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We determined that the number of insect fragments, quantified using the standard flotation method, in flour milled from wheat infested with larvae, pupae, or preemergent adults of the lesser grain borer, Rhyzopertha dominica (F.), was proportional to infestation level. Wheat infested with a single preemergent adult contributed 28 and 10X as many fragments as wheat infested with a single larva or pupa, respectively. Using regression models that were developed from these data, we predicted that the maximum infestation level that would result in flour with fragment counts below the Food and Drug Administration defect action level (75 fragments/50 g of flour) was 0.95 and 1.5% (380-640 infested kernels/kg of wheat) for pupae and larvae, but it decreased to 0.05% (20 infested kernels/kg) when the grain was infested with preemergent adults. We also reexamined the accuracy and sensitivity of near-infrared spectroscopy (NIRS) for detecting insect fragments in flour by testing three different NIR spectrometers. NIRS-predicted numbers of insect fragments were correlated with the actual number of fragments. NIRS is less precise than the standard flotation method, but it is rapid, nondestructive, does not require extensive sample preparation, and could easily be automated for a more sophisticated sampling protocol for flour based on prescreening samples with NIRS followed up by use of the standard flotation method when necessary.

An automated near–infrared (NIR) reflectance system was used over a two–month storage period to detect single wheat kernels that contained live or dead internal rice weevils at various stages of growth. Correct classification of sound kernels plus kernels containing live pupae, large larvae, medium–sized larvae, and small larvae averaged 94%, 93%, 84%, and 63%, respectively. Pupae + large larvae calibrations were developed for live (day 1) and dead (days 7, 14, 28, 42, and 56) internal insects. Validation results showed that the live pupae +live large larvae calibration correctly classified 86% to 96% of dead pupae + dead large larvae validation samples. The dead pupae + dead large larvae calibration correctly detected the presence of live pupae + live large larvae with an accuracy of 92% to 93%. Thus, wheat kernels containing either live or dead insects can be used to develop calibrations for detecting both live and dead insects in wheat. These findings will impact how calibration sample sets can be handled. Results indicated that immediate sample processing for creating calibrations may no longer be necessary; internal insects can be killed and calibrations created at a later time without sacrificing accuracy. Additionally, laboratories can share these same calibration samples to save time and resources.

An automated NIR system was used over a two-month storage period to detect single wheat kernels that contained live or dead internal rice weevils at various stages of growth. Correct classification of sound kernels and kernels containing live pupae, large larvae, medium-sized larvae, and small larvae averaged 94, 92, 84, and 62%, respectively. Pupae + large larvae calibrations were developed using live or dead internal insects. Validation results showed correct classifications ranging from 86 to 96% over the two-month storage period. Thus, wheat kernels containing either live or dead insects can be used to develop calibrations for detecting both live and dead insects in wheat.