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The oriental fruit fly Bactrocera dorsalis learns and remembers sugar quality

Yu, Jinxin, Yang, Weiping, Zeng, Xinnian, Liu, Jiali
Journal of insect physiology 2019 v.117 pp. 103895
Bactrocera dorsalis, arabinose, glucose, insect physiology, memory, nutrition, nutritive value, odors, proboscis, sorbitol, sucrose, sweetness, taste
The oriental fruit fly Bactrocera dorsalis can learn to associate an odor with a sugar reward. However, it is still unclear whether they will learn with different sugar rewards equally. Here, we used a proboscis extension conditioning procedure to investigate the contribution of taste and nutritional value of sugars to learning and memory formation. Three types of sugar were used for conditioning: sweet and nutritional sugar, sucrose; sweet sugar without nutrition, D-arabinose and L-glucose; tasteless sugar with nutritional value, D-sorbitol. The sweet taste is sufficient to produce associative conditioning with an odor and form short-term memory, and the learning and short-term memory performance showed a similar rank order to the proboscis extension reflex evoked by each sugar. However, memory decayed at a greater rate 24 h after conditioning for flies conditioned with sweet tasting but non-metabolizable sugars D-arabinose and L-glucose. When D-arabinose or L-glucose was supplemented with D-sorbitol, the deficit of 24 h memory was rescued, suggesting that the nutrient value of sugar plays a key role in memory persistence. Our results indicate that B. dorsalis could learn and evaluate sugar quality via both taste and nutritional value, as well as remember nutrient sugars for a long time using a postingestive mechanism.