Stink bugs, particularly the invasive Brown Marmorated Stink Bug (Halyomorpha halys), are notorious pests that feed on a wide range of agricultural crops and ornamental plants. The primary challenge in finding natural predators lies in their chemical defense mechanism. When threatened, stink bugs release a blend of volatile organic compounds from specialized glands, producing the foul odor that gives them their common name. This warning chemical spray limits the number of animals willing to consume them, making effective natural control difficult.
Specialized Parasitoid Insects
The most significant natural enemies of stink bugs are specialized parasitoid wasps that bypass the adult’s chemical defense by targeting the eggs. These insects do not consume the stink bug directly, but use it as a host for their developing offspring, resulting in mortality. This method of biological control is highly effective because it prevents the next generation of pests from hatching.
The Samurai Wasp, Trissolcus japonicus, is a well-known example and a major focus in the fight against the invasive Brown Marmorated Stink Bug. This wasp, native to Asia, is an egg parasitoid that seeks out fresh stink bug egg masses. The female wasp deposits a single egg inside each stink bug egg, where the developing larva consumes the host embryo.
The developing wasp then pupates inside the stink bug eggshell, and an adult wasp emerges in approximately 10 to 14 days, having killed the original inhabitant. In the Samurai Wasp’s native range, it can destroy between 60% and 90% of BMSB egg masses, demonstrating its high specialization and impact. Other native parasitoid species also attack stink bug eggs, but they are generally less successful at completing their life cycle in the eggs of the invasive BMSB.
The search for effective control also includes other parasitoids, such as the Trichopoda pennipes fly, a tachinid species that attacks adult stink bugs. The fly deposits its eggs onto the adult stink bug’s body, and the emerging larva burrows inside to feed on the host’s internal tissues. This internal feeding eventually kills the adult pest, though the fly has a lower rate of successful emergence from the invasive species compared to native stink bugs.
Generalist Avian and Mammalian Predators
Vertebrate predators that consume stink bugs are generally opportunistic feeders, and their impact on large pest populations is typically minimal compared to specialized insects. Birds, however, are showing increasing signs of adapting to the unpleasant taste and odor of the bugs. Species like the Northern Cardinal, Tufted Titmouse, Carolina Wren, and Bluebirds have been documented consuming the Brown Marmorated Stink Bug.
Birds may target the bugs more readily during specific times, such as the nesting season, when they require protein-rich food for their young. Some birds, including woodpeckers and nuthatches, may also forage for overwintering adult stink bugs in tree bark crevices, where the pests are less likely to release their full defensive spray. This consumption suggests a slow adaptation to the new invasive food source.
Small rodents also prey on stink bugs, consuming the vulnerable egg stage or encountering hibernating adults. Mice and rats have been documented feeding on stink bug eggs, which lack the chemical defense of the adults. Shrews, with their high metabolism and voracious insectivorous diet, may also consume stink bugs they encounter on the ground or in leaf litter.
Opportunistic Arthropods and Egg Eaters
Generalist arthropods actively prey on the most vulnerable life stages of the stink bug: the eggs and young nymphs. These predators include spiders, ground beetles, and other predatory insects. Since the eggs lack the scent glands of the adults, they are a more palatable target.
Chewing predators, such as katydids and ground beetles, are highly effective at destroying egg masses. Studies have shown that katydids can completely devour an entire clutch of eggs, leaving no residue behind. Earwigs are also known to feed on the eggs, often chewing a ring around the egg’s top to consume the contents.
Other predatory insects, including the Spined Soldier Bug, a type of stink bug, will prey on the smaller, softer nymphs. These generalist predators typically use piercing mouthparts to inject digestive enzymes and then suck out the internal fluids, effectively avoiding the full strength of the defensive chemicals concentrated in the adults. This consumption of nymphs and eggs reduces the number of individuals that survive to the reproductively active adult stage.