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Title: Rapid assessment of insect fragments in flour milled from wheat infested with known densities of immature and adult Sitophilus oryzae (L.) (Coleoptera: Curculionidae)

Author
item Toews, Michael
item PEREZ-MENDOZA, JOEL - SCHENDEL PEST SERVICES
item Throne, James
item Dowell, Floyd
item Maghirang, Elizabeth
item Arthur, Franklin
item Campbell, James - Jim

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/2007
Publication Date: 10/1/2007
Citation: Toews, M.D., Perez-Mendoza, J., Throne, J.E., Dowell, F.E., Maghirang, E.B., Arthur, F.H., Campbell, J.F. 2007. Rapid assessment of insect fragments in flour milled from wheat infested with known densities of immature and adult Sitophilus oryzae (L.) (Coleoptera: Curculionidae). Journal of Economic Entomology 100: 1714-1723.

Interpretive Summary: The process of milling wheat infested with low densities of internal feeding insects can result in flour containing insect fragments. We milled small lots of wheat infested with known densities and life stages of the rice weevil to determine how many fragments would be produced; additionally, we tested near-infrared spectroscopy as a novel method to rapidly estimate the number of fragments in a sample. Immature insects produced 0.4 to 1.5 fragments per insect, but adults produced an average of 27 fragments per insect. Spectroscopy was successfully used to categorize samples containing fragments of immature insects but not fragments resulting from adult insects. These data will enable millers to better predict how many fragments may result in a lot of flour, and rapidly test a finished flour sample to determine if it contains violative numbers of insect fragments.

Technical Abstract: Milling wheat infested with low densities of internal feeding insects can result in flour containing insect fragments. The Food and Drug Administration (FDA) enforces a standard or defect action level stating that a maximum of 75 insect fragments per 50 g flour is allowed. However, the relationship between level of infestation and number of resulting fragments is not well documented, and a more rapid method for enumerating insect fragments is needed. We characterized the number of insect fragments produced from milling small lots of wheat spiked with known densities and life stages of Sitophilus oryzae. Insect fragments were enumerated with near-infrared spectroscopy (NIRS), a quick non-destructive procedure, and with the industry standard flotation method. Results showed that an individual small larva, large larva, pupa, or adult produced 0.4, 0.7, 1.5, and 27.0 fragments, respectively. NIRS-predicted counts of less than 51 (from small larvae), less than 53 (from large larvae), less than 43 (from pupae), or 0 (from adults) indicated that there were less than 75 actual fragments in that sample because the upper bound of associated 95% inverse prediction confidence intervals was less than the standard; NIRS-predicted counts of greater than 98, greater than 117, greater than 108, or greater than 225 fragments (same life stages as above) signaled that these flour samples contained more than 75 actual fragments. These data suggest that NIRS could be adopted for rapid assessment of insect fragments resulting from relatively low levels of infestation with immature life states, but was not accurate enough for enumerating fragments resulting from adults at densities relevant to FDA standards.