The hazelnut green stink bug, scientifically known as Palomena prasina (Linnaeus, 1761), is an insect species classified within the family Pentatomidae of the order Hemiptera. It is recognized as a significant economic pest in hazelnut cultivation. In Türkiye, it is locally referred to as the "hazelnut stink bug" or "green stink bug." Adult individuals range in body length from 11 to 14 mm. The general body coloration is green or greenish-brown. The tips of the antennae and legs display reddish hues. The dorsal side of the body exhibits a bright green tone, while the ventral side can appear lighter green or reddish. This species possesses five-segmented antennae and exhibits sexual dimorphism, with females generally larger than males. Its barrel-shaped eggs are light green and are laid in orderly rows on the undersides of leaves.

^{Visual of the Green Hazelnut Stink Bug (İl ve Tarım Orman Müdürlüğü)}

Life Cycle and Biology

The green hazelnut stink bug spends the winter in the adult stage. During this time, it remains in diapause under fallen leaves, in crevices between stones, and other sheltered areas. As air temperatures rise to 18–20 °C, typically at the end of March or beginning of April, the bugs wake up from hibernation and emerge into the environment. The adults mate shortly after emerging, and females lay their eggs, usually in groups of 14 to 28, on the underside of hazelnut leaves. These eggs hatch into nymphs within 8 to 10 days. The nymphs go through five stages and become adults in approximately two months. First-instar nymphs feed collectively near the egg cluster, while second-instar nymphs disperse across herbaceous plants. From the third instar onward, they move onto hazelnut fruits, becoming harmful.

In laboratory conditions, the egg hatch rate is over 96%. However, only about 28% of developing individuals reach the adult stage. The duration of the nymphal stages ranges from approximately 40 to 60 days. In each of the five instars, the body size and prothorax width gradually increase. Individuals that hatch from eggs generally complete their development by mid-summer. By July, new-generation adults start to appear and continue feeding on hazelnut fruits and leaves until the end of September.

In natural environments, color changes in adults have been observed throughout the year. Overwintered individuals are dull green, while new-generation adults emerging at the end of summer show an equal distribution of green and brown coloration. Studies have found that these individuals are highly attracted to the color yellow.

^{Visual of Green Hazelnut Stink Bug Eggs (İl ve Tarım Orman Müdürlüğü)}

Damage Type

The green hazelnut stink bug causes damage to hazelnut fruits through sap feeding in both the adult and nymph stages. The type of damage varies depending on the fruit's developmental stage. The primary types of damage caused by feeding are referred to as "yellow kernel," "black kernel," "deformed interior," and "stained interior." Yellow kernel occurs when feeding takes place before the fruit has reached its normal size; the fruit's flesh turns yellow and the shell shows indentations. Black kernel appears after the fruit has grown and during the filling stage; it is characterized by darkening and rotting of the interior, with black liquid seeping from the shell.

Deformed interior damage primarily results from feeding during the fruit's internal formation stage; the interior of the fruit becomes wrinkled and sunken. Stained interior damage occurs in July, during the fruit's ripening phase, and can lead to significant quality losses in international trade. These types of damage, which affect the quality of the hazelnut's interior, reduce both the quantity and marketability of the product.

^{Hazelnut Fruit Damaged by Green Hazelnut Stink Bug(İl ve Tarım Orman Müdürlüğü)}

Distribution and Hosts

The green hazelnut stink bug is commonly found in Türkiye's hazelnut production regions. The population density is high in the hazelnut orchards of the Black Sea region. In addition to hazelnuts, plants such as cherry, mulberry, apple, citrus, blackberry, saparna, and alder, as well as weeds in the hazelnut orchards, also serve as hosts. Therefore, the bug's habitat is not limited to hazelnut areas and can expand in relation to the surrounding vegetation.

Population Dynamics

According to long-term field observations, overwintered adult individuals begin to appear in hazelnut orchards in the second half of April. The population density peaks in May and June, when the hazelnut clusters reach the size of lentils or chickpeas. A second peak in population density is observed in July with the emergence of the new generation of adults. Nymph population density reaches its highest level in early June, and by the end of September, the population disappears.

Population dynamics are influenced by climatic factors such as temperature and humidity. It has been determined that the population remains active between April and September. Studies have shown that meteorological factors, such as rainfall and temperature, directly affect the development of the pest.

Economic Importance

The green hazelnut stink bug is an economically significant pest that exceeds the economic damage threshold for hazelnut producers. It affects the interior filling of the hazelnut and causes stained interior damage, which impacts quality standards in international trade. In post-harvest analyses conducted in Sakarya province, deformed interior damage ranged from 0.7% to 1.9%, while stained interior damage ranged from 0.5% to 1.3%. The damage caused by this pest, along with the hazelnut weevil, can lead to a combined damage rate of up to 30%. Such damage can result in significant economic losses, particularly in batches designated for export.

Control Methods

Cultural Practices

Early-stage nymphs of the green hazelnut stink bug feed on weeds, making weed control in hazelnut orchards crucial. Removing potential host plants from the orchard borders can help reduce population density.

Chemical Control

Chemical control is recommended when the pest population exceeds the economic damage threshold. Control measures for overwintered adults are planned during the second half of April, using a blanket method for counting under orchard trees in the early morning or evening cool. Pesticide application should occur when an average of one or more adults is seen per 10 trees. In the first half of July, when the nymph population increases, chemical treatment should be applied if an average of one nymph is found per tree. Chemical control measures should follow the pesticide application guidelines set by regional agricultural authorities. Additionally, treatments for hazelnut weevil are often effective against the overwintered green hazelnut stink bug.

The green hazelnut stink bug (Palomena prasina) is a polyphagous insect that causes serious economic damage to hazelnut farming, especially in the Black Sea Region of Türkiye, where hazelnuts are intensively cultivated. Both adults and nymphs feed on hazelnut fruits, leading to various types of damage that negatively impact both the quantity and quality of the product. Although population development and the level of harm vary with seasonal conditions and environmental factors, field studies have shown that both adult and nymph stages can exceed the economic damage threshold during certain times of the year. Damaged fruits exhibit quality losses, including yellow kernel, black kernel, deformed interior, and stained interior, and it is emphasized that correct timing of control measures is critical to preventing such losses, especially in terms of international trade. Considering the bug's life cycle on weeds increases the effectiveness of cultural control measures. Integrated approaches based on both biological and chemical control are essential for ensuring sustainable yield and quality in hazelnut production.