Meet Mabel, an aphid, a tiny insect belonging to the same order as cicadas, stink bugs, and bed bugs. These insects share a common trait: they pierce their prey to extract vital fluids. For aphids like Mabel, their prey is plants, and their target is the plant’s sap, a nutrient-rich fluid flowing through sieve tubes made of single cells.
Sap, primarily composed of water and sugar, is a plant’s most valuable resource. In some species, the sugar concentration in sap rivals that of a can of soda. Photosynthesis continuously produces sugar, creating high pressure within the sieve tubes—up to nine times that of a car tire. To feed, Mabel uses her stylet, a long, flexible needle, to penetrate the plant tissue and access the sieve tubes. Due to the high pressure, Mabel doesn’t need to suck the sap; she simply opens a valve in her head, allowing the sap to flow through her digestive system.
Plants have developed defenses to deter aphids. One such defense is the sap itself. If another insect’s digestive system were exposed to a steady stream of sap, the high sugar content would cause water to leave the insect’s cells through osmosis, eventually leading to dehydration and death. However, Mabel’s gut contains an enzyme called sucrase, which breaks down sucrose into fructose and a three-unit sugar. By reducing the number of sugar molecules in the sap, Mabel minimizes its ability to dehydrate her cells, allowing her to feed for extended periods and gather energy for reproduction.
Aphids exhibit a fascinating reproductive strategy. Take the green peach aphid, for example. In the fall, males and females mate, and females lay eggs. In spring, these eggs hatch into female nymphs, which mature and give birth to live young—clones of themselves that are already pregnant with their own clones. This process, known as telescopic development, enables rapid population growth, with up to 20 generations in a single season.
Mabel’s prolific feeding results in significant waste production. She can excrete her body weight in waste every two hours, making aphids one of the most prolific poopers on the planet. This waste, known as honeydew, is chemically similar to sap—a clear, sweet, syrupy liquid. Honeydew is a favorite among various species, including ants, which herd and protect aphid colonies in exchange for a steady supply of this sugary treat. Humans, too, have found uses for honeydew. Several Native American tribes harvested it from reeds to make cakes, and some bees produce honey from honeydew, which humans then enjoy.
The journey of sap is a remarkable cycle. Plants produce sap, which aphids consume and excrete as honeydew. This honeydew is then collected by bees or harvested by humans, ultimately finding its way into our foods and beverages, such as a sweet addition to a cup of Earl Grey tea.
Draw and label the life cycle of an aphid, from egg to adult. Include details about their reproductive strategy, such as telescopic development. Use different colors to make your diagram visually appealing and easy to understand.
Construct a model demonstrating how plants defend themselves against aphids. Use materials like clay, paper, and markers to show the sieve tubes, high-pressure sap, and how aphids like Mabel use their stylets to access the sap. Explain how sucrase helps aphids survive.
Simulate the high pressure in plant sieve tubes using a plastic bottle filled with water and a small hole to represent the stylet. Observe how water flows out without squeezing the bottle. Discuss how this relates to how aphids feed without needing to suck the sap.
In groups, role-play the relationship between aphids and ants. One student can be an aphid producing honeydew, while others act as ants protecting the aphid in exchange for honeydew. Discuss how this mutualistic relationship benefits both species.
Research how different cultures and species use honeydew. Create a presentation or poster showcasing your findings. Include examples like how Native American tribes used honeydew to make cakes and how bees produce honey from honeydew.
Aphids – Small insects that feed on the sap of plants. – Aphids can often be found on the underside of leaves, where they suck the sap from the plant.
Sap – A liquid that circulates through a plant, carrying water and nutrients. – The sap of the tree is rich in nutrients that help it grow.
Plants – Living organisms that typically grow in soil and use sunlight to make their food. – Plants need sunlight, water, and air to perform photosynthesis and grow.
Sugar – A sweet substance made by plants during photosynthesis. – Plants produce sugar as a source of energy through the process of photosynthesis.
Photosynthesis – The process by which green plants use sunlight to make food from carbon dioxide and water. – Photosynthesis is essential for plants to create the energy they need to grow.
Osmosis – The movement of water through a membrane from an area of low concentration to an area of high concentration. – Osmosis helps plants absorb water from the soil through their roots.
Reproduction – The process by which plants and animals produce offspring. – Flowering plants use seeds for reproduction to create new plants.
Honeydew – A sticky substance produced by aphids as they feed on plant sap. – Ants are often attracted to the honeydew left by aphids on leaves.
Enzymes – Proteins that speed up chemical reactions in living organisms. – Enzymes in the plant help break down nutrients so they can be used for growth.
Cycle – A series of events that happen in a particular order and are repeated regularly. – The water cycle is important for providing fresh water to plants and animals.
