Retardation of acquisition upon backward conditioning. (A) Schematic overview of the experiment using three backward trials with an ISI of 2 sec or three CS only trials. Honeybees were treated with three backward trials (BWISI2) or three CS trials alone (CSonly), or were untreated (Naive). (B) Thirty minutes later the BWISI2 group (black), the CSonly group (gray), and the Naive group (white) were conditioned with two forward trials (first acquisition trial a1 and second acquisition trial a2) using the same CS (clove oil) as in backward conditioning. (C) Schematic overview of the experiment using three-trial US pre-exposure or three backward trials with an ISI of 2 sec. Honeybees were treated with three US trials (US), with three backward trials (BWISI2), or were left untreated (Naive). (D) Thirty minutes later the US group (gray), the BWISI2 group (black), and the Naive group (white) were conditioned with two forward trials (a1 and a2) using the same CS (clove oil) as in backward conditioning. (*) P < 0.05.
