Exploring the sophisticated dietary preferences of Nezara viridula and its global agricultural impact
Imagine an insect with such refined tastes that it can trigger massive economic losses across continents, yet whose culinary preferences remain as mysterious as they are destructive.
Meet Nezara viridula, commonly known as the southern green stink bug, a cosmopolitan pest with a particular palate for some of the world's most important crops. This dazzling emerald-shaped insect may look innocuous, but its feeding choices have consequences that ripple through global agriculture, affecting everything from soybean fields in Argentina to tomato harvests in Florida.
What makes this bug choose one plant over another? Why does it prefer unripe tomatoes to red ones? And perhaps most intriguingly, do stink bugs from different parts of world have different food preferences?
The answers to these questions matter far beyond scientific curiosity. With the potential to cause substantial economic damage to legumes, cereals, and vegetables, understanding the feeding behavior of N. viridula has become a critical mission for entomologists and agricultural scientists worldwide 2 . Their research is revealing a complex story of evolution, adaptation, and biological nuance that challenges our understanding of what drives insect feeding behavior—knowledge that could lead to more sustainable ways to protect our crops.
The southern green stink bug causes significant damage to over 30 families of plants, including major crops like soybeans, tomatoes, and beans 2 .
Before delving into the culinary preferences of this six-legged gourmet, it helps to understand its fundamental biology. The southern green stink bug is a shield-shaped insect that typically measures 12-13 millimeters in length, with females slightly larger than males 2 . Its most common form sports a vibrant green coloration that helps it blend seamlessly into the foliage of its host plants, though several color morphs exist across its global range.
This insect is truly a citizen of the world, having spread from its suspected Ethiopian origins to virtually every tropical and subtropical region between 45 degrees north and 45 degrees south latitude 2 . This global expansion has been facilitated by both its strong flight capabilities and human transportation along trade routes, making it a classic example of accidental globalization with significant agricultural consequences.
N. viridula leads a complex life marked by five developmental stages before reaching maturity, with each nymphal stage bringing it closer to its full plant-damaging potential 2 . The bug's remarkable ability to reproduce throughout the year in warmer climates, coupled with its highly polyphagous nature (feeding on plants from over 30 families), makes it a persistent and adaptable threat to farmers worldwide 2 3 .
These visual differences hint at the genetic diversity within the species, diversity that may extend to their feeding behaviors 2 .
To understand the feeding preferences of N. viridula, we must first appreciate the sophisticated tools and techniques it employs. This isn't a simple matter of chewing and swallowing; the stink bug possesses a specialized piercing-sucking mouthpart that functions like a biological hypodermic needle .
Through detailed scanning electron microscopy, scientists have revealed that this intricate apparatus consists of a long beak (labium) housing two pairs of stylets—the outer mandibular stylets with serrated edges that lacerate plant tissue, and the inner maxillaries that form separate food and salivary canals .
The feeding process is a masterclass in biological engineering. The bug secretes two types of saliva: a gelling saliva that forms a protective sheath around the stylets, and a watery, enzyme-rich saliva that dissolves plant tissues . This enzymatic cocktail contains digestive proteins, signal transduction molecules, and metabolites that both prepare the plant material for ingestion and trigger defensive responses in the plant .
The damage caused isn't merely superficial; the bug's feeding destroys seed architecture, reduces germination power, and creates entry points for pathogens 5 .
Recent research has revealed that the bug's saliva contains specific organic compounds including:
This complex chemical mixture represents the bug's toolkit for overcoming plant defenses and accessing nutrients—a toolkit that may vary between populations and influence their feeding preferences .
In 1978, scientists Jerald R. DeWitt and Edward J. Armbrust embarked on a fascinating comparative study that would become a classic in the field of entomology. Their mission was straightforward yet profound: to determine whether N. viridula morphs from India and the United States showed different feeding preferences when presented with pods of soybeans (Glycine max) and green beans (Phaseolus vulgaris) 1 .
The researchers designed a laboratory comparison that would eliminate external variables and focus squarely on the insects' innate preferences. Adults of different morphs were placed in controlled environments and presented with both soybean and green bean pods. The experimental design allowed the bugs to express their preferences freely, with scientists carefully documenting their choices over multiple observation periods. The study compared the behavior of a U.S. morph against three sympatric (co-existing) morphs from India, creating a robust cross-continental comparison of feeding behavior under identical laboratory conditions 1 .
The findings revealed a striking difference in feeding behavior between the geographic populations. The American morphs appeared to select pods at random, showing no statistically significant preference for one pod type over the other. In contrast, the three Indian morphs consistently preferred green bean pods over soybean pods 1 .
| Geographic Origin | Number of Morphs Tested | Preferred Host | Feeding Behavior Pattern |
|---|---|---|---|
| United States | 1 | No clear preference | Random selection |
| India | 3 | Green bean pods | Distinct preference |
This discovery was significant for several reasons. First, it demonstrated that feeding behavior in this species isn't uniform across global populations. Second, it suggested that localized evolution or adaptation had shaped the food preferences of these insects in different regions. Third, it highlighted the importance of considering geographic origin when studying insect behavior—what's true for a population in one region might not hold for the same species elsewhere.
Understanding the feeding preferences of insects like N. viridula requires more than just observation; it demands specialized tools and techniques that allow researchers to peer into the hidden world of insect-plant interactions.
| Tool/Method | Primary Function | Application Example |
|---|---|---|
| Electropenetrography (EPG) | Records electrical signals generated during feeding | Characterizing feeding waveforms on different plant structures 9 |
| Gas Chromatography-Mass Spectrometry (GC-MS) | Identifies and quantifies volatile organic compounds | Analyzing plant volatiles that attract or repel stink bugs 5 |
| Nuclear Magnetic Resonance (NMR) Spectroscopy | Determines structure and composition of metabolites | Profiling metabolites in stink bug saliva |
| Liquid Chromatography-Mass Spectrometry (LC-MS/MS) | Identifies proteins and peptides in complex mixtures | Analyzing protein composition in watery saliva |
| Choice Tests | Measures insect preference between multiple options | Determining attraction to different soybean genotypes 6 |
Electropenetrography has been particularly revolutionary in this field. This technique involves attaching a fine wire to the insect's back and connecting it to an electrical circuit that monitors feeding behaviors in real-time.
Through EPG, researchers have identified distinct waveforms corresponding to different feeding activities—non-feeding periods, stylet penetration through plant tissues, xylem ingestion, and the crucial laceration and ingestion of nutrient-rich materials 9 . These electrical "fingerprints" allow scientists to understand exactly how, when, and where insects are feeding on different plants.
Meanwhile, choice tests in laboratory settings provide crucial information about host plant preference. In these experiments, insects are presented with multiple food options and their selections are carefully documented.
Such tests have revealed, for instance, that certain soybean genotypes like 'IAC 17' and PI 227687 are less attractive to stink bugs, often due to morphological characteristics like trichome density that create an unwelcoming surface for feeding 6 .
The DeWitt and Armbrust study opened doors to a deeper understanding of N. viridula's feeding ecology, inspiring decades of subsequent research that has revealed additional layers of complexity in the bug's dietary choices.
We now know that these insects don't just choose between plant species; they make sophisticated decisions about which parts of plants to consume. When it comes to tomatoes, for instance, N. viridula strongly prefers green, unripe fruits over breaker, pink, or red stages 5 . This preference appears to be influenced by visual cues (color) and olfactory signals (volatile compounds), which change as the fruit matures. Similarly, in bell peppers, these bugs show distinct color preferences, though the specific preferred stage varies between stink bug species 5 .
The ripening stage of plants matters because it affects both the nutritional content and defensive compounds present in the tissues. As fruits mature, their volatile profiles become more complex—tomatoes, for example, may emit between 181 (green stage) to 367 (red stage) different volatile compounds 5 . These chemical signals serve as dinner bells or deterrents to would-be insect diners.
Recent research has revealed another fascinating factor in stink bug feeding: the role of gut bacteria. The midgut of N. viridula hosts a community of non-transient microbiota, including Yokenella sp., Pantoea sp., and Enterococcus sp., that may help the insect deactivate soybean chemical defenses 3 .
These bacterial partners display β-glucosidase and raffinase activities, plus the ability to degrade isoflavonoids and deactivate soybean protease inhibitors—key defensive compounds that would otherwise protect plants from herbivory 3 .
This discovery suggests that feeding preferences may be influenced not just by the insect's own biology, but by the microbial symbionts it harbors. The presence or absence of specific bacteria could determine whether a plant is digestible or toxic to the bug, adding another dimension to the already complex story of host selection.
Plants are not passive victims in this story; they've evolved sophisticated defense systems that detect feeding and mount protective responses. When sweet pepper plants are inoculated with the beneficial fungus Trichoderma harzianum T22, for example, they undergo metabolic changes that make them less palatable to stink bugs 4 .
The fungus doesn't just directly affect the plant; it primes its defense systems, resulting in reduced growth rates for N. viridula nymphs feeding on treated plants 4 .
This induced resistance involves accumulation of compounds from the shikimate-phenylpropanoid pathway, part of the plant's chemical arsenal against herbivores 4 . The defensive response is particularly strong in locally damaged leaves, suggesting that plants can strategically allocate defensive resources where they're most needed.
The seemingly simple question of what a stink bug prefers to eat has led scientists down a remarkable path of discovery, revealing layers of complexity in insect-plant interactions.
From the initial observation that Indian and American morphs have different preferences 1 to our current understanding of the role of gut microbiota 3 and salivary enzymes , each piece of knowledge brings us closer to sustainable management strategies for this significant agricultural pest.
This research matters far beyond academic circles. Understanding feeding preferences helps develop more targeted monitoring programs—knowing that N. viridula prefers green tomatoes, for instance, allows farmers to focus their scouting efforts at the most vulnerable fruit stage 5 . Discovering that certain soybean genotypes are less attractive or nutritious for stink bugs enables plant breeders to develop resistant varieties 6 8 .
Learning how plants naturally defend themselves against these insects points the way toward biological control approaches that could reduce our reliance on chemical pesticides.
The story of Nezara viridula's feeding preferences reminds us that even the smallest creatures live complex lives intertwined with their environment and what's on their menu. As research continues to unravel these relationships, we move closer to a more sustainable agriculture—one that works with, rather than against, the intricate ecological networks that surround us.