Feeding behavior of honey bees on dry sugar

Abstract

The feeding habits of insects can be influenced by food abundance, nutrition, physical forces, and many other variables, which is why this topic is multidisciplinary and perennially fascinating. Although honey bees primarily feed on liquid nectar, they also can feed on dry sugar; however, the feeding mechanism for feeding on dry substances by a primarily fluid-feeding insect remains unexplored. We observed that, when honey bees are accessible to both dry sugar and liquid nectar, they prefer to feed on the latter. To elucidate the diet preference, we conducted a comparative study between feeding on dry-sugar and drawing up liquid-nectar, from the tongue kinematics and dynamic configuration, friction force, glossal durability, and feeding efficiency. Using a high-speed camera, we discovered that the hairy tongue of the honey bee uses back-and-forth movements to furrow a groove on pieces of dry sugar, with saliva simultaneously dissolving the sugar. We found that the lapping frequency of the tongue on dry sugar reduces from 4.5 Hz to 1.6 Hz when compared to feeding on the liquid diet; a 64% decrease in average tongue speed. Through tribological tests, we revealed that the friction forces when feeding on dry sugar is approximately 5 times that of dipping nectar, and the glossal hairs wear 4 times faster when feeding on dry sugar compared to the sucrose solution. We built a mathematical model to bridge the gap between energy intake rate and tongue dynamics of these two feeding modes. The theoretical net energy intake rate of feeding on dry sugar is 50% lower than when feeding on sucrose solutions. Both experimental and theoretical discoveries revealed that although honey bees can feed on dry substances, natural selection has forged their tongue structures primarily for a liquid diet. This study combined behavioral and mechanical tests with mathematical modeling, which highlights the advantages of using multidisciplinary approaches for uncovering the feeding physiology of insects.