Carl Reed

Management of Stored Wheat Insect Pests in the USA

Management of stored-grain insect pests by farmers or elevator managers should be based upon a knowledge of the grain storage environment and the ecology of insect pests. Grain storage facilities and practices, geographical location, government policies, and marketing demands for grain quality are discussed as factors influencing stored-grain insect pest management decisions in the United States. Typical practices include a small number of grain samples designed to provide grain quality information for segregation, blending and marketing. This low sampling rate results in subjective evaluation and inconsistent penalties for insect-related quality factors. Information on the efficacy of insect pest management practices in the United States, mainly for farm-stored wheat, is discussed, and stored-grain integrated pest management (IPM) is compared to field-crop IPM. The transition from traditional stored-grain insect pest control to IPM will require greater emphasis on sampling to estimate insect densities, the development of sound economic thresholds and decision-making strategies, more selective use of pesticides, and greater use of nonchemical methods such as aeration. New developments in insect monitoring, predictive computer models, grain cooling by aeration, biological control, and fumigation are reviewed, their potential for improving insect pest management is discussed, and future research needs are examined.

Simulation model of Rhyzopertha dominica population dynamics in concrete grain bins.

Rhyzopertha dominica is one of the most damaging insect pests in grain elevators and causes millions of dollars worth of stored grain losses annually in the USA. A simulation model was developed for predicting R. dominica population dynamics in concrete grain bins. The model used a two-dimensional representation of a cylindrical concrete bin (33 m tall 6.4 m wide), and used hourly weather data to predict changes in grain temperature. Output from the grain bin temperature and moisture module was used by the insect module to predict changes in insect density in 32 different bin regions. When compared to validation data from nine grain bins, the model accurately predicted insect vertical distribution and insect density. In December, the highest insect density was in the top center of the grain mass, and decreased steadily with increasing depth and towards the periphery of the grain mass. R. dominica attains this spatial distribution because immigration is primarily through the top of the bin, and higher populations occur in the interior of the grain mass because of warmer temperatures there. Initially, the model underestimated actual insect density in the grain bins. We increased the immigration rate by 50% and this resulted in a much better prediction of R. dominica density by the model. From 20 September to 14 December, populations of R. dominica increased from 0.1 to 3.5 insects per kg of wheat. Published by Elsevier Science Ltd.

Loss of phosphine from unsealed bins of wheat at six combinations of grain temperature and grain moisture content

Hard red winter wheat (1.4 t) at 11.1 or 13.5% moisture content (wet basis) and 20, 25, or 30 degrees C was fumigated with tablets of an aluminum phosphide formulation in unsealed, cylindrical grain bins of corrugated metal. The fumigant leakage rate was manipulated to approximate that commonly encountered in farm and commercial-scale bins of this type. Phosphine concentration profiles were recorded and phosphine loss and sorption were characterized to determine which conditions provided the greatest probability of successful fumigation in these bins. Phosphine leakage and sorption were both positively related to grain temperature and moisture content. The fumigant concentration profiles were compared with previously-published data relating temperature to the developmental rate and fumigant susceptibility of lesser grain borer eggs, which are phosphine-resistant but become less resistant as they age. The mean phosphine concentration observed at the time corresponding to one-half of the calculated egg development time was compared to the lethal concentration (LC(99)) for a 2-day exposure at each temperature-moisture combination. In the low-moisture grain at 20 degrees C, the observed fumigant concentration was below the lethal concentration, due to the long development time under these conditions. At 25 and 30 degrees C in the low-moisture wheat, the likelihood of complete kill appeared more favorable because the fumigant concentration remained above the published LC(99) for more than half of the egg development time. In the wheat with 13.5% moisture content, rapid fumigant sorption and loss resulted in phosphine concentrations below the LC(99) at one-half of the development time at 20 or 25 degrees C. At 30 degrees C, due to the very rapid development rate, the observed phosphine concentration exceeded the LC(99) half-way through the egg development period despite the rapid rate of fumigant sorption and loss. Repeated fumigation of the same grain reduced the rate at which phosphine sorbed into the grain.

The precision and accuracy of the Standard Volume Weight method of estimating dry weight losses in wheat, grain sorghum and maize, and a comparison with the Thousand Grain Mass method in wheat containing fine material☆

Abstract The accuracy and precision of the Standard Volume Weight (SVW) method of estimating dry weight loss of grain with and without a special grain cleaning procedure were tested using wheat, grain sorghum, and maize. The baseline relationship between bulk density and moisture content was adequately described by a straight line between 10.0 and 16.0% moisture content, but a curvilinear model was significantly less variable in all wheat lots tested and in four of the seven lots of maize. The precision of the SVW method was greater when used with wheat than when used with the other grains but did not directly predict observed loss except in cleaned wheat. Conversion factors were employed to convert SVW estimates to observed loss. The SVW method of loss estimation was found to be less variable than the Thousand Grain Mass (TGM) method on six lots of wheat with and without fine material. Both SVW and TGM were reduced by the addition of fine material, but TGM was affected more than SVW.

CONDITIONING PRACTICES AND THEIR EFFECTS ON INFESTATION AND QUALITY OF CORN STORED ON KANSAS FARMS

To determine the effects of various conditioning practices on grain quality in northeast Kansas, corn stored in farm bins of various sizes was sampled and field simulations were conducted in 3.6-m (12-ft) diameter bins. Grain quality deterioration, as evidenced by insect infestation and mold infection, was common in farm-stored corn when storage extended into the summer months. Inefficient conditioning practices were observed commonly in farm grain. Excessively long fan operation, combined with failure to remove peaks and accumulations of fine material in spoutlines before aeration often resulted in over-dried grain in lower and outer parts of the grain mass and unconditioned grain in the center. In the field simulation bins, caged adult insects did not survive the winter in grain cooled rapidly by forced air. However, adult sawtoothed grain beetles were found in March in cages placed in unaerated grain the previous fall, and adults of all species of test insects were present in cages left in the grain from binning until the following summer, regardless of whether the grain had been cooled by forced air.

Area-Wide IPM for Commercial Wheat Storage

The United States Department ofAgriculturesAgricultural Research Service (USDA- ARS) funded a demonstration project between 1998 and 2003 for area-wide integrated pest management (AW-IPM)ofcommercialstoredwheatinKansasandOklahoma.TheAW-IPMconceptisusefultostored grainbecauseitreducesthemixingofinfestedanduninfestedgrainattheterminalelevatorbycontrolling insect problems in small country elevators before the grain is shipped to the terminal elevator.This proj- ectwasacollaborationoftheUSDA-ARSGrainMarketingandProductionResearchCenterinManhattan, Kansas, Kansas State University, and Oklahoma State University. The project utilized two elevator net-