Laboratory evaluation of traps for the detection of beetle pests in bulk grain

Traps have been evaluated against three species of storage beetle in plastic bins containing 150 kg wheat. The bins were used to generate data for a comparison of the trapping effectiveness of the pitfall cone (PC), pitfall beaker and insect probe traps. The data produced reflect those obtained from field studies and illustrate the advantages of this method over less rigorously controlled field trials. The PC trap, a single type developed to replace both of the previously recommended traps, buried to a 5 cm depth in grain, was as effective as the insect probe for detecting Cryptolestes ferrugineus. The buried PC trap was also as effective as the insect probe trap for trapping Oryzaephilus surinamensis below the grain surface, and the PC trap on the surface was as effective as the pitfall beaker trap. The PC trap below the surface was more effective for trapping Sitophilus granarius than the insect probe trap. This pilot-scale method is a cost-effective alternative to field-scale trials and could be used to investigate various factors influencing trap catch.     

Electronic and manual monitoring of Cryptolestes ferrugineus (Coleoptera: Laemophloeidae) in stored wheat

Trapping studies were conducted with field populations of Cryptolestes ferrugineus in small steel bins filled with stored wheat. Traps tested in a comparison experiment included two types of commercially available probe-pitfall trap and the trapping body of the electronic grain probe insect counter (EGPIC) system. Quantities of insects captured were compared among the three traps. Insect captures in PC pitfall traps, whether at the grain surface or 17 cm below the surface, exceeded those found in WB II probe and EGPIC probe bodies. The number of adult C. ferrugineus captured was similar between the EGPIC probe bodies and WB II probe traps. With probes positioned near the grain surface, insect counts generated by the EGPIC system were analyzed for changes in rate of capture after inserting the probe, changes within a single 24-h period, and variation with temperature. EGPIC counts varied from 0.5 counts per hour to 5.9 counts per hour throughout the study. Cryptolestes ferrugineus counts increased with increasing daily mean air temperature and decreased when air temperature decreased. There was a consistent increase in the rate of counts during the early evening hours. Increased activity of C. ferrugineus in the early evening hours may have been due to insect response to higher air temperatures near the grain surface late in the day, although grain temperature near the trap varied little throughout the day. Alternatively, diel periodicity in C. ferrugineus may be due to an independent circadian rhythm as evidenced in other grain insects. Variation in counts among days after the probe was inserted was not consistent.     

History of an insect infestation in durum wheat during transport and storage in an inland terminal elevator in Canada

A bulk of 242 tonnes of infested durum wheat from a primary elevator was sampled when it was loaded into four boxcars in August 1974, when it was unloaded at the inland terminal elevator and when it was turned in the terminal elevator. During a storage period of 1 year, the wheat was cleaned once and turned 4 times. Grain temperature was recorded each time samples were taken. Three methods of collecting 1-kg samples were used; dip sampling during transfer of the grain at both elevators, vacuum probe sampling in the terminal elevator bin and drop sampling from the bottom of the terminal elevator bin. Samples were placed in Berlese-Tullgren funnels for 6 hr to remove insects. Adults and larvae of Cryptolestes ferrugineus (Stephens) and of Tribolium castaneum (Herbst) were found, with larvae of the former species being most prevalent. In insect traps placed in the loaded boxcars, an adult C. ferrugineus was caught in one, T. castaneum adults in three, and adult Lathridius minutus (L.) in all of the boxcars; no insects were found in traps placed in the grain in the terminal elevator bin in September and October. Cleaning the grain during storage was ineffective as a means of disinfestation. The number of insects in the samples decreased as the duration of storage increased and as grain temperature decreased. Only four insects were found after November, three of which were C. ferrugineus larvae (one third and two fourth instar) and one was a Trogoderma larva. The last insect found was a fourth instar larva of C. ferrugineus in February 1975. It had a starved desiccated appearance. Even after 1 year of storage, grain temperature did not exceed the 19°C recorded at the time the grain was placed in the elevator.     

Immigration of insects into bins storing newly harvested wheat on 12 Kansas farms

Adult insects entering 34 bins (36-238 t capacity) storing newly harvested hard red winter wheat on 12 farms in Kansas were sampled from July through December 1998 using ventilation traps. Insects moving through the grain stored in these bins were sampled using probe traps. During the fourth week of storage, probe traps captured Cryptolestes ferrugineus in all bins, Ahasverus advena in 32 bins, Typhaea stercorea in 31 bins, and Rhyzopertha dominica in 13 bins. Means+/-SE of 5.6+/-0.7 C. ferrugineus, 0.5+/-0.2 R. dominica, 3.5+/-0.3 A. advena, and 3.5+/-0.7T. stercorea were caught per day in probe traps. Ventilation traps provided a more direct measure than probe traps of the total numbers of insects entering bins storing newly harvested wheat. Immigration of A. advena and T. stercorea increased more than that of other species during the storage period, exceeding that of C. ferrugineus and R. dominica during some weeks. Rhyzopertha dominica had the lowest immigration rate. Bin size did not influence ventilation trap catch but as many as a third more insects may immigrate into large bins at the eaves compared with small bins because of their larger circumference. The mean numbers of C. ferrugineus, R. dominica, A. advena and T. stercorea captured in ventilation traps at the bin cap were 7.8, 2.7, 15.1 and 18.3 times, respectively, those captured in ventilation traps at the bin eaves. The estimated means+/-SE for total numbers of insects entering a bin each day were 13.6+/-4.2 C. ferrugineus, 6.3+/-4.7 R. dominica, 5.8+/-1.4 A. advena, and 21.9+/-8.2T. stercorea. Estimates of immigration rates can improve the accuracy with which insect densities are predicted using insect population growth models, and allow computer models to be used more effectively in managing insect pests. Insect infestations may be reduced by screening the openings between the bin cap and the roof, or the roof and the side walls.     

Evaluation of different temperature management strategies for suppression of Sitophilus zeamais (Motschulsky) in stored maize

Three years of experimental trials (2001–2003) were conducted in 12.7 t capacity pilot-scale bins to determine the survival, reproduction and suppression ofSitophilus zeamais Motschulsky under three temperature management strategies, no aeration (NA, control), ambient aeration (AA, 23.9 °C), and chilled aeration (CA, 18.3 °C) from May to November in Indiana, USA. One-way ANOVA indicated that the number of progeny for small adult populations of caged insects (0.14–0.28 insects per gram maize) embedded 0.6 m deep in the stored grain mass varied among temperature strategies for some, but not all of the storage periods. Progeny numbers in the CA strategy were significantly lower (P<0.05) than those for the NA and AA strategies for periods with longer hours of grain temperature 15.0 °C. There were no differences in progeny numbers between the NA and AA strategies for most of the storage periods. This may have been due to higher mortality, lower oviposition and fecundity from overcrowding of S. zeamais under the NA strategy caused by factors in the caged insect microclimate (e.g., rapid food depletion, heating, moisture, molding, and high CO₂ levels). Our results suggest that maintaining stored maize at temperatures 15.0 °C for longer periods suppressed S. zeamais progeny more effectively than at 18.3 °C. In addition, leaving the stored grain bulk unaerated early in the spring so it remained cool at 15.0 °C due to winter aeration resulted in early suppression of S. zeamais progeny.     

The mortality of Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) and Sitophilus oryzae (L.) (Coleoptera: Curculionidae) at moderate temperatures

A method using conductive heating is described for quickly obtaining and maintaining moderate temperatures in grain while minimising grain moisture loss. A model is developed to analyse insect mortality at a range of conditions on log-time logit and log-time probit scales. Values of LT 50, LT 99, and LT 99.9 are presented for adult and immature stages of Sitophilus oryzae in wheat from 42 to 48°C at 12% m.c. and for immature stages of Rhyzopertha dominica in wheat from 45 to 53°C at 9, 12 and 14% m.c. Data show that the heat tolerance of all life cycle stages for both species are different, with a degree of progressive change relative to each other as temperature changes. For R. dominica, the thermal tolerance of life cycle stages also changes relatively with changes in grain moisture content. In general, all stages survive longer at a given temperature as grain moisture increases and the effect of moisture on survival increases as temperature decreases. Values for LT 99.9 for the most heat tolerant stage of R. dominica at 9% m.c. range from 78.22 to 2.49 h between 45 and 53°C. At 12% m.c. they range from 96.81 to 3.36 h, and at 14% m.c. from 114 to 4.14 h. In general, at 12% m.c. the heat tolerance of S. oryzae is about 5°C less than R. dominica with LT 99.9 ranging from 37.36 to 3.71 h between 42 and 48°C. At this level of mortality, immature stage three is generally the most heat tolerant stage of R. dominica, whereas it is stage two for S. oryzae. The results are discussed in relation to practical applications of heat disinfestation and in terms of a general model of mortality. The results are also considered in the context of other available information on the heat treatment of both species.     

Efficacy of surface applications with diatomaceous earth to control Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) in stored wheat

Commercial formulations of diatomaceous earth (DE) products labeled for use as grain protectants usually specify on the label the depth for using them as a surface treatment, which is often 30.5 cm. An experiment was conducted at two temperatures (27 and 32 °C) and three exposure intervals (7, 10 and 14 d), at a relative humidity of 57–60% to determine if Rhyzopertha dominica (F.), the lesser grain borer, could penetrate a 30.5-cm layer of wheat treated with the labeled rates of three commercial formulations of DE, and, if so, to measure rates of adult survival and progeny production. When R. dominica adults were introduced to this surface layer of 30.5-cm wheat admixed with DE, they were able to penetrate the DE-treated layer and oviposit in the untreated wheat below. Both adult survival and progeny production were significantly lower in wheat with a surface-layer treatment of Dryacide^® (1000 ppm) as compared to Insecto™ (500 ppm), Protect-It^® (400 ppm) or the untreated control. Temperature and exposure interval had no effect on adult survival or progeny production. The vertical displacement patterns of adults were significantly different among DE treatments, but not for temperature or exposure intervals. More R. dominica traveled a greater distance in the untreated control, followed by Insecto™, Protect-It^®, and then Dryacide^®. Results indicate that R. dominica can penetrate a surface layer of DE-treated wheat and reproduce within and below it, but it is possible that pest suppression is dose dependent, or it may depend on a combination of application rate and specific DE formulation.     

Moisture content gradient and ventilation in stored wheat affect movement and distribution of Oryzaephilus surinamensis and have implications for pest monitoring

This study was carried out primarily to ascertain whether the movement of Oryzaephilus surinamensis and Sitophilus granarius from low to high humidity zones occurs in bins of wheat and whether aeration of the grain (10 m³/h/t) affects this movement. The second aim was to ascertain the best placement of insect detection traps under the different conditions. Insects were introduced into the lower half of the grain in the bins and their movement was monitored using traps placed at various depths in the grain. Sitophilus granarius did not move through the grain into the top layer regardless of the moisture content, temperature or aeration status of the grain. More O. surinamensis were caught in unventilated bins than in ventilated bins. More insects were caught in the ventilated bins containing layers of both dry and wet grain than in the bins containing only dry grain. The spatio-temporal distribution of O. surinamensis varied significantly. The depth at which insects were trapped varied between treatments: in ventilated dry grain, most insects were trapped at the surface; in ventilated wet and dry grain, most insects were trapped at 10 cm and 0.75 m; in unventilated wet and dry grain, the vast majority of the insects were trapped at 0.75 m. Very few insects were trapped at 1.75 m regardless of the treatment. The proportions of the initial population of O. surinamensis which were recaptured in the top layer of grain varied between treatments. Most were recaptured in the unventilated bins containing wet and dry grain followed by ventilated bins containing wet and dry grain. The smallest proportion of the population was recaptured in the ventilated bins containing only dry grain. Immediate practical implications for pest monitoring based on physical control measures in use are discussed.     

Stored Grain Advisor Pro: Decision support system for insect management in commercial grain elevators

A decision support system, Stored Grain Advisor Pro (SGA Pro) was developed to provide insect pest management information for wheat stored at commercial elevators. The program uses a model to predict future risk based on current insect density, grain temperature and moisture. A rule-based system was used to provide advice and recommendations to grain managers. The software was tested in a research program conducted at commercial grain elevators in Kansas and Oklahoma, USA. A vacuum-probe sampler was used to take ten 3-kg grain samples in the top 12 m of each bin that contained wheat. After the insect species and numbers were determined for each sample, the data were entered into SGA Pro. A risk analysis and treatment recommendation report for all bins was presented to the grain managers every 6 weeks. SGA Pro correctly predicted for 71–80% of bins whether the grain was safe or at high risk of dense infestation and grain damage. SGA Pro failed to predict “unsafe” insect densities in only 2 out of 399 Kansas bins (0.5%) and in none of 114 bins in Oklahoma. Grain managers who followed SGA Pro's recommendations tended to fumigate only the bins with high insect densities instead of fumigating all bins at their facility. This resulted in more efficient insect pest management because fumigating bins only when insect densities exceeded economic thresholds and treating only the bins that required fumigation minimized the risk of economic losses from insects, reduced the cost of pest management, and reduced the use of grain fumigant.     

Evaluation of methoprene alone and in combination with diatomaceous earth to control Rhyzopertha dominica (Coleoptera: Bostrichidae) on stored wheat

A series of experiments were conducted in which different formulations of the insect growth regulator methoprene were evaluated for control of Rhyzopertha dominica (F.), the lesser grain borer, a major internal insect pest of stored wheat. In the first test, application rates of 10-ppm R,S-methoprene (a racemic mixture of the R and S isomers of methoprene) and 1 and 5-ppm S-methoprene (S-isomer only) gave 100% suppression of F₁ adult progeny of R. dominica for 24 weeks. In the second test, adult R. dominica were exposed at 27°C and 32°C, 57% and 75% relative humidity (r.h.) on untreated wheat and wheat treated with 1- to 10-ppm S-methoprene dust. Survival after a 3-week exposure decreased with increasing concentration of dust, and ranged from 69% to 99%, but no F₁ adult progeny were produced in treated wheat. In the final test, concentrations of 0, 0.25, 0.50, 0.75, and 1.0 ppm S-methoprene EC were combined with concentrations of 0, 75, 150, 225, and 300 ppm of the commercial diatomaceous earth (DE) Protect-It^®. Within each methoprene concentration, survival generally decreased with increasing concentration of DE, and was generally greater at 75% than at 57% r.h. Only the wheat treated with 0-ppm methoprene contained an appreciable number of F₁ adults. In summary, both the dust and EC formulations of S-methoprene gave 100% suppression of F₁ adult progeny R. dominica at application rates of 1 ppm, and combination treatments involving reduced rates of methoprene and DE gave effective control of R. dominica.     

Trap catches of stored-product insects before and after heat treatment in a pilot feed mill

The pilot feed mill at Kansas State University was heated to temperatures of 50°C for 28–35 h during August 4–6, 1999 using natural gas heaters to kill stored-product insects. A three-parameter nonlinear regression model satisfactorily described temperature profiles on each of the four mill floors and was useful in showing differences among floors in the number of hours taken to reach 50°C and hours above 50°C. Pitfall traps with food and pheromone lures and sticky traps with pheromone lures were used to sample adults of beetles and moths, respectively, between July 8 and December 1, 1999 to evaluate heat treatment effectiveness. A total of 32 insect species representing 26 families in seven orders were captured in traps. Immediately after heat treatment, there was 95% reduction in total beetle captures in pitfall traps and 99% reduction in moth captures in sticky traps. Trap captures of the almond moth, Cadra cautella (Walker) and cigarette beetle, Lasioderma serricorne (L.) were significantly reduced and remained low after heat treatment. However, trap captures of the flat grain beetle, Cryptolestes pusillus (Schöenherr), Indianmeal moth, Plodia interpunctella (Hübner), and red flour beetle, Tribolium castaneum (Herbst) increased gradually after heat treatment, especially on the 1st and 4th floors. Our results indicated that traps are valuable tools for gauging the degree and duration of insect suppression obtained by heat treatment. In addition to trapping, visual inspection of the mill areas and absolute sampling of ingredients, products and spillage should be undertaken, so that areas of incipient insect reinfestation can be identified and potential problems rectified or averted.     

Using five sampling methods to measure insect distribution and abundance in bins storing wheat

Newly-harvested wheat stored in each of two bins on each of two farms in Kansas during each of 3 years was sampled every 3-4 days at two locations (in the center and midway between the center and bin wall) within each bin. The variation in insect numbers between bins, locations within a bin, farms and years differed with insect species and sampling method. Five sampling methods were used to monitor insect populations in three regions of each bin: (1) in the head space above the grain; (2) on the grain surface; and (3) within the top 50 cm of the grain mass. Cryptolestes ferrugineus (Stephens) and Ahasverus advena (Waltl) were more evenly distributed among these three regions of a bin than the other species. Typhaea stercorea (L.) were found mainly in the head space and on the grain surface. These distribution patterns were consistent throughout the 126-day storage period. R. dominica (F.) were found in the head space and within the grain mass early in the storage period, and mainly in the grain mass as grain cooled in the autumn. The majority of Plodia interpunctella (Hübner) (91%) were caught in sticky traps in the head space. Two of the three less abundant species, Sitophilus oryzae (L.) and Tribolium castaneum (Herbst), tended to be found most often on the grain surface and the other, Oryzaephilus surinamensis (L.), within the grain mass. The sampling method often influenced the results. Emergence traps captured greater numbers of A. advena than other species. More R. dominica were found in grain samples than in traps in the autumn. Pushing probe traps below the surface of the grain reduced the numbers of T. stercorea, A. advena, S. oryzae and T. castaneum captured. Differences between species and times during the storage period in the effectiveness of different sampling methods need to be considered in making pest management decisions.     

Efficacy of diatomaceous earth and methoprene, alone and in combination, against Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) in rough rice

Combination treatments of diatomaceous earth (DE) (Protect-It^®) and the insect growth regulator (IGR) methoprene (Diacon^® II) were evaluated against Rhyzopertha dominica (F.), the lesser grain borer, on stored rough rice. Application rates of DE and methoprene ranged from 0 to 500 ppm and 0 to 1 ppm, respectively, in 25 treatment combinations. Tests were conducted by exposing 20 adults for 2 weeks at 32 °C and 75% relative humidity on single varieties of long-, short-, and medium-grain rough rice, removing adults, and holding the rice for 8 weeks at the same conditions to collect F₁ progeny. In the absence of methoprene, mortality of exposed adults increased as the concentration of DE increased, but even at the highest rate of 500 ppm, mortality was only 57.5±12% and 58.8±9.7% in long and medium-grain rice, respectively, and 26.3±4.7% in short-grain rice. Mortality of R. dominica exposed on short-grain rice was lower than mortality on long-and medium-grain rice at several combinations with 375 and 500 ppm DE. There was also an unexpected increase in adult mortality with the addition of methoprene so that at 1 ppm methoprene and 500 ppm DE, mortality in long-, medium-, and short-grain rice was 77.5±9.0%, 77.5±10.0%, and 58.5±3.0%, respectively. In the absence of methoprene, progeny produced on long- and short-grain rice ranged from 48.0±21.2 to 87.2±9.0, compared to 16.5±5.5 to 33.5±8.6 progeny produced on medium-grain rice. With the inclusion of methoprene there were few progeny produced in any of the treatment combinations, and the overall average was 0.6±0.3. Similarly, with no methoprene the range of insect-damaged kernels (IDK) was 5.2±2.7 to 12.2±3.1%, but with methoprene the overall average was reduced to 1.8±0.2%. While control of R. dominica was somewhat limited with DE, the differences among rice varieties seems to indicate that the specific type and possibly variety of rough rice may influence mortality and reproduction of R. dominica exposed to DE. With methoprene, progeny production was greatly suppressed regardless of DE concentration, but combining DE with methoprene would give some measure of adult control.     

Insect pests associated with rural maize stores in Mexico with particular reference to Prostephanus truncatus (Coleoptera: bostrichidae)

A survey was carried out into the occurrence of insect pests infesting rural stores in five regions of Mexico. Stores were sampled using pheromone-baited crevice traps, bait-bags and maize samples every 28 d for an entire storage season. Maize and store temperatures, and grain moisture content were measured. The most numerous primary pests were Sitophilus zeamais Motsch., Sitotroga cerealella (Olivier) and Prostephanus truncatus (Horn). P. truncatus was more abundant in stores in the drier, temperature regions of Guanajuato, La Laguna and Jalisco than in the more tropical regions, Veracruz or Chiapas. In La Laguna (and to some extent in Jalisco), many more P. truncatus were detected in the store using the crevice trap than were counted in the maize samples, perhaps because crevice traps may attract beetles from outside the store. La Laguna and Chiapas had significantly fewer larvae of P. truncatus in the samples than other regions, probably a result of the lower grain moisture content. Grain damage levels were very low in La Laguna and they occurred later in Guanajuato than elsewhere. The three pest species causing most damage were S. zeamais, S. cerealella and P. truncatus. It is suggested that P. truncatus was important in causing damage primarily in Guanajuato, whereas S. zeamais and S. cerealella caused more damage elsewhere, particularly in more humid areas.     

Modelling biological efficacy decrease and rate of degradation of chlorpyrifos-methyl on wheat stored under controlled conditions

Insecticide residue degradation and pest survival were observed in wheat treated with a low dose of chlorpyrifos-methyl. Treated wheat was stored in small batches at three controlled temperatures and two levels of moisture content of grain, in equilibrium with r.h. in order to stabilise the water activity in the grain during a storage period of 126 d after insecticide application. Every 3 weeks, samples were taken from treated and untreated control grain in each storage condition. Chlorpyrifos-methyl residues declined regularly with time of storage and an exponential negative regression was fitted with high correlation coefficients in most situations of storage temperature and grain water activity (Aw). A multivariate model to show the respective influence of controlled variables involved in the model of residues breakdown (time, Aw, and temperature) was built up through a multiple regression. This model showed the respective importance of the water activity of grain kernels, temperature and formulation of chlorpyrifos-methyl and their combinations on the decline of residues. Simultaneously, the effectiveness of the residues was checked through bioassays with two target species: Sitophilus oryzae and Tribolium castaneum. Taking into account the intentionally low initial applied dose of chlorpyrifos-methyl, the period after application achieving complete kill of the two test insects was rather short and did not exceed 105 d for S. oryzae in the best conditions for control, i.e. low moisture content and temperature. For high Aw (0.8) and storage temperature 30°C, T. castaneum was effectively controlled (more than 95% kill) only on the day after the treatment, survival occurring at the next test date 21 d after the application. High moisture content and temperature and their interactions were the main variables influencing the decrease in the biological effectiveness with time. The concentration threshold for insect survival was slightly below 1 ppm chlorpyrifos-methyl and was influenced by storage and grain conditions. Implications of these findings on storage pest management practices and on the ability to predict the period of biological effectiveness of residues of chlorpyrifos-methyl are discussed.     

Integrated pest management in stored grain: Combining surface insecticide treatments with aeration

Three aerated, commercial stores of 5000–10,000 t of wheat in England were discovered to have surface infestations of Sitophilus granarius in mid-winter when the grain temperature was 4–9°C. The infestations were monitored using pitfall and probe traps and catches dropped to zero after the application of etrimfos or pirimiphos-methyl 2% dust into the top 0.3 m at 50g/m². The effects of surface treatments in cooled bins were also examined in a farm scale experiment. Six, 20 t bins of wheat, were each aerated at 10 m³/h/t with an 0.02 kW fan and infested with 1/kg each of S. granarius and Oryzaephilus surinamensis and 0.5/kg of Cryptolestes ferrugineus as well as the mites Glycyphagus destructor and Acarus siro. The surface of three bins were treated with 45 g/m² of 2% pirimiphos-methyl dust. Insect numbers, as determined by pitfall traps and probe traps at the surface, 1 and 2 m, fell in all bins during the winter as temperatures fell to 5°C. As the bins warmed up in the spring, numbers of O. surinamenis rose again in the untreated bins. In the second year, S. granarius reached peak numbers in the untreated bins in mid-winter. The much lower numbers of insects trapped in the treated bins were a result of the surface treatment and the few found may have been attributable to migration from the untreated bins. A. siro and G. destructor, together exceeded 1500/kg at the surface of untreated bins, but were less than 10/kg in treated bins. In the second year, few of either species were found and the predatory mite, Cheyletus eruditus, reached 200/kg in all bins, before declining. The experiment showed some of the shortcomings of an integrated pest management system for stored grain, based on cooling, storage at 15% m.c. and monitoring of pest numbers. These were surface populations of mites in the first winter, spring surface re-occurrence of O. surinamensis and surface populations of S. granurius in the second winter. These were overcome by adding surface admixture to the other elements of the IPM system. The IPM programme cost less than half of the cost of admixing the bulk with the cheapest insecticide and used 10% of the insecticide.     

Susceptibility of stored-product beetles on wheat and maize treated with thiamethoxam: effects of concentration, exposure interval, and temperature

Sitophilus zeamais Motschulsky, the maize weevil, Oryzaephilus surinamensis (L.), the saw-toothed grain beetle, and Tribolium castaneum (Herbst), the red flour beetle, were exposed for 1, 2, 3, and 6 d at 22°C, 27°C, and 32°C on maize treated with 0, 0.5, 1.0, 2.0, or 4.0 ppm thiamethoxam, a new-generation neonicotenoid insecticide. A second series of tests was conducted on hard winter wheat using S. oryzae (L.), the rice weevil, Rhyzopertha dominica (F.), the lesser grain borer, and T. castaneum. Mortality of all species on both commodities generally increased with insecticide concentration, exposure interval, and temperature, and data were described by linear and non-linear regressions with concentration as the independent variable. Mortality of S. zeamais ranged from 58% to 90% on maize treated with 0.5 ppm thiamethoxam, and approached 95–100% as concentration increased to 4 ppm. Oryzaephilus surinamensis appeared to be slightly less susceptible than S. zeamais; mortality ranged from about 18% to 80% at 5 ppm and there was a more gradual increase in mortality as concentration increased. Mortality of T. castaneum generally did not exceed 40% at any concentration unless the beetles were exposed for 6 d. Mortality of R. dominica and S. oryzae was less than 60% when exposed on treated wheat for 1 and 2 d, but increased to nearly 100% when exposed for 6 d at 27°C and 32°C. Mortality of T. castaneum did not exceed 20% at the 1- and 2-d exposures, and approached 100% only when beetles were exposed for 6 d at 32°C. Few F₁ adults of any species were found in treated maize or in treated wheat but the number of F₁ T. castaneum in untreated maize and untreated wheat was very low compared with the other species. Results show that thiamethoxam would be an effective protectant of stored maize seed and stored wheat seed.     

Detection of internal wheat seed infestation by Rhyzopertha dominica using X-ray imaging

Standardization for grain grades has been established in most countries to maintain the quality of a crop until it reaches consumers. Different methods have been investigated for their potential to detect insect infestations in grain destined for domestic and export markets. The potential of detecting infestations caused by Rhyzopertha dominica in wheat kernels using a real-time soft X-ray method was determined in this study. Artificially infested wheat kernels were incubated at 30°C and 70% relative humidity and X-rayed sequentially for larval, pupal, and adult stages of R. dominica. Algorithms were used to extract histogram features, textural features, and histogram and shape moments from the X-ray images of wheat kernels. A backpropagation neural network (BPNN) and statistical classifiers were used to identify uninfested and infested kernels using the 57 extracted features. The BPNN correctly identified all uninfested and infested kernels and more than 99% of kernels infested by R. dominica larvae. The classification accuracies determined by the BPNN were higher using all 57 features than when using the histogram and textural features separately. The BPNN performed better than the parametric and non-parametric classifiers in the identification of uninfested and infested kernels by different stages of R. dominica.     

Unbaited probe traps and grain trier: a comparison of the two methods for sampling Coleoptera in stored barley

Inside a Central Greece storeroom containing 80 metric tons of barley, 10 unbaited probe traps were placed at a depth of 80 cm from January 1997 to January 1998. The traps were inspected every 20 days. Additionally, during the same period, samples were taken every 20 days using a non-partitioned grain trier. More adults were found in the traps than in the grain trier, especially during the warm months. Twenty-one species were found. Cryptolestes ferrugineus, Alphitobius diaperinus, Oryzaephilus surinamensis, Ahasverus advena, Tribolium castaneum and Rhyzopertha dominica were the most abundant species in the traps, whereas Sitophius oryzae and Oryzaephilus surinamensis were the most abundant in the grain trier samples. Probe traps were more sensitive in detection of adults, with the exception of S. oryzae and S. granarius. Iwao’s regression analysis indicated repulsion among individuals in both techniques. Furthermore, all species (except for C. ferrugineus in grain trier samples) showed an aggregated distribution among sampling units. For Iwao’s model, the greatest r² values were those for the species C. ferrugineus and A. diaperinus in the traps, while the values for the same species in the grain trier samples were the lowest.     

Influence of temperature on the functional response of Anisopteromalus calandrae (Hymenoptera: Pteromalidae), a parasitoid of Rhyzopertha dominica (Coleoptera: Bostrichidae)

The functional response of Anisopteromalus calandrae (Howard) parasitizing 4th-instar Rhyzopertha dominica (F.) on wheat was estimated over a range of temperatures and host densities. A functional response equation was used in which a quadratic component that included temperature was substituted for handling time. The instantaneous search rate increased with increasing temperatures. The maximum rate of parasitization was 13 larvae/24 h at 30°C and 35°C. Handling time was lowest at 30°C and highest at 20°C. The ability of A. calandrae to find and parasitize R. dominica over a broad range of temperatures makes it a good candidate for natural control of stored grain pests.