Interaction between toxigenic fungi and weevils in corn grain samples

This study investigated the ability of weevils to transmit Aspergillus flavus and Fusarium verticillioides fungal spores and the consequent production of mycotoxins. For this purpose, corn grain samples were stored in flasks connected to a hose to form a closed system (flasks A and B). Flasks A were inoculated with the following groups: group 1 (corn + weevil); group 2 (corn + A. flavus); group 3 (corn + A. flavus + weevil); group 4 (corn + F. verticillioides); group 5 (corn + E verticillioides + weevil), and group 6 (corn + A. flavus + E verticillioides + weevil). Flasks B contained sterile grains. The samples were incubated for 10, 20 and 30 days, posteriorly, weight, water activity, mycoflora, aflatoxins and fumonisins. The corn grain samples were also submitted to scanning electron microscopy. Our results showed that weevils could enhance corn grains contamination by these fungi, hence, could increase mycotoxins production. These findings demonstrate the importance of weevils as fungal vectors and the need for good manipulation and storage practices of grains. (C) 2012 Elsevier Ltd. All rights reserved.

Aqua ammonia's economic potential as a preservative for stored high-moisture corn /

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Impact of resistance on the efficacy of binary combinations of spinosad, chlorpyrifos-methyl and s-methoprene against five stored-grain beetles

Laboratory experiments were conducted to determine the efficacy of spinosad (a biopesticide), chlorpyrifos-methyl (an organophosphorus compound (OP)) and s-methoprene (a juvenile hormone analogue) applied alone and in binary combinations against five stored-grain beetles in wheat. There were three strains of Rhyzopertha dominica, and one strain each of Sitophilus oryzae, Tribolium castaneum, Oryzaephilus surinamensis and Cryptolestes ferrugineus. These strains were chosen to represent a range of possible resistant genotypes, exhibiting resistance to organophosphates, pyrethroids or methoprene. Treatments were applied at rates that are registered or likely to be registered in Australia. Adults were exposed to freshly treated wheat for 2 weeks, and the effects of treatments on mortality and reproduction were determined. No single protectant or protectant combination controlled all insect strains, based on the criterion of >99% reduction in the number of live F1 adults relative to the control. The most effective combinations were spinosad at 1 mg kg-1+chlorpyrifos-methyl at 10 mg kg-1 which controlled all strains except for OP-resistant O. surinamensis, and chlorpyrifos-methyl at 10 mg kg-1+s-methoprene at 0.6 mg kg-1 which controlled all strains except for methoprene-resistant R. dominica. The results of this study demonstrate the difficulty in Australia, and potentially other countries which use protectants, of finding protectant treatments to control a broad range of pest species in the face of resistance development.

Potential of piperonyl butoxide-synergised pyrethrins against psocids (Psocoptera: Liposcelididae) for stored-grain protection.

BACKGROUND: Piperonyl butoxide (PB)-synergised natural pyrethrins (pyrethrin:PB ratio 1:4) were evaluated both as a grain protectant and a disinfestant against four Liposcelidid psocids: Liposcelis bostrychophila Badonnel, L. entomophila (Enderlein), L. decolor (Pearman) and L. paeta Pearman. These are key storage pests in Australia that are difficult to control with the registered grain protectants and are increasingly being reported as pests of stored products in other countries. Firstly, mortality and reproduction of adults were determined in wheat freshly treated at 0.0, 0.75, 1.5, 3 and 6 mg kg-1 of pyrethrins + PB (1:4) at 301C and 702% RH. Next, wheat treated at 0.0, 1.5, 3 and 6 mg kg-1 of pyrethrins + PB (1:4) was stored at 301C and 702% RH and mortality and reproduction of psocids were assessed after 0, 1.5, 3 and 4.5 months of storage. Finally, the potential of synergised pyrethrins as a disinfestant was assessed by establishing time to endpoint mortality for adult psocids exposed to wheat treated at 3 and 6 mg kg-1 of synergised pyrethrins after 0, 3, 6, 9 and 12 h of exposure. RESULTS: Synergised pyrethrins at 6 mg kg-1 provided 3 months of protection against all four Liposcelis spp., and at this rate complete adult mortality of these psocids can be achieved within 6 h of exposure. CONCLUSION: Piperonyl butoxide-synergised pyrethrins have excellent potential both as a grain protectant and as a disinfestant against Liposcelidid.

Individual-based modelling of the efficacy of fumigation tactics to control lesser grain borer (Rhyzopertha dominica) in stored grain

Increasing resistance to phosphine (PH 3) in insect pests, including lesser grain borer (Rhyzopertha dominica) has become a critical issue, and development of effective and sustainable strategies to manage resistance is crucial. In practice, the same grain store may be fumigated multiple times, but usually for the same exposure period and concentration. Simulating a single fumigation allows us to look more closely at the effects of this standard treatment.We used an individual-based, two-locus model to investigate three key questions about the use of phosphine fumigant in relation to the development of PH 3 resistance. First, which is more effective for insect control; long exposure time with a low concentration or short exposure period with a high concentration? Our results showed that extending exposure duration is a much more efficient control tactic than increasing the phosphine concentration. Second, how long should the fumigation period be extended to deal with higher frequencies of resistant insects in the grain? Our results indicated that if the original frequency of resistant insects is increased n times, then the fumigation needs to be extended, at most, n days to achieve the same level of insect control. The third question is how does the presence of varying numbers of insects inside grain storages impact the effectiveness of phosphine fumigation? We found that, for a given fumigation, as the initial population number was increased, the final survival of resistant insects increased proportionally. To control initial populations of insects that were n times larger, it was necessary to increase the fumigation time by about n days. Our results indicate that, in a 2-gene mediated resistance where dilution of resistance gene frequencies through immigration of susceptibles has greater effect, extending fumigation times to reduce survival of homozygous resistant insects will have a significant impact on delaying the development of resistance. © 2012 Elsevier Ltd.

Dosage consistency is the key factor in avoiding evolution of resistance to phosphine and population increase in stored-grain pests

BACKGROUND Control of pests in stored grain and the evolution of resistance to pesticides are serious problems worldwide. A stochastic individual-based two-locus model was used to investigate the impact of two important issues, the consistency of pesticide dosage through the storage facility and the immigration rate of the adult pest, on overall population control and avoidance of evolution of resistance to the fumigant phosphine in an important pest of stored grain, the lesser grain borer. RESULTS A very consistent dosage maintained good control for all immigration rates, while an inconsistent dosage failed to maintain control in all cases. At intermediate dosage consistency, immigration rate became a critical factor in whether control was maintained or resistance emerged. CONCLUSION Achieving a consistent fumigant dosage is a key factor in avoiding evolution of resistance to phosphine and maintaining control of populations of stored-grain pests; when the dosage achieved is very inconsistent, there is likely to be a problem regardless of immigration rate. © 2012 Society of Chemical Industry

Networks of stored grain diseases and pests: Strategies for sampling and mitigation

Pathogens and pests of stored grains move through complex dynamic networks linking fields, farms, and bulk storage facilities. Human transport and other forms of dispersal link the components of this network. A network model for pathogen and pest movement through stored grain systems is a first step toward new sampling and mitigation strategies that utilize information about the network structure. An understanding of network structure can be applied to identifying the key network components for pathogen or pest movement through the system. For example, it may be useful to identify a network node, such as a local grain storage facility, through which grain from a large number of fields will be accumulated and move through the network. This node may be particularly important for sampling and mitigation. In some cases more detailed information about network structure can identify key nodes that link two large sections of the network, such that management at the key nodes will greatly reduce the risk of spread between the two sections. In addition to the spread of particular species of pathogens and pests, we also evaluate the spread of problematic subpopulations, such as subpopulations with pesticide resistance. We present an analysis of stored grain pathogen and pest networks for Australia and the United States.

Managing resistance to chemical treatments in stored products pests

This review focuses on key trends in resistance to chemical treatments in stored product pests, and advances in resistance management, with an emphasis on resistance to the fumigant phosphine. Findings: Phosphine resistance continues to be a major concern. In particular, phosphine resistance in Cryptolestes ferrugineus has emerged as a serious issue, with some populations exhibiting the strongest level detected so far for this fumigant. In response, a 'quick knock down test' has been established to deliver industry and scientists 'same day' advice on the resistance status of field samples; sulfuryl fluoride is being developed as a 'resistance breaker' and phosphine dosages are being revised to manage this problem. There has been major progress in identifying the genes responsible for phosphine resistance and the development of molecular resistance diagnostics for key pests. Several studies on Rhyzopertha dominica have demonstrated that molecular screening can be used to determine the frequency of resistance alleles in samples collected from farm storages. Despite on-going research in several pests, there is no definitive answer to the question of whether there is a fitness cost associated phosphine resistance, with some studies showing a clear cost and others none. Evidence continues to emerge of resistance to grain protectants, including the juvenile hormone analogue methoprene. The development and adoption of spinosad, as a next generation 'green' treatment, and the use of protectant combinations provides opportunities to counter the problem of protectant resistance.Directions for future research: A uniform set of protocols should be developed for phosphine resistance detection for all major species. It should combine 'quick tests' and molecular diagnostics to be adopted internationally. Research is required on the establishment of a decision making system that integrates newly developed grain protectants and fumigants, other alternative control methods, as well as an accurate and rapid resistance detection system for early warning of the emergence of new resistances.

Electrical conductivity testing of corn seeds as influenced by temperature and period of storage

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of harvest time and drying on supersweet sweet corn seed quality

A supersweet sweet corn hybrid, Pacific H5, was grown under field conditions in South-East Queensland to study the effects of harvest time and drying conditions on seed quality. Cobs were harvested at different times to obtain seed with two moisture percentage ranges (20-30% and 40-50%) and dried to 12% moisture under different combinations of drying temperatures (30 degrees C, 40 degrees C and 50 degrees C) and air velocities (1.25 m/s, 2.75 m/s and 4.30 m/s). Dried seed was stored at 30 degrees C with bimonthly monitoring of seed quality for 12 months. For standard as well as cold test germinations, statistical analysis yielded significant main effects for temperature, air velocity and harvest moisture content and significant interactions for drying temperature by harvest moisture and drying temperature by air velocity. Germination at the beginning of storage was unaffected by drying temperatures up to 40 degrees C regardless of harvest moisture but was lower at 50 degrees C for higher moisture. However, germination at the end of the storage period of 12 months was greatest for seed harvested at higher moisture and dried at temperatures up to 40 degrees C. Germination was not affected by air velocity for drying temperatures up to 40 degrees C but at 50 degrees C it generally decreased with increase in air velocity. To slow down seed deterioration during storage, it is recommended that sweet corn seed should be harvested at a higher moisture range (40-50%) and dried at 40 degrees C and 4.30 m/s air velocity. The drying temperature can be raised to 50 degrees C for seed harvested at a low moisture range (20-30%) provided the air velocity is kept low (1.25 m/s).

Nitrogen fertilizer management for nitrous oxide (N2O) mitigation in intensive corn (Maize) production: an emissions reduction protocol for US Midwest agriculture

Nitrous oxide (N2O) is a major greenhouse gas (GHG) product of intensive agriculture. Fertilizer nitrogen (N) rate is the best single predictor of N2O emissions in row-crop agriculture in the US Midwest. We use this relationship to propose a transparent, scientifically robust protocol that can be utilized by developers of agricultural offset projects for generating fungible GHG emission reduction credits for the emerging US carbon cap and trade market. By coupling predicted N2O flux with the recently developed maximum return to N (MRTN) approach for determining economically profitable N input rates for optimized crop yield, we provide the basis for incentivizing N2O reductions without affecting yields. The protocol, if widely adopted, could reduce N2O from fertilized row-crop agriculture by more than 50%. Although other management and environmental factors can influence N2O emissions, fertilizer N rate can be viewed as a single unambiguous proxy—a transparent, tangible, and readily manageable commodity. Our protocol addresses baseline establishment, additionality, permanence, variability, and leakage, and provides for producers and other stakeholders the economic and environmental incentives necessary for adoption of agricultural N2O reduction offset projects.

Improving detection probabilities for pests in stored grains

BACKGROUND: The presence of insects in stored grains is a significant problem for grain farmers, bulk grain handlers and distributors worldwide. Inspections of bulk grain commodities is essential to detect pests and therefore to reduce the risk of their presence in exported goods. It has been well documented that insect pests cluster in response to factors such as microclimatic conditions within bulk grain. Statistical sampling methodologies for grains, however, have typically considered pests and pathogens to be homogeneously distributed throughout grain commodities. In this paper we demonstrate a sampling methodology that accounts for the heterogeneous distribution of insects in bulk grains. RESULTS: We show that failure to account for the heterogeneous distribution of pests may lead to overestimates of the capacity for a sampling program to detect insects in bulk grains. Our results indicate the importance of the proportion of grain that is infested in addition to the density of pests within the infested grain. We also demonstrate that the probability of detecting pests in bulk grains increases as the number of sub-samples increases, even when the total volume or mass of grain sampled remains constant. CONCLUSION: This study demonstrates the importance of considering an appropriate biological model when developing sampling methodologies for insect pests. Accounting for a heterogeneous distribution of pests leads to a considerable improvement in the detection of pests over traditional sampling models.

Insect distributions and sampling protocols for stored commodities

Purpose of review: This review provides an overview on the importance of characterising and considering insect distribution infor- mation for designing stored commodity sampling protocols. Findings: Sampling protocols are influenced by a number of factors including government regulations, management practices, new technology and current perceptions of the status of insect pest damage. The spatial distribution of insects in stored commodities influ- ences the efficiency of sampling protocols; these can vary in response to season, treatment and other factors. It is important to use sam- pling designs based on robust statistics suitable for the purpose. Future research: The development of sampling protocols based on flexible, robust statistics allows for accuracy across a range of spatial distributions. Additionally, power can be added to sampling protocols through the integration of external information such as treatment history and climate. Bayesian analysis provides a coherent and well understood means to achieve this.