Effect of Pisum sativum fractions on the mortality and progeny production of nine stored-grain beetles

Yellow field pea (Pisum sativum L.) fractions that were mainly protein (50%), fibre (90%) or starch (85%) were obtained from a commercial pea mill and mixed with wheat kernels or wheat flour. Based on the mortality and the number of offspring produced, protein-rich pea flour was more toxic than fibre, which was more toxic than starch. For the protein-rich pea flour mixed with wheat kernels, the most sensitive insects were Sitophilus oryzae (L.), Sitophilus zeamais Motschulsky and Sitophilus granarius (L.), followed by Cryptolestes ferrugineus (Stephens) which was more sensitive than Tribolium castaneum (Herbst) and Rhyzopertha dominica (F.). For the protein-rich pea flour mixed with wheat flour, Cryptolestes pusillus (Schönherr) was most sensitive, followed by C. turcicus (Grouvelle) and T. confusum (Jacquelin du Val), with T. castaneum being the most resistant. Although protein-rich pea flour did not kill adults to a great extent when mixed with flour, it reduced offspring production significantly. Again C. pusillus was the most sensitive, followed by T. confusum, with T. castaneum offspring being the most resistant. The insecticidal activity of pea fractions decreased after treated wheat kernels were held at 30 °C, 70% r.h. for 8 months. The potential of using pea fractions to control stored-product insects is discussed.     

Insect population dynamics in commercial grain elevators

Data were collected in 1998-2002 from wheat stored in commercial grain elevators in south-central Kansas. Bins at these elevators had concrete walls and were typically 6-9 m in diameter and 30-35 m tall. A vacuum-probe sampler was used to collect grain samples in the top 12 m of the wheat in each bin. The primary insect species found in the wheat samples were: Cryptolestes ferrugineus, Rhyzopertha dominica, and Tribolium castaneum. In the top 3.7 m of grain, R. dominica, C. ferrugineus, T. castaneum and Sitophilus oryzae made up 44, 36, 19 and 1% of the insects found in the samples, respectively. From 3.8 to 12.2 m, R. dominica, C. ferrugineus, T. castaneum and S. oryzae were present at 84, 8, 8, and 1%, respectively. The most prevalent species also changed over time. In June, the start of wheat harvesting and storage in Kansas, insect density was low in the bins. At this time, C. ferrugineus was the most common insect, and it was found mostly in the top grain sample (0-1.2 m). In September through November, C. ferrugineus and R. dominica were at similar densities; however, from February to March, R. dominica was more common.Generally, insect density was greatest at the top and decreased with grain depth. Very few insects were found in samples collected from greater than 12 m (most of the bins contained grain to depths of 24-36 m). Insect density for all species increased rapidly from June through October. During this period less than 20% of the bins had economically significant insect densities (>2 insects/kg). From October until February, the average insect density remained fairly constant but it was greatly reduced in April, May, and June. Bins that had insect densities >2 insects/kg tended to be located adjacent to other heavily infested bins.     

Interspecific associations among stored-grain beetles

Recent increases in prices of raw grain, including wheat, will reduce action thresholds for insect damage and therefore justify more research into management practices and understanding of pest ecology in stored grain. Compared to most other habitats, natural or man-made, a filled grain silo constitutes a unique and fairly homogeneous habitat in which food availability for many grain-feeding insects is unlimited. A fundamental aspect of stored-grain insect ecology is a better understanding of associations among common beetle species. We analyzed the densities of three important stored-grain beetle species, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae), and Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) in wheat samples collected in 1999–2001 from 129 grain silos in Kansas. The beetles studied here are highly mobile, and the number of insects in each grain sample is a result of the beetles' preference for favorable micro-environmental conditions and possibly of intra- and interspecific associations. In general, the number of T. castaneum in a grain sample increased as the number of R. dominica increased, but the number of C. ferrugineus was not correlated with the number of R. dominica. The densities of both T. castaneum and R. dominica decreased as the number of C. ferrugineus increased. Cryptolestes ferrugineus and T. castaneum can be predators and the species composition of insects in a grain sample may be modified by predation. As T. castaneum populations increased, so did R. dominica but not C. ferrugineus. Our analysis of the species composition in grain samples is discussed in an ecological context.     

Heat treatment for disinfestation of empty grain storage bins

An alternative to fumigants and insecticides for controlling stored-product insects in empty grain storage bins prior to filling is heat treatment, in which the temperature is quickly raised to a minimum of 50 °C and held there for 2-4 h. Effectiveness of heat treatment on empty grain storage bins was evaluated for five commercial propane and electric heat-treatment systems by measuring air temperature and associated mortality of Tribolium castaneum (Herbst), the red flour beetle, Sitophilus oryzae (L.), the rice weevil, and Rhyzopertha dominica (F.), the lesser grain borer, exposed for different time intervals. Eleven locations, six above and five below the drying floor, were monitored for air temperature and associated mortality of the three insect species, using arenas initially stocked with live adult insects. Data were analyzed separately for each heating system, with floor location and time interval as main effects for insect mortality. A high-output propane heater (29 kW) produced 100% mortality in 2 h for the three insect species at all test locations. An electric duct-heater system (18 kW) also produced 100% mortality at all test locations after 40 h when aided by a complicated interior heat-distribution system. The other three systems produced less than 100% mortality.     

Feeding bioassay for stored-product insect pests using an encapsulated food source

A procedure that was developed to encapsulate liquid and semiliquid diets was used to encapsulate dry diet for use in a feeding bioassay for beetles that are pests of stored products. Vacuum was used to form Parafilm^® into numerous 6 mm diameter wells. The wells were filled with clean sand (control) or ground dry dog food (test), and the Parafilm^® sealed to produce individual pellets. A single pellet was then placed in the center of a 9 cm diameter Petri dish and feeding activity of groups of ten adults of Sitophilus oryzae (L.), the rice weevil; Oryzaephilus surinamensis (L.), the sawtoothed grain beetle; and Tribolium castaneum (Herbst), the red flour beetle, was tested. The number of insects on the encapsulated pellet and the amount of food or sand scattered were checked hourly for the first 8 h of the study and after 24 h. Few insects were observed on pellets containing sand and little or no sand was observed scattered outside of the pellet, so the presence of dog food in the pellet was needed for insects to feed on the pellet. In tests with encapsulated dog food, the amount of food scattered provided a better quantitative measure of feeding than the number of insects on the pellet. Insects that were starved for 48 h caused greater amounts of food scatter than insects starved for 24 h prior to the test. In direct comparisons among all three species, T. castaneum responded the most slowly and the bioassay may be improved by increasing the amount of time starved. Sitophilus oryzae responded very quickly and the entire pellet was essentially consumed within the first 4-5 h of the study. The encapsulated diets provide a promising method to evaluate feeding behavior of stored-product insect pests.     

The effect of repellents on penetration into packaging by stored-product insects

Two known repellents of stored-product insects, DEET and neem, were compared to protein-enriched pea flour, defatted protein-enriched pea flour, and pea protein extract for their efficacy at reducing penetration and invasion by several common stored-product insects: Sitophilus oryzae (L.), Tribolium castaneum (Herbst), Cryptolestes ferrugineus (Stephens), and Oryzaephilus surinamensis (L.). The methods of preparation of pea extract affected the penetration of S. oryzae. Protein-enriched pea flour, DEET and neem reduced the penetration of S. oryzae, but defatted protein-enriched pea flour and pea protein extract did not. The number of S. oryzae, T. castaneum, C. ferrugineus and O. surinamensis entering pierced paper envelopes that contained wheat and were treated with DEET was reduced by 99%, 86%, 97% and 91%, respectively. Neem was less effective than DEET in reducing penetration and invasion of insects. Protein-enriched pea flour did not prevent insects entering pierced envelopes.     

Factors affecting the behaviour of beetle pests in stored grain, with particular reference to the development of lures

This review summarises the published information on the behaviour of beetles in grain bulks that could lead to the identification of additional factors with the potential for enhancing existing lures or developing new ones. The review concentrates mainly on the adult stage of the five beetle pest species Oryzaephilus surinamensis (L.), Sitophilus granarius (L.), Cryptolestes ferrugineus (Stephens), Typhaea stercorea (L.) and Ahasverus advena (Waltl). After an analysis of the grain store environment and the origins of storage pests, particular attention is paid to behaviour associated with beetle movement and distribution within grain bulks, and their response to food and other multi-species attractants. Potential sources of new semiochemicals are identified; as well as the grains themselves, these include attractive volatiles associated with hot spots in grain, mouldy grain, and alternative insect pest habitats such as mammals’ and birds’ nests. It might also be worth looking for new semiochemicals produced during the mass upward movements of beetles from grain often seen following disturbance, although these could be repellents rather than attractants. Other sources of repellent semiochemicals with potential as grain protectants could be predatory and parasitic species of insects. Consideration is given to behavioural influences that may conflict with the intended response to attractive lures; for example, the presence of damaged grains, moisture and temperature gradients in the grain bulk may act as rival attractants, while many species prefer to hide away from bright light. As population densities rise, inter- and intra-specific competition becomes increasingly important. Human activities associated with grain handling, drying, cooling and pest control, as well as the presence of natural enemies and pathogens, all have the potential to affect insect response to a lure. Opportunities for the development of more effective lures are highlighted.     

Pathogenicity of three species of entomopathogenic nematodes to some major stored-product insect pests

Entomopathogenic nematodes (Nematoda: Heterorhabditidae and Steinernematidae) are commonly used biological control agents of insects in cryptic habitats, but their potential for suppressing stored-product insects in these habitats has not been explored previously. Here, we provide data from the first step in a program to evaluate entomopathogenic nematodes in the genus Steinernema as biological control agents of stored-product pests by determining their pathogenicity to some of the major stored-product pest species. When evaluated against larvae, pupae and adults of six pest species (Plodia interpunctella, Ephestia kuehniella, Oryzaephilus surinamensis, Tenebrio molitor, Tribolium castaneum, and Trogoderma variabile), and the adults of two additional pest species (Sitophilus oryzae and Rhyzopertha dominica), Steinernema riobrave was either the most pathogenic or of similar pathogenicity compared to S. carpocapsae and S. feltiae. A dose of 10 infective juveniles of S. riobrave caused 80% or higher mortality against larvae of P. interpunctella, E. kuehniella, T. castaneum, and O. surinamensis, pupae of T. castaneum and T. molitor, and adults of T. molitor and the two moth species. All stages of Trogoderma variabile exhibited 70% or higher mortality. Adults of S. oryzae and R. dominica exhibited low susceptibility with 15% and 35% mortality, respectively. On the basis of these results, S. riobrave was selected for further evaluation under more field-like conditions.     

Protection of stored maize from insect pests using a two-component biological control method consisting of a hymenopteran parasitoid, Theocolax elegans, and transgenic avidin maize powder

The hymenopteran parasitoid, Theocolax elegans (Westwood), and transgenic avidin maize powder were tested to determine if their individual or combined use would protect stored grain from infestation by both internal and external insect pests. Small-scale tests were conducted in plastic jars containing 3 kg of non-transgenic maize. We tested treatments of 0.3% powdered avidin maize, the parasitoid wasp, and the combination of the parasitoid plus 0.3% powdered avidin maize. One pair each of Sitophilus zeamais Motschulsky, Tribolium castaneum (Herbst), and Cryptolestes ferrugineus (Stephens) was added to each jar. After 8 weeks, the entire contents of each jar were examined for adult insects. Control and avidin maize powders had no detrimental effects on the beneficial insect parasitoid T. elegans. The parasitoid suppressed populations of the internal feeder S. zeamais. The avidin maize powder treatment had no effect on S. zeamais because these larvae developed inside the maize kernels where no avidin maize powder was present. For S. zeamais, the combination treatment was not significantly different from the parasitoid treatment. In contrast, populations of the external feeder T. castaneum were not suppressed by the parasitoid but were suppressed by the avidin maize powder treatment. The parasitoid-avidin combination treatment produced the greatest percentage reduction for all three insect species and resulted in 78%, 94%, and 70% reductions in populations of S. zeamais, T. castaneum, and C. ferrugineus, respectively, when compared to the control treatment. The percentage reductions for the parasitoid treatment were 70%, 8%, and 20% for S. zeamais, T. castaneum, and C. ferrugineus, respectively. For the avidin maize powder treatment, populations of S. zeamais, T. castaneum, and C. ferrugineus were reduced by 10%, 85%, and 40%, respectively. The combination treatment of avidin maize powder plus the release of parasitoid wasps was superior to either treatment alone when applied to mixed populations of internal and external feeders.     

Survival and reproduction of Tribolium castaneum (Herbst), Rhyzopertha dominica (F.) and Sitophilus oryzae (L.) following periods of starvation

This study determined the starvation tolerance of Tribolium castaneum (Herbst), Rhyzopertha dominica (F.) and Sitophilus oryzae (L.) in terms of both adult survival and reproduction, the impact of starvation on reproduction not having been studied before. Experiments were conducted at 30 °C and 55% or 70% r.h. using a laboratory strain and a field strain of each species. The number of progeny was a better indicator of the impact of starvation on a species than adult survival. Tribolium castaneum was the most tolerant species, requiring up to 35 d starvation before no progeny were produced. Rhyzopertha dominica and S. oryzae required up to 8 d starvation before no progeny were produced. The results suggest that hygiene will have a greater impact on populations of S. oryzae and R. dominica than T. castaneum.     

Enhanced fumigant toxicity of allyl acetate to stored-product beetles in the presence of carbon dioxide

Toxicity of allyl acetate (5-25 mg/l doses) to mixed-age cultures of stored-product beetles including Cryptolestes ferrugineus, Lasioderma serricorne, Oryzaephilus surinamensis, Rhyzopertha dominica, Sitophilus oryzae and Tribolium castaneum in the presence of carbon dioxide (CO₂) (10% and 20%) with a 48-h exposure period was studied in the laboratory at 27±2 °C. Depending on dosage and the insect species, the fumigant toxicity of allyl acetate was enhanced by CO₂. At most of the allyl acetate+CO₂ combinations, increased mortality was observed in C. ferrugineus, O. surinamensis and S. oryzae. In L. serricorne and T. castaneum, which are tolerant to allyl acetate, higher mortality due to CO₂ was achieved at selected dose combinations only (e.g. 15 mg/l allyl acetate+20% CO₂). Significant increase in mortality of R. dominica (the most susceptible species to allyl acetate) exposed to allyl acetate in the presence of CO₂ was not evident except at the lower dose of 5 mg/l allyl acetate+CO₂ that caused 31.7% mortality. The mortality data show that CO₂ could be used as an adjuvant for allyl acetate.     

Laboratory assessment of insecticidal effectiveness of natural zeolite and diatomaceous earth formulations against three stored-product beetle pests

The insecticidal effectiveness of two natural zeolite formulations (Minazel plus and Minazel), applied to wheat at selected rates of 0.25, 0.50 and 0.75 g/kg, and a diatomaceous earth formulation (DE) (Protect-It™), applied at the recommended rates of 0.15 g/kg for Sitophilus oryzae, 0.20 g/kg for Rhyzopertha dominica and 0.30 g/kg for Tribolium castaneum, were tested under laboratory conditions (24 ± 1 °C temperature and 45 ± 5% relative humidity). The highest adult mortality was observed after the longest exposure period of 21 days and 7 days of recovery, when all three zeolite dosage rates and the recommended DE dosage caused 97-100% mortality of S. oryzae and 94-100% of T. castaneum. On the other hand, 100% mortality was not achieved in any test variant involving R. dominica; the highest (about 92%) was detected for DE, while 52% and 79% mortality was achieved with the zeolites at the highest rate of 0.75 g/kg. Progeny reduction by >90% was achieved after 21 days of contact of all three beetle pests with DE-treated wheat, while the same level of reduction was achieved for S. oryzae and T. castaenum only after contact with the highest rate of the zeolite product, Minazel. Thus the two zeolite formulations are comparable to diatomaceous earth in controlling adult S. oryzae, R. dominica and T. castaneum, but only the Minazel formulation could effectively protect wheat from attack by S. oryzae or T. castaneum, and only with a higher rate of application than for the DE formulation.     

Simulation model of Rhyzopertha dominica population dynamics in concrete grain bins

Rhyzopertha dominica is one of the most damaging insect pests in grain elevators and causes millions of dollars worth of stored grain losses annually in the USA. A simulation model was developed for predicting R. dominica population dynamics in concrete grain bins. The model used a two-dimensional representation of a cylindrical concrete bin (33 m tall×6.4 m wide), and used hourly weather data to predict changes in grain temperature. Output from the grain bin temperature and moisture module was used by the insect module to predict changes in insect density in 32 different bin regions. When compared to validation data from nine grain bins, the model accurately predicted insect vertical distribution and insect density. In December, the highest insect density was in the top center of the grain mass, and decreased steadily with increasing depth and towards the periphery of the grain mass. R. dominica attains this spatial distribution because immigration is primarily through the top of the bin, and higher populations occur in the interior of the grain mass because of warmer temperatures there. Initially, the model underestimated actual insect density in the grain bins. We increased the immigration rate by 50% and this resulted in a much better prediction of R. dominica density by the model. From 20 September to 14 December, populations of R. dominica increased from 0.1 to 3.5 insects per kg of wheat.     

Effect of suboptimal temperatures and sublethal CO2 levels on multiplication of Tribolium castaneum (Coleoptera: Tenebrionidae), alone or competing with Cryptolestes ferrugineus (Coleoptera: Cucujidae)

Groups of adults of Tribolium castaneum alone, or in combination with adults of Cryptolestes ferrugineus, were exposed to suboptimal temperatures (15°C, 20°C, and 25°C) and sublethal CO₂ levels (2%, 5%, and 10%) in dry (12%, wet mass basis) and damp (15%, wet mass basis) stored wheat in the laboratory, to investigate effects on population size. The mean adult numbers in single- and mixed-species tests were positively correlated with higher temperature and moisture content and negatively correlated with higher CO₂ levels. Adult numbers in single- and mixed-species tests were lower at sublethal CO₂ levels compared to ambient CO₂ levels at all the test temperatures and decreased in dry grain compared to damp grain. Although, a specific trend was not observed in population inhibition between mixed-species and single-species tests, overall the adult populations of T. castaneum were reduced in the presence of C. ferrugineus. A mathematical model was derived to predict the size of adult populations of T. castaneum alone, or in the presence of C. ferrugineus considering all the variables in this study. The model had an R² value of 0.72 but needs to be validated and refined with field data.     

Toxicity of ethyl formate to adult Sitophilus oryzae (L.), Tribolium castaneum (herbst) and Rhyzopertha dominica (F.)

Fumigations were conducted using a continuous flow-through laboratory process to maintain constant concentrations of ethyl formate and low levels (<0.8%) of respiratory carbon dioxide. The procedure minimised the effects of sorption by exposing test insects without media and minimised the effect of carbon dioxide by use of continuous flow. The concentration×time (Ct) products of ethyl formate for adult Sitophilus oryzae, Tribolium castaneum and Rhyzopertha dominica at 25 °C and 70% relative humidity for the 6 h exposure were, respectively: (1) LD₅₀ 107.8, 108.8 and 72.8 mg h L⁻¹ and (2) LD_99.5 207.4, 167.1 and 122.2 mg h L⁻¹. Endpoint mortality was reached within 24 h of initial exposure.     

Effect of “soft-electron” (low-energy electron) treatment on three stored-product insect pests

Developmental stages of three stored-product insect pests viz. Tribolium castaneum (Herbst), Plodia interpunctella (Hübner) and Callosobruchus chinensis (L.) were exposed to “soft electrons”, low-energy electrons. Soft electrons at an acceleration voltage of 170 kV effectively inactivated eggs, larvae and pupae of T. castaneum and P. interpunctella. The adults of T. castaneum and P. interpunctella were inactivated by treatment for 10 min (4.8 kGy) and 15 min (7.2 kGy), respectively. Soft electrons at 170 kV also inactivated the eggs of C. chinensis effectively. The adults of C. chinensis survived a 15 min exposure (7.2 kGy), but were inactivated having lost the ability to walk after a 5 min exposure (2.4 kGy). Soft electrons at 170 kV could not completely inactivate the larvae of C. chinensis inside beans, because the electrons with low penetration did not reach the larvae due to the shield of beans. The movement of T. castaneum larvae exposed to soft electrons was sluggish for several days, and then the larvae died with their hindguts emerged from their posterior ends 17 days after the treatment. DNA comet assay of cells of P. interpunctella larvae indicated that soft electrons at 170 kV damaged DNA in the larvae.     

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.     

Efficacy of diflubenzuron plus methoprene against Sitophilus oryzae and Rhyzopertha dominica in stored sorghum

The efficacy of diflubenzuron (1 mg kg⁻¹)+methoprene (1 mg kg⁻¹) against Sitophilus oryzae (L.) and Rhyzopertha dominica (F.) in sorghum was evaluated in a silo-scale trial in southeast Queensland, Australia. Sorghum is normally protected from a wide range of insects by mixtures of grain protectants. The chitin synthesis inhibitor diflubenzuron was evaluated as a potential new protectant for S. oryzae in combination with the juvenile hormone analogue methoprene, which is already registered for control of R. dominica. Sorghum (ca 200 t) was treated after harvest in 2000 and assessed for treatment efficacy and residue decline during 6.5 months storage. The reproductive capacity of S. oryzae and R. dominica was greatly reduced in bioassays of treated sorghum throughout the trial, and efficacy remained relatively stable during the trial. An initial exposure of S. oryzae adults to treated sorghum for 2 weeks reduced F₁ progeny production of all strains by 80.8-98.8%, but a second exposure of 4 weeks reduced F₁ progeny production by 98.5-100%. In addition, the reproductive capacity of any S. oryzae progeny produced was greatly reduced. Exposure of R. dominica adults to treated sorghum for 2 weeks reduced F₁ progeny production of all strains by 99.6-100%, including a methoprene-resistant strain. The results indicate that S. oryzae or R. dominica adults invading sorghum treated with diflubenzuron (1 mg kg⁻¹)+methoprene (1 mg kg⁻¹) would be incapable of producing sustainable populations.     

Movement of Cryptolestes ferrugineus (Coleoptera: Cucujidae) in grain columns containing pockets of high moisture content wheat and carbon dioxide gradients

The movement of the adult rusty grain beetle, Cryptolestes ferrugineus (Stephens), in 100 cm long, 10 cm diameter columns, filled with wheat of uniform or non-uniform moisture content (m.c.), was determined for horizontal and vertical placement of columns at 30°C.In horizontal columns filled with wheat of 13.5% uniform m.c., adult C. ferrugineus exhibited a trend of distributing themselves uniformly in the columns after 5 d. In the vertical columns filled with 14.7% uniform m.c. wheat, 44% of the insects moved downward after 7 d showing positive geotaxism. In the horizontal or vertical columns containing pockets of high m.c. wheat, 43-48% of the beetles aggregated in the region of high m.c. after 7 d exhibiting a hygrotactic response. Under CO₂ gradients in the columns filled with uniform m.c. wheat, 65% of C. ferrugineus moved towards higher levels of CO₂ after 1 and 5 d. Also, high levels of CO₂ were more influential in attracting C. ferrugineus (60%) after 1 d in horizontal columns containing high m.c. wheat at one end and high CO₂ levels at the other. In the vertical columns filled with pockets of high m.c. wheat and subjected to CO₂ gradients, movement of C. ferrugineus was more influenced by the combined effects of any two factors out of the three, viz., gravity, higher levels of CO₂ and high m.c. than a single factor.     

Grain loss caused by Tribolium castaneum, Sitophilus oryzae and Acanthoscelides obtectus in stored durum wheat and beans treated with Beauveria bassiana

The effect of the fungal entomopathogen Beauveria bassiana (Balsamo) Vuillemin (Hyphomycete) on the losses caused to durum wheat and beans by storage insects was investigated. Grains were infested with Tribolium castaneum (Herbst), Sitophilus oryzae (L.) and Acanthoscelides obtectus (Say). Beauveria bassiana was produced in inoculated autoclaved rice. The spore formulation (ground rice and B. bassiana) was applied to grain (wheat or bean) and shaken to evenly cover the grain. Adults of T. castaneum or S. oryzae were added to wheat and adults of A. obtectus to bean. Five replicates were set up for each treatment and controls (milled rice but no conidia). The insecticidal effect of B. bassiana was tested by measuring the fresh weight and weight loss of grains after four months of storage. Wheat grains infested with S. oryzae without the conidia was significantly more damaged by weevils than grains treated with B. bassiana. The mean fresh weight of grains with the conidia was significantly greater (18.4%) than the corresponding mean without the fungus when S. oryzae were present. Percentage weight loss decreased by 81.5% and was significantly smaller than the loss from the untreated grain. Significant differences were not found in the fresh weight of seed infested with T. castaneum or A. obtectus in treated or untreated grain nor in the percentage weight loss of grains infested with these insects, with and without B. bassiana.