Stink Bugs

Green stink bug

Egg

The egg is barrel shaped. Eggs are laid in clusters of about 30 to 40 on the undersides of leaves.

Nymph

The color of the nymph varies from instar to instar and from individual to individual. Young nymphs are generally dark with red or orange markings. Older nymphs are mostly green, with orange markings at the edge of the thorax and abdomen and several large black disks down the center of the upper surface of the abdomen. The first instar is 1/25 to 1/17 inch (1 to 1.5 mm) long, and the fifth instar is 2/5 to 1/2 inch (10 to 13 mm) long.

Adult

The adult is 1/2 to 3/4 inch (14 to 18 mm) long and is a bright green. It has inconspicuous yellow-orange and black markings along the lateral edge of the abdomen. The lateral margins of the head and thorax are yellowish.

Life history

Adults overwinter beneath weeds or honeysuckle on the orchard floor or in protected places outside the orchard such as brush piles or bin stacks. They become active in April and feed on broadleaf weeds either in or outside the orchard, usually when the trees are in the pink to early bloom period. Females lay eggs on the leaves of host plants. Some stink bugs move into orchards as soon as they emerge in the spring and deposit eggs on fruit trees. When this happens, fruit can be damaged by feeding nymphs.

Adults often migrate to orchards in late summer from surrounding areas in search of moisture when uncultivated vegetation starts to dry. Trees in outside rows are likely to be the most severely damaged. Eggs for the second generation are usually laid on broadleaf plants in the cover crop. There are 2 or 3 overlapping generations each season. Adults seek overwintering sites in October or before fall frosts.

Damage

Pome fruits

Adults puncture fruit with their beaks and feed in the fruit flesh. The puncture may not be visible, but the surrounding area is sunken and often dark green. Beneath the skin is a group of loose spongy cells, often with brown discoloration. Damage looks similar to the disorder bitter pit, but bitter pit tends to be around the bottom of the fruit, while stink bug damage is typically around the top. Also, bitter pit produces a mass of corky brown cells beneath the skin, whereas the spongy cells caused by stink bug injury are only slightly discolored. Pome fruits tend to be damaged in late summer as they approach maturity.

Peaches

Feeding of adults causes cat-facing or dimpling on fruit. If fruit is almost mature when injured, the flesh does not turn corky but begins to decay. Damage on peaches is more noticeable than on apples or pears.

Cherries

Early season feeding causes cat-facing, dimpling and deformity. Feeding later in the year discolors the flesh around the pit. Because the damage is not visible from the outside, cherries with this type of injury are generally not sorted out during packing.

Monitoring

Stink bugs are easy to see on trees because of their large size. However, they will quickly move to the opposite side of the fruit when disturbed. Look also for spots of excrement, which they deposit while feeding. They can be found in beating-tray samples, but this method is not practical when fruit nears maturity, as more fruit than bugs will drop onto the tray. If the orchard has a history of stink bug damage, herbaceous hosts at the orchard borders can be swept with a canvas sweep net.

Biological control

Telenomus podisi and T. utahensis, two scelionid wasp egg parasitoids, will help suppress stink bug populations.

Management

It is difficult to detect and control stink bugs because of the sporadic nature of damage and problems involved with sampling. Adults usually migrate into orchards from nearby uncultivated plants when they dry out. Damage will usually be concentrated at borders near wild hosts, and spot treatments or border treatments can be effective. If the orchard has a history of damage, be on the alert during critical times of the season (fruit set on cherries and late summer on apple and pear). Although a number of materials will kill stink bugs on contact, providing residual control of new migrants is difficult. Treatments may have to be repeated as adults continue to be found.