Adult Rice Weevils Research Articles

Deep-freezing as a novel disinfestation strategy to rice weevil (Sitophilus oryzae Linnaeus) in packaged milled rice grains: Factors and lethal behaviors

Rice weevil (Sitophilus oryzae Linnaeus) is a major insect pest of milled rice grains, which poses a great threat to food security. In this study, the feasibility of three deep-freezing regimes (-20, -80, and -196 oC) to disinfest packaged milled rice grains was explored. It was found that the disinfestation efficiency increased with the decrease in freezing temperature. For naked insects, complete mortality was achieved by the regimes at -20, -80, and -196 oC with the exposure time of 8 min, 2 min, and as short as 1 s, respectively. For insects in packaged rice grains (5 insects/500 g rice; package size: 8 cm × 5 cm × 13 cm), the corresponding exposure time was determined as 100, 40, and 4 min, respectively. Upon the increase in insect population density and package size, the longer exposure time was required for complete mortality. When the regime at -196 oC (1.5 min) was used as a pretreatment at -20 oC (60 min), the highest combination index (2.12) was obtained for the complete mortality. In one word, deep-freezing was successfully developed as a novel method to disinfest adult rice weevil in packaged milled rice grains.

Correlation Analysis of Sitophilus oryzae (Linnaeus) Real-Time Monitoring and Insect Population Density and Its Distribution Pattern in Wheat Grain Piles

The traditional manual sampling method for detecting stored grain insect pests is labor-intensive and time-consuming, often yielding non-representative samples. However, to achieve more accurate monitoring, it is necessary to understand the distribution patterns of different insect pests within grain silo and their correlation with monitoring and sampling data. This study aimed to assess the population density and distribution of Sitophilus oryzae (rice weevil) in bulk wheat grain to predict insect dynamics effectively. Utilizing a probe trap in a wheat silo, adult insects were tracked across different population densities. The traps recorded captured pests, alongside temperature and humidity data. The correlation analysis revealed that rice weevils were active throughout the silo but less prevalent at the bottom, with the highest distribution near the upper surface. Temperature and humidity significantly influenced their activity, particularly within the 22 °C to 32 °C range. Higher population densities correlated with increased relative humidity, impacting weevil activity. Trapping data aligned with overall population density changes in the silo. This study will provide an accurate assessment of the population density of adult rice weevils in grain silos based on temperature changes in the upper part of the grain silo.

Protecting Rice Grains from Sitophilus oryzae L. Infestation using Plant Extracts under Controlled Conditions

Three plant extracts - Thymus vulgaris, Schinus molle, and Melia azedarach - were tested against adult rice weevils at 25, 50, and 100% concentrations. All extracts caused significant mortality, reaching 100% with 50-100% solutions after one day. Extracts also reduced grain weight loss, damage, and adult emergence. S. molle was effective at 25% concentration (30-44% reduction), with higher efficacy at 100% (98% reduction). M. azedarach showed similar trends (62-69% at 25%, 100% at 100%). T. vulgaris was the most effective, achieving 69-73% reduction at 25% and 100% at all levels. These results suggest significant potential for these plant extracts in eco-friendly rice weevil control programs.

Attraction of Sitophilus oryzae (L.) (Coleoptera: Curculionidae) to the semiochemical volatiles of stored rice materials

AbstractIn order to explore the influence of stored cereal volatiles on the behavior of Sitophilus oryzae, the olfactory responses of adult rice weevils to the volatiles of different rice cultivars [Red brown rice (RBR), Daohuaxiangmi (DHXM), Baishuigongmi (BSGM), Yashuixinmi (YSXM), and white glutinous rice (WGR)] were studied using electroantennography (EAG) and behavioural bioassays in different types of olfactometers. S. oryzae showed significantly different preferences for these rice cultivars, in the order RBR > DHXM = YSXM ≥ BSGM > WGR. Furthermore, 26 components were identified in the volatile profile of RBR. Nonanal (29.37%), hexanal (16.08%), and 1-octen-3-ol (8.83%) were the most abundant compounds. EAG recordings showed that the antennae of S. oryzae were able to perceive these three compounds in a dose-dependent manner. The compounds elicited significant EAG responses at various concentrations, with the strongest responses at 100 μg μL−1. S. oryzae had a significant positive behavioural response to nonanal, hexanal, and 1-octen-3-ol at various concentrations, with the most attractive being 50, 100, and 100 µg µL−1, respectively. The olfactory preferences of S. oryzae, based on a comparison of these compounds at their optimal concentrations, were nonanal > 1-octen-3-ol = hexanal. These results indicated that the volatiles of the preferred rice cultivar (RBR) were perceived by the peripheral olfactory system of S. oryzae adults and individually elicited positive chemotaxis. These findings offer new insights into the mechanism of host preferences of stored-grain pests. Nonanal showed the greatest potential for use as a novel monitoring and control tool against this storage-beetle pest.

Efficacy of Plant- Powders Against Rice Weevil, Sitophilus oryzae (Linnaeus) (Curculionidae: Coleoptera) at Laboratory Condition

An experiment was conducted to evaluate the efficacy of plant-based repellent powders for S. oryzae at the National Rice Research Program, Hardinath, Dhanusha, Nepal in 2020 at laboratory condition. Two hundred gram of paddy grains of cv. Sambha Mansuli Sub-1 was kept in each plastic jar in the experiment. Ten pairs of newly emerged adult rice weevil, S. oryzae of uniform age obtained from stock culture were released in each plastic jar. Laboratory bioassay contained Acorus calamus (rhizome powder) @10 gm/kg, Piper nigrum (seed powder) @10 gm/kg, Curcuma longa (rhizome powder) @10 gm/kg, Azadirachta indica (kernel powder) @ 10gm/kg, Zingiber officinale (rhizome powder) @10 gm/kg, and Malathion powder 5% dust @2 gm/kg were used for the rice weevil. Acorus calamus was the most effective botanical powder followed by P. nigrum to reduce grain damage percent on number basis (1.15%) and on weight basis (1.22%), weight loss percent (0.84%) & weevil population count (1.54). The efficacy ranks of the botanicals were: A. calamus>P. nigrum>A. indica>Z. officinale>C. longa. Thus, use of A. calamus powder is recommended to manage rice weevil in the storehouse condition. SAARC J. Agric., 19(2): 331-338 (2021)

Essential oil bioactivity evaluation of the different populations of Cupressus against adult rice weevil (Sitophilus oryzae L.)

Essential oil bioactivity evaluation of the different populations of Cupressus against adult rice weevil (Sitophilus oryzae L.)

Essential oil bioactivity evaluation of the different populations of Cupressus against adult rice weevil (Sitophilus oryzae L.)

Essential oil bioactivity evaluation of the different populations of Cupressus against adult rice weevil (Sitophilus oryzae L.)

Insecticide effect of pennyroyal and rosemary essential oils on the rice weevil

The study aims at evaluating the potential insecticide essential oils from two plants of the family Lamiaceae pushing the spontaneous state in the Tiaret region (western Algeria). Insecticides tests were performed in the laboratory by the direct contact method. The results of these tests have shown that rosemary essential oil has remarkable insecticidal properties. They induced 100% mortality of adult rice weevils to 15 μ l dose after only 24 hours of exposition. The essential oil of pennyroyal induced 70 % mortality at the same dose and for the same exposure time. Lethal doses (LD50) are determined in the order of 5,58 for rosemary and 7,36 μ l for pennyroyal. The LD90 Are in order of 9.36 μ l it mean between the second and third dose tested for the rosemary and of 12.52µl for the pennyroyal and in the same two essential oils experimental conditions prevent the development of rice weevil larvae Sitophylus oryzae to 5 µl dose.

Industrial-scale radio frequency treatments to control Sitophilus oryzae in rough, brown, and milled rice

Many previously studies have confirmed that radio frequency (RF) treatments have the potential to be developed as non-chemical alternative disinfestation methods. However, most of them are conducted in laboratory scale RF systems, and it is necessary to scale up the treatment protocol for industry scale applications. A pilot-scale, 27.12 MHz, 6 kW RF system was used to simulate the continuous industrial processing and finally estimate the heating efficiency and throughput for controlling adult rice weevils, Sitophilus oryzae (L.), in milled, brown, and rough rice. An electrode gap (11.5 cm) was chosen based on the appropriate heating rate (6–8 °C/min). RF heating uniformity in the three types of rice samples was improved by adding 50 °C forced hot air surface heating, sample movements on the conveyor belt at a speed of 12.5 m/h, and holding in 50 °C hot air for 6 min. The final industrial RF treatment achieved a complete mortality of adult S. oryzae and provided acceptable quality attributes in moisture content, water activity, color, protein, free fatty acid, and ash. The average heating efficiency and throughput of the RF treatments were 77.7, 76.3, and 74.3%, and 268.8, 247.3, and 224.8 kg/h for milled, brown, and rough rice, respectively. The industrial scale-up studies provide alternative physical methods for disinfesting milled, brown, and rough rice to replace chemical fumigation.

Fumigant Toxicity of Lamiaceae Plant Essential Oils and Blends of Their Constituents against Adult Rice Weevil Sitophilus oryzae.

To find a new and safe alternative to conventional insecticides, we evaluated the fumigant toxicity of eight Lamiaceae essential oils and their constituents against the adult rice weevil Sitophilus oryzae. Of the eight species tested, hyssop (Hyssopus offcinalis), majoram (Origanum majorana), and Thymus zygis essential oils showed strong fumigant toxicity against S. oryzae adults at 25 mg/L air concentration. Constituents of active essential oils were analyzed by gas chromatography coupled to flame ionization detector (FID) and gas chromatography-mass spectrometry. A total of 13, 15, and 17 compounds were identified from hyssop, majoram, and Thymus zygis essential oils, respectively. Pinocamphone and isopinocamphone were isolated by open column chromatography. Among the test compounds, pinocamphone and isopinocamphone showed the strongest fumigant toxicity against S. oryzae. Sabinene hydrate, linalool, α-terpineol, and terpinen-4-ol exhibited 100% fumigant toxicity against S. oryzae at 3.9 mg/L air concentration. The measured toxicity of the artificial blends of the constituents identified in hyssop, majoram, and Thymus zygis oils indicated that isopinocamphone, terpine-4-ol, and linalool were major contributors to the fumigant toxicity of the artificial blend, respectively.

Verification of radio frequency heating uniformity and Sitophilus oryzae control in rough, brown, and milled rice

Radio frequency (RF) heating is considered to be an alternative physical method for disinfesting postharvest agricultural products to replace chemical fumigation due to its inherent dangers on human health and environment. A pilot-scale, 27.12 MHz, 6 kW RF system was used to study the RF heating uniformity and validate the developed RF treatment protocols for disinfesting rough, brown, and milled rice. The results showed that the optimum RF heating uniformity in rough and brown rice was obtained by an appropriate electrode gap of 11 cm with a forced hot air heating at 50 °C, movement of the conveyor with a speed of 12.4 m/h, two mixings, and holding at 50 °C hot air for 5 min. Mortality of adult rice weevils, Sitophilus oryzae (L.), increased with increasing heating temperature and holding time, and reached 100% while RF heating at 50 °C holding in hot air for at least 6 min. There were no significant differences in quality parameters (moisture, protein, water activity, starch, free fatty acid, ash, and color) between RF treatments and untreated controls during storage (P > 0.05). The developed non-chemical alternative RF technology may hold potential for disinfesting rough, brown, and milled rice required by the growing organic market.

The effect of toxin-producing Fusarium fungi on behavior of the rice weevil Sitophilus oryzae (Coleoptera, Dryophthoridae)

The paper describes laboratory tests in which the behavior response of adult rice weevils Sitophilus oryzae L. to the presence of seven species of micromycetes of the genus Fusarium (F. graminearum, F. culmorum, F. cerealis, F. poae, F. sporotrichioides, F. langsethiae, and F. sibiricum; 3 strains for each species) infecting cereals was characterized. The chemicals of unkown structure, released by the fungi, can have both attractive and repellent effects on the weevils; in some cases a neutral response was observed. The strains of Fusarium species characterized as weak pathogens (F. langsethiae, F. poae, and F. sibiricum) in most cases stimulated attractive and neutral responses. Relatively strong pathogens (F. cerealis, F. culmorum, F. graminearum, and F. sporotrichioides) generally had a repellent effect. The results obtained are discussed in the context of possible relationships between Fusarium fungi and the rice weevil during their utilization of cereals as a shared food substrate.

Thermal death kinetics of adult Sitophilus oryzae and effects of heating rate on thermotolerance

Information on thermal death kinetics of targeted stored insects under different heating conditions is essential for developing postharvest disinfestation treatment protocols. Using a heating block system, the thermal death kinetics of adult rice weevil, Sitophilus oryzae (L.), were determined at temperatures from 44 to 50 °C at 2 °C intervals and a heating rate of 5 °C/min. The effects of heating rates (0.1, 0.5, 1, 5 and 10 °C/min) on mortality were also examined. The results showed that thermal death curves of S. oryzae followed a 0-order kinetic reaction model. The required holding times for achieving 100% mortality were 130, 50, 12, and 4 min at 44, 46, 48, and 50 °C, respectively. The activation energy for killing S. oryzae was 505 kJ/mol and the z value obtained from the thermal-death-time curve was 3.9 °C. Insect mortality after a 20 min exposure to 46 °C at low heating rates (0.1 or 0.5 °C/min) was significantly lower than that at high heating rates (1–10 °C/min). The information provided by thermal death kinetics for S. oryzae is useful in developing effective postharvest thermal treatment protocols.

Rice weevil response to basil oil fumigation

Basil oil, Ocimum basilicum L., is a volatile plant essential oil that is known to have insecticidal activity against stored product pests such as rice weevil, Sitophilus oryzae (L.). Basil oil was diluted in acetone and applied to a sponge held inside a tea strainer for fumigations in containers with and without rice. Basil oil fumigation (3ml, 10% concentration) caused high mortality in adult rice weevils when weevils were exposed in air in a sealed 1L plastic container. However, when basil oil was placed in packaged rice, weevil mortality was low and reproduction was not affected. Effectiveness of plant essential oil fumigation should be conducted under realistic conditions to avoid experimental artifacts and misleading results.

Fumigant toxicity of Apiaceae essential oils and their constituents against Sitophilus oryzae and their acetylcholinesterase inhibitory activity

We evaluated the insecticidal and acetylcholinesterase (AChE) inhibition activities of the essential oils and their constituents of 10 Apiaceae on the adult rice weevil, Sitophilus oryzae. Of the 10 species tested, dill (Anethum graveolens), caraway (Carum carvi), and cumin (Cuminum cyminum) essential oils showed strong fumigant toxicity against adult S. oryzae. LC50 values of caraway, dill, and cumin essential oils were 2.45, 3.29, and 4.75mg/L air, respectively. Among the test compounds, (+)-carvone, (−)-carvone, cuminaldehyde, dihydrocarvone, linalool oxide, carveol, trans-anethole, and neral demonstrated strong fumigant toxicity against adult S. oryzae with LC50 values of 0.61, 0.84, 1.12, 2.92, 3.76, 4.29, 5.02, and 6.60mg/L air, respectively. α-Pinene showed the strongest AChE inhibition activity followed by β-pinene and limonene. The measured toxicity of the artificial blends of the constituents identified in dill and cumin oils indicated that (+)-carvone and cuminaldehyde were major contributors to the fumigant toxicity of the artificial blend.

Mella (Olax zeylanica) Leaves as an Eco-friendly Repellent for Storage Insect Pest Management

Among the cereals, rice is the most important staple food supplying energy requirements for mostof the worlds’ population. However during storage a loss of about 10-20% rice grains occurs due to storedgrain pests. Repellents are considered as the best source of protection against insect attack upon storedproducts as they have potential for the exclusion of stored product pests from grain, and therebypreventing insect feeding and oviposition on food materials. Various plant materials have been utilizedeffectively through time as safe and ecofriendly insect pest control measures due to their repellentactivity. The aim of the present study was to investigate the potential of powdered leaves and leaf extractsof Olax zeylanica as repellents against the rice weevil, Sitophilus oryzae. All the experiments were carriedout under laboratory conditions using 1-7 day old unsexed adults. Four different doses (1.0g, 3.0g, 5.0gand 7.0g).of powdered leaves were tested for fumigant repellency in a dual-choice bio-assay apparatus.Repellent action of leaf extracts was evaluated by means of an area preference test using methanol,ethanol and n- hexane as solvents. Repellent effect of powdered leaves against the adult rice weevils wasfound to be significantly high (P< 0.05) at all doses. The highest repellent effect was produced by 7.0g ofleaf powder resulting in repellency of 97%, while the lowest dose (1.0g) also elicited more than 50%repellency in weevils indicating a very strong repellent action of the powdered leaves. In comparison,methanol extract of leaves produced the highest repellent effect (96%) on weevils whereas n-hexaneextract elicited the lowest. Nevertheless, at higher concentrations all three extracts produced more or lesssignificantly similar repellent effect on the weevils. The findings of the present study suggest that certainactive materials of Olax zeylanica leaves have potential to act as a grain protectant and may be exploitedfor the control of Sitophilus oryzae in rice storage in an environment-friendly way.Keywords: Olax zeylanica, Sitophilus oryzae, Repellent effect, Stored rice

Inhibitory Effect of Buprofezin on the Progeny of Rice Weevil, Sitophilus oryzae L. (Coleoptera: Curculionidae)

The rice weevil Sitophilus oryzae (L.) (Coleoptera: Curculionidae), is an important pest of stored grains throughout the world. Different biopesticides and synthetic insecticides have been used for a long time to minimize the rice weevil infestation but their efficacy is not satisfactory yet. The climate and storage conditions are highly favorable for quick progeny which may be responsible for lower efficiency of insecticides and higher level of infestation. Insect growth regulators (IGRs) like buprofezin are the semi-synthetic insecticides, mimic the insectproduced hormones and don’t kill the insects directly but reduces pest populations by affecting mating behavior, reproduction, egg viability, pre and post embryonic development etc. Laboratory experiments were conducted from August to November 2012, to evaluate the efficacy of buprofezin on the mortality and the suppression of progeny production of rice weevil. Ten adult rice weevils were exposed on three types of rice grains (long, medium and short) treated with buprofezin at 100, 200 and 300 ppm. Mortality was counted at 15, 21 and 28 days after treatment while adult progeny was counted at 6, 7 and 8 weeks after buprofezin treatment to get a new generation. The data showed that buprofezin had no direct effect on the mortality of rice weevils regardless the concentrations. Buprofezin at 300 ppm in rice grains significantly inhibited progeny production while lower doses (200 and 100 ppm) had no significant effect but virtually reduces progeny number. Types of grains were not factor for increasing or decreasing the rice weevils populations. In conclusion, buprofezin caused decreasing progeny productivity by S. oryzae (L.) with increasing concentrations regardless the types of rice grains.

Susceptibility of stored product insects to high concentrations of ozone at different exposure intervals

Ozone is a highly reactive gas with insecticidal activity. Past studies have indicated that ozone technology has potential as a management tool to control insect pests in bulk grain storage facilities. The objective of this study was to determine the efficacy of short periods of exposure to high ozone concentrations to kill all life stages of red flour beetle ( Tribolium castaneum (Herbst)) (Coleoptera: Tenebrionidae), and Indianmeal moth ( Plodia interpunctella (Hübner)) (Lepidoptera: Pyralidae), adult maize weevil ( Sitophilus zeamais (Motsch.)) (Coleoptera: Curculionidae) and adult rice weevil ( S. oryzae (L)) (Coleoptera: Curculionidae). Insects were treated with six ozone concentrations between 50 and 1800 ppm. The specific objective was to determine minimal time needed to attain 100% mortality. The most ozone-tolerant stages of T. castaneum were pupae and eggs, which required a treatment of 180 min at 1800 ppm ozone to reach 100% mortality. Eggs of P. interpunctella also required 180 min at 1800 ppm ozone to reach 100% mortality. Ozone treatments of 1800 ppm for 120 min and 1800 ppm for 60 min were required to kill all adult S. zeamais and adult S. oryzae, respectively. The results indicate that high ozone concentrations reduce the treatment times significantly over previously described results. Our results also provide new baseline information about insect tolerance to ozone treatment.

Diatomaceous earth enhances the toxicity of garlic, Allium sativum, essential oil against stored-product pests

Laboratory bioassays were carried out to determine the efficacy of garlic, Allium sativum L. (Amaryllidaceae), essential oil applied alone or with diatomaceous earth (DE) against adult rice weevils, Sitophilus oryzae (L.) (Coleoptera: Curculionidae) and red flour beetles, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). The results showed that the combination treatment was significantly more effective than either treatment alone. In addition, the results also showed that the simultaneous application of essential oil plus DE significantly reduced the concentration of essential oil alone required for an effective treatment and the application rate of DE can be reduced when combined with essential oil. Moreover, the activity of the combination treatment lasted longer than that of essential oil alone and the survival of eggs or larvae to adult stage was significantly inhibited in the combined treatments against both species, compared with the use of essential oil alone. Our results suggested that garlic essential oil combined with DE has a strong additive effect, and therefore may have potential as an alternative to synthetic insecticides for the control of insect pests of stored products.

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.