Survival of Sitophilus oryzae (L.) on wheat treated with diatomaceous earth: impact of biological and environmental parameters on product efficacy

A series of experiments was conducted to evaluate the effects of temperature, relative humidity (r.h.), population density, concentration, exposure interval, and residual aging on susceptibility of Sitophilus oryzae (L.), the rice weevil, to diatomaceous earth (DE). In the first experiment, hard red winter wheat was treated with 300 ppm of the Protect-It™ formulation of DE, and 10, 20, or 30 1-2 week-old mixed-sex adult weevils were exposed on 35 g of wheat for 1 week at combinations of 22°C, 27°C, or 32°C; 40%, 57%, or 75% r.h. No weevils survived when exposed at 40% or 57% r.h., but at 75% r.h. survival was related to both population density and temperature. A higher percentage of adults survived when 30 were exposed compared to 10 and 20, and within each density, survival decreased with increasing temperature. No F₁s were produced at any r.h. on wheat held at 22°C. At 27°C and 32°C, the maximum number of F₁s was produced on wheat held at 75% r.h. In the second experiment, wheat was treated with 25%, 50%, 75%, or 100% of the label rate of 300 ppm, and 10 mixed-sex adult S. oryzae were exposed on 35 g of wheat for either 1, 2, or 3 weeks at 27°C, 57% and 75% r.h. Survival decreased with increasing exposure interval and concentration, but within exposure interval and concentration, survival was usually greater at 75% versus 57% r.h. In the final experiment, wheat was treated with 300 ppm, held at 22°C and 27°C, 57% r.h., and bioassayed at monthly intervals for 3 months by exposing 20 adult mixed-sex S. oryzae on 35 g of wheat for 1 or 2 weeks. At each month, survival of S. oryzae was greater when exposed at 22°C compared to 27°C and when exposed for 1 week compared with 2 weeks. Survival gradually increased with each monthly bioassay, except for those conducted at 3 months. Results of these studies show that S. oryzae is susceptible to DE, but survival of exposed insects will depend in part on the temperature and r.h. humidity (or grain moisture content) at which they are exposed. Survival is directly related to temperature, and as r.h. increases either higher concentrations or longer exposure intervals will be necessary to maintain a certain level of mortality. There may also be a loss of efficacy with residual aging.     

Initial and delayed mortality of late-instar larvae, pupae, and adults of Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae) exposed at variable temperatures and time intervals

Late-instar larvae, pupae, and adults of Tribolium castaneum (Herbst), the red flour beetle, or Tribolium confusum (DuVal), the confused flour beetle, were exposed for variable durations at 36-54 °C. Beetles were placed in laboratory ovens set at a baseline of 27 °C, the temperature was increased by 0.1 °C per minute until the target temperature was achieved, and beetles were then held for specified exposure durations. There was no mortality after initial exposure or after a 1-week holding period of any life stage of T. castaneum or T. confusum exposed for 32 h to 36, 39, or 42 °C. At 45 °C, there was no initial mortality of either species exposed for different time intervals except for those exposed for 28 h. However, there was a significant increase in mortality after the 1-week holding period of those beetles exposed initially for at least 16 h to 45 °C. There was a sharp increase in mortality after the initial exposures of 4 h at 48 °C; mortality of T. confusum larvae was 90.0±5.7% but was only 10.0±10.0% for larvae of T. castaneum, and no pupae of either species were dead. All life stages of both species were killed after the initial exposure of 12 h, and 1-week mortality of beetles exposed for 4 and 8 h was generally greater than initial mortality. At 51 and 54 °C, 2- and 1-h exposures, respectively, killed all life stages of each species. Mortality in conditions of gradual temperature increase was less than previous studies with sudden temperature increases.     

Calorimetric evaluation of responses of Sitophilus oryzae and Tribolium confusum to elevated temperatures and controlled atmospheres

Metabolic heat rates, determined by microcalorimetry, were used to measure the effect of controlled atmospheres (CAs) and elevated temperatures on the stored-product insects Sitophilus oryzae (rice weevil) and Tribolium confusum (confused flour beetle). Results for larval and adult stages in air, and in a range of low O₂ and/or high CO₂ CAs, at temperatures from 15 to 45 °C, showed the general effectiveness of such atmospheres in lowering the lethal temperatures relative to those in air. Effects on adult S. oryzae at 25 °C were explored in more detail in experiments using the following conditions: exposure to anoxic CAs for extended times; exposure to hypoxic CAs; and simulated hermetic storage. A simple scanning calorimetric method was developed for determining lethal temperatures and a combined thermo-gravimetric and differential thermal-analysis method was used to interpret the thermal events, due to loss of water, occurring at and above these temperatures.     

Insecticidal effect of Steinernema feltiae (Filipjev) (Nematoda: Steinernematidae) against Tribolium confusum du Val (Coleoptera: Tenebrionidae) and Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae) in stored wheat

The confused flour beetle, Tribolium confusum, and the Mediterranean flour moth, Ephestia kuehniella, are important pests of stored grain products. The insecticidal effect of three strains (UK 76 [=Nemasys], USA/SC, and Hawaii) of the entomopathogenic nematode Steinernema feltiae was determined in the laboratory, in wheat, against these pests. The nematodes were applied at three dose rates: 100, 300 and 900 nematodes/insect individual. The Hawaii strain was most virulent against T. confusum adults and larvae, with a significant dose effect in the case of the larvae. Larval mortality of this species reached 79% and 100% after 7 and 14 d of exposure to the nematodes, respectively, at the highest dose applied. On the other hand, adult mortality of T. confusum did not exceed 66%. In the case of E. kuehniella larvae, USA/SC performed best causing 52% and 69% mortality after 7 and 14 d exposure, respectively, at the highest dose tested. Since very few data are available on the effect of entomopathogenic nematodes against these pests, it is concluded that the Hawaii and USA/SC strains of S. feltiae should be further investigated as promising biological control agents for T. confusum and E. kuehniella.     

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.     

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.     

Insecticidal and residual effect of three pyrethroids against Sitophilus oryzae (L.) (Coleoptera: Curculionidae) on stored wheat

Laboratory tests were conducted to assess the use of the pyrethroids, deltamethrin, beta-cyfluthrin and alpha-cypermethrin at the rates of 0.125 and 0.25 ppm, as grain protectants in stored wheat against the rice weevil, Sitophilus oryzae (L.). For this purpose, clean untreated wheat was sprayed with these insecticides and stored for 6 months. During this period, four bioassays were carried out, in order to evaluate the residual efficacy of each pyrethroid. In each bioassay, treated wheat was infested with S. oryzae adults, and dead insects were counted after 1, 2 and 7 d of exposure. In addition, S. oryzae progeny production was estimated on each bioassay, until the production of the F₄ generation. The results indicated that deltamethrin and beta-cyfluthrin, both at 0.25 ppm, were significantly more efficient than the other treatments. Efficacy was notably higher after 7 d of exposure, than after 1 and 2 d. At the same exposure level, 1, 2 and 3.5 months after treatment, at 0.25 ppm, mortality for deltamethrin was approximately 89%, 92% and 86%, respectively, while the corresponding percentages for beta-cyfluthrin were 97%, 83% and 62%, and for alpha-cypermethrin 50%, 49% and 33%. However, at the rate of 0.125 ppm, mortality was ?58% in all cases. In all treatments appearance of F₁-F₄ generations was observed, with the exception of both deltamethrin and beta-cyfluthrin at 0.25 ppm, where only a few F₁ adults were noted, without the production of subsequent generations.     

Evaluation of kaolinite-based particle films to control Tribolium species (Coleoptera: Tenebrionidae)

Adults of Tribolium castaneum (Herbst), the red flour beetle, and Tribolium confusum (du Val), the confused flour beetle, were exposed to kaolinite-based particle film dusts. When beetles were continuously exposed to the hydrophobic particle film M-96-018 at the rate of 0.1-0.5 mg/cm², all the T. castaneum at 0.1 mg/cm² were dead after 3 days, but 40±13.8% of the exposed T. confusum were still alive after 7 days. At higher concentrations, all the T. castaneum were dead after 2 days, but 5-6 days of exposure were needed to kill all T. confusum. In a subsequent test, adults of both species were exposed for 8-72 h to 0.5 mg/cm² of the particle film M-96-018, removed, then held without food for 1 week. No T. castaneum survived, while survival of the T. confusum ranged from 0 to 55±17.3%, depending on the exposure interval. In a test conducted at controlled conditions of 40%, 57% and 75% r.h., 27°C, T. confusum were exposed for 8-72 h to the particle film M-96-018 and a hydrophilic particle film M-97-009 at the rate of 0.5 mg/cm², then removed and held either with or without wheat flour for 1 week. All the T. confusum exposed to the particle film M-97-009 usually survived, while survival of the T. confusum exposed to the particle film M-97-018 after the 1-week holding period increased with increasing relative humidity and with the presence of food. The particle film M-96-018 was effective against both the Tribolium species, and appears to have a potential for use in management programs to control beetles within storage facilities.     

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.     

Effectiveness of spinosad combined with diatomaceous earth against different European strains of Tribolium confusum du Val (Coleoptera: Tenebrionidae): Influence of commodity and temperature

Laboratory bioassays were carried out to assess the effects of combining spinosad at 0.01, 0.1 and 0.5 ppm, with the diatomaceous earth (DE) formulation SilicoSec at rates of 150, 300 and 600 ppm, against larvae and adults of three different populations of Tribolium confusum du Val (Coleoptera: Tenebrionidae), originating from different European countries (Greece, Portugal and Denmark). Tests were conducted on wheat and maize at 25 and 30 °C. Survival of T. confusum larvae was assessed after 7 d exposure and survival of adults was assessed after 7 d and 14 d of exposure. At each dose of spinosad, survival of T. confusum individuals decreased as the rate of DE increased. As temperature increased, the efficacy of spinosad and Silicosec applied either alone or in combination also increased. The efficacy of spinosad alone was slightly higher on maize than wheat, while the reverse was noted for all the tested combinations of spinosad with DE as well as in the case of the application of DE alone. The strain from Portugal was always the least susceptible of the three tested. Our study indicates that it is possible to combine low doses of DE (<600 ppm) with spinosad (<1 ppm) to control adults and larvae of T. confusum, especially at temperatures >25 °C.     

Heat combined with diatomaceous earth to control the confused flour beetle (Coleoptera: Tenebrionidae) in a flour mill

An alternative to methyl bromide fumigation for controlling stored-product insects in food processing facilities is to heat part or all of a facility to 50-60°C for 20-30 h. However, some equipment or structures cannot tolerate these conditions, or it is difficult or expensive to attain these high temperatures. It may be possible to reduce the temperature requirements necessary for effective control by using a desiccating dust, such as diatomaceous earth (DE), in combination with the heat treatment. The objectives of this study were to examine the combined impact of high temperature and DE on the mortality of Tribolium confusum (du Val) in a flour mill environment and to evaluate the effects of DE application rate on insect mortality in a mill environment during heat treatment. In areas of the mill where temperatures were in excess of 47°C, DE applications of 0.3 g/m² in combination with heat were no more effective than the heat treatment alone. At higher application rates, the DE was more effective. In cooler areas, adult beetles exposed to DE died sooner than insects not exposed to the insecticidal dust. These results indicate that application of DE in areas that cannot be heated to 47°C is effective for controlling T. confusum in a flour mill. A comparison is made with a parallel study conducted in Canada.     

Impact of physical and biological factors on susceptibility of Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae) to new formulations of hydroprene

Three separate experiments were conducted to: (1) evaluate two new commercial formulations (202-080 and 202-084) of the insect growth regulator hydroprene, (2) determine residual efficacy of hydroprene-treated concrete stored at different environmental conditions, and (3) assess the impact of accumulated flour on residual efficacy. In the first test, late instars of Tribolium castaneum (Herbst), the red flour beetle, and Tribolium confusum (du Val), the confused flour beetle, were exposed on concrete treated with hydroprene. At 40% relative humidity (r.h.), there was no difference between species regarding the percentage of individuals that stopped development in the larval stage (arrested larvae), but at 75% r.h. there were more arrested T. castaneum than T. confusum in all treatments except the low rate of formulation 202-084. No adult T. castaneum lived after emergence (live adults) at either relative humidity, but the percentage of live adult T. confusum ranged from 1.0% to 41.0%, depending on treatment. In the second test, late instars of T. confusum were exposed at 6 and 12 weeks post-treatment on concrete treated with the two experimental formulations and stored under different environmental conditions. At 6 weeks there was no difference between formulations. At 12 weeks, fewer live adults and more dead emerged adults with gross morphological deformities were found on concrete treated with formulation 202-084 and stored at 32°C, 75% r.h. compared to other treatment combinations. In the final experiment, wheat flour was added to treated concrete for 5 weeks before the bioassays were conducted with late-instar T. confusum. There were few live adults produced in the initial bioassays, and dead adults with gross morphological deformities ranged from 83.1% to 97.6%. However, in bioassays conducted with late-instar larvae at 6 weeks, most adults eventually emerged with few deformities. The presence of the flour apparently compromised residual control and the hydroprene was no longer effective. In summary, the new hydroprene formulations were equivalent to the registered product Gentrol^®. Tribolium confusum was less susceptible than T. castaneum, and residual control of T. confusum on a clean surface without flour lasted about 6-12 weeks.     

Effectiveness of spinosad dust against different European populations of the confused flour beetle, Tribolium confusum Jacquelin du Val

Six populations of the confused flour beetle, Tribolium confusum, obtained from Greece, Italy, Portugal, Denmark, Germany and France were tested for their susceptibility to a spinosad dust formulation, containing 0.125% spinosad. For this purpose, adults and larvae of T. confusum were exposed on wheat treated with two dose rates of the dust formulation, 0.06 and 0.19 ppm of a.i. corresponding to 50 and 150 ppm of the formulation, at 25 °C and 65% r.h. Mortality of the exposed individuals was assessed after 7, 14 and 21 days of exposure on the treated substrate. The increase of dose and exposure interval increased mortality, while adults were more tolerant to spinosad than larvae. Significant differences were noted among populations, for both adults and larvae. The most tolerant to spinosad was the strain from Greece, while the least tolerant were the strains from Germany and Denmark. After 7 days of exposure, on wheat treated with 50 ppm, mortalities of adults of the Greek, German and Danish strains were 2%, 25% and 62% respectively, while the respective figures for 150 ppm were 1%, 31% and 81% respectively. In the case of larvae, of the same strains, mortality at 50 ppm was 6%, 27% and 28% and at 150 ppm 11%, 23% and 40%, respectively. The results of the present study suggest that different strains and stages of T. confusum differ widely in their susceptibility to spinosad-treated wheat.     

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.     

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.     

Influence of grain type on the susceptibility of different Sitophilus oryzae (L.) populations, obtained from different rearing media, to three diatomaceous earth formulations

Bioassays were carried out to assess whether the commodity, from which adults of the rice weevil Sitophilus oryzae emerged, influences the insecticidal efficacy of three diatomaceous earth (DE) formulations: Protect-It™, PyriSec^® and DEBBM. Protect-It™ is a DE formulation that contains 10% silica gel, while PyriSec^® and DEBBM are enhanced DEs that contain natural pyrethrum and the plant extract bitterbarkomycin, respectively. The S. oryzae populations tested were reared on wheat, barley or maize and the susceptibility of each to the DE formulations was assessed on all three commodities. The DE application doses were: 500 ppm for Protect-It™ and PyriSec^®; 150 and 75 ppm for DEBBM. Mortality of S. oryzae adults was counted 7 and 14 d after their exposure on the treated commodities. Bioassays were carried out at 25 °C and 55% r.h. Barley-reared S. oryzae were the most tolerant of all formulations and treated commodities, whereas maize-reared were the most susceptible ones. DE effectiveness was always lower in maize than in wheat or barley irrespective of the commodity from which the populations were obtained. Furthermore, Protect-It™ and PyriSec^® were more effective than DEBBM in wheat or barley, but not in maize.     

Control of the lesser grain borer (Rhyzopertha dominica (F.), Coleoptera: Bostrichidae) by treatments with residual formulations of Metarhizium anisopliae (Metschnikoff) Sorokin (Deuteromycotina: Hyphomycetes)

Treatments with conidia of the entomopathogenic fungus Metarhizium anisopliae formulated in invert emulsion (water-in-oil formulation) or in wheat flour were applied to Rhyzopertha dominica adults infesting Cicer arietinum grains. The application rates were 4.1×10⁵ conidia/cm² of treated area using a concentration of 1.8×10⁷ conidia/ml of the invert emulsion and 8.2×10⁶ conidia/cm² of treated area using a concentration of 6.5×10⁸ conidia/g of the wheat flour formulation. Results have indicated significant mortality (P<0.05) when newly emerged R. dominica adults were introduced and then treated with the invert emulsion and wheat flour formulations (86.7-93.3%, control treatment 10.0-26.7% mortality). When treated grains were left until the emergence of F₁ adults, there was also significant mortality (P<0.05) in both treatments (28.3-60.0%, control treatment 1.7-8.3% mortality). This indicates a residual effectiveness of the treatment with the two formulations against R. dominica adults which extended to >2 months (equivalent to the duration of the insect life-cycle at 23±2°C and 75±5% r.h.). Infestation rate of C. arietinum grains by R. dominica at 23±2°C and 75±5% r.h. was significantly reduced in the treatments with the fungal conidia formulated in invert emulsion (0.7%) or in wheat flour (1.0%) when compared with the control treatment (19.0-23.3%). The preventive treatments significantly retarded R. dominica development (P<0.05) by 8-12 days compared with the control treatment. The infection with the fungus thus delayed adult emergence of R. dominica by 8-12 days. Overall results give promise for control of R. dominica with M. anisopliae mixed with wheat flour or introduced into invert emulsion.     

Insecticidal effect of spinosad dust, in combination with diatomaceous earth, against two stored-grain beetle species

Laboratory bioassays were carried out to determine the efficacy of spinosad applied alone or combined with the diatomaceous earth (DE) SilicoSec against adult rice weevils, Sitophilus oryzae and confused flour beetles, Tribolium confusum. Efficacy was assessed on wheat and maize at three dosages of spinosad dust formulation (corresponding to 0.0625, 0.1875 and 0.625 ppm of active ingredient [AI] for S. oryzae and to 0.1875, 0.625 and 1.25 ppm of AI for T. confusum), alone or combined with SilicoSec at 150 ppm for S. oryzae and 250 ppm for T. confusum. The mortality of S. oryzae exposed for 14 d on wheat treated with spinosad ranged between 83% and 100%. Conversely, the mortality of S. oryzae on maize treated with DE or on maize treated with lower doses of spinosad dust did not exceed 19% and was only 59% on maize with the highest spinosad dust treatment. Generally, the presence of SilicoSec combined with spinosad did not significantly increase S. oryzae mortality compared with spinosad alone. For T. confusum, mortality on both commodities was lower than for S. oryzae. After 14 d of exposure on wheat, mortality was 14% at the highest dose of spinosad, but increased to 33% in the presence of DE. Similar results were also obtained for T. confusum exposed on treated maize, which indicated a joint action between spinosad and DE. In the case of S. oryzae, the inclusion of DE reduced progeny production in comparison with spinosad alone. Progeny production of T. confusum was relatively low in all treatments, compared to progeny production of S. oryzae. The results of the study show the potential of combination treatments of spinosad dust and DE, but efficacy varies with the target insect species and commodity.     

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.     

Efficacy of a volatile formulation of hydroprene (Pointsource™) to control Tribolium castaneum and Tribolium confusum (Coleoptera: Tenebrionidae)

Three- and 4-week-old Tribolium castaneum (Herbst), the red flour beetle, and Tribolium confusum (du Val), the confused flour beetle, were exposed at five different temperature-relative humidity (r.h.) combinations to a volatile formulation of the insect growth regulator (IGR) hydroprene (called Pointsource™). Typical effects associated with IGR exposure, such as arrested larval growth, morphological deformities in adults, twisted and deformed wings, and incomplete adult emergence were produced in both species. Tribolium castaneum and T. confusum were susceptible to Pointsource™, but T. castaneum appeared to be the more susceptible species. More 3-week-old larvae of both species were arrested in that stage compared to the 4-week-old larvae. Nearly all of the 3- and 4-week-old T. castaneum larvae that were able to complete development to the adult stage quickly died after they emerged and were grossly morphologically deformed. In contrast, some emerged adult T. confusum remained alive after they emerged and were not deformed in any manner or had only twisted and incomplete wings. A greater percentage of larvae of both species were arrested in the larval stage and more adults died after they emerged in exposure studies conducted at 32°C, 75% r.h. as compared with 32°C, 30% r.h., but the reverse was true for exposures conducted at 27°C. Pointsource™ appears to have excellent potential for use in controlling Tribolium species within indoor facilities.