Wheat disinfestation using microwave energy

A pilot-scale industrial microwave system operating at 2.45 GHz was used to determine the mortality of three common species of stored-grain insects, namely Tribolium castaneum, Cryptolestes ferrugineus, and Sitophilus granarius. Wheat samples (50 g each) at 14%, 16%, and 18% moisture content (wet basis) were infested with 5, 10, or 15 insects. The infested samples were then exposed to microwave energy at four different power levels 250, 300, 400, and 500 W for two exposure times of 28 and 56 s. Complete kill of adults of all three species and of post-embryonic stages of T. castaneum was achieved at 500 W with an exposure time of 28 s. There was a significant difference in the mortality of T. castaneum and C. ferrugineus adults at 14% and 16% moisture content (m.c.) wheat but there was no significant difference in the mortality at 16% and 18% m.c. Mortality of insects increased with either power or exposure time or both. Germination of wheat kernels was lower after treatment with microwave energy. Milling and baking tests were done for the samples at which 100% mortality was obtained. There was no significant difference in the quality of grain protein, flour protein, flour yield, flour ash, and loaf volume of wheat treated with microwave energy.     

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.     

Repellent effect of pea (Pisum sativum) fractions against stored-product insects

Peas (Pisum sativum) are toxic to some stored-product insects. The repellent effect of fractions of pea seed to stored-product insects was evaluated in multiple-choice tests in which wheat kernels were dusted with fractions rich in either protein, fibre or starch at 0.001 to 10% (wt:wt). There was a negative correlation between pea protein concentration and the number of adults found in grain for Cryptolestes ferrugineus and Sitophilus oryzae, but not for Tribolium castaneum. Pea fibre repelled C. ferrugineus adults but not S. oryzae and T. castaneum. Pea starch did not repel any of the insects. One-week old and 6-week old C. ferrugineus were equally repelled by pea protein. Repellency was detectable 1 h after exposure. Cryptolestes ferrugineus and S. oryzae did not become habituated to the repellent action of pea protein even after 4 weeks of exposure. Habituation was observed, however, when C. ferrugineus was exposed to pea fibre for 4 weeks. In a two-choice bioassay (0 vs. 0.1% and 0 vs. 1% pea protein), the pea-protein-treated grain had significantly fewer insects (C. ferrugineus, S. oryzae, Sitophilus zeamais, T. castaneum, and Tribolium confusum) than untreated grain. The properties of the pea protein fractions seem well suited for developing a natural stored grain protectant.     

Evaluation of two new diatomaceous earth formulations, enhanced with abamectin and bitterbarkomycin, against four stored-grain beetle species

Two new natural diatomaceous earth (DE) formulations, enhanced with abamectin (DEA-P/WP), or bitterbarkomycin (DEBBM-P/WP), were tested under laboratory conditions against adults of the rice weevil, Sitophilus oryzae, the lesser grain borer, Rhyzopertha dominica, the red flour beetle, Tribolium castaneum and the rusty grain beetle, Cryptolestes ferrugineus. The bioassays were carried out on wheat, at 30±1 °C and 70±5% r.h. The two enhanced DEs were applied either as dusts (P) or as wettable powders (WP) at the dose rates of 75, 100 125 and 150 ppm. Adult mortality was assessed after 14 and 21 d of exposure on the treated substrate. After this interval, the treated wheat was retained for an additional period of 49 d in the case of S. oryzae and 63 d in the case of the other three species, in order to evaluate progeny production. Generally, for all species tested, mortality was higher on wheat treated with powders in comparison with wettable solutions. After 14 d of exposure, all adult rice weevils were dead even at the lowest dose rate of DEA-P, while 100% mortality was noted at doses 125 ppm of DEBBM-P. For the other species, mortality was 100% on wheat treated with 75 ppm of DEBBM-P, with the exception of T. castaneum for which all adults were dead at doses 100 ppm. Progeny production was low, and no progeny were produced in the cases of R. dominica and C. ferrugineus, for both DEs. However, for S. oryzae, progeny production was high on wheat treated with WP formulations, at dose rates 100 ppm. Similar trends were noted for T. castaneum, at 100 ppm of DEBBM-WP. The results of the present study indicate that both DEA-P/WP and DEBBM-P/WP are more effective against the four beetle species examined in comparison with the currently commercially available DE formulations.     

Detection of internally infested popcorn using electrically conductive roller mills

To detect popcorn kernels infested by the internal feeding stored-product insect pest Sitophilus zeamais, maize weevil, a laboratory roller mill was modified so that the electrical conductivity of the grain is measured while the kernels are milled between the rolls. When a kernel with a S. zeamais larvae inside is milled, the moisture from the crushed insect abruptly changes the conductivity of the test circuit. The objective of this study was to determine the potential of the modified conductance mill to detect popcorn infested with different developmental stages. Two laboratory milling units were tested that had differing sharpness, which affected the feed-rate through the rolls. One mill averaged 135 s to feed 1 kg of popcorn while the second mill with sharper teeth averaged 100 s to feed 1 kg of popcorn. Four popcorn varieties were evaluated, with their average kernel weight ranging from 12.5 g to 18.5 g per 100 kernels. Known numbers of infested popcorn kernels were added to 1 kg samples of popcorn. The slower feeding mill detected 81% of the pupae, 91% of the medium larvae, and 47% of the small larvae. The faster feeding mill detected 75% of the pupae, 80% of the medium larvae, and 43% of the small larvae. Our results indicate that the conductance mill is a good method for quickly evaluating popcorn samples for kernels infested with late stage larvae and pupae.     

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.     

Two-dimensional diffusion of Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae) populations in stored wheat under constant environmental conditions

Insect movement inside a stored-grain bulk increases the chance for the pests to find biologically suitable locations for their development and multiplication. The movement of rusty grain beetle, Cryptolestes ferrugineus, adults was determined in a 0.1×1×1 m wooden box filled with wheat. There were 12 combinations of temperature (20, 25, 30, or 35 °C), number of adults (125, 250, or 500), moisture content (12.5, 14.5, or 16.5%), and time periods (3, 6, 12, 24 or 72 h) over which movement could occur. The diffusivities in each set of environmental conditions were calculated using a developed procedure (program) and experimental data. The diffusivity at 14.5% m.c. and 20 °C in the 24 h movement period was 2.5±0.3×10⁻⁴ m²/h. The diffusivity increased with increasing temperature, decreasing moisture contents, decreasing movement periods, and increasing insect numbers. Adult numbers in each section of the wooden box were predicted using an analytical model and calculated diffusivities. There were no significant differences between measured and predicted adult numbers. This research suggests that distribution and dispersal of the C. ferrugineus adults in stored wheat follow a diffusion pattern under constant environmental conditions.     

A novel use of modified atmospheres: Storage insect population control

The research described here aimed to establish the feasibility of using modified atmospheres (MA) to protect commodities throughout their storage life by using oxygen (O₂) levels that disrupt the life cycles of the target beetle species. Rather than achieving complete mortality of all stages, the aim was to identify more easily obtainable MAs that would kill the most susceptible stage and prevent population growth. Simulated burner gas and nitrogen (N₂) atmospheres with O₂ contents between 3% and 6%, were tested, along with a N₂-based MA with elevated carbon dioxide (CO₂) (10–20%).

Laboratory tests were carried out on five species of stored-product beetles, Cryptolestes ferrugineus, Oryzaephilus surinamensis, Sitophilus granarius, S. oryzae and Tribolium castaneum. After exposure to the MAs for 28 d an assessment was made of the mortality of adults, the number of adults from progeny produced under the MAs and, for the simulated burner gas, the number of adults from progeny produced in a 28-d period after exposure to the MA. The tests were carried out at 20 and 25 °C with 75% and 85% r.h. at each temperature.

The O₂ content preventing population growth varied with species and temperature. For simulated burner gas or N₂ it was about 4% for O. surinamensis, S. granarius and S. oryzae, and about 3% for C. ferrugineus and T. castaneum at 25 °C. At 20 °C it was about 3% for all species tested. When CO₂ was increased to 10% or 20%, reducing O₂ to 5% was sufficient to eliminate emergence of S. granarius at 20°C, but a few individuals emerged at 25 °C. For C. ferrugineus there was a 95% reduction with 5% O₂ plus 20% CO₂ at 20 °C, but not at 25 °C.     

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.     

Mass loss determination of wheat kernels infested by granary weevil from X-ray images

Mass losses in wheat kernels infested by the granary weevil were determined using soft X-ray imaging. The mass loss strongly depended on the life stage of the pest insect. Hence, determination of the correlation between developmental stage and mass loss may help to decide management strategies and can also be used to determine time and place of infestation. The mass losses were calculated from X-ray images, taken from 20 to 66 days after infestation, using the grey scale. To compare calculated mass loss (CML) with the actual mass loss, wheat kernels were weighed. Interdependence of the mean values of the CML and weighed mass (WM) on infestation time was determined and fitted by linear and polynomial curves. During these studies kernels from the infested sample were assigned to six categories based on the CML and morphological features obtained from the X-ray images. The categories were as follows: sound, small larva, medium larva, large larva, pupae and emerged. Comparison of kernels assigned to categories based on mass with kernels classified by area of grey scale revealed that mass was more reliable in assigning grain to particular classes. The mass index decreased the number of wrongly classified kernels. The polynomial curve for mass loss can be used to give an indication of the time and place of infestation.     

Predicting insect density from probe trap catch in farm-stored wheat

Insect populations infesting wheat stored in four bins on two Kansas farms were monitored from early July 1996 through to the middle of January 1997. Estimates of adult insect density based upon the numbers of adult insects caught using probe traps differed from those based upon the number of insects found in grain samples. These differences were a result of differences in numbers of insects found and percentages of traps or grain samples with insects. Traps detected insects 15 to 37 d earlier than grain samples. The depth of traps below the grain surface tended to influence both the total number and species composition of the insects that were caught. Traps inserted with the top just below the grain surface collected an average of 1.9 times more Cryptolestes ferrugineus (Stephens), 1.2 times more Rhyzopertha dominica (F.), 4.1 times more Ahasverus advena (Waltl) and 77.4 times more Typhaea stercorea (L.) than traps inserted with the top 7.6 cm below the grain surface. However, trap depth did not have a significant effect on the number of R. dominica caught and on only 12 to 21% of sampling dates did trap depth have a significant effect on the number of insects of other species that were caught. Grain temperatures in three of the bins averaged 30°C during the first 70 d of storage and then decreased by 0.2°C/d. Grain in the other bin was initially more than 10°C warmer and grain temperature decreased by 0.2°C/d over the full storage period. The numbers of insects captured in traps decreased as grain temperature decreased even though grain samples indicated that insect populations were still growing. Thus, trap catches did not estimate insect population density consistently throughout the storage period. A method was developed in the current paper to adjust for the effect of seasonal changes in temperature on trap catch.     

The influence of relative humidity and thermal acclimation on the survival of adult grain beetles in cooled grain

The influence of humidity and thermal acclimation on the survival of Cryptolestes ferrugineus, Oryzaephilus surinamensis, Rhyzopertha dominica, Sitophilus granarius, S. oryzae and Tribolium castaneum in cooled wheat or flour at 45 and 70% relative humidity was studied in the laboratory. Young adults were held continuously at 30 or 32°C; cooled gradually to 13.5°C and held at that temperature; cooled gradually to 9°C and held at that temperature; or transferred directly to 9°C.

Survival at low temperatures differed, often considerably, between species, being generally shortest in T. castaneum (0.7–16 weeks) and longest in S. granarius (5–40 weeks). There was considerable interaction between the effects of temperature and humidity, with survival being, to varying degrees, shorter in 45% r.h. than in 70% r.h. At 45% r.h., an equilibrium relative humidity common in Australian storages, all species survived when the grain was cooled to 13.5°C but only S. granarius survived 26 weeks in grain cooled to 9°C.

Chill-coma temperature and acclimation temperature were linearly related in all species at each humidity. Neither the slopes nor intercepts of the relationships were influenced by humidity. There was generally an inverse relationship between survival and chill-coma temperature.

At 45% r.h., the increase in survival at 9°C attributable to acclimation ranged from 2-fold in S. oryzae (0.9 weeks) to 3.5-fold in C. ferrugineus (3.8 weeks). Corresponding values for beetles at 70% r.h. ranged from 2.3-fold in R. dominica (2.4 weeks) to 7.9-fold in C. ferrugineus (6.9 weeks).     

Mortality of Sitophilus oryzae (L.) and S. granarius (L.) in atmospheres produced by an exothermic inert atmosphere generator

The exposure to atmospheres with low O₂ required to kill 50 and 95% of the developing Sitophilus oryzae (L.) and S. granarius (L.) indicated that the earlier and later stages were more susceptible and the middle stages were less susceptible. At 27°C, the duration of exposure required to produce 95% mortality during the 4th instar through early pupal development was about 10 days for S. oryzae and 6 days for S. granarius. The toxicity of the atmosphere produced by an exothermic inert atmosphere generator to each stage of S. oryzae was higher at 27°C than at 21°C. Larvae and pupae of S. granarius were more susceptible to the atmosphere than corresponding stages of S. oryzae. The type of grain in which the S. oryzae were developing did not significantly alter the mortality due to the generated atmosphere.     

Comparison of seven methods for stored cereal losses to insects for their application in rural conditions

There are several methods for assessing harvest losses during storage with varying degrees of accuracy, reliability and practical application, however, field conditions may limit their use among subsistence farmers and traders in developing nations. We compared seven standard grain loss methods during natural and controlled infestation by Sitophilus oryzae L. in wheat and barley to select the best procedures for use in farm storage. Methods tested were: 1) visual inspection of infested lots, 2) uncorrected weight loss, 3) modified standard volume/weight ratio, 4) grain count and weight, 5) percentage of damaged grains converted to weight loss, 6) one thousand grain mass, and 7) one thousand grain mass including dust. Previously disinfested cereal lots (wheat, barley, 500 g fresh w) were exposed to 20 newly emerged adult S. oryzae for 90 d at 28 °C and 70% r.h. Naturally- infested wheat lots were also monitored under the same conditions. Before and after this period, fresh and dry weight, number, moisture content of uninfested and damaged grains, weight of 1 L of seeds and dust produced by insect activity, fresh and dry weight of 1000 kernels, and number of adult weevils was determined and applied to appropriate equations of methods (1), (2), (3), (4), (5), (6) and (7). Grain mass loss estimations varied by wide margins (9.3 ± 1.3% to 25.8 ± 2.3% in barley, 2.2 ± 0.7% to 12.5 ± 2.5% in wheat) depending on method employed, suggesting the need for careful selection of the most appropriate procedure under field conditions and farmer/trader interests. While accurate procedures such as method 7 provided dependable results, methods 3 and 5 appear most practical for wheat and barley.     

Effects of insect-infested kernels on bulk flow properties of wheat

Insect damage to kernels during storage affects the processing quality of wheat and as well as bulk wheat properties, which in turn causes hopper flow problems such as funnel flow, ratholing, arching, or flushing. This study focused on kernel damage by Rhyzopertha Dominica F. (lesser grain borer), one of the most commonly found insects in wheat, and resulting changes in physical properties, such as bulk density, tapped density, true density, and angle of repose, and in flow properties, such as basic flowability energy, stability, aeration, compressibility, and permeability. Bulk and tapped densities of sound hard red winter wheat kernels and infested wheat kernels were about 720 kg/m³ and 775 kg/m³, respectively. Compressibility index (CI), Hausner ratio (HR), and angle of repose of infested wheat kernels were higher than for sound hard red winter wheat kernels, indicating decreased flowability. Grain dust and insect-infested kernels could form localized compacted areas within the grain bins, resulting in uneven flow during discharge. Results from this study indicate that the presence of insect-infested kernels could lead to arching and bridge formation in grain bins, thus affecting the flow characteristics of bulk wheat.     

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.     

Hermetic storage of pearl millet, Pennisetum americanum (L.) Leeke; laboratory studies

The effect of airtight storage of pearl millet, Pennisetum americanum (L.) Leeke, on intergranular atmosphere, insects, mold infection, grain viability and moisture content (m.c.) was investigated in the laboratory. Six hermetically sealed 19-1 cans were used to store millet of three moisture contents (9.9, 12.8 and 15.6%) for 76 days at 27 ± 1°C. One can of grain of each m.c. was infested with 150 adult Sitophilus oryzae L./kg; the others remained uninfested. Carbon dioxide concentrations increased and oxygen concentrations decreased in all cans infested with insects, and in uninfested grain of 15.6% m.c. The changes in atmospheric concentrations were slower in the uninfested grain than in the infested 15.6% m.c. grain. No live insects were found in any treatment, percentages of mold-infested kernels were not significantly different among treatments, and m.c. did not change due to treatment or time. Kernel viability decreased significantly only in the 15.6% m.c. gram. All grain appeared normal; but the 15.6% m.c. grain had a slightly sour odor.     

Temperature and relative humidity profiles during heat treatment of mills and its efficacy against Tribolium castaneum (Herbst) life stages

Heat treatment involves raising the temperature of a food-processing facility to 50–60°C and maintaining these elevated temperatures for 24–36 h to kill stored-product insects. The pilot feed and flour mills at Kansas State University, Manhattan, KS, were subjected to heat treatment using gas and steam heaters, respectively, during 4–8 August 2001 to characterize temperature and relative humidity profiles and to determine efficacy against developmental stages of the red flour beetle, Tribolium castaneum (Herbst). Temperature and relative humidity profiles in each mill were electronically monitored in 10 different locations. Susceptibility of eggs, young instars, old instars, pupae, and adults of T. castaneum to heat was determined at the same 10 locations within each mill. The number of hours required to reach the target temperature of 50°C, number of hours above 50°C, and maximum temperatures varied between the mills and among mill locations. Relative humidity decreased predictably with an increase in temperature, and was 21% in most locations at 50°C or above. Two separate three-parameter non-linear regression models best described temperature and relative humidity profiles observed in each mill. Despite non-uniform heating at the sample locations, mortality of T. castaneum life stages was 100% in most locations, except in areas where temperatures were <50°C. Old instars and pupae appeared to be relatively heat tolerant when compared with other life stages, especially in the flour mill where lethal temperatures were attained. Possible reasons for the non-uniform heating observed at mill locations and survival of certain T. castaneum developmental stages are discussed.     

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.     

A simple flight chamber to determine flight activity in small insects

A flight chamber has been developed to enable the influence of temperature and other factors on the flight activity of small insects to be determined. The minimum temperatures for flight initiation in the grain beetles Ahasverus advena and Cryptolestes ferrugineus were 17.5 °C and 20 °C, respectively. When four strains of each species were compared, there was little difference between strains in their low temperature flight thresholds but greater differences in flight initiation at the near optimum temperature of 25 °C. No flight was observed in any of four strains of Oryzaephilus surinamensis over the temperature range 25–30 °C. The number of A. advena flying to a grain-filled bait unit suspended inside the top of the flight chamber increased when a pad moistened with water was added to the bait unit.