Hard red winter wheat kernels were infested with eggs of Rhyzopertha dominica . After 20 d, when the larvae reached the fourth instar, they were killed by exposing the infested kernels to phosphine gas for 24 h. The infested kernels were then divided into four portions and treated as follows: one portion was immediately frozen at −80 °C to avoid myosin degradation; the other three portions were kept at 32 °C and 65% relative humidity, and then frozen at −80 °C after 14, 28, and 56 d post-fumigation, respectively. Each treatment was replicated five times. Myosin was measured using a commercial enzyme linked immunosorbent assay (ELISA) method that specifically detects this protein (Biotect ® , Austin, TX). Myosin degradation was most rapid in the first 2 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 d 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. Insect fragment estimates for previously fumigated grain could be underestimated by as much as 58%.

Current tests for assessing insect contamination in stored grain and milled products are based on insect fragment counts. These procedures have a certain degree of subjectivity, are time consuming, require highly trained personnel, and are relatively expensive. The ELISA test is a novel tool for detecting insects and their fragments inside the kernels or in flours. The method is based on the immuno-diagnostic assay of insect muscle myosin. However, myosin tends to degrade after the insect dies. Therefore, the aim of this research is to measure myosin degradation in flour samples over a period of time and to evaluate the efficiency of ELISA in detecting decreasing amounts of this muscle protein. Testing was carried out using flour samples obtained from 1500 g of wheat kernels, some of which were infected with Rhyzopertha dominica larvae. The samples were kept at room temperature (24°C) for 32 days. At the beginning of the study (day 1), insect myosin concentration in the samples averaged 3.3 ng/well. At the end (day 32) the concentration had decreased to an average of 2.3 ng/well. The study showed that the ELISA methodology is appropriate for measuring myosin content in flour samples, which results from the presence of insect muscle fragments in the kernels. Equations were developed to predict the original amount of myosin in the samples, based on time and temperature. Although the test is sensitive to small amounts of myosin, it is best to process samples within one week of milling, or to freeze the samples if they cannot be processed within a week. Further studies are needed to improve this methodology and to develop specific ELISA kits for the main stored-insect species.

In the research reported, the ELISA method to detect the insect muscle myosin was tested and compared with a traditional method of counting insect fragments in flour using acid hydrolysis. One kilogram samples of wheat were infested with 0, 1, 2, 4, 8, and 16 adults of Rhyzopertha dominica (Coleoptera: Bostrichidae), and milled to obtain wheat flour. The samples were analysed according to the AOAC method and by the immunoassay kit to detect myosin. The numbers of insect fragments detected by both methods were proportional to the infestation level. The number of insect fragments ranged from 4.4 in the lowest infestation level, to 73.2 in the highest infestation level. The lowest detection level of the immunoassay is 0.5 insects/50 g sample, and maximum 10 insects/50 g sample. The ELISA test represents a valuable tool for screening insect infestation in stored wheat kernels and flour in order to monitor sanitary quality, but modifications are required to increase the kit sensitivity for the lesser grain borer and other insects.

O uso de terra diatomácea e de outros pós inertes vem se tornando uma prática comum no controle de insetos de produtos armazenados. Elas podem ser usadas em associação com fumigantes, criando uma barreira física que impede a infestação das partes inferiores e superiores da massa de grãos com insetos vindos de fora da estrutura. A existência de uma metodologia que permita a detecção de pós inertes, no caso, terra diatomácea, em grãos é de grande importância para a indústria e para os laboratórios oficiais. Sendo assim, o objetivo deste trabalho foi o desenvolvimento de uma metodologia para detectar a presença de terra diatomácea em grãos de trigo. Para isto, foram tomadas amostras de 1 Kg de grãos de trigo tratados com diferentes dosagens de terra diatomácea: 250 g/t; 500 g/t; 750 g/t; 1000 g/t; 2000 g/t; 4000 g/t; 6000 g/t; 8000 g/t; 10000 g/t. O método proposto utilizou água filtrada para lavagem dos grãos e extração das algas diatomáceas em substituição ao álcool a 95% utilizado no método original. Foram recuperadas arapaças/fragmentos de algas diatomáceas em todas as amostras analisadas, mesmo naquelas tratadas com pequenas quantidades de terras diatomáceas. O método proposto mostrou-se adequado para avaliar a presença...