The olfactory response of the sorghum plant bug, Stenotus rubrovittatus (Matsumura) (Het., Miridae), to rice, Oryza sativa L., and paddy weed, Scirpus juncoides Roxb. var. ohwianus T. Koyama, was investigated with an olfactometer to clarify the mechanism of the invasion of the bugs in paddy fields. Both adult females and males were significantly attracted to panicles of rice in the flowering and full-ripe stages. Whole plants (aboveground parts) of rice in the panicle-formation stage, and stems and leaves of rice in the flowering stage significantly attracted only adult females. Other rice structures tested did not attract males or females. Both males and females were attracted to the flowering spikelets of S. juncoides. Although females showed no olfactory response to stems of S. juncoides in the flowering stage, males were repelled by them. Only females were attracted to whole plants of flowering S. juncoides. Whole plants of S. juncoides in the spikelet-formation stage significantly attracted only females. The findings suggest that the invasions of S. rubrovittatus into paddy fields are caused by their olfactory responses to the volatiles emitted from rice and some paddy weeds such as S. juncoides.
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