An investigation into the bee's gustatory mechanisms for the detection of toxins in nectar

许多动物、植物和真菌通过产生或封存有毒化学物质来保护自己不被吃掉。已经从植物中鉴定出数千种这样的化合物。对于饥饿的动物来说，通过防御化合物避免死亡或中毒与识别食物中的营养物质一样重要。味觉是调节食物摄入的看门人：它允许化学识别并指导适当的行为反应。例如，在开始进食之前，蜜蜂等昆虫利用口器、触角和跗骨上毛发状感受器神经元中表达的味觉受体（Grs）对食物进行取样。如果在食物中检测到有毒化合物，昆虫会拒绝食物并继续前进。当昆虫被用作理解感觉系统如何运作的模式生物时，它们经常引领人们更深入地了解神经元机制。先前的研究表明，脊椎动物和昆虫的味觉系统是这样组织的：一部分味觉细胞或神经元受到糖和其他营养物质的刺激，而另一部分则受到有毒（苦味）化合物的刺激。然而，对昆虫的新研究表明，一些味觉受体神经元（grn）可以被营养物质和潜在毒素激活。一个简单的模型，其中糖感知神经元的活动唤起进食，苦味感知神经元的活动导致昆虫拒绝食物，可能是不正确的。相反，整个grn群体可能都参与了信息编码。很少有人对此进行研究。赖特的实验室正在开发蜜蜂作为一种模式生物，以了解味觉的功能。蜜蜂的味觉感受器种类很少，因此很容易识别它们能检测到什么，以及它们的味觉系统是如何运作的。她实验室的研究表明，蜜蜂在检测花蜜等含糖溶液中的潜在毒素（如杀虫剂）方面的敏锐度很差。目前还不清楚是这些溶液中的糖掩盖了毒素的味道，还是蜜蜂根本无法检测到这些物质。本研究将全面研究黄尾大黄蜂口器上的grn对糖和非营养性化合物混合物的反应。我们将测量这些神经元如何对几种潜在毒素的刺激做出反应，包括天然存在于花蜜中的化合物。作为现代农业的结果，蜜蜂越来越多地暴露于它们作为食物收集的花粉和花蜜中的杀虫剂和其他农用化学品中。因此，我们将测量另外3种蜜蜂对非营养性化合物（包括杀虫剂、杀菌剂和除草剂）的检测阈值。我们还将进行行为分析，以确定grn的输入如何指导摄食行为。这项研究将首次描述昆虫的味觉系统如何在食物是营养物质和潜在毒素的混合物时对食物的价值进行编码。这些实验还将确定某些蜜蜂物种是否比其他蜜蜂物种更善于探测和避免毒素，为土地管理者和政策制定者提供有关喷洒或输送到开花作物上的特定农用化学品对蜜蜂的风险的数据。在未来，这些信息也可以用于设计新的杀虫剂，当这些化合物被用来保护作物时，蜜蜂可以发现并避免这些含有这些化合物的花蜜的花朵。

Many animals, plants, and fungi defend themselves from being eaten by the production or sequestration of toxic chemicals. Thousands of these compounds have been identified from plants. For hungry animals, avoiding death or intoxication by defence compounds can be as important as identifying nutrients in food. Taste is the gatekeeper regulating food ingestion: it permits chemical identification and instructs the appropriate behavioural response. For example, before staring a meal, insects like bees sample food using gustatory receptors (Grs) expressed in neurons in hair-like sensilla on the mouthparts, antennae, and tarsi. If a toxic compound is detected in food, the insect will reject the food item and move on. Insects have often led the way to greater insight into neuronal mechanisms when they are used as model organisms for understanding how sensory systems function. Previous research has shown that the gustatory systems of vertebrates and insects are organized such that a subset of gustatory cells or neurons is excited by sugars and other nutrients, whereas others are excited by toxic (bitter) compounds. New research in insects, however, has revealed that some gustatory receptor neurons (GRNs) can be activated by both nutrients and potential toxins. A simple model, where the activity in sugar-sensing neurons evokes feeding and the activity in bitter-sensing neurons causes an insect to reject food may be incorrect. Instead, whole populations of GRNs are likely to be involved in encoding information. This has rarely been studied.Wright's laboratory is developing the bee as a model organism for understanding how taste functions. Bees have few gustatory receptor types, making it tractable to identify what they can detect and how their taste system functions. Research from her laboratory has shown that bees have poor acuity for the detection of potential toxins like pesticides in sugary solutions like nectar. It is unclear whether the sugars in these solutions mask the taste of the toxins, or whether the bees cannot detect the substances at all. The research proposed here will comprehensively study the responses of GRNs on the mouthparts of buff-tailed bumblebees to mixtures of sugars and non-nutrient compounds. We will measure how populations of these neurons respond to stimulation with several types of potential toxins including compounds naturally found in floral nectar. As a result of modern agriculture, bees are increasingly exposed to pesticides and other agrochemicals in floral pollen and nectar which they collect as food. For this reason, we will measure the detection thresholds of 3 additional bee species towards non-nutrient compounds including pesticides, fungicides, and herbicides. We will also perform behavioural assays to identify how the input from the GRNs instructs feeding behaviour. This research will be the first to characterize how an insect's gustatory system encodes the value of food when it is a mixture of nutrients and potential toxins. These experiments will also identify whether some bee species are better than others at detecting and avoiding toxins, providing data for land managers and policy makers regarding the risks of specific agrochemicals to bees when they are sprayed or delivered to flowering crops. In the future, this information could also be used to design new pesticides that permit bees to detect and avoid these flowers with nectar containing these compounds when such compounds are used to protect crops.