A Pilot Study of Natural Formulation Activity in the Protection of Stored Wheat and Barley Against the Stored-Product Insects

The stored-product insects are one of the major causes of losses in the stored cereals. Most of control measures still rely on a synthetic pesticide usage, but due to its negative side effects on the goods, human health, and the environment, there is an urgent need for an alternative control. A natural formulation based on the diatomaceous earth (DE) SilicoSec®, enhanced with the botanicals (essential oil lavender, corn oil, and bay leaves dust) and the silica gel was developed. The aim of the study was to test the activity of the developed formulation as a postharvest protectant of seed wheat and barley in the suppression Sitophilus oryzae (L.), Rhyzopertha dominica (F.) and Tribolium castaneum (Herbst). As a reference comparative value, the DE SilicoSec® was applied. Subsequent to the six months of storage under the simulated warehouse conditions, the formulation has completely suppressed the initial population development of all three tested insect species, both in wheat and barley. In wheat, a complete suppression was detected at the dose of 500 ppm against T. castaneum and 600 ppm against both R. dominica and S. oryzae. In barley, a complete suppression was detected at the doses of 500 ppm, 400 ppm, and 600 ppm against R. dominica, T. castaneum and S. oryzae, respectively. Conclusively, the results of this study indicate that the developed natural formulation based on the DE, botanicals, and silica gel was highly effective against the three major stored‐product insect species, providing a long-term safe storage of wheat and barley seeds.

Toxicity of diatomaceous earth on seed weevil, Sitophilus oryzae L. and its effect on agro-morphological characters of maize seeds

Sitophilus oryzae L. (Curculionidae; Coleoptera) is considered to be a serious internal feeder of stored cereals. The use of insecticides results in the development of resistance among the pests and residues in the produce. Diatomaceous Earth (DE) is from a natural source, environment-friendly, safe to humans and natural enemies. In addition, it is highly effective against a wide range of stored pest species and has no toxic residues on the treated seeds. The promising alternative to synthetic insecticides is the application of DE in storage pest management under physical control. With this background, the present study was aimed to find the efficacy of DE against rice weevil, S. oryzae L. and their effect on the agro-morphological characters of maize (Zea mays L.) seeds. Contact toxicity bioassays were carried out with different concentrations of DE against S. oryzae. The results of the bioassay studies revealed LD50 at the concentration of 1.27 mg/100 gm of maize seeds. Further, 100 per cent mortality was achieved at the dose of 15 mg/100 gm of maize seeds within six days of exposure. The effect of DE on the germination provided a significant increase in germinability of maize seeds (LD50= 94%, LD95= 98% and control= 96%). DE at the concentration of LD95 had a beneficial effect on the seedling parameters, especially germination% (98%) and seedling length (53.02 cm) of maize. The present study concluded that DE could be effectively utilised as an alternative management tool to chemical insecticides in the management of rice weevil under storage conditions.

Pesticidal Activity of Sundarban Mangrove Plant Extracts against Sitophilus Pests and Identification of Active Constituents Using LC-MS

Plants act as a rich source of novel natural pesticides. In the backdrop of the recent revival of interest in developing plant-based insecticides, this study was carried out to investigate the pesticidal activity of Sundarban mangrove plants. A total of nine different plant parts from five plants, namely, Aegiceras corniculatum, Excoecaria agallocha, Heritiera fomes, Xylocarpus moluccensis, and Xylocarpus granatum, were extracted with methanol and tested for insecticidal activity against two common stored product pests Sitophilus oryzae and Sitophilus zeamais using direct contact feeding deterrent wafer disc method. Three bark extracts from A. corniculatum, E. agallocha, and H. fomes showed potent and statistically significant insecticidal activity against both S. oryzae and S. zeamais pests (80–100% mortality). All the active bark extracts were further fractionated using C-18 solid-phase extraction (SPE) columns and tested for their insecticidal activity against S. oryzae pest to identify the active fraction. Only the SPE4 fraction (100% MeOH) from all the three active plants showed the activity against S. oryzae pest with a lethal concentration 50% (LC50) value of 0.5, 1.0, and 1.5 mg/disc for A. corniculatum, E. agallocha, and H. fomes, respectively. The active fraction of A. corniculatum was further profiled for identification of active compounds using LC-ESI-MS and identified (along with some unknown peaks) two previously reported compounds at m/z 625.17630 (isorhamnetin 3-O-rutinoside) and 422.25346 (paspaline) as major constituents. Insecticidal activities of these plants are reported in this study for the first time and would be useful in promoting research aiming for the development of new biopesticides from mangrove plants.

Immediate and Delayed Mortality of Four Stored-Product Pests on Concrete Surfaces Treated with Chlorantraniliprole

Chlorantraniliprole is an effective pesticide against a plethora of pests, but its efficacy against stored-product pests is very poorly explored. In this study we treated concrete surfaces with four different doses of chlorantraniliprole (0.01, 0.05, 0.1, and 0.5 mg a.i./cm2) against the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) adults and larvae, the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) adults, the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae) adults, and the flour mite, Acarus siro L. (Sarcoptiformes: Acaridae) adults and nymphs, to examine the immediate mortalities after 1, 2, 3, 4, and 5 days of exposure. Additionally, the delayed mortality of the individuals that survived the 5-day exposure was also evaluated after a further 7 days on untreated concrete surfaces. We documented high mortality rates for all tested species and their developmental stages. After 5 days of exposure to 0.5 mg a.i./cm2, T. castaneum larvae and A. siro adults exhibited the highest immediate mortality levels, reaching 96.7% and 92.2%, respectively. Delayed mortality was also very high for all tested species and their developmental stages. Nymphs of A. siro displayed a 96.3% delayed mortality followed by the adults of R. dominica (98.6%) after exposure to 0.5 mg a.i./cm2. All other tested species and their developmental stages reached complete (100.0%) delayed mortality, where even 0.01 mg a.i./cm2 caused ≥86.6% delayed mortality in all species and their developmental stages. Taking into consideration the effectiveness of chlorantraniliprole on this wide range of noxious arthropods, coupled with its low toxicity towards beneficial arthropods and mammals, this pesticide could provide an effective management tool for stored-product pests in storage facilities.

Repellent Activity of Cymbopogon citratus Essential Oil Against Four Major Stored Product Pests: Plodia interpunctella, Sitophilus oryzae, Acanthoscelides obtectus and Tribolium castaneum

Summary The purpose of this study is to assess the repellent activity of lemongrass (Cymbopogon citratus) essential oil (EO), grown in Serbia under greenhouse conditions, against four prevalent stored product pests: Plodia interpunctella (larvae), Sitophilus oryzae, Acanthoscelides obtectus and Tribolium castaneum (adults). The lemongrass EO repellency was tested using filter paper in Petri dishes and a Y-tube olfactometer. According to the repellency index (RI), the lemongrass EO repellency was divided into 5 classes. Prior to biotesting, the chemical characterization of lemongrass EO was performed and the following main compounds were detected: myrcene (31.0%), geranial (30.0%), and neral (23.6%). The C. citratus EO considered was found to exhibit the Class III repellent activity against P. interpunctella larvae only at the highest concentration (namely 0.5%). This is the very first report on the C. citratus EO repellent activity against this pest. The lemongrass EO examined showed strong repellency (Class IV) against S. oryzae (0.2% and 0.5% of EO), A. obtectus (0.1% and 0.2%), and T. castaneum (0.05-0.1%). Moreover, higher lemongrass EO concentrations (0.5%) were found to exhibit extreme repellency (Class V) against A. obtectus and T. castaneum. The results obtained were confirmed in the bioassays performed, indicating the great potential of lemongrass EO as a bio-repellent when applied in higher concentrations to all the insects considered, regardless of the exposure period.