In addition to visual learning, olfactory learning and memory have been demonstrated in multiple wasps. However, many details of learning acquisition and memory, particularly long-lasting memories, remain unexplored in wasps, hornets, and other social insects. 

Odor detection plays an important role in the foraging and intraspecific communication of Asian hornets (Vespa velutina). Previous studies have shown that multiple V. velutina castes (gynes, drones, and workers) have olfactory detection pathways and therefore potentially possess olfactory learning. 

In a recent issue of Journal of Experimental Biology, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) provided the first evidence of olfactory learning and long-term olfactory memory in all three castes of an Asian hornet. 

The researchers compared the learning and memory of V. velutina gynes, drones, and workers. They also tested the ability of drones to learn and remember gyne sex pheromone: 4-oxo-decanoic acid/4-oxo-octanoic acid (4-ODA/4-OOA). 

They used classical conditioning and developed the first proboscis extension reflex (PER) for hornets or wasps. By using PER, they found that all hornet castes could learn and remember odors associated with a food reward. 

All three hornet castes exhibited olfactory learning and memory, and gynes and drones were able to retain this memory for a long period of time, up to 30 days. 

Because of the evidently shorter life spans of the workers, the researchers could not assess whether they possess such long-lasting memory. 

"Our results suggest an intriguing persistence of memory that may be a general ability in social insects and point to the need for more study of life-long memories and their adaptive value", said Prof. TAN Ken, principal investigator of the study.