Staining procedure to identify paddy with gaps vulnerable to Stenotus rubrovittatus and Trigonotylus caelestialium (Hemiptera: Miridae)

Abstract

Stenotus rubrovittatus (Matsumura) and Trigonotylus caelestialium (Kirkaldy) (Hemiptera: Miridae) are major rice pests in Japan. Since both species feed on rice grain through the gap between the lemma and palea, the paddy grains with gap (including split-hull) is vulnerable to them. The aim of this study was to develop a staining procedure to identify the vulnerable paddy with gap. The paddy samples were first stained under different conditions to select the optimal staining conditions that could highlight the gap and help sort the split-hull paddy clearly by visual inspection. After optimization experiments, 0.05% aqueous methylene blue solution was selected for staining, and 3 min was set as the staining and pretreatment times. The efficiency of this staining procedure was evaluated by applying it to the paddy harvested from fields to examine how well it could sort the vulnerable paddy. The stained paddy percentages were similar in the five replicates for the staining test, thereby confirming its reliability. The gap detection rate determined by the staining technique was approximately 30% higher than that determined by visual inspection. These results indicate that the staining technique enables the identification of vulnerable paddy, and may be useful for estimating vulnerable product and analyzing potential damage.