Granary Weevil Adults Research Articles

Bioactivity of Cereal- and Legume-Based Macaroni Pasta Volatiles to Adult Sitophilus granarius (L.).

Simple SummaryPasta factories can be infested by insects. By following the odour of cereal-based pasta, insects can enter packages of commercial products. The aim of this work was to compare the bioactivity of volatiles produced by cereal- and legume-based macaroni pasta on adults of granary weevil, Sitophilus granarius, in multi-choice behavioural bioassays. Tests were performed with ten commercially available Italian macaroni pastas made from six different cereals or four different legumes. Granary weevil adults were more attracted to cereal-based pastas than legume-based pastas, but the differences in attractiveness were not always significant. Gas chromatography-mass spectrometry analysis of head-space solid-phase microextraction collections from the different pasta samples highlighted marked qualitative and quantitative differences, with aliphatic aldehydes and aliphatic alcohols being the most abundant volatile components of cereal- and legume-pastas, respectively. Moreover, the results of the two-choice behavioural bioassays suggested that the low level of attraction to legume pasta is mainly due to the lack of attractant stimuli other than emission of repellent compounds.The attractiveness of ten commercially available Italian macaroni pastas made from different cereals [Triticum durum; Triticum durum (whole wheat); Triticum dicoccum; mixture of five cereals; Triticum turgidum; Triticum turanicum] or legumes (Cicer arietinum; Lens culinaris; Pisum sativum; Vicia faba) to Sitophilus granarius, was compared. S. granarius adults were more attracted to cereal pastas than legume pastas, but the differences in attractiveness were not always significant. Consistent with the results of behavioural bioassays, the mortality of adults over 20 days exposed to pasta samples was 100% with the legume pasta samples and only 8% with the T. turanicum pasta. GC-MS analysis of HS-SPME extracts from the different pasta samples highlighted marked qualitative and quantitative differences, with aliphatic aldehydes and aliphatic alcohols being the most abundant volatile components of cereal- and legume-pastas, respectively. In two-choice behavioural bioassays, insect attraction to a 1:1 combination of T. turanicum and C. arietinum pastas (80%) was even higher than that observed in T. turanicum pasta alone (64%) and in C. arietinum pasta alone (20%). This strongly suggested that the low attractiveness of legume pasta is mainly due to the lack of attractant stimuli rather than emission of repellent compounds.

Kernel volatiles of some pigmented wheats do not elicit a preferential orientation in Sitophilus granarius adults

The granary weevil, Sitophilus granarius (L.) (Coleoptera, Dryophthoridae), is a primary pest of stored cereals worldwide. To identify possible sources of wheat resistance toward this pest, two commercial durum and bread wheat varieties with yellow pericarp were compared with anthocyanin-pigmented durum and bread wheat genotypes that have never entered commercial production. The composition of the kernel head-space volatile organic compounds (VOCs) and the olfactory responses of granary weevil adults to these kernel VOCs were investigated. Head-space solid-phase micro-extraction and gas chromatography–mass spectrometry analysis highlighted 17 and 13 kernel VOCs from durum and bread wheats, respectively. These compounds mainly included aldehydes and alcohols, and to a lesser extent, terpenes and benzene derivatives. Quantitative and qualitative differences were seen between the odor profiles of yellow and pigmented wheat kernels. In two-choice behavioral bioassays, granary weevil adults were significantly attracted by the kernel odors from the yellow commercial wheat varieties and their hexane extracts, but not by those of the pigmented wheat genotypes and their hexane extracts. Electroantennography confirmed the presence of VOCs in all of the hexane extracts that stimulated the olfactory system of both sexes of the granary weevil in a dose-dependent manner. Thus, differences among the odor blends were responsible for the different olfactory responses of granary weevils to the yellow and pigmented wheat kernels. These differences in VOC emissions and olfactory responses induced in granary weevils by the yellow and pigmented wheat kernels can be exploited to characterize resistance mechanisms associated with different genotypes and to incorporate resistance into improved varieties.

Comparison of insecticidal efficacy of four natural substances against granary weevil (Sitophilus granarius [L.]) adults: does the combined use of the substances improve their efficacy?

Laboratory tests were carried out to evaluate the insecticidal efficacy of different natural inert dusts (diatomaceous earth, wood ash, quartz sand) and the leaf powder of Azadirachta indica A. Juss. against granary weevil (Sitophilus granarius [L.]) adults. The efficacy of the substances was tested individually and in combination with each other. The substances were applied at different concentrations, and bioassays were carried out at four different temperatures (20, 25, 30 and 35°C) and two different relative humidity (RH) levels (55% and 75%). The adult mortality was recorded after the 7th, 14th and 21st days of exposure. The progeny production of individuals exposed to different combinations was also assessed. Wood ash proved to be the most efficient inert dust in our research. We detected 100% mortality in the treatment exposed to a higher concentration (5 w%) of wood ash at 35°C and 55% RH after 7 days of exposure. A lower RH level had also a negative impact on the progeny production. We can conclude that wood ash can be efficient in controlling granary weevil adults as a single substance or in combination with other substances. Further surveys should focus on the impact of the wood ash dose rates. Due to the high percentage of area covered with forest in some European countries, the main ingredient is present locally, but additional surveys are needed to help improve the practical use of wood ash.

Efficacy of four essential oils against Sitophilus granarius (L.) adults after short-term exposure

A trial was conducted to assess the fumigant toxicity of the essential oils from Rosmarinus officinalis L., Salvia officinalis L., Lavandula angustifolia Mill. and Mentha balsamea Willd. against the adults of Sitophilus granarius (L.). The relationships between the time after treatment (1, 2, and 3 days), temperature (20, 25, 30, 35, and 40°C), concentrati on of essential oils (2.4 and 7.4 ml/L air) and mortality were investigated. In the experiment, the efficacy of the essential oils at 40°C was 95%, whereas thei r efficacy was considerably lower at lower temperatures (from 12 to 36%). Throughout the experiment, the essential oil of rosemary proved to be the most effective fumigant, causing more than 60% mortality of the granary weevil adults. When applying the essential oil of rosemary, more than 50% mortality in the adults of granary weevil was attained at 35°C ( 89%) and 40°C (99%). A satisfactory efficacy of the other essential oils, common lavender (90%), peppermint (97%) and common sage (94%), was attained only at the highest temperature. The activities of the essential oils were better at higher concentrations (36%) than at lower concentrations (32%). When assessing the effect of the concentration on the adult mortality, we achieved more than 50% efficacy only with rosemary (2.4 ml/L of air, 58%; 7.4 ml/L of air, 63%). The data for the other essential oils ranged between 19% (peppermint, 2.4 ml/L of air) and 34% (common sage, 7.4 ml/L of air). The calculated values for the LC 50 and LC 90 showed that only rosemary produced satisfactory fumigant activity on the adult granary weevils, especially in relation to the temperature. However, the positive efficacy identified in our laboratory experiments needs to be validated under conditions similar to those of the applied conditions, that is, warehouses.

Behavioral Responses of Adult Sitophilus granarius to Individual Cereal Volatiles

The antennae of Sitophilus granarius (L.) (Coleoptera: Curculionidae) adults detect a wide variety of compounds in the odor blend of various cereal grains (Germinara et al., Tec. Molit., 53:27-34, 2002). In the present study, we looked at the behavioral responses of the granary weevil to 20 of these individual volatiles (aliphatic alcohols, aldehydes, ketones, and aromatics) in a two-choice pitfall olfactometer, using the aggregation pheromone and propionic acid as the attractant and repellent controls, respectively. Five doses, ranging from 1 microg to 1 mg, of each compound were tested. At least one concentration of eight compounds attracted beetles but required doses 1,000- to 5,000-fold higher than the concentration of aggregation pheromone to elicit a response. Three compounds, while attractive at lower concentrations, acted as repellents at higher doses. Twelve compounds were repellent at concentrations similar to the quantity of propionic acid that significantly repelled beetles. The data show that granary weevil adults have the ability to respond behaviorally to a wide range of cereal volatiles and that responses may change as a function of concentration. The results suggest that host finding behavior of weevils will depend on the balance of positive and negative volatile stimuli from grain as the relative concentrations of volatiles may change during storage. An understanding of how the weevils respond to such changes could be useful for the development of effective integrated pest management strategies.

Effectiveness of wheat-applied contact insecticides against Sitophilus granarius (L.) originating from different populations

Toxicity parameters were determined for granary weevil Sitophilus granarius adults in the laboratory after treatment of wheat grains with several contact insecticides: dichlorvos, malathion, chlorpyrifos-methyl, pirimiphos-methyl, deltamethrin, and deltamethrin with the piperonyl butoxide (PBO) synergist. The impact was determined on three populations: an insecticide-susceptible laboratory population, a population originating from Belgrade Port (Serbia) selected once previously with pirimiphos-methyl at the LD 70 level, and one from Bijeljina (Bosnia and Herzegovina) selected once at the LD 70 level with deltamethrin. After exposure of granary weevil adults to treated wheat for 48 h, deltamethrin with PBO was the most effective insecticide against the laboratory population (LD 50=0.10 mg/kg and LD 95=0.25 mg/kg) and dichlorvos the least effective (LD 50=1.80 mg/kg and LD 95=5.35 mg/kg). Regarding the selected weevils from Belgrade Port and Bijeljina, the most effective insecticide was chlorpyrifos-methyl (LD 50=0.25 and 0.22 mg/kg; LD 95=0.40 and 0.28 mg/kg, respectively), and the least effective was dichlorvos (LD 50=6.56 and 4.99 mg/kg; LD 95=26.78 and 16.14 mg/kg). Insecticide minimum effective doses (MED) able to prevent an F 1 or F 2 generation were determined. Deltamethrin+PBO had the lowest (0.2 mg/kg) and malathion the highest MED (>5.0 mg/kg) in both generations of laboratory weevils. The lowest MED for the selected weevils from Belgrade Port was recorded for deltamethrin+PBO (0.5 mg/kg for the F 1 and 0.3 mg/kg for the F 2 generation) and the highest for dichlorvos (6.0 mg/kg for both generations); while the lowest MED for the selected Bijeljina weevils was achieved by chlorpyrifos-methyl (0.3 mg/kg for the F 1 and 0.2 mg/kg for the F 2 generation) and the highest by malathion and dichlorvos (5.0 mg/kg) in the F 1 generation, and malathion (3.0 mg/kg) in the F 2 generation.

Concentration of suspension and temperature as factors of pathogenicity of entomopathogenic nematodes for the control of granary weevil, Sitophilus granarius (L.) (Coleoptera: Curculionidae)

Efficacy of four species of entomopathogenic nematodes (Steinernema feltiae, S. carpocapsae, Heterorhabditis bacteriophora, H. megidis) for the control of granary weevil adults (Sitophilus granarius) was tested under laboratory condition. Suspensions of nematodes were applied in three concentrations (5.000, 10.000, and 20.000 IJs per ml) at three temperatures (15oC, 20oC and 25oC). After one week mortality of the beetles was assessed. No significant differences in the percentage of mortality were determined between treatments with S. feltiae, S. carpocapsae and H. bacteriophora, while H. megidis was the least efficient. Mortality of the beetles was statistically significantly higher at 20 and 25 oC. Influence of the concentration of the nematode suspension was proved to be less important in biological activity of biological agents in question.

Ice-Nucleating Active Bacteria Decrease the Cold-Hardiness of Stored Grain Insects

This report provides further evidence that a freeze-dried, concentrated form of Pseudomonas syringae , an ice-nucleating active bacteria, reduces the cold tolerance of stored grain insect pests. Application of ice-nucleating bacteria to wheat or corn that contained insect pests decreased the insects’ supercooling capacity: after treatment with 100 ppm of P. syringae the mean supercooling points of five insect species increased from 4.7 to 11.9°C above untreated controls. Treatment with P. syringae also decreased the capacity of insects to survive a 24-h exposure to subzero temperatures. Decreases in cold tolerance were observed in eight species of stored grain pests: Indianmeal moth larvae, Plodia interpullctella (Hubner); red flour beetle adults, Tribolium castaneum (Herbst); flat grain beetle adults, Cryptolestes pusillus (Schon herr); rusty grain beetle adults, Cryptolestes ferrugineus (Stephens); Gibbium psylloides (Czenpinski); lesser grain borer adults, Rhyzopertha dominica (F.); yellow meal worm larvae, Tenebrio molitor (L.); and granary weevil adults, Sitophilus granarius granarius (L.). Results of this study provide further support for the use of ice-nucleating active bacteria as biological insecticides to kill overwintering insects by decreasing their low temperature tolerance. The approach may be particularly appropriate for the control of a variety of insect pests in restricted areas such as grain bins.

Protection of Stored Wheat from the Granary Weevil by Vegetable Oils12

Vegetable oils (cottonseed, soybean, maize, and peanut) were used to suppress Sitophilus granarius (L.) in wheat grain. Insect progeny production decreased significantly at a 5-ml/kg dosage. At the 10-ml/kg level, complete control was achieved which lasted at least 60 days. These oils also repelled granary weevil adults. There was no obvious effect of the oil treatment on water absorption by the wheat seeds, but 5- or 10-ml/kg dosages reduced seed germination.

Effects of Low Temperature Acclimation on Developmental Stages of Stored-product Insects 1

We studied low temperature acclimation by 4 immature age groups (21–24, 14–17, 7–10 or 0–3 days after oviposition), by adults from laboratory-cultured strains, and by a field strain of each of 3 species: Sitophilus oryzae (L.), rice weevil; Sitophilus granarius (L.), granary weevil; and Rhyzopertha dominica (F.), lesser grain borer. Insects were acclimated for 3 days at 21.1, 7 days at 15.5 and 7 days at 10.0°C, then placed in 4.4°C 2, 4, or 6 weeks. Non-acclimated samples were placed directly in 4.4°C. Prior acclimation increased survival of all insects at 4.4°C. The most cold-tolerant rice weevils and granary weevils were those of 14–17 days development, and most tolerant lesser grain borers, of 21–24 days. More granary weevil adults from the field strain than from the laboratory strain survived. Granary weevil adults (field or lab) were more cold-tolerant than adults of the other 2 species. The least cold-tolerant stages of all species were 0–3 days development (eggs).

Effect of Atmospheric Gases Alone or in Combination on the Mortality of Granary and Rice Weevils1

The time required to obtain 50 and 95% mortality of the granary weevil, Sitophilus granarius (L.), and the rice weevil, S. oryzae (L.), in atmospheres of CO2, N2, or He and in various combinations of CCvair and CO2-O2 was determined. The order of susceptibility of granary and rice weevil adults in CO2, N2, or He atmospheres was 80° > 70° > 60°F. Granary weevil adults were the most susceptible stage to atmospheres of CO2, N2, or He, followed by larvae, pupae, and eggs. Rice weevil adults were the most susceptible stage to atmospheres of CO2, N2 or He, followed by larvae, eggs, and pupae. CO2 concentrations of 90–40% in air were more toxic to rice weevil adults than 100% CCy Concentrations of 90–60% CO2 in air were more toxic to granary weevil adults than 100% CO2. The time required for 50 or 95% kill of granary weevil adults was about the same whether exposed to various CO2-air or CO2-O2 combinations, and a similar response was obtained for rice weevil adults.

Rearing Stored-Product Insects for Laboratory Studies: Lesser Grain Borer, Granary Weevil, Rice Weevil, Sitophilus zeamais, and Angoumois Grain Moth1234

Cultures of Rhyzopertha dominica (F.), lesser grain borer; Silophilus granaries (L.), granary weevil; S. oryzne (L.), rice weevil; S. zeamais Motschulsky; and Sitotroga cerealella (Olivier), Angoumois grain moth, were reared in a room maintained at 80±2°F and 55±5% relative humidity on Ramona wheat contained in gallon jars. The moisture of wheat used as media was adjusted to contain 13±0.3% moisture content. Systematic rotation of the lesser grain borer was based on food consumption; rotation of cultures of the other species was based on the age of insects in each. A 30-ml measure of lesser grain borer adults (approximately 9000 live insects) emptied onto 2 quarts of wheat resulted in an average of 29,000 insects per jar in 8 weeks Parent stock of Silophilus spp. was left on 2/½ quarts of media I week, and the same stock was used for 3 consecutive weeks to establish new cultures. Starting with a 40-ml measure of granary weevil adults (approximately 7000), cultures of this species yielded an average of 10,000 insects in 7 weeks; cultures started with a 27-ml measure of the rice weevil (approximately 5200) and a 30ml measure of S . zeamais (approximately 5200) yielded an average of 12,000 insects in 6 weeks. Adult progeny of the Angoumois grain moth began emerging during the third week after 300 moths were placed on 2½pints of wheat. Emergence reached its peak 5 weeks after initial infestation, and an average of 2850 moths was produced in each culture.

Laboratory Evaluation of Diazinon as a Wheat Protectant

When diazinon sprays and dusts were applied to wheat at 1, 2.5, and 5 ppm and stored for 168 days in open jars at ambient room temperature, the toxicity of the treated grain to insects was markedly reduced after 7 days. Granary weevil adults, Sitophilus granaries (L.), were considerably more resistant than the red flour beetle, Tribolium castaneum (Herbst), or the saw-toothed grain beetle, Oryzaephilus surinamensis (L.). The red flour beetle was most susceptible. The dusts were more effective than the sprays and the efficacy of both was reduced more in the 13.4±0.5% moisture wheat as compared with the wheat maintained at 10.6±0.6%. Chemical estimations indicated considerable loss of dizainon immediately after treatment. The dusts generally persisted in greater amounts than the sprays. The residues from wheat within 168 days varied from 0.29 ppm from samples receiving an initial application of 1 ppm to 2.47 ppm from an initial treatment of 5 ppm. Quality evaluations on milling, baking, and flavor indicated no untoward effects when wheat was treated with 8 ppm diazinon and evaluated at a maximum of 9 days later.

The khapra beetle,Trogoderma granariumEverts

The khapra beetle, Trogoderma granarium Everts, a serious pest of stored grains and other food products in India and elsewhere, has recently been found in 23 counties of California, Arizona, and New Mexico. It thrives on hot, dry conditions and has proved exceptionally difficult to control. The State Department of Agriculture is conducting an eradication program against it in California. Studies have been conducted on factors affecting the development of this beetle and on its climatic adaptation, and tests have been carried out to find more effective control measures. The following are the principal results to date. An increase in temperature from 70°F to 93°-95° decreased the average length of a generation from 220 days to 26 days; light conditions had little effect on it. At 90° egg viability averaged 94 per cent, and 93 eggs were laid per female. The length of a generation varied widely on different foods. A few larvae survived exposures of 240 minutes to -6°F and of 51 days to temperatures fluctuating daily between 25° and 48°. Eggs and pupae were more susceptible. To obtain a 95 per cent kill (at 50 per cent relative humidity) required 960 minutes for larvae and 420 minutes for pupae at 118°, 8 minutes for both stages at 131°. These findings indicate that the species is capable of becoming a pest of grain stored in piles or sacks in the field in such ellmctes as that of Imperial Valley, California. Among ten fumigants tested (at 70°F and with 2-, 8-, and 24-hour exposures), hydrocyanic acid and acrylonitrile were the most toxic to khapra-beetle larvae and pupae. Eggs were more susceptible than the other immature stages to the majority of these fumigants. Hydrocyanic acid was the only one tested to which all three immature stages of the khapra beetle were more susceptible than granary-weevil adults. Fumigation for 12 hours with methyl bromide, hydrocyanic acid or acrylonitrile showed little evidence of reduced seed germination when moisture content of seed was less than 10 per cent. Khapra-beetle larvae were more resistant to wheat treated with a piperonyl butoxide-pyrethrin dust mixture or with a malathion dust than were the adults of the granary weevil, rice weevil, and lesser grain borer.