Euschistus heros, commonly known as the Neotropical brown stink bug, is an insect species in the Pentatomidae family, known for its shield-like body and characteristic odor. This species is significant due to its widespread presence and impact in agricultural systems. This article covers its identification, life cycle, feeding habits, damage, and control strategies.
Identifying the Pest and Its Range
Euschistus heros adults are dark brown, 10 to 15 mm long, with a broad, shield-shaped body. A distinguishing feature is a half-moon shaped spot at the end of their scutellum. They also have two horn-like lateral projections on their prothorax. Summer adults may be a lighter reddish-brown, while overwintering forms are darker brown.
This species is widespread across South America. While its native range is not definitive, it is presumed introduced to the region. It is prevalent in Brazil, especially in central regions and northern Paraná, thriving in warmer climates. Its distribution has expanded south to Rio Grande do Sul, Brazil, and Entre Rios, Argentina, likely due to soybean trade and climate change. Preferred habitats include agricultural fields, particularly soybeans, and surrounding vegetation.
Life Cycle and Feeding Behavior
The life cycle of Euschistus heros involves incomplete metamorphosis, progressing through egg, nymphal, and adult stages. Females deposit eggs in batches of 5-7 on leaves or stems. These eggs are initially yellow and become pink as they near hatching. The incubation period for eggs lasts around seven days.
Upon hatching, nymphs emerge, approximately 1 mm and yellowish. They undergo five nymphal instars, changing color to greenish or gray as they develop. First instar nymphs remain on the egg mass and do not feed due to fragile mouthparts. Feeding intensifies from the third instar as nymphs become more active and disperse. The entire nymphal stage lasts about 25 days, with faster development in warmer temperatures.
Both nymphs and adults are piercing-sucking insects, feeding by inserting mouthparts into plant tissues to extract sap and nutrients. They commonly feed on economically important crops like soybeans, cotton, maize, beans, and sunflower, as well as plants from the Fabaceae and Brassicaceae families. They primarily target reproductive structures like pods and seeds. Adults can live for 4 to 10 months, with peak incidence in Brazil from November to April.
Agricultural Damage Caused
The feeding activity of Euschistus heros can lead to economic and yield losses. When feeding on early pod and seed development, the insect injects toxic saliva containing tissue-digesting enzymes, which can cause pod abscission or the abortion of young seeds. This damage can result in deformed seeds, reduced seed germination, and overall yield reduction. Feeding at later stages of pod fill leads to shriveled and deformed seeds.
Soybeans are susceptible to damage, with the brown stink bug being a significant pest in Brazil’s soybean cultivation. Beyond direct yield reduction, feeding can also cause abnormal leaf physiology, and in soybeans, this can lead to “mad soybean.” The quality of harvested products also degrades due to their feeding, impacting the market value of crops like cotton and maize. The economic impact includes direct harvest losses and increased costs associated with control measures.
Controlling Euschistus heros
Managing Euschistus heros populations involves a combination of strategies. Chemical control, while frequently used, requires careful consideration of pesticide classes like organophosphates, pyrethroids, and neonicotinoids to reduce environmental effects and avoid resistance. Application during crop development stages such as R5.2 to R6 in soybeans is recommended.
Biological control methods employ natural enemies to regulate pest populations. Predators such as Podisus spp. consume eggs, nymphs, and adults. Parasitoids like Telenomus podisi and Trissolcus basalis lay eggs inside Euschistus heros eggs, preventing host nymph hatching. Commercial use of Telenomus podisi as a biological control agent began in Brazil in 2020, with potential for deployment across millions of hectares of soybean crops.
Cultural practices also play a role. These include crop rotation, adjusting planting times to avoid peak pest activity, selecting resistant plant varieties, and removing host vegetation near fields. Proper decomposition of crop residues from previous harvests is beneficial, reducing overwintering sites for adults. Integrated Pest Management (IPM) combines these tactics, emphasizing monitoring populations to determine action levels and reduce reliance on a single control method for sustainable management.