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United States Department of Agriculture

Agricultural Research Service

Title: Insect Fragments in Flour: Relationship to Lesser Grain Borer (Coleoptera: Bostrichidae) Infestation Level in Wheat and Rapid Detection Using Near-Infrared Spectroscopy

Authors
item Perez-Mendoza, Joel - MONTANA STATE UNIV
item Throne, James
item Maghirang, Elizabeth
item Dowell, Floyd
item Baker, James

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 20, 2005
Publication Date: December 1, 2005
Repository URL: http://naldc.nal.usda.gov/download/1586/PDF
Citation: Perez-Mendoza, J., Throne, J.E., Maghirang, E.B., Dowell, F.E., Baker, J.E. 2005. Insect fragments in flour: relationship to lesser grain borer (Coleoptera: Bostrichidae) infestation level in wheat and rapid detection using near-infrared spectroscopy. Journal of Economic Entomology 98: 2282-2291.

Interpretive Summary: The milling industry routinely checks flour for insect fragments to determine whether the level is below the FDA defect action level (75 fragments/50 g flour). However, the standard chemical extraction method used to detect insect fragments in flour is costly and time-consuming; thus, a rapid detection method is desirable. In addition, little is known about differences in the number of fragments produced from different stages of different insect species. In this study, we determined that wheat infested with a single adult lesser grain borer contributed 28 times and 10 times as many fragments as wheat infested with a single larva or pupa, respectively. Using regression models that we developed from these data, we predicted that 1-kg samples of wheat with more than 20 kernels infested with adult borers would be above the FDA defect action level for insect fragments. Similarly, it would take an infestation level of 300-500 kernels (in a 1-kg sample) containing larvae or pupae to exceed the defect action level. We also determined the accuracy and sensitivity of near-infrared spectroscopy (NIRS) for detecting insect fragments in flour using three different NIR-spectrometers. The number of insect fragments predicted by NIRS was correlated with the actual number of fragments. NIRS was less precise than the standard flotation method, but it has the advantages that it is rapid, non-destructive, does not require extensive sample preparation, and can be automated for a more sophisticated sampling protocol for flour.

Technical Abstract: We determined that the number of insect fragments, quantified using the standard flotation method, in flour milled from wheat infested with larvae, pupae, or adults of the lesser grain borer, Rhyzopertha dominica (F.), was proportional to infestation level. Wheat infested with a single adult contributed 28 times and 10 times as many fragments as wheat infested with a single larva or pupa, respectively. Using regression models that we developed from these data, we predicted that the maximum infestation level that would result in flour with fragment counts below the FDA defect action level (75 fragments/50 g flour) was 0.75 and 1.25% (300 to 500 infested kernels/kg wheat) for pupae and larvae, but decreased to 0.05% (20 infested kernels/kg) when the grain was infested with newly eclosed adults. We also re-examined 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, non-destructive, 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 and following up by use of the standard flotation method when necessary.

Last Modified: 7/30/2014