Leafhoppers are small, wedge-shaped insects characterized by their ability to jump and their exclusive reliance on plant matter for survival. They extract plant sap using specialized mouthparts. Understanding their feeding mechanics and host range is important for grasping their overall impact on agriculture.
The Mechanism of Sap Feeding
Leafhoppers possess highly modified mouthparts known as a stylet, a needle-like structure formed by four interlocking filaments. The stylet is used to pierce the rigid outer layers of the plant tissue, reaching the internal vascular system. As sap-suckers, they bypass protective cell layers to access the plant’s nutrient streams.
They primarily target the plant’s vascular tissues: the phloem and the xylem. Phloem carries sugar-rich sap, the main energy source for many species. Other species, often called sharpshooters, feed predominantly on the xylem, which transports water and dissolved minerals. To facilitate feeding, the insect injects saliva that forms a protective sheath around the stylet bundle as it penetrates the plant cells.
The stylet sheath remains in the plant tissue after the insect withdraws, providing evidence of the feeding pathway. While some leafhoppers specialize in one tissue, many species probe both the phloem and xylem when seeking water or specific nutrients. Accessing these internal transport systems defines their feeding strategy.
Host Range: Generalists and Specialists
The diet of leafhoppers varies widely across thousands of species, leading to a classification of feeding habits. Generalist (polyphagous) leafhoppers feed on a broad array of unrelated plant species. The potato leafhopper (Empoasca fabae) is a well-known example, feeding on hundreds of hosts including alfalfa, beans, potatoes, and ornamental shrubs.
Specialist leafhoppers are either monophagous or oligophagous, feeding on only one or a few closely related plant species. These specialists restrict their diet to specific hosts, such as grasses, a type of fruit tree, or a single garden vegetable. Generalist species can move freely between different crop types, while specialists may be limited to a particular habitat.
Specific host plants frequently attacked include common agricultural crops like grapes, citrus, and vegetables such as carrots and celery. Ornamental plants like roses, asters, and rhododendrons are also commonly affected.
Consequences of Their Diet
Leafhopper feeding causes direct physical injury to the plant. As they extract sap and inject salivary toxins, they cause a symptom known as stippling, which appears as tiny white or yellow specks on the leaves. Severe feeding can lead to damage known as “hopperburn,” where leaf edges curl, turn yellow or brown, and become brittle.
Hopperburn results from a toxin injected by the insect, which blocks the vascular flow in the leaf veins, causing the tissue at the leaf margins to die. For crops like potatoes, this damage can severely reduce yields. Nymphs and adults excrete a sugary waste product called honeydew, which can promote the growth of black sooty mold, further hindering photosynthesis.
Their feeding mechanism turns leafhoppers into vectors for plant pathogens, including bacteria, viruses, and phytoplasmas. By probing the vascular tissue, they can acquire these pathogens from an infected plant and transmit them to a healthy one during subsequent feeding. The aster leafhopper (Macrosteles quadrilineatus) transmits the phytoplasma responsible for Aster Yellows disease, affecting carrots, lettuce, and numerous ornamental flowers. Other species spread Xylella fastidiosa, a bacterium that causes Pierce’s disease in grapes and leaf scorch in trees.