No evidence for olfactory blocking in honeybee classical conditioning.

We use binary odorant compounds to investigate 'blocking' in honeybees which learn to associate an odorant (A-D) with a sucrose reward as the reinforcer (+). 'Blocking' means that learning about a stimulus B is reduced when trained in compound with a stimulus A that has previously been trained alone. Thus, reinforcement of B in these circumstances is not sufficient to induce learning. Such blocking is a frequently observed phenomenon in vertebrate learning and has also recently been reported in honeybee olfactory learning. To explain blocking, current models of conditioning include cognition-like concepts of attention or expectation which, consequently, seem also to apply to honeybees. Here, we first reproduce a blocking-like effect in an experimental design taken from the literature. We identify two confounding variables in that design and experimentally demonstrate their potential to support a blocking-like effect. After eliminating these confounding variables using a series of different training procedures, the blocking-like effect disappeared. Thus, convincing evidence for blocking in honeybee classical conditioning is at present lacking. This casts doubt on the applicability of cognition-like concepts to honeybees.