Stored-grain Insect Pests Research Articles

Unveiling the molecular composition and biological properties of essential oil derived from the leaves of wild Mentha aquatica L.: A comprehensive in vitro and in silico exploration

Abstract The purpose of the current study is to assess the chemical profile, antioxidant, antimicrobial, and insecticide efficacy of essential oil derived from the leaf of Moroccan Mentha aquatica L. (MA-EO) using in vitro and in silico analysis. Using GC-MS/MS analysis, 18 components of MA-EO were identified, including linalool (42.42%), α-elemol (10.45%), α-terpineol (8.07%), linalyl acetate (7.37%), and caryophyllene (4.05%). Additionally, MA-EO has a strong antioxidant capacity with IC50 values of 0.64 ± 0.01 µg/mL using the DPPH assay and 0.167 ± 0.13 µg/mL using the ABTS test. Total antioxidant capacity activities were found to be 188.21 ± 0.31 mg EAA/g, while RP activities were 1.95 ± 0.023. The powerful antibacterial properties of MA-EO were proven to be effective against Escherichia coli and Candida albicans. MA-EO showed insecticidal potential using the fumigation experiment, with an LC50 of 3.33 μL/L in the air after 24 h of exposure. At a dose of 20 µL/mL, MA-EO reduced fertility, fecundity, and emergence of adult C. maculatus. MA-EO had 95% mortality at the same dosage. In silico analysis revealed that the antioxidant activity of MA-EO is linked to γ-eudesmol, while its antibacterial efficacy is associated with phenol, 2,4-di-tert-butyl-, and its antifungal capacity with phenol, 2,4-di-tert-butyl-. MA-EO demonstrates potent bactericidal, fungicidal, and bioinsecticide properties, making it effective for controlling bacteria, fungi, and insect pests in stored grains.

Insecticidal activity of crude olive pomace oils from Kabylia (Algeria) against the infestation of Rhyzopertha dominica (F.) and Sitophilus oryzae (L.) in stored wheat grains

The insecticidal effect of four crude olive pomace oils extracted from pomace collected from four localities of Kabylia, refined olive pomace oil and extra virgin olive oil were assessed under laboratory conditions for the control of adults of Rhyzopertha dominica (Fabricius, 1792) (Coleoptera: Bostrychidae)) and Sitophilus oryzae (Linnaeus, 1763) (Coleoptera: Curculionidae). The doses used ranged from 0.1 to 0.4 ml/25 g of durum and soft wheat seeds. In addition, the quality indices and the fatty acid composition of these oils were evaluated. The results show that the legal quality indices were well within the legal limits for crude olive-pomace oil (COP), refined pomace oil (ROP) and extra-virgin olive oil (EVO) categories. The effectiveness of these vegetable oils is highly dependent on the insect species, the dose rate, the exposure time and the type of oil tested The main fatty acids from all samples tested, were oleic (61.89–79.25%), palmitic (8.34–15.71%) and linoleic (8.17–16.52%) acids. For both species and substrates tested, mortality is dose and time of exposure dependent. The highest dose (0.4 ml/25 g) causes ≥ 63.75% mortality, after 24 h of exposure. Comparison of LD50 (ml/25 g) indicates that olive oil was generally more toxic than crude and refined pomace oils, for both insects and substrates, values varies from 0.005 to 0.189. The most sensitive insect was S. oryzae for most vegetable oils tested. Likewise, oils significantly reduced the F1 offspring of both insects and seed weight losses. No progeny were observed in the two pests at the highest dose, and therefore no weight loss was recorded. The results also revealed that the six oils affect the germination capacity of durum and soft wheat seeds when the dosage is increased. The results collected remain encouraging for the recommendation of natural substances as part of integrated pest management programmes against insect pests of stored grains.

A Systematic Review of the Bioactivity of Jatropha curcas L. (Euphorbiaceae) Extracts in the Control of Insect Pests

The use of botanical extracts of the plant Jatropha curcas (Euphorbiaceae) represents a valuable alternative to control insect pests and avoid the detrimental effects on the environment and health that arise due to synthetic chemical insecticides. Thus, we conducted a systematic review to summarize the published evidence on the bioactivity of J. curcas against insect pests. Electronic databases were searched to identify studies that assessed J. curcas extracts against insect pests in various types of crops. We included 39 articles that reported the insecticidal and insectistatic activity of several botanical extracts from J. curcas against insects of eight different taxonomic orders. The evidence demonstrates that aqueous and methanolic extracts from seeds and leaves, seed oil, and petroleum ether seed extracts were effective against insect pests of stored grains, aphids of cabbage and sorghum, fruit flies, and desert locusts. The extracts caused high mortality, controlled the populations, reduced oviposition, diminished hatchability, and increased the antifeedant effect. However, the type of solvent used to obtain the botanical extract and the method of application (contact or food) are fundamental to increase its bioactivity. Therefore, botanical extracts from seeds and leaves of J. curcas should be considered as an alternative against insect pests and may be incorporated into integrative and sustainable management for insect control.

Impact of insect growth regulators on reproduction and life stages of Tribolium Castaneum (Coleoptera: Tenebrionidae)

Tribolium castaneum is devastating cosmopolitan insect pest of stored grain. The present study investigated the impact of three insect growth regulators on different life stages of T. castaneum. Percent mortality (%) induced was observed at 0.75. 1.25, 2.5, 5, 10, and 20 ppm doses of each IGR after 7, 14 and 21 day exposure. In addition to larval and parental mortality, progeny suppression data was also recorded. The larvae of the 2nd instar were more susceptible to lufenuron, with mortality reaching 100% at 10ppm even after a 14-day interval. In the case of pyriproxifen, 2nd instar did not responded to all dose rates until 14 days however 21 days, statistically corresponding 2.5 to 10 ppm dose rates was detected. At 20 ppm, methoxy fenazide resulted in 92 percent mortality of 2nd larval instar mortality, and the larvae responded to all dose rates at all exposure intervals that varied significantly among themselves. The mean mortality of the 4th instar larvae at 20 ppm for lufenuron after a 21-day interval was 90%, which was not significantly different from the mortalities (62 and 80%) at the same dose rate after 7 and 14 days, respectively. All the IGRs were very effective in progeny suppression (>80%) and complete progeny suppression (100%) was observed in adults treated with methoxyfenazide and lufenuron at 2.5 and 10 ppm doses, respectively. It is concluded that all the screened IGRs were effective in progeny suppression and in some cases, complete progeny suppression was achieved

Ozonation of Cowpea Grains: Alternative for the Control of Callosobruchus maculatus and Maintenance of Grain Quality

Nowadays, the modified atmosphere with ozone is one of the main alternatives for controlling insect pests in stored grains, as it allows grain quality to be maintained while causing no environmental damage. In light of this, the purpose of this study was to assess the toxicity of ozone to C. maculatus in cowpea grains as well as how it affects the physiological and physical properties of the grains. The toxicity was determined by estimating lethal doses (mg/g) at the top and bottom of the fumigation chamber for 50% and 95% of adult insects (LD50 and LD95). Cowpea grain samples were removed after being exposed to ozone, and the effect of ozonation on the physical and physiological quality of the grains was assessed. The electrical conductivity, water content, and germination were all examined in this manner. The lethal doses LD50 were 65.97 and 45.52 mg/g when the insects were distributed at the top and bottom of the fumigation chamber, respectively. As a result, ozone toxicity was higher at the bottom than at the top. The increase in ozone doses resulted in a decrease in water content. The germination rate exceeded 90% in both locations where ozone was applied. The electrical conductivity remained constant, ranging between 152.01 and 239.59 S cm−1 g −1. The findings indicate that ozone is toxic to C. maculatus but has no effect on grain quality. Ozone may therefore be used to manage C. maculatus in cowpea that has been stored.

Bioatividade de óleo essencial de Piper aduncum L. para insetos-praga de produtos armazenados

ABSTRACT Determining the bioactivity of essential oils extracted from plants is crucial for the development of alternatives for controlling insect pests in stored grains. This study aimed to investigate the bioactivity of Piper aduncum L. essential oil for the control of Sitophilus zeamais (Coleoptera: Curculionidae), Sitophilus oryzae (Coleoptera: Curculionidae) and Cryptolestes ferrugineus (Coleoptera: Cucujidae). Bioassays were conducted to determine the oil toxicity, sublethal effects, attractiveness and flight initiation behavior. Toxicity tests were carried out to determine the lethal concentrations for 50 and 95 % of the insects (LC50 and LC95). Tests were also performed with sublethal exposures to C. ferrurineus, S. oryzae and S. zeamais, using their respective LC5 values (0.0002, 0.097 and 0.11 µL cm-2), to investigate effects on the attraction or repellency activity, as well as flight tests. C. ferrugineus showed greater LC50 (0.0005 µL cm-2) and LC95 (0.0012 µL cm-2) susceptibility, in relation to S. oryzae LC50 (0.35 µL cm-2) and LC95 (1.26 µL cm-2), and S. zeamais LC50 (0.39 µL cm-2) and LC95 (1.40 µL cm-2). The exposure to the sublethal LC5 concentration influenced the behavioral responses of attractiveness/repellency and flight activity. The oil had a neutral effect on C. ferrugineus LC5 (0.0002 µL cm-2) and an attractive effect on S. oryzae and S. zeamais LC5 (0.097 and 0.11 µL cm-2), and can be considered a potential insecticide for controlling pest weevil species of stored grains.

EFFICACY OF SOME INDIGENOUS PLANT SMOKE AGAINST RED FLOUR BEETLE, TRIBOLIUM CASTANEUM (L)


 Red flour beetle, Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) is one of the major insect pests of stored grains. Due to export legislation and zero-tolerance for live insects in trade commodities, extensive use of synthetic insecticides is in practice to eliminate pest infestations from the lots. Currently, the only acceptable chemical to be used in stored grain is phosphine but due to its excessive usage, the stored grain pests are becoming resistant to it. Hence, the discovery of alternative compounds is much needed. In this study, we have compared the repellency of different plants smoke from five commonly found plants of Pakistan, viz. neem Azadirachta indica (Meliaceae), costus Saussurea lappa (Asteraceae), turmeric Curcuma longa (Zingiberaceae), sweet flag Acorus calamus (Acoraceae) and valerian Valeriana officinalis (Caprifoliaceae) against T. castaneum. After two hours of smoke, Azadirachta indica showed a maximum 75.89±2.14% repellency followed by Saussurea lappa (44.15±1.87%), Curcuma longa (43.22±2.51%), Acorus calamus (23.15±1.75%;) and Valeriana officinalis (18.40±1.40%). This is a baseline study for the management of T. castaneum, further research on this aspect is required to be investigated. The results of this study support the use of botanicals alternative to synthetic insecticides for stored product pest management.

Bio-efficacy of ground plant powders on the population of Tribolium castaneum (Herbst) in stored green gram

Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) is one of the major insect pests of stored grains. Experiment was conducted for studying the efficiency of ground plant materials for management of T. castaneum in stored green gram and effect of plant powders on seed germination in laboratory of Department of Entomology, CoA, CAU, Imphal during the period 2021-2022. Studies on effect of plant powders on management of T. castaneum revealed that Black pepper @ 1.5g/kg seed shows maximum mean adult mortality of 100.00 per cent and Sweet flag @ 1.5g/kg seed shows lowest mean adult mortality of 33.33 per cent. Highest seed damage was recorded in Sweet flag @ 1.5g/kg seed (8.00 per cent) and least was in Black pepper @ 1.5g/kg seed (1.67 per cent). Maximum adult emergence was noted in treatment of Sweet flag @ 1.5g/kg seed (8.00 per cent) and lowest was in China berry @ 1.5g/kg seed (1.33 per cent). Evaluation of germination percentage reveals that minimum germination percentage was recorded in Black pepper @ 1.5g/kg seed (91.33 per cent) and maximum was in Indian wormwood @ 1.5g/kg seed (98.67 per cent) but none of the treatment recorded the percentage below the prescribed germination percentage of green gram. Plant powders offers efficient control of red flour beetle and these are available locally and did not show any adverse on the environment and hence can be recommended as alternatives to the chemical insecticides.

Role of Lipids in Phosphine Resistant Stored-Grain Insect Pests Tribolium castaneum and Rhyzopertha dominica.

Simple SummaryThe red flour beetle, Tribolium castaneum, and lesser grain borer, Rhyzopertha dominica, cause significant damage to stored commodities, including grains. The most widely used fumigant to control stored-product insects is phosphine. However, resistance to this fumigant is worldwide problem. In this study, we examined the lipid content of phosphine resistant and susceptible strains of T. castaneum and R. dominica. The results showed that the resistant strains of both species contained more lipids than the susceptible strains. The finding will contribute to the understanding of the mechanisms of phosphine resistance and provide additional information for developing strategies for managing the resistance problem.Insects rely on lipids as an energy source to perform various activities, such as growth, flight, diapause, and metamorphosis. This study evaluated the role of lipids in phosphine resistance by stored-grain insects. Phosphine resistant and susceptible strains of the two main stored-grain insects, Tribolium castaneum and Rhyzopertha dominica, were analyzed using liquid chromatography-mass spectroscopy (LC-MS) to determine their lipid contents. Phosphine resistant strains of both species had a higher amount of lipids than susceptible stains. Significant variance ratios between the resistant and susceptible strains of T. castaneum were observed for glycerolipids (1.13- to 53.10-fold) and phospholipids (1.05- to 20.00-fold). Significant variance ratios between the resistant and susceptible strains of R. dominica for glycerolipids were 1.04- to 31.50-fold and for phospholipids were 1.04- to 10.10-fold. Glycerolipids are reservoirs to face the long-term energy shortage. Phospholipids act as a barrier to isolate the cells from the surrounding environment and allow each cell to perform its specific function. Thus, lipids offer a consistent energy source for the resistant insect to survive under the stress of phosphine fumigation and provide a suitable environment to protect the mitochondria from phosphine. Hence, it was proposed through this study that the lipid content of phosphine-resistant and phosphine-susceptible strains of T. castaneum and R. dominica could play an important role in the resistance of phosphine.

Resistance to Phosphine In Rice Weevil <i>Sitophilus oryzae</i> (L.) from South India

Rice weevil Sitophilus oryzae (L.) is one of most serious insect pests of stored grains. Management of this is thus vital and fumigation with phosphine gas is the most common method. However, overreliance on this has resulted in the development of heritable resistance in S. oryzae. The detection of frequency and distribution of phosphine resistance is crucial for the development of resistance management strategy. This study assesses the frequency, strength and distribution of phosphine resistance in S. oryzae populations from four southern states of India viz., Tamil Nadu, Kerala, Andhra Pradesh and Telangana. The bioassay results revealed that all these survived at both the discriminating concentrations of 0.04 and 0.25 mg/ l. There were no susceptible and weak resistant populations, and exhibited varied frequency of strong resistance ranging from 13.33 to 80.90%. The populations from Pudukottai (80.90%) recorded high frequency of strong resistance followed by Trichy (68.97%) and Tirunelveli (67.82%) ones; the one from Thiruvarur exhibited lowest (13.33%). The results indicated that the resistance to phosphine in S. oryzae was common and prevalence of strong resistant individuals was prevalent across the sampled regions.

Tandemly duplicated genes encoding polygalacturonase inhibitors are associated with bruchid (Callosobruchus chinensis) resistance in moth bean (Vigna aconitifolia)

Bruchids are stored-grain insect pests responsible for serious seed loss in legume crops. A previous study using an F2 population (F2OA) derived from a cross between wild moth-bean (Vigna aconitifolia [Jacq.] Maréchal) accession TN67 (resistant) and cultivated moth-bean accession ICPMO056 (susceptible) revealed that resistance to the azuki bean weevil (Callosobruchus chinensis L.) in TN67 was regulated by a single gene located in the major quantitative trait locus—qVacBrc2.1. In this study, qVacBrc2.1 was finely mapped and candidate genes in this locus were identified using F2OA and another large F2 population (F2NB) derived from the cross mentioned previously. In contrast to the previous study, segregation analysis in the F2NB population revealed that resistance against this pest was controlled by two genes. Furthermore, the addition of novel markers to qVacBrc2.1 and reanalysis of the QTL in the F2OA population demonstrated that qVacBrc2.1 constituted two linked QTLs—qVacBrc2.1-A and qVacBrc2.1-B. The presence of qVacBrc2.1-B was verified using the population F2NB. Comparative genomics using three Vigna spp. strongly suggested the presence of two tandemly duplicated genes, VacPGIP1 and VacPGIP2, which encoded polygalacturonase inhibitors (polygalacturonase-inhibiting proteins) as the candidates for conferring resistance, but only VacPGIP1 could be successfully cloned and sequenced. The alignment of VacPGIP1 coding sequences of TN67 and ICPMO056 revealed eight single nucleotide polymorphisms, three of which altered the amino-acid sequence of the predicted domains of polygalacturonase inhibitors in ICPMO056. Overall, these findings indicate that VacPGIP1 and VacPGIP2 regulated C. chinensis resistance in TN67.

Interaction between Certain Natural Enemies and some Stored-Grain Insect Pests

Interaction between Certain Natural Enemies and some Stored-Grain Insect Pests

Comparative Bioactivity of Bamboo Leaf Ash and Bularafa Diatomaceous Earth against Maize Weevil (Sitophilus zeamais Motschulsky)

Maize is one of the major staple foods in Sub-Saharan Africa and there is serious loss in maize storage due to insect damage. This study compared the bioactivity of Bamboo Leaf Ash (BLA) and Bularafa Diatomaceous Earth (BDE) against Maize Weevil (Sitophilus zeamais Motschulsky) under laboratory conditions. Insecto®, a commercialized DE was also tested as standard check. Adults of the insects were exposed on maize admixed with the BLA at dose rate of 5,000, 10,000 and 20,000ppm; BDE and insecto® at a dose rate of 1,000ppm, at 28.20C and 82.2% relative humidity. Mortality increased with increasing exposure duration and all treatments showed mortality of more than 80% after 14days post-treatment compared to negative control with 0%.The treatments suppressed F1 progeny. Treated grains have weight loss less than 4%, kennel damage less than 14% and grain germination showed no significant change. The decreasing efficacy of the dusts against this insect is Insecto®> BLA > BDE. BLA and BDE have potential for the management of insect pests of stored grain in Nigeria.

Insecticidal Effects of Neem Leaf Extract, Inert Dust, and Entomopathogenic Fungi on Control of Khapra Beetle (Trogoderma granarium); A Stored Grain Pest

Infestation by different insect pests of stored cereals and the storage of their products is a serious problem. Khapra beetle (Trogoderma granarium) is one of the most common, devastating insect pests of stored grains. It causes both nutritional and economical losses to stored cereals. Six different concentrations of three protectants (neem leaf extract, inert dust, and entomopathogenic fungus) were used for the bioassay in the present study. For neem leaf extract dose rates were 5%, 10%, 15%, 20%, 25% 30% and leaves were collected from University of Agriculture Faisalabad, Pakistan. For DE formulation (Conern®) doses rates were 200ppm, 400ppm, 600ppm, 800ppm, 1000ppm 1200 ppm/kg and 1g, 2g, 3g, 4g, 5g 6g/ kg of wheat grains doses of Beauveria bassiana (Racer Bb) (1 g of Racer containing 108 conidia) imported from Agri Life, Medak District. Hyderabad, India was used. 30 larvae were used in each bioassay. Different doses of insecticides showed remarkable toxicity and significantly higher mortality rates in Khapra beetle. The toxic effect was found to be dependent on dose and duration. Summarizing, these insecticides could have likely practical utilizations in the protection of stored grain products against the attack by Trogoderma granarium.

Identification of Biomarker Volatile Organic Compounds Released by Three Stored-Grain Insect Pests in Wheat.

Monitoring and early detection of stored-grain insect infestation is essential to implement timely and effective pest management decisions to protect stored grains. We report a reliable analytical procedure based on headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry (HS-SPME-GC-MS) to assess stored-grain infestation through the detection of volatile compounds emitted by insects. Four different fibre coatings were assessed; 85 µm CAR/PDMS had optimal efficiency in the extraction of analytes from wheat. The headspace profiles of volatile compounds produced by Tribolium castaneum (Herbst), Rhyzopertha dominica (Fabricius), and Sitophilus granarius (Linnaeus), either alone or with wheat, were compared with those of non-infested wheat grains. Qualitative analysis of chromatograms showed the presence of different volatile compound profiles in wheat with pest infestation compared with the wheat controls. Wheat-specific and insect-specific volatile compounds were identified, including the aggregation pheromones, dominicalure-1 and dominicalure-2, from R. dominica, and benzoquinones homologs from T. castaneum. For the first time, the presence of 3-hydroxy-2-butanone was reported from S. granarius, which might function as an alarm pheromone. These identified candidate biomarker compounds can be utilized in insect surveillance and monitoring in stored grain to safeguard our grain products in future.

Insecticidal and repellency effects of a Turkish diatomaceous earth formulation (Detech) on adults of three important pests of stored grain

In this study, laboratory experiments were conducted in order to assess the insecticidal and repellency effects of a novel Turkish diatomaceous earth (DE) formulation (Detech) on adults of the rice weevil, Sitophilus oryzae (L., 1763) (Coleoptera: Curculionidae), the confused flour beetle, Tribolium confusum du Val., 1863 (Coleoptera: Tenebrionidae), and the lesser grain borer, Rhyzopertha dominica (F., 1792) (Coleoptera: Bostrichidae). For the insecticidal activity, bioassays were conducted with soft wheat treated with 0, 600 and 900 ppm of Detech at 25 ± 1°C and 65 ± 5% RH and progeny production was assessed after 45 days. For the repellency tests, two-choice tests on mono-layer wheat were conducted at 1,000 ppm of Detech at 25 ± 1°C and 65 ± 5% RH. Overall, Detech was effective against T. confusum and S. oryzae adults in wheat, causing 82% to 100% mortality at 600 and 900 ppm after 7 and 14 days exposure. The complete, or almost complete, progeny inhibition of S. oryzae were found at both concentrations, whereas the highest reduction in R. dominica progeny (84%) was obtained at 900 ppm. Detech was highly and moderately repellent to T. confusum and S. oryzae adults, respectively, whereas it had no or low repellency effect on R. dominica adults. In conclusion, Detech, which consists of a mixture of three DE deposits with different diatom frustules has potential for use against stored-grain insect pests as a promising grain protectant. Experiments were conducted in 2020-2021 in Entomology Laboratory of Tekirdağ Namık Kemal University and Kahramanmaraş Sütçü İmam University.

Reducing Postharvest Loss of Stored Grains Using Plant-Based Biopesticides: A Review of Past Research Efforts

The world population is projected to be 9.1 billion by the year 2050, and about 70% extra food will be required. One of the main challenges regarding food security is postharvest loss due to insect pests. The overall postharvest grain losses for sub-Saharan Africa could be as high as US$4 billion/year. This is around 15% of the total production of cereal crops. The use of chemical pesticides to reduce grain damage by insects over the past five decades has led to a range of environmental and human health problems. These problems forced researchers to develop alternative methods that have lower adverse effects. Alternative strategies focus on new forms of pesticides that are effective against a specific target species, have fewer residues in food, are unlikely to contaminate the environment, and have lower potential to produce resistance, are biodegradable, and are suitable for use in integrated pest management programs. Some natural plant products effectively meet these criteria and have the potential to manage insect pests of stored grains. However, the understanding of the use of botanical pesticides in storage pest management systems is limited in most parts of sub-Saharan African countries. Effective plant products are not formulated and used widely. To fill the gaps the first step is to synthesize the available information and disseminate it. This review is, therefore, a summary of the current developments and improvements of botanical pesticides in the management of stored grain pests including challenges and future issues in insect pest management.

Integrated Pest Management for Stored Grain: Potential Natural Biological Control by a Parasitoid Wasp Community.

Simple SummaryParasitoid wasps are well-known biological control agents for arthropod pests in agricultural and forest ecosystems. The stored food product environment is generally also favourable for the parasitoid wasps of the insect pests that infest those food products. Nevertheless, most studies suggest that biological control can reduce pest populations sufficiently only when combined with additional pest-management tools. Combining natural enemies and synthetic chemical pesticides is one of the main challenges in integrated pest management (IPM). We estimated, for the first time, the naturally occurring parasitoid community in grain stores before and after use of synthetic chemical pesticides. There is strong evidence that despite the immediate effect of the pesticides on the parasitoid community, over time, the community can recover. Undoubtedly, a lot of research, particularly of the nature of parasitoid wasps’ recovery in grain-storage facilities, is still required. This will reduce chemical use and implement biological control as a successful and important component of stored-product IPM.Insect contamination of stored grain is a major concern for the grain industry. Phosphine is currently the standard fumigant used to control insect pests in stored grain. However, some species and populations of insects that infest stored grain exhibit resistance to this fumigant and consumers are concerned about pesticide residues. Therefore, alternative methods of effective pest control are needed to partially or completely replace the use of phosphine. There is growing interest in biological control via parasitoid wasps. However, there is evidence that biological control will succeed only if used alongside other pest-management measures. Integrating biological control with the use of chemical insecticide is challenging and may lead to severe reductions in parasitoid survival and success. The main aim of the current study is to shed light on a greatly overlooked issue: the parasitoid community found in stored grain before and after phosphine treatment. The current study results indicate that there is a high level of parasitoid biodiversity within grain stores. We found common parasitoids at both semi-arid and Mediterranean sites, suggesting that those parasitoids can be active across a wide range of abiotic conditions. This research indicates that the community may recover even though phosphine has an immediate negative effect on a parasitoid community. Nevertheless, the parasitoid wasps seem to reduce the host population insufficiently. In light of the findings presented here, those interested in implementing pest-management strategies that include both phosphine treatment and biological control should consider conservation and augmentation of the naturally occurring parasitoid population. These studies should take into account interactions between and within parasitoid populations and phosphine distribution within the grain storage. To limit the effect of phosphine on the parasitoids, pest-management strategies should also reflect careful consideration of the timing of phosphine treatment and the need for sufficient refuge for the parasitoids.

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).

Efficacy of different entomopathogenic fungal isolates against four key stored-grain beetle species

The development of resistance in stored-grain insect pests can be effectively reduced by using biological control methods. Entomopathogenic fungi have been under consideration as complementary and alternative agents to synthetic insecticides. The aim of this study is to identify the pathogenic potential of four different fungal isolates of Beauveria bassiana (Bals.-Criv.) Vuill. (Hypocreales: Cordycipitaceae) (WG-47, WG-48, WG-50, WG-51) and three isolates of Metarhizium anisopliae (Metchnikoff) Sorokin (Hypocreales: Clavicipitaceae) (WG-46, WG-49, WG-52) against the adult stages of the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae), the granary weevil, Sitophilus granarius (L.) (Coleoptera: Curculionidae), the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) and the khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae) at 1 × 106, 1 × 107, 1 × 108 and 1 × 109 conidia/kg wheat. Mortality was found dose dependent among all the tested species. Rhyzopertha dominica was the most susceptible followed by S. granarius, T. castaneum and T. granarium. Among the different isolates B. bassiana caused higher mortality compared to M. anisopliae. The isolates WG-50 and WG-51 of B. bassiana provided maximum mortality among the different tested species and led to lower F1 individuals compared to the controls. Our study indicates that entomopathogenic fungi have an elevated potential to successfully manage the aforementioned coleopteran species on stored wheat.