Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/6/2006
Publication Date: 1/31/2007
Citation: Atui, M.B., Flinn, P.W., Lazzari, S.M., Lazzari, F.A. 2007. Detection of Rhyzopertha dominica larvae in stored wheat using ELISA: The impact of myosin degradation following fumigation. Journal of Stored Products Research 43: 156-159. Interpretive Summary: The insect fragment count has been used as the standard procedure for food analysis for a long time; however, it requires technical training, it is time consuming, and relatively expensive. An alternative to the insect fragment count is a commercial immunoassay method that detects the insect muscle protein myosin. However, this assay has not been evaluated with fumigated grain to see if internal insects that have been dead for several weeks are accurately detected. Hard red winter wheat that was infested with larvae of the lesser grain borer was fumigated to kill the larvae inside the kernels. These infested kernels were then “aged” at 32ºC for either 0, 14, 28, and 56 days post-fumigation. Myosin degradation was most rapid in the first two weeks after the larvae were killed, decreasing 58.4%. There were no significant differences in myosin degradation between samples that were 14, 28, and 56 days post-fumigation. Results from this study are important to the grain industry because it showed that the myosin ELISA test may underestimate the amount of insect contamination in grain that has been previously fumigated.
Technical Abstract: Hard red winter wheat kernels were infested with eggs of Rhyzopertha dominica. After 20 days, when the larvae reached the 4th instar, they were killed by exposing the grain to phosphine gas for 24 hours. The infested kernels were then divided into four portions and treated as follows: one portion was immediately frozen at -80ºC to avoid myosin degradation; the other three samples were kept at 32ºC and 65% relative humidity, and then frozen at -80ºC after 14, 28, and 56 days post-fumigation, respectively. Myosin was measured using a commercial ELISA method that specifically detects this protein (Biotect®, Austin, TX). Myosin degradation was most rapid in the first two weeks after the larvae were killed, decreasing from 1.672 to 0.695 ng/well during this period, a (58.4% reduction). There were no significant differences in myosin degradation between samples that were 14, 28, and 56 days post-fumigation. Grain is often fumigated to control insects. Frequently, this occurs many weeks before the grain is milled and may be repeated during the storage period. Therefore, estimates using the ELISA test may underestimate internal insect infestation because of myosin degradation. Based on the rapid degradation of myosin, flour samples should be analyzed soon after milling; alternatively, the flour samples could be stored at -25ºC until tested to prevent myosin degradation.