Studies were conducted to examine the behavioral response of Þfth-instar and adult Lygus hesperus Knight (Heteroptera: Miridae) to odors associated with a host plant (alfalfa) when presented singly or in combination with a visual plant cue (530 nm, green light-emitting diode [LED]). Bioassays were conducted in a modiÞed Y-tube olfactometer, where incoming air was Þltered and humidiÞed before passing through chambers that held plant/conspeciÞc treatments. A LED, placed behind an organdy screen

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... the end of one arm of the Y-tube, simulated a visual plant cue. In agreement with our previous Þndings, Þfth-instar and adult female L. hesperus were attracted to plant/conspeciÞc odor combinations, but adult males were not. Independently, the LED also was attractive to immature and adult female L. hesperus, and for all life stages, a much larger percentage of the bugs walked to the extreme end of the Y-tube when the visual cue was present. When visual and volatile cues were presented simultaneously, responses by both immature and adult (male and female) L. hesperus were signiÞcantly enhanced. Plant/conspeciÞc treatments that had been marginally acceptable when only volatile stimuli were available showed the greatest enhancement in response with the addition of the visual cue. Presentation of visual and volatile cues together led to a mean increase in the percentage of bugs that walked to the extreme end of the Y-tube (nymphs, 36.6%; females, 23.4%; males, 26.1%). Results are discussed in terms of stage-speciÞc responses and how these behavioral differences will likely play a role in developing effective trapping and monitoring systems for this important pest.