Nezara viridula, known as the southern green stink bug, is a prevalent insect species found across tropical and subtropical regions globally. This insect is recognized by its shield-like body shape and vibrant green coloration. It has spread across the Americas, Africa, Asia, Australasia, and Europe, establishing itself in diverse environments.
Identifying the Southern Green Stink Bug
The adult southern green stink bug measures around 13 millimeters in length and possesses a dull green, shield-shaped body, though its color can shift to brownish in cooler temperatures. They have dark red or black eyes and display three to five pale dots on the front of their pronotum, with small black spots visible along the sides of their abdomen even when wings are closed. The antennae alternate between dark and light segments, further aiding in identification.
The life cycle of Nezara viridula begins with eggs laid in clusters of 30 to 130, often on the undersides of leaves or on fruits. These barrel-shaped eggs are initially pale yellow and darken to a clear orange as they develop, possessing a distinctive girdle of spines around their flat tops. Upon hatching, nymphs emerge, undergoing five developmental stages, or instars, before reaching adulthood. First instar nymphs are yellowish-orange to brown and do not feed, often aggregating near their empty eggshells. Subsequent instars exhibit varying color patterns.
Impact on Agriculture
The southern green stink bug inflicts damage using its piercing-sucking mouthparts, which it inserts into plant tissues to extract sap. Both adults and nymphs cause damage by feeding on various plant parts, preferring growing shoots and developing fruits. This feeding can lead to hard brownish or black spots on fruits, and affected shoots may wither or die.
In crops like soybeans, feeding can result in shriveled, deformed, or shrunken seeds, or a dark spot and depression at the feeding site. Damage to corn ears can cause deformities and abortion of kernels, while feeding on fruits can lead to dimpling or premature dropping. These bugs can also introduce bacteria and yeast, creating entry points for disease organisms and leading to fruit decay. Crop losses, including control costs, are estimated to be in the millions of dollars annually.
Control and Prevention Strategies
Managing Nezara viridula populations involves a combination of approaches. Cultural practices include removing weeds that can serve as alternate hosts and practicing crop rotation to disrupt their life cycle. Insect netting can also prevent their entry into protected environments.
Biological control methods leverage natural enemies. Parasitic wasps, such as Trissolcus basalis, are effective, as female wasps lay their eggs inside the stink bug eggs, and the developing larvae consume the host. This can lead to high parasitization rates. Predatory insects and organisms can also prey on eggs and young nymphs.
Physical removal, such as hand-picking eggs, nymphs, and adults from plants, can be effective for smaller infestations. Chemical control methods can be employed, though their use should be targeted to minimize harm to beneficial insects and the environment. Insecticides like organophosphates, pyrethroids, and neonicotinoids are effective, but alternating products with different mechanisms of action helps prevent resistance. An integrated pest management (IPM) approach, combining these strategies, offers an effective solution for managing southern green stink bug populations.