Using choice and no-choice probing behavioral assays, we studied the orientation of adult Asian citrus psyllids (ACP) to chemical odorants from a distance and the interaction between visual attraction to yellow and olfaction or gustation. We confirmed that the 3-component blend of 3.5 formic:1.6 acetic acid:1.0 p-cymene is the optimal blend of those compounds to maximize ACP probing behavior. The yellow color acts as a long range cue that attracts the psyllids to the point of alighting on a yellow wax substrate. Probing is thought to be a reflexive action that is initiated upon landing on any substrate. Once the psyllids initiated probing on wax beads containing odorant blends, the 3-component blend had a stimulatory effect that increased the number of probes along with the size and complexity of the salivary sheaths left behind in the wax substrate. To support the hypothesis that increased probing was due to phagostimulants perceived by mouthparts and not olfactory cues perceived by antennal receptors, a no-choice experiment was performed to study ACP probing behavior through plastic film into wax beads thereby isolating antennal receptors from the odorant or tastant cues. Yellow w wax beads were prepared without tastants or with the 3-component blend (3.5:1.6:1 formic acid: acetic acid: p-cymene). Wax beads were covered with a polyethylene/polybutylene plastic film (Saran� Cling Plus� Wrap, S. C. Johnson & Son, Inc., Racine, WI, USA) to minimize the potential for olfaction or contact chemoreception associated with antennal tapping behavior. The film is impermeable to water and we assume to the larger molecules of the phagostimulant blend. Fifty D. citri adults were placed in each of four cages for 21 h. Each cage contained 5 cover slips with yellow wax beads prepared with or without tastants and with or without a covering of plastic film. The wax beads were collected, stained with Commassie Blue and scored for salivary sheaths. Stained salivary sheaths were removed from the wax substrate by gently lifting the plastic film and separating it from the substrate. The length of the stained salivary sheaths adhering to the plastic film was measured under a stereo microscope. Ten salivary sheaths were measured for each treatment (plastic film over wax beads without tastants and plastic film over wax beads with the 3-component tastant blend). The number of salivary sheaths produced on the plastic film were counted. The length of salivary sheaths were measured using a Cell Sens Dimension software (Olympus Corporation, Tokyo, Japan). ACP adults probed more on yellow wax beads containing the 3 component blend compared with wax beads without tastants. There was no effect of plastic film on the number of salivary sheaths observed in the wax beads. The mean number (+ SEM, n = 10) of salivary sheaths observed on yellow beads without tastants was 47.5 + 5.3 and on yellow wax beads containing the 3-component blend was 94.5 + 8.5 sheaths. Microphotography of the salivary sheaths that adhered to the plastic film revealed differences between sheaths recovered from beads containing the 3-component tastant blend and sheaths recovered from beads without tastants. Salivary sheaths recovered from beads containing tastants were 4.5 times longer (208 + 22 �m) compared with sheaths recovered from beads without tastants (46 + 7 �m). Sheaths recovered from beads with tastants were longer with filamentous portions extending beyond the thicker initial sheath. We conclude that the blend of 3 tastants is a phagostimulant that acts through perception by chemoreceptors located on the psyllids� mouthparts. George, J., P. S. Robbins, R. T. Alessandro, L. L. Stelinski and S. L. Lapointe. 2016. Formic and acetic acids in degradation products of plant volatiles elicit olfactory and behavioral responses from an insect vector. Chem. Senses doi: 10.1093/chemse/bjw005