Stored Grain Pests and Current Advances for their Management

During the offseason, when fresh food is not available, humans have to consume stored grain food. Unfortunately, these stored grains are later infested with many pests. Foods stored in bags and bins are very much susceptible to infestation with several pests which can cause extensive post-harvest losses, spoilage, and less demand in markets, causing a huge economic crisis. Hence, successful management of stored grain pests becomes necessary to prevent these from insect pests. Current approaches for their management are one of the promising goals, as it includes preventive practices, monitoring, sanitation, and identification of main pathogens. Different management strategies of all the common stored grain pests viz. grain weevils, grain borers, grain moths, flour moths, mealworms, grain and flour beetles, booklice, mites, and parasites are enlisted here.

Biological activities and chemical composition of Mentha piperita and Syzygium aromaticum essential oil fractions against cowpea weevil, Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae)

Callosobruchus maculatus (Fabricius) is one of the major, common, pests of stored grains as it causes quantitative and qualitative losses in legume crops. This research sought to find the most active fraction in Mentha piperita and Syzygium aromaticum essential oils, to evaluate bioactivity of those crude essential oils and active fractions against C. maculatus, and to identify the compounds contained in the active fraction. The essential oils were fractionated using three solvents, namely n-hexane, ethyl acetate, and methanol. The n-hexane fraction was identified as the active fraction, causing mortality, oviposition deterrence, and ovicidal effects. In fumigation chambers, LD95 values of M. piperita (Mnf) and S. aromaticum n-hexane fractions (Snf) were 0.045 ml/l and 0.057 ml/l respectively. ED50 values for oviposition deterrence were 0.016 ml/l for Mnf and 0.022 ml/l for Snf. ED50 value of ovicidal effects for Mnf- and Snf-treated eggs were 0.014 ml/l for both fractions. GC-MS analysis showed 8 dominant compounds in Mnf and 5 dominant compounds in Snf. Overall it is concluded that Mnf and Snf oils have effective biological activities against stored pest C. maculatus and have potential to be considered as alternatives to synthetic insecticides.

The Potency of Six Medicinal Plant Extracts Against the Stored Grain Insect Pest Sitophilus granarius L.

Jawalkar, N.B., S.P. Zambare and M.I. Al Ghannoum. 2021. The Potency of Six Medicinal Plant Extracts Against the Stored Grain Insect Pest Sitophilus granarius L. Arab Journal of Plant Protection, 39(4): 323-328. https://doi.org/10.22268/AJPP-039.4.323328 This study was conducted on six medicinal plants viz., Vitex negundo (leaves), Xanthium strumarium, Caesalpinia bonduc, Mucuna pruriens, Moringa oleifera (seed kernels), Tagetes erecta (petals) for their bio-insecticidal activity. The powders of various parts of plants were extracted using the MARS6 microwave acid digestion system. Three different concentrations (20, 30, and 40%) of plant extracts were tested against granary weevil, Sitophilus granarius L. (Coleoptera: Curculionidae) for their bio-insecticidal activities under laboratory conditions. The results of statistical analysis showed a good performance of all plant extracts, especially at the high concentrations of the extracts, where they showed different levels of insect mortality and their developmental rate was also reduced leading to significant reduction in insect numbers. The mortality rate ranged was 0-100% with S. granarius adults (p < 0.01). There was significant correlation (R=1) between mortality rate and the concentration of plant extracts. However, the extract of Mucuna pruriens with solvents (Acetone + Petroleum Ether) showed the highest mortality rate of 100% at the three concentrations used (p < 0.01), whereas, the lowest average mortality of 43.3% (p < 0.01) was observed with Xanthium strumarium and Vitex negundo extracts with solvents (Methanol + n-Hexane) compared with 0% mortality in the control. All plant extracts have revealed insecticidal as well as propitious protective effect on grains, and it can be selected as effective control treatment after proper dose formulation to prevent weevil infestation in stored grains. Keywords: Bioinsecticide, stored grains, Sitophilus granarius, mortality, medicinal plants, MARS 6.

Method Validation and Evaluation of Safrole Persistence in Cowpea Beans Using Headspace Solid-Phase Microextraction and Gas Chromatography

Bioinsecticides are regarded as important alternatives for controlling agricultural pests. However, few studies have determined the persistence of these compounds in stored grains. This study aimed at optimizing and validating a fast and effective method for extraction and quantification of residues of safrole (the main component of Piper hispidinervum essential oil) in cowpea beans. It also sought to assess the persistence of this substance in the grains treated by contact and fumigation. The proposed method used headspace solid-phase microextraction (HS-SPME) and gas chromatography with a flame ionization detector (GC/FID). Factors such as temperature, extraction time and type of fiber were assessed to maximize the performance of the extraction technique. The performance of the method was appraised via the parameters selectivity, linearity, limit of detection (LOD), limit of quantification (LOQ), precision, and accuracy. The LOD and LOQ of safrole were 0.0057 and 0.019 μg kg−1, respectively and the determination coefficient (R2) was >0.99. The relative recovery ranged from 99.26 to 104.85, with a coefficient of variation <15%. The validated method was applied to assess the persistence of safrole residue in grains, where concentrations ranged from 1.095 to 0.052 µg kg−1 (contact) and from 2.16 to 0.12 µg kg −1 (fumigation). The levels measured up from the fifth day represented less than 1% of the initial concentration, proving that safrole have low persistence in cowpea beans, thus being safe for bioinsecticide use. Thus, this work is relevant not only for the extraction method developed, but also for the possible use of a natural insecticide in pest management in stored grains.

Entomotoxicity of TiO2 and ZnO Nanoparticles Against Adults Tribolium Castaneum (Herbest) (Coleoptera: Tenebrionidae)

The red flour beetle Tribolium castaneum is one of the common pests of stored grains distributed worldwide. In this study, testing the effect of TiO2 and ZnO nanoparticles as insecticides on adults of T. castaneum was achieved. Results showed that the high concentration of TiO2 and ZnO nanoparticles recorded high cumulative mortality of the adult insects after exposure time 1, 3, and 5 days from treatments 15.30, 23.57, and 29.85% respectively of TiO2 nanoparticles compared with 20.42, 27.08, and 33.96 % respectively of ZnO nanoparticles. The result showed that TiO2 and ZnO nanoparticles are effective in controlling and can be introduced in the future in integrated pest management of T. castaneum.

Abundance and diversity of insects associated with stored grains and tamarind in Nigeria

Detailed information on insect pests of stored grains in Nigeria is lacking. A two-year survey was conducted to determine the species composition and abundance of insects associated with maize, millet, rice, sorghum and tamarind in eighteen locations across five agro-ecological zones in Nigeria. Sixteen coleopteran, lepidopteran and hymenopteran species were associated with stored products, with high species richness on cereal grains but low species richness on tamarind. Most of these insects are polyphagous on cereal grains, whereas the tamarind weevil Sitophilus linearis (Herbst, 1797) (Curculionidae), and Caryedon serratus (Oliver, 1790) (Chrysomelidae) were found only on tamarind in this study. The maize weevil Sitophilus zeamais (Motschulsky, 1758), rice weevil Sitophilus oryzae (Linneaus, 1763), lesser grain borer Rhyzopertha dominica (Fabricius, 1792) (Bostrichidae), rusty grain beetle Cryptolestes ferrugineus (Stephens, 1831) (Laemophloeidae) and red flour beetle Tribolium castaneum (Herbst, 1797) (Tenebrionidae) were most abundant on stored grains. The tamarind weevil, C. serratus and the sawtoothed grain beetle Oryzaephilus surinamensis (Linneaus, 1758) (Silvanidae) were most abundant on tamarind. The hymenopterans Theocolax elegans (Westwood, 1874) (Pteromalidae), Anisopteromalus calandrae (Howard, 1881) (Pteromalidae) and Cephalonomia waterstoni (Gahan, 1931) (Bethylidae) were the dominant parasitoids of larvae and pupae of the storage pests. Simpson index of diversity of insect species across locations ranged from low (0.63) to high (0.89).

On-Farm Grain Storage and Challenges in Bagmati Province, Nepal

Farmers in Nepal lose up to one-third of stored grain to pests and diseases. This results in food insecurity and loss of income. To mitigate these losses, farmers use several approaches including pesticide applications on stored grains. We interviewed 241 farmers in Bagmati Province, Nepal, to assess the current on-farm grain storage practices and challenges to improve postharvest management. The results show that rice was the most stored crop (median 1150 kg). About half of farmers stored for at least nine months and grain was mainly used for home consumption. Grain was stored by 66.5 and 69.8% of farmers in granaries (rice) and plastic drums (legumes), respectively. Insects were the most important challenge during storage, and farmers used pesticides to control them. Farmers were more likely to use insecticide on grain (p = 0.000) if they stored rice, used traditional granaries, and had insect damage during storage. The use of improved storage methods (e.g., hermetic bags) was very low for rice (3.5%). There is a need to improve on-farm grain storage by disseminating storage innovations to address postharvest challenges in important crops such as rice.