Shield bugs, also known as stink bugs, are insects belonging to the order Hemiptera, commonly referred to as “true bugs.” They are characterized by a distinctive shield-like shape and are found in diverse ecosystems across the globe. Shield bugs feed on a wide variety of food sources, from plants to smaller invertebrates. Understanding their diet requires examining their specialized anatomy and ecological roles.
How Shield Bugs Consume Food
Shield bugs possess specialized mouthparts, unlike the chewing mouthparts of beetles or grasshoppers. They are equipped with a long, segmented structure called a rostrum or proboscis. This rostrum contains needle-like stylets used to penetrate the surface of a food source, such as plant tissue or the exoskeleton of prey.
The stylets interlock to form two canals: one for injecting saliva and another for sucking up liquefied food. The injected saliva often contains enzymes that pre-digest the food outside the bug’s body, turning solid tissues into a consumable liquid. This piercing-sucking mechanism allows the insect to extract sap, juices, or the internal fluids of other organisms. Nymphs and adult shield bugs share this same feeding strategy.
The Primary Diet: Plant Matter
The majority of shield bug species are herbivorous, using their piercing mouthparts to extract sap and nutrients from plants. This plant-based diet makes many species contributors to agricultural damage worldwide. Their feeding can target nearly any part of a plant, from roots to flowers, depending on the species and its development stage.
Reproductive Parts
Shield bugs frequently target nutrient-dense reproductive parts of plants, such as fruits, seeds, and nuts. Species like the Brown Marmorated Stink Bug damage orchard fruits, including apples, peaches, and pears, by creating sunken, discolored spots where they feed. They also cause economic loss to row crops, such as soybeans and cotton, by feeding directly on developing seeds. Feeding on immature seeds can cause them to shrivel or become deformed, rendering the crop unmarketable.
Vegetative Parts
When reproductive structures are unavailable, shield bugs feed on vegetative parts like stems and leaves. They tap into the plant’s vascular system to draw out sap, which can weaken the host plant. The Green Stink Bug, for example, feeds on vegetables like tomatoes, peppers, and beans, causing discoloration and deformities in the tissues. While many shield bugs are generalists, some species are highly specialized, such as the Hawthorn Shield Bug, whose nymphs feed primarily on the berries of hawthorn, rowan, and whitebeam.
Predatory and Alternative Food Sources
While most shield bugs are herbivores, a subgroup of species belonging to the subfamily Asopinae are predatory. These carnivorous shield bugs feed on other insects, a behavior that distinguishes them from their plant-feeding relatives. They use their specialized rostrum to pierce the body of their prey, injecting toxic saliva to subdue it before sucking out the internal fluids.
Their diet consists mainly of soft-bodied, slow-moving insects, such as moth caterpillars, sawfly larvae, and beetle larvae. For instance, the Blue Shield Bug preys on blue flea-beetles, making certain predatory species beneficial in managing agricultural pests. Beyond predation, some typically herbivorous species opportunistically consume insect eggs or decaying organic matter when plant food is scarce. This alternative feeding demonstrates adaptability, allowing shield bugs to survive food stress.