Storage Insect Research Articles

Hypoxic environment protects cowpea bruchid (Callosobruchus maculatus) from electron beam irradiation damage.

Electron beam (eBeam) irradiation and hermetic storage are safe and effective technologies to protect stored products. Although hypoxic environment improves performance of some irradiated insects, whether hypoxia affects irradiation of storage insects and impacts pest control efficacy remains to be investigated. Using cowpea bruchid (Callosobruchus maculatus) larvae, we showed that, relative to eBeam irradiation under normoxia, the adult emergence rate increased substantially if they were exposed to hypoxia prior to and during eBeam treatment. Conversely, exposure to hypoxia only after eBeam irradiation did not have this protective effect. eBeam irradiation caused an increase in reactive oxygen species (ROS) in normoxic larvae but not in hypoxic larvae. The activity of citrate synthase, a pace-making enzyme in the citric acid cycle, was suppressed under hypoxia but resumed normal function within hours of reoxygenation, suggesting that reduced mitochondrial activity, and thus less ROS production under hypoxia increased insect tolerance to irradiation. Furthermore, reoxygenation accelerated eBeam-induced glutathione-S-transferase activation and potentiated eBeam-enhanced catalase activities. Faster and stronger detoxification capacity in eBeam-irradiated, hypoxic larvae may have protected them from oxidative damage. Hypoxic environment enhanced radiotolerance of bruchid larvae, presumably due to limited ROS production and elevated antioxidant enzymatic activities after reoxygenation. © 2018 Society of Chemical Industry.

English

Common bean (Phaseolus vulgaris L.) is a legume that contributes to food security and poverty reduction in Benin. However, there is very little information on its production constraints, varietal diversity, storage practices, storage insect management, and seed system. While these information are necessary for use in breeding programs and a better conservation of this legume. To fill these gaps, ethnobotanical surveys were conducted in 23 villages selected through central Benin using participatory rural appraisal tools and techniques. The number of beans landraces ranged from 3 to 5 per village (4.7 on averages) and from 1 to 4 per household (1.7 on average). A total of 26 common beans folk varieties, corresponding to 12 climbing bean landraces were recorded in the study area. A high rate of threat of landraces disappearance was recorded through surveyed villages. Various seeds storage tools were recorded and the seed system was essentially informal. The use of inert substances, chemical insecticides and insect repellent/insecticidal plants to control storage insects has been reported in the study area. Farmers noted a differential susceptibility of common bean landraces to storage insect pest. Our findings showed that there is an urgent need of development of integrated bean storage insect management strategies. Key words: Constraints, common bean, insect pests, seed system, varietal diversity.

Effect of Storage Containers and Lengths of Storage on the Germination, Moisture Content and Pest Infestation of Wheat Seed

Abstract A laboratory experiment was conducted at the Department of Agronomy, Hajee Mohammad Danesh Science and Technology University, Dianjpur-5200, Bangladesh to evaluate the storage containers and duration of seed storage on the germinability and health of wheat seeds. The experiment was carried out in two factors, viz. three storage containers naming i) sealed tin container, ii) plastic container, iii) gunny bag, and four storage periods of i) 15 days, ii) 30 days, iii) 45 days, and iv) 60 days. Completely randomized design (CRD) was used in this experiment with eight replications. The results revealed that the germination percentages (GP) of the seeds stored in the gunny bag decreased quickly from 66.1 to 32.8% due to contained with high moisture content in seed. But, slowly decreasing trends of GP from 80.4% to 69.2% was observed in the sealed tin container seeds with lesser moisture content than that of gunny bag and plastic container. The reduction of GP was so higher of 50.38% in the seeds contained in gunny bag than that of only 13.93% in the seeds contained sealed tin container. Wheat seeds stored in sealed tin container, plastic container and gunny bag significantly increased moisture content in ambient condition for 60 DAS. The moisture content of the seeds stored in gunny bag was found to rise remarkably more than other containers. This escalation of seed moisture content was closely related to the surrounding environmental conditions, like temperature and relative humidity where seeds were stored. The rate seed deterioration in gunny bag and plastic container paralleled the level of invasion by storage insect was found. During storage period, insect infected the seeds, and the insect bitten seeds were also found higher in gunny bag and plastic container, but lower in sealed container. Wheat seeds should be stored in air tight sealed container and drying should be done after some days of storage (45-60 DAS).

Augmentation of pyrethrins content in callus of Chrysanthemum cinerariaefolium and establishing its insecticidal activity by molecular docking of NavMS Sodium Channel Pore receptor.

Pyrethrins are effective food-grade bio-pesticides obtained from the flowers of Chrysanthemum cinerariaefolium and this crop cannot be cultivated widely in India due to its specific agro-climatic requirement. Hence pyrethrins are mostly imported from Kenya. Therefore, the present study aims to develop a process for augmentation of pyrethrin contents in C. cinerariaefolium callus and establish the correlation between early knockdown effects through docking on grain storage insect. In vitro seedlings were used as explants to induce callus on MS medium with different concentrations of auxins and cytokinins. Pyrethrin extracted from the callus was estimated by RP-HPLC. In callus, total pyrethrin was found to be 17.5µg/g, which is higher than that found in natural flowers of certain Pyrethrum cultivars. The concentrations of cinerin II, pyrethrin II and jasmoline II were quite high in callus grown on solid medium. Bio-efficacy of pyrethrum extracts of flower and callus on insect Tribolium sp., showed higher repellency and early knock-down effect when compared with pure compound pestanal. Further, the rapid knockdown effect of all pyrethrins components was established by molecular docking studies targeting NavMS Sodium Channel Pore receptor docking followed bymultiple ligands simultaneous docking, performed to investigate the concurrent binding of different combinations of pyrethrin. Among the six pyrethrin components, the pyrethrin I and II were found to be a more efficient, binding more firmly to the target, exhibiting higher possibilities of insecticidal effect by an early knockdown mechanism.

Diversity, evolution, and function of myriapod hemocyanins

BackgroundHemocyanin transports O2 in the hemolymph of many arthropod species. Such respiratory proteins have long been considered unnecessary in Myriapoda. As a result, the presence of hemocyanin in Myriapoda has long been overlooked. We analyzed transcriptome and genome sequences from all major myriapod taxa – Chilopoda, Diplopoda, Symphyla, and Pauropoda – with the aim of identifying hemocyanin-like proteins.ResultsWe investigated the genomes and transcriptomes of 56 myriapod species and identified 46 novel full-length hemocyanin subunit sequences in 20 species of Chilopoda, Diplopoda, and Symphyla, but not Pauropoda. We found in Cleidogona sp. (Diplopoda, Chordeumatida) a hemocyanin-like sequence with mutated copper-binding centers, which cannot bind O2. An RNA-seq approach showed markedly different hemocyanin mRNA levels from ~ 6 to 25,000 reads per kilobase per million reads. To evaluate the contribution of hemocyanin to O2 transport, we specifically studied the hemocyanin of the centipede Scolopendra dehaani. This species harbors two distinct hemocyanin subunits with low expression levels. We showed cooperative O2 binding in the S. dehaani hemolymph, indicating that hemocyanin supports O2 transport even at low concentration. Further, we demonstrated that hemocyanin is > 1500-fold more highly expressed in the fertilized egg than in the adult.ConclusionHemocyanin was most likely the respiratory protein in the myriapod stem-lineage, but multiple taxa may have independently lost hemocyanin and thus the ability of efficient O2 transport. In myriapods, hemocyanin is much more widespread than initially appreciated. Some myriapods express hemocyanin only at low levels, which are, nevertheless, sufficient for O2 supply. Notably, also in myriapods, a non-respiratory protein similar to insect storage hexamerins evolved from the hemocyanin.

Impact of Insect Densities Tribolium Castaneum on the Benzoquinone Secretions and Aflatoxins Levels in Wheat Flour During Storage Periods

Objectives: The present study was prepared to investigate the impact of insect density, adult emergence of Tribolium castaneum on the secretion of Benzoquinones (BQs) consist of methyl-1,4-benzoquinone(MBQ) and Ethyl-1,4-Benzoquinone (EBQ), and accumulation of Aflatoxins (AFs) in wheat flour stored at different periods. Methods: Forty grams of wheat flour were put into small glass jars (8 cm diameter and 12 cm length). Then T. castaneum was put in each jars at rates of 10, 20 and 30 unsexed pairs of insect adult. The jars were covered with muslin cloth and the rubber band was fixed to prevent insects to escape. A glass jar without any insects served as the control. The jars lifted on bench in the laboratory for two, three and four months of storage under laboratory temperature conditions (with average 28 ± 20C and 65±5 R.H). The previous design was replicated three times. At the end of each storage period, the jars containing the flour were sieved thoroughly by 40 wire mesh size to separate the insects. The insects have been counted on the other hand wheat flour was prepared to determine MBQ, EBQ and AFs by HPLC methods. Results: The results indicated the levels of EBQ higher than MBQ in all infested samples at all insect densities (No. of insect pairs). The concentrations of MBQ in wheat flour released by ten adult pairs (10P) with the three storage periods two, three and four months were 10.42 ± 0.56, 22.38 ± 3.67, 27.06 ± 6.71µg/g, respectively. These results increased with insect densities to (30p) were 39.67 ± 0.10, 63.58 ± 2.35 and 106.24 ± 7.4 µg/g after storage periods two, three and four months, respectively. In addition to the concentrations of EBQ with (10P) were 67.45 ± 3.64, 98.0 ± 6.1 204.66 ± 5.8 µg/g with storage periods two, three and four months, respectively. In case (30P) the levels of EBQ were 376.7 ± 0.87, 570.1 ± 2.11 and 1558.66 ± 10.88 (µg/g). The highest concentration of the BQs 1664.90 ± 11.43 (µg/g) released by T. castaneum achieved with the highest adult emergence (1021 insect adult) and the highest insect density (30p) at four months storage period. In general, AFs levels enhanced with a period of storage and insect densities. Conclusion: Levels of the BQs (MBQ and EBQ) increased with an increase of storage periods and insect densities. Therefore, the presence of this insect should be prevented in stored wheat flour reducing AFs contamination is possible by storage for short time and prohibit insects which causes an increase temperature of the flour and moisture, all of which promote production of AFs.

Identification and differentiation of insect infested rice grains varieties with FTNIR spectroscopy and hierarchical cluster analysis

The potential and practicality of FTNIR as a screening tool, with ward’s algorithms, was performed for two different varieties of rice namely, ‘badshah bhog’ and ‘swarna’, followed by cluster, dendrogram, histogram, and conformity analysis with different storage periods (0–225) and insect infestation. Dendrogram analysis resulted in a clear differentiation between infested rice varieties with non-infested ones while hierarchical cluster analysis, lead to detection of different levels of infestations. Histograms analysis of averaged FTINR spectra of rice grains samples provided 100% classification between infested and non-infested samples. Dissimilarities between rice grains were calculated using Pearson’s correlation coefficients which were further converted to D values, and heterogeneity among the different varieties of rice along with a different level of infestation was identified. The results further revealed that the percentage accuracy (%) of classification for badshah bhog varied from 93.10 to 98.84%, while that for the swarna rice was between 95.75 and 99.74%.

From lethality to mortality: exploring the “grey area” of knockdown as an efficacy indicator of different insecticides against major storage insects using a lethality index

In the present work, a lethality index was applied for the evaluation of three insecticides with different modes of action, i.e., thiamethoxam, chlorfenapyr and lambda-cyhalothrin, as surface treatment against adults of Sitophilus oryzae (L.), Oryzaephilus surinamensis (L.) and Tribolium confusum Jacquelin du Val, in laboratory bioassays. The insecticides were applied at their highest label dose, while insect knockdown and mortality were evaluated after 1, 3, 5 and 7 days of exposure to the treated surfaces according to the Standardized Lethality Index, by ranking each insect from “0” to “4,” with “0” corresponding to insects moving normally and “4” corresponding to dead individuals. After the end of the exposure, the surviving insects were transferred to clean, untreated dishes and delayed mortality was assessed after an additional period of 1, 3, 5 and 7 days. Based on the results, initial knockdown was high for S. oryzae after exposure to thiamethoxam and lambda-cyhalothrin even after 1 day of exposure, whereas for longer exposures high mortality levels were recorded. In contrast, in the case of chlorfenapyr knockdown was low after 1 day of exposure; however, high mortality levels were noted after 3 and 5 days of exposure. Similar results were noted for O. surinamensis, which was highly susceptible to all three insecticides tested. The most tolerant insect species to the tested insecticides was T. confusum, since a noticeable number of T. confusum adults were still active at the end of the exposure (7 days). Our results indicate that knockdown is most likely to lead to mortality than to recovery, but there were important differences among the three insecticides tested.

Microbial Dynamics during Industrial Rearing, Processing, and Storage of Tropical House Crickets (Gryllodes sigillatus) for Human Consumption.

In this study, the microbiota during industrial rearing, processing, and storage of the edible tropical house cricket, Gryllodessigillatus, was investigated. To this end, we analyzed samples from the cricket feed, obtained before feeding as well as from the cages, and from the crickets during rearing, after harvest, and after processing into frozen, oven-dried, and smoked and oven-dried (smoked/dried) end products. Although the feed contained lower microbial numbers than the crickets, both were dominated by the same species-level operational taxonomic units, as determined by Illumina MiSeq sequencing. They corresponded, among others, to members of Porphyromonadaceae, Fusobacterium, Parabacteroides, and Erwinia The harvested crickets contained high microbial numbers, but none of the investigated food pathogens Salmonella spp., Listeria monocytogenes, Bacillus cereus, or coagulase-positive staphylococci. However, some possible mycotoxin-producing fungi were isolated from the crickets. A postharvest heat treatment, shortly boiling the crickets, reduced microbial numbers, but an endospore load of 2.4 log CFU/g remained. After processing, an increase in microbial counts was observed for the dried and smoked/dried crickets. Additionally, in the smoked/dried crickets, a high abundance of a Bacillus sp. was observed. Considering the possible occurrence of food-pathogenic species from this genus, it is advised to apply a heat treatment which is sufficient to eliminate spores. Nevertheless, the microbial numbers remained constant over a 6-month storage period, whether frozen (frozen end product) or at ambient temperature (oven-dried and smoked/dried end products).IMPORTANCE The need for sustainable protein sources has led to the emergence of a new food sector, producing and processing edible insects into foods. However, insight into the microbial quality of this new food and into the microbial dynamics during rearing, processing, and storage of edible insects is still limited. Samples monitored for their microbiota were obtained in this study from an industrial rearing and processing cycle. The results lead first to the identification of process steps which are critical for microbial food safety. Second, they can be used in the construction of a Hazard Analysis and Critical Control Points (HACCP) plan and of a Novel Food dossier, which is required in Europe for edible insects. Finally, they confirm the shelf-life period which was determined by the rearer.

English

Maize weevil (Sitophilus zeamais Motschulsky) is a major maize (Zea mays L.) storage insect pest in the tropics which reduces the quantity and quality of maize hence facilitating establishment of aflatoxin and other mycotoxins. The objective of this study was to evaluate maize weevil resistance on selected inbred lines. Twenty eight inbred lines with 2 checks (MTPO701-reistant and Duma 41-susceptible) were used in this experiment. Thirty unsexed adult insects were introduced into 250 ml glass jars with grains of the lines at room temperature. Evaluation of weevil damage was done at 10, 60 and 120 days after maize weevil infestation. Each category of storage period was replicated 4 times and experiment was set at the same time. Data was collected on percent weevil damage, grain weight loss and number of live and dead weevils on each inbred line. ANOVA analysis showed significant differences (P ≤ 0.05) on weight loss. The selection of the resistant genotypes was based on percent weight loss after 60 days. Resistant lines selected included KEN2/TZL2.25# and LEPOOL-1/TZL2-2-1. These lines showed resistance to maize weevil damage and hence can be stored up to 4 months. At 120 days there was maximum damage and most lines could not be differentiated on the basis of resistance. KEN2/TZL2-2-5# showed consistency in resistance to maize weevils at all storage periods. High heritability at 60 days showed that selection for weevil resistance in these inbred lines is effective and feasible. Results in this study also revealed high, positive and significant correlation relationship between percent damage, weight loss and live weevils. The maize weevil resistant lines can be used to improve resistance of high yielding varieties in breeding programmes. Key words: Inbred lines, maize, post-harvest, resistance, Sitophillus zeamais.

Efficacy of non formulated entomopathogenic fungi (Beauveria bassiana) to control the storage insect pests of green gram (Vigna radiata) seeds

The concepts and practical applications of fungal biotechnology continue to make significant contributions to food science. Storage of grains is part of the post-harvest system through which food material passes on its way from field to consumer. Stored pulses are severely infested by beetles of the family Bruchidae (Coleoptera). The present study was focused on the efficacy of microbial pesticides, i.e entomopathogenic fungus (Beauveria bassiana) on the Callosobruchus species were investigated in laboratory in stored green gram (Vigna radiata) seeds. Four different conidial concentrations of B. bassiana were sprayed (1 mL) based on the logarithmic series (4×102, 4×103, 4×104 and 4×105 conidia mL-1) and incubated for 10 days. Twenty four experiments were conducted with a complete randomized block design (CRD) with three replications. B.bassiana, concentration of, 4×105 conidia mL-1 at exposure day 10 gave maximum (99.00 %) insect mortality, moisture content of seed was 11.48% and protein content was 24.5%. Optimally fungal treated samples were devoid of any mycotoxins thereby implying their safety for human consumption. The results indicated that the fungal treatment retain the germination quality of seed. This study provided a novel and environmentally safe technique.

Identification of Insecticidal Constituents from the Essential Oil from the Aerial Parts Stachys riederi var. japonica.

The essential oil of Stachys riederi var. japonica (Family: Lamiaceae) was extracted by hydrodistillation and determined by GC and GC-MS. A total of 40 components were identified, representing 96.01% of the total oil composition. The major compounds in the essential oil were acetanisole (15.43%), anisole (9.43%), 1,8-cineole (8.07%), geraniol (7.89%), eugenol (4.54%), caryophyllene oxide (4.47%), caryophyllene (4.21%) and linalool (4.07%). Five active constituents (acetanisole, anisole, 1,8-cineole, eugenol and geraniol) were identified by bioactivity-directed fractionation. The essential oil possessed fumigant toxicity against maize weevils (Sitophilus zeamais) and booklice (Liposcelis bostrychophila), with LC50 values of 15.0 mg/L and 0.7 mg/L, respectively. Eugenol and anisole exhibited stronger fumigant toxicity than the oil against booklice. 1,8-Cineole showed stronger toxicity, and anisole as well as eugenol exhibited the same level of fumigant toxicity as the essential oil against maize weevils. The essential oil also exhibited contact toxicity against S. zeamais adults and L. bostrychophila, with LC50 values of 21.8 µg/adult and 287.0 µg/cm2, respectively. The results indicated that the essential oil of S. riederi var. japonica and its isolates show potential as fumigants, and for their contact toxicity against grain storage insects.

Dicationic ionic liquids as new feeding deterrents

In this study, new quaternary bis(ammonium) salts with alkyl-1,X-bis(dimethyldecylammonium) cation and saccharinate, acesulfamate, lactate and pyroglutamate anions were synthesized and characterized by 1H and 13C NMR spectroscopy. Thermal gravimetric and differential scanning calorimetry analyses confirmed that all salts were thermally stable and the majority of them exhibited melting points below 100 °C. The physicochemical properties (viscosity, density, refractive index values, and solubility) of the obtained salts were determined for three compounds with lactate anions. All the tested salts have suitable properties which, in practical application, will reduce the losses caused by the most important storage insects. Most of the synthesized ionic liquids had comparable or better deterrent activity than azadirachtin—an alkaloid known as the most active antifeedant.Graphical abstract

Bioactivity of Pistacia atlantica desf. Subsp. Kurdica (Zohary) Rech. F. and Pistacia khinjuk stocks essential oils against Callosobruchus maculatus (F, 1775) (Coloeptera: Bruchidae) under laboratory conditions

One of the major storage insect pests of cowpea and many other grains is Callosobruchus maculatus (F.) (Col.: Bruchidae). The use of plant materials rather than conventional pesticides to control these pests is a promising alternative to neurotoxic insecticides. In this study, for the first time, the fumigant, contact toxicity and repellent activity of Pistacia atlantica Desf. Subsp. kurdica (Zohary) Rech. f. (gum, fruit and leaves) and Pistacia khinjuk Stocks (fruit and leaf) essential oils were tested against adults of C. maculatus. The essential oil from P. khinjuk fruit showed a stronger fumigant activity against C. maculatus after 24 h exposure (LC50 = 22 μl/l air) compared to the leaves (LC50 = 29 μl/l air). As for P. atlantica subsp. kurdica, the essential oil from the gum showed the highest activity at 24 h (LC50 = 7.0 μl/l air) compared to the fruit (LC50 = 18 μl/l air) and leaves (LC50 = 24 μl/l air). In contact toxicity bioassays, the P. khinjuk fruit and leaf oils caused significant mortality to C. maculatus adults upon contact for 24 h (LC50 = 0.12 μl/cm2 and LC50 = 0.14 μl/cm2, respectively), while the P. atlantica subsp. kurdica gum was the most toxic at 24 h (LC50 = 0.07 μl/cm2) compared to the fruit oil (LC50 = 0.11 μl/cm2) and leaf oil (LC50 = 0.08 μl/cm2). At the highest concentration of 0.0234 μl/cm3, the respective repellency percentages for P. atlantica subsp. kurdica gum, leaves and fruit oils at 24 h were 82%, 77% and 70%. For P. khinjuk, the respective repellency percentages for the leaf and fruit oils at 24 h were 76% and 67% at the highest concentration (0.0234 μl/cm3). These results indicate strong fumigant and contact toxicity, and repellent activity for all the tested essential oils against C. maculatus. Hence, the data can be exploited further to develop a management strategy against C. maculatus.

Potential of pyrethroid-synergised pyrethrum on stored product insects and implications for use as prophylactic sprays.

The study was conducted to evaluate the synergistic effects of 2% pyrethrum extract with synthetic pyrethroids on the mortality of stored product insects. Contact toxicity was performed at variable concentrations observing mortality at 12, 24 and 48h durations. The results of the present study indicated that, pyrethrum + deltamethrin combination (25:1 ratio) was effective on the adults of Rhyzopertha dominica (F.) and Tribolium castaneum (Herbst). On the other hand, pyrethrum + cypermethrin combination proved effective against Sitophilus oryzae (L.). The efficacy of the tested combination showed reasonable increase in mortality response in treated insects over increasing exposures. At 48h, 450ppm pyrethrum + deltamethrin combination induced 25, 90 and 97% mortalities in S. oryzae, T. castaneum and R. dominica adults; while, pyrethrum-cypermethrin combination recorded 75, 45 and 75% mortalities respectively. On the other hand, it was observed that, among the pyrethrum alone treatments i.e. at 300, 450 and 600ppm concentrations, maximum mortality (62.5%) was observed in S. oryzae exposed to 600ppm pyrethrum for 48h. The effective LC50 concentrations for pyrethrum (600ppm) + deltamethrin combination was estimated to be as 0.1987 and 0.7039µl/cm2 for R. dominica and T. castaneum adults respectively. Contrastingly, for treatments with S. oryzae, a LC50 value of 0.8673µl/cm2 was recorded for pyrethrum (600ppm) + cypermethrin mixture. This investigation strengthens the fact that pyrethrum along with pyrethroids is effective against storage insect pests which can be promisingly a safer insecticidal combination.

Cumulative oxygen consumption during development of two postharvest insect pests: Callosobruchus maculatus Fabricius and Plodia interpunctella Hübner

Insect pests such as Callosobruchus maculatus Fabricius and Plodia interpunctella Hübner cause substantial losses to grain during postharvest storage. In the last few years, hermetic storage technologies have been successfully used by smallholder farmers in Africa and Asia to protect their harvested grain against insect pests. Hermetic technologies owe much of their effectiveness to restricting oxygen availability to insects confined in the containers. There is a need to better understand the biology of specific storage insect pests and their responses to hypoxia. We employed a novel and non-invasive analytical technology, the OxySense 5250i, to measure oxygen levels in closed containers, and evaluated its effectiveness in measuring the total oxygen consumption of two insect pests during their development: C. maculatus and P. interpunctella. The total amount of oxygen consumed by C. maculatus during its larval development period determined with the OxySense apparatus was not different from that previously recorded using another instrument, the Mocon Pac Check 325 gas analyzer. Using the OxySense 5250i, we found that P. interpunctella consumes nearly three times as much oxygen per insect over its larval-to-adult developmental period compared to C. maculatus. Information on the lifetime oxygen consumption of insects provides relevant information to the effectiveness and ability of hermetic technologies to protect stored products against insect pests.

Blanket application rates for synthetic grain protectants across agro-climatic zones: Do they work? Evidence from field efficacy trials using sorghum grain

Many smallholder farmers in sub-Saharan Africa rely on synthetic pesticides for protecting stored-grain. Recommendations on use of these grain protectants are typically based on “blanket” application rates which are fixed rates that are not varied according to grain type, pest range or agro-climatic regions. There are numerous anecdotal reports of storage pesticide failure or reduced efficacy from farmers. Might rising global temperatures be a contributory factor? Smallholder farmers are responding by over-applying pesticides, increasing the application frequency or switching to non-recommended pesticides; leading to a pesticide treadmill. Trials to determine the efficacy and persistence of five commercially-available synthetic pesticides applied at manufacturer's recommended rates on stored sorghum grain under contrasting climatic conditions were conducted in Mbire (mean temperatures of 32–42 °C and 30–50% rh) and Harare (18–32 °C; 42–75% rh) districts in Zimbabwe. Grain samples were collected at 8-week intervals throughout a 10 month period in the 2014/15 and 2015/16 storage seasons. The samples were analyzed for insect grain damage, weight loss, total number of storage insects by species and grain moisture content. Results showed significant differences in the performance of treatments (p < 0.001). Grain damage was consistently higher in Harare than in Mbire. Tribolium castaneum was the dominant pest in Mbire, while Sitotroga cerealella and Sitophilus oryzae were dominant in Harare. Tribolium castaneum populations were high in the Shumba Super dust® (fenitrothion 1% + deltamethrin 0.13%) treatment in Mbire, while S. cerealella was dominant in Super guard® (pirimiphos-methyl 1.6% + permethrin 0.4%) and Actellic Gold dust® (pirimiphos-methyl 1.6% + thiamethoxam 0.36%) treated grain in Harare. Grain moisture content varied with ambient conditions, and was high in treatments with high insect pest levels. The results show that differences in climatic conditions influence insect pest species dynamics and response to pesticide treatments. Storage pesticides are not equally effective across different climatic conditions; thus more context-specific application recommendations are required.

On-farm comparison of different postharvest storage technologies in a maize farming system of Tanzania Central Corridor

Seven methods for storing maize were tested and compared with traditional storage of maize in polypropylene bags. Twenty farmers managed the experiment under their prevailing conditions for 30 weeks. Stored grain was assessed for damage every six weeks. The dominant storage insect pests identified were the Maize weevil (Sitophilus zeamais) and the Red flour beetle (Tribolium castaneum). The moisture content of grain in hermetic conditions increased from 12.5 ± 0.2% at the start of storage to a range of 13.0 ± 0.2–13.5 ± 0.2% at 30 weeks. There was no significant difference (F = 87.09; P < 0.0001) regarding insect control and grain damage between hermetic storage and fumigation with insecticides. However, the insecticide treatment of polypropylene yarn (ZeroFly®) did not control the insect populations for the experimental period under farmers' management. Grain damage was significantly lower in hermetic storage and fumigated grain than ZeroFly® and polypropylene bags without fumigation. No significant difference in grain damage was found between airtight treatment alone and when combined with the use of insecticides. During storage, S. zeamais was predominant and could be of more economic importance than T. castaneum as far as maize damage is concerned. At 30 weeks, the germination rate of grain stored with insecticides or in hermetic storage (68.5 ± 3.6% to 81.4 ± 4.0%) had not significantly reduced from the rate before storage (F = 15.55; P < 0.0001) except in ZeroFly®, also in polypropylene bags without treatment. Even though such bags did not control storage pests, farmers still liked this cheap technology. Hermetic storage techniques can be recommended to farmers without the use of insecticides provided they are inexpensive, and the proper application of technologies is ensured.

English

A study was carried out on the insecticidal effects of the powdered stem bark extract of Uvaria chamae and its ethanolic extract on three most devastating stored products pests (Coleopterous) in Nigeria, namely: Callosobruchus maculatus F. (Bruchidae), Rhizopertha dominica F. (Bostrichidae) and Sitophilus zeamais Motschulsky (Curculionidae). Graded concentrations of each formulation of the powdered bark and ethanolic extracts were in exposure chambers of each insect in laboratory bio-assays under ambient conditions (25±2°C). S. zeamais, R. dominica and C. maculatus were exposed to the following concentrations 0.00, 0.10, 0.20, 0.40, 0.80, and 1.60 mg/L grains in three replicates per treatment and control. The mortality of the insects was used to compute mean lethal concentration (LC50) values by probit analysis. All the concentrations tested showed appreciable toxicity against each test insect species. The computed LC50 values for powder formulation gave significantly (P≤0.05) higher toxicity against C. maculatus (1.281 g/kg) than either S. zeamais (2.145 g/kg) or R. dominica (5.189 g/kg). However, the ethanolic extract was more toxic on C. maculatus (0.134 mL/L), S. zeamais (0.173 mL/L) or R. dominica (0.359 mL/L). It was found that the higher the concentration of the ethanolic extract, the higher the mortality. The result implies that, U. chamae powdered and ethanolic stem bark extracts have potentials for use during storage of grains, ensuring food security, profit maximization and availability of seeds for the next planting season without being damaged by these test insect species. The presence of high concentration of steroids and terpenes may be responsible for the observed high insecticidal activity of the test extracts. Key words: Bioassay, Callosobrochus maculatus, storage insect, Uvaria chamae.

Field efficacy and persistence of synthetic pesticidal dusts on stored maize grain under contrasting agro-climatic conditions

Grain storage trials were conducted in two districts of Zimbabwe with contrasting agro-climatic conditions (mean annual temperature of 18–30 °C and 28–42 °C; total rainfall of 750–1000 mm per annum and <450 mm per annum; respectively) to determine the comparative efficacy of commercially-available grain storage synthetic pesticides under contrasting climatic conditions. The five grain protectants, namely Shumba super dust® (fenitrothion 1% + deltamethrin 0.13%), Actellic gold dust® (pirimiphos-methyl 1.6% + thiamethoxam 0.36%), Super guard® (pirimiphos-methyl 1.6% + permethrin 0.4%), Chikwapuro® (pirimiphos-methyl 2.5% + deltamethrin 0.1%) and Ngwena yedura® (pirimiphos-methyl 2.5% + deltamethrin 0.2%) were evaluated at manufacturer's rates on stored shelled maize. The trials were conducted for a 40 week-long storage season in 2014/15 and again in 2015/16. Samples were analysed for insect grain damage, total insects per kilogram, grain weight loss, insect feeding dust and chaff as well as grain moisture content. Temperature and relative humidity within stores were recorded using data loggers. The results highlighted the generally poor efficacy of the synthetic pesticides under both cooler and hotter climatic test conditions. The pesticides failed to prevent insect grain damage or suppress insect pest numbers. Only Actellic gold dust®, introduced in the 2015/16 storage season was effective under both the agro-climatic conditions. The current study suggests that only Actellic gold dust® can be recommended for smallholder farm grain protection under both cooler and hotter climatic conditions. The findings confirm the frequent claims of smallholder farmers in east and southern Africa regarding poor storage pesticide performance, and emphasize the need to develop alternative effective storage insect pest control options.