and P. interpunctella were 433 and 1610 (maximum number per 20 g), respectively, and the population growth rates (r) were 1.2 and 1.3, respectively. Ecological balances of the two species were close to each other from the first to the third week. The population of O. surinamensis decreased in the fourth week of the competition. The highest population balance of the two species was in the 14th week. The potential of exploitable ecological niches (e_ij) and the amount of non-exploited ecological niches by any species (z_ij) for O. surinamensis was higher than for P. interpunctella from the 8th week untill the end of sampling period. The overlap of ecological niches in the two species (D) ranged from 0.94 to 1, indicating a complete overlap of temporal activity in the two populations on date palm. The current results of this study can be used by integrated pest management specialists. Information over the effects of species competition on population dynamics and their coexistence can be used to predict population status and to adopt simple pest control methods.     

Biochemical mechanisms of resistance in strains of Oryzaephilus surinamensis (Coleoptera: Silvanidae) resistant to malathion and chlorpyrifos-methyl.

The acetylcholinesterase, carboxylesterase, and cytochrome P450 monooxygenase activities of three strains of Oryzaephilus srinamensis (L.) were examined to better understand biochemical mechanisms of resistance. The three strains were VOS49 and VOSCM, selected for resistance to malathion and chlorpyrifos-methyl, respectively, and VOS48, a standard susceptible strain. Cross-resistance to malathion and chlorpyrifos-methyl was confirmed in VOS49 and VOSCM. Acetylcholinesterase activity was not correlated to resistance among these strains. VOS49 and VOSCM showed elevated levels of carboxylesterase activity based on p-nitrophenylacetate, alpha-naphthyl acetate, or beta-naphthyl acetate substrates. PAGE zymograms showed major differences in caboxylesterase isozyme banding among strains. VOSCM had one strongly staining isozyme band. A band having the same Rf-value was very faint in VOS48. The VOS49 carboxylesterase banding pattern was different from both VOSCM and VOS48. Cytochrome P450 monooxygenase activity was based on cytochrome P450 content, aldrin epoxidase activity, and oxidation of organophosphate insecticides, all elevated in resistant strains. The monooxygenase activity varied with insecticide substrate and resistant strain, suggesting specific cytochromes P450 may exist for different insecticides. The monooxygenase activity of the VOS49 strain was much higher with malathion than chlorpyrifos-methyl as substrates, whereas VOSCM monooxygenase activity was higher with malathion than chlorpyrifos-methyl as substrates. Results are discussed in the context of resistance mechanisms to organophosphate insecticides in O. surinamensis.     

Effect of five diatomaceous earth formulations against Tribofium castaneum （Coleoptera： Tenebrionidae）, Oryzaephflus surinamensis （Coleoptera： Silvanidae） and Rhyzopertha dominica （Coleoptera： Bostrychidae）

Laboratory bioassays were conducted to determine the effect of food source on the survival of Tribolium castaneum Herbst, Oryzaephilus surinamensis L. and Rhyzopertha dominica F., after exposure to five diatomaceous earth （DE） formulations： Protect-It, Insecto, Perma-GuardTM, Dryacide and SilicoSec. Adults of these species were exposed to DEs at the rate of 0.5 mg/cm^2 for 1 day on filter paper inside plastic Petri dishes. After exposure, the initial mortality was counted and live individuals of the three species were held for a week in glass vials containing 50 mg wheat flour, rice and whole wheat, respectively. In the second experiment, after 1 day exposure to DEs, beetles were transferred to Petri dishes without food and held for a week to determine if the presence of food source would decrease the mortality of beetles. Experiments were carried out at 27℃ and 55% RH in the dark. The initial mortality in both of the experiments reached 100% for the three species exposed to Protect-It and in the case ofR. dominica and O. surinamensis exposed to Dryacide. In contrast, low level of mortality （〈 10%） was observed for T. castaneum exposed to Perma-GuardTM and Insecto. The mortality after the post-treatment period on food was decreased for the three species exposed to Perma-GuardTM and in the case of T. castaneum and R. dominica exposed to Insecto and SilicoSec. Adults of O. surinamensis were the most susceptible followed by R. dominica and 100% adult mortality was obtained, whereas T. castaneum were the least susceptible beetles to DEs. Protect-It and Dryacide were the most efficient DE formulations and can be used effectively in a stored grain integrated pest management program.     

Fine structure, function and distribution of antennal sensilla in the saw-toothed grain beetle, Oryzaephilus surinamensis

ABSTRACT. Antennae of the saw-toothed grain beetle ( Oryzaephilus surinamensis L.) (Coleoptera: Silvanidae) were examined using scanning and transmission electron microscopy to determine the fine structure and distribution of sensilla. Seven morphologically different sensilla types are distinguished. Mechanoreceptor hairs account for over 68% of all sensilla. Mechanoreceptors are also found in conjunction with contact chemo-receptors; this dual function is demonstrated by electrophysiological recordings. Three different types of olfactory chemoreceptor are found, accounting for 26% of all sensilla, plus two sensilla types with possible hygro/thermo-receptor functions. Counts show the numbers of chemo-receptors to be small, though this many simply reflect the small size of these beetles.     

Progeny production by Tribolium castaneum (Coleoptera: Tenebrionidae) and Oryzaephilus surinamensis (Coleoptera: Silvanidae) on maize previously infested by Sitotroga cerealella (Lepidoptera: Gelechiidae)

A laboratory experiment was conducted to quantify the effects of infestation of maize by Sitotroga cerealella (Olivier) on progeny production by two common secondary colonizers of grain, Tribolium castaneum (Herbst) and Oryzaephilus surinamensis (L.). Adults of both secondary pest species were allowed to oviposit for 3 wk on intact kernels of 'DeKalb 689', mechanically split kernels, kernels that had been infested for 3 mo by S. cerealella, and kernels that had been infested for 6 mo. Progeny of both species reached highest numbers on 6-mo infested maize. Prior infestation for 6 mo by S. cerealella makes maize a more suitable medium for reproduction by T. castaneum and O. surinamensis, much more than can be accounted for by mere disruption of kernel integrity resulting from larval feeding. The results highlight the importance of limiting establishment by S. cerealella on maize in storage.