An evaluation of insect expulsion from wheat samples by microwave treatment for disinfestation

• Different replicates generated different temperature distributions.
• Longer treatment time generated a dry and hot spot at the same position.
• Intermittent treatment did not generate a more even temperature distribution.
• All of the introduced adults were expelled and sieved out of the wheat.
• Insect offspring was decreased by over 75% in microwave treated wheat.

The non-uniform temperature distribution created in the processed materials limits the wide application of microwave treatment. The non-uniform temperature also increases the chance of insects surviving or moving out from the treated materials. Wheat (14, 16 and 18% moisture contents, wet basis) with or without insects (Cryptolestes ferrugineus (Stephens)) was continuously or intermittently treated inside a microwave oven for 30, 60 and 90 s. Three dimensional distributions were determined by measuring temperatures and moisture contents at 27 locations inside a 10 × 9 × 9 cm3 plastic container. The adults and larvae of C. ferrugineus, which did not escape from the treated wheat, were sieved out or forced out using the Berlese funnel method. Temperatures and moisture contents had different mean, maximum and minimum values in different replicates when treatment time was 30 s. Long treatment time (90 s) generated a dry and hot spot at the same position even though the hot and dry spots were not at the same position in different replicates. Intermittent treatment did not generate more even distributions of temperatures and moisture contents in dry grain, while wet grain (>16% MC) did. Most of the introduced adults were extracted and there was no significant difference between intermittent or continuous treatment methods. Microwave treatment did not kill all insects, however the number of offspring decreased by >75%. Driving insects out of wheat could be an alternative method for insect disinfestation and detection.