Tarnished plant bug and other stinging insects

Excerpt from Publication 310, Integrated Pest Management for Apples.
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Table of Contents

1. Introduction
2. Plant Bugs
   • Description
   • Biology
   • Damage
   • Monitoring and threshold
   • Management
3. Stink bugs
   • Description
   • Biology
   • Damage
   • Monitoring and threshold
   • Management

Introduction

Feeding activity of insects with piercing-sucking mouthparts result in either depressions (cat-facing) or upraised bumps on the developing apple, which are visible at harvest and affect the marketability of the fruit. There are two main groups of Hemiptera or true bugs causing this type of damage in Ontario apple orchards - plant bugs (Family Miridae) and stink bugs (Family Pentatomidae).

Plant bugs

Tarnished plant bug Lygus lineolaris (Palisot de Beauvois), apple red bug Lygidea mendax (Reuter) and green apple bug Lygocoris communis (Knight) are all members of the large insect family Miridae or plant bugs. Each causes distinct damage in apples. Tarnished plant bug is one of the most important stinging insects of apples.

Description

Adult tarnished plant bug, apple red bug and green apple bug are similar in size (6-7 mm) and shape, but have characteristic colour patterns used for identification. Tarnished plant bug nymphs are greenish with black spots (Figure 4-63). Wing pads are present on older nymphs. They are distinguished from aphids by their lack of cornicles and rapid movement when disturbed.

Adult tarnished plant bugs are oval, 5-6 mm long, with a brown-yellow mottled appearance (Figure 4-64). A diagnostic feature is the buff or yellow Y on the triangular area between the wings (scutellum). Adults from the overwintering generation tend to be much darker than the summer generation.

Figure 4-63. Tarnished plant bug nymph (Dr. Art Agnello, Cornell University)

Figure 4-64. Tarnished plant bug adult (Agriculture and Agri-Food Canada, Saskatoon Research Centre)
As the name implies, apple red bug is a predominantly orange-red insect with brown wings (Figure 4-65). Nymphs are bright red. Green apple bug is a brownish yellow with two dark bands on the thorax behind the head.

Figure 4-65. Apple red bug (Bernard Drouin, Ministry of Agriculture, Fisheries, and Food, QC)

Biology

Apple red bugs and green apple bugs have similar biologies. Both species overwinter as eggs inserted into young bark of apple trees. Eggs hatch by full bloom and nymphs feed on developing fruitlets though the petal fall period.

Adult tarnished plant bugs overwinter under leaf debris, bark, logs and under broadleaf weed litter. They become active on warm days in early spring and attack apple buds before green tissue is even present. In late spring (late May and early June), the insects migrate to herbaceous weeds, flowers and vegetables where they insert eggs into stems and stalks. Nymphs progress through five instars before moulting to adults. The final three instars have wing pads. There are two generations per year.

The tarnished plant bug has a very broad host range, feeding on more than 300 plant species including weeds, vegetables, fruit, flowers, shrubs and trees. They prefer feeding on meristematic tissues, floral buds and immature fruit. Adults are mobile and move from one crop to another as the season progresses, in search of alternate hosts. Damage symptoms are as variable as the host list, and occur as a result of both feeding and egg-laying activities.

Damage

Adult tarnished plant bugs begin feeding on apple buds on warm days in early April, inserting their piercing, sucking mouth parts into plant tissue. Damaged buds exude clear liquid ooze, which becomes amber after several hours. Affected buds do not set and subsequently abort. Adults continue to feed on developing flowers from pink through the petal fall period, when most abandon the crop in search of alternative flowering hosts. Flowers attacked prior to petal fall abort. Fruitlets stung after calyx fall off the tree during June drop, but some hang on through to harvest. Injury on mature fruit usually consists of a dimple or a deeply sunken conical area caused by the injection of a toxin during feeding (Figure 4-66). In general, early season tarnished plant bug damage occurs near the calyx end. Later season damage may be anywhere on the apple. Longitudinal sections cut through the depressions or dimples show that tarnished plant bug feeding causes a narrow tube extending to the core (but not into the core) or calyx (Figure 4-67).

Figure 4-66. Tarnished plant bug injury

Figure 4-67. Artist figure of damage by stinging insects

Apple red bug feeding injury appears as areas of smooth russeting on the fruit surface, with or without a depression (Figure 4-68). Green apple bug scars appears as raised russeted bumps on the fruit (Figure 4-69).

Figure 4-68. Apple red bug injury

Figure 4-69. Green apple bug injury
The amount of injury depends on numbers of adults successfully overwintering and on spring temperatures. Warm weather in early April, prior to broadleaf weed emergence often results in adult migration into trees. Cool springs usually result in less damage. Some studies indicate tarnished plant bug injury is heaviest on lower branches. While damage to bearing orchards is minimal after June, nurseries and newly planted blocks are susceptible throughout the summer.

Damage by tarnished plant bug can be confused with apple seed chalcid damage. This insect - a small wasp - is an occasional problem in some orchards, and usually controlled by insecticides applied for other pests. Larvae of this insect overwinter in seeds of apples. Pupation occurs in late May and adult emerge mid June. Adults damage fruit by stinging the surface and depositing an egg into the fruit. At harvest, injury appears as a depression on the fruit surface. Cutting the apple open shows a brown, narrow tunnel running through the flesh to the core. Figure 4-67 illustrates different injury type patterns caused by stinging insects.

Monitoring and threshold

There are no set monitoring protocols for these insects. Trapping tarnished plant bug adults with white sticky boards - recommended in some other provinces and states - gives irregular and often unreliable results, and is not recommended in Ontario. Adult insects are wary and quick to take flight. Walking through the orchard every few days in early spring and looking for ooze near or on flower buds gives an indication of adult feeding activity. Alfalfa is a favoured host and when it is harvested, adults will move to adjacent crops in large numbers.

Management

Injury from tarnished plant bug at harvest normally ranges from 0.25% to 1.00%. At this level, pesticide applications targeted at the pest are not economical. Injury levels occasionally increase to 2% or more. Unless tarnished plant bug is a perennial problem in an orchard, treatments are not recommended due to unpredictability of pest activity.

Pre-bloom and petal fall insecticide applications - targeted at other early season pests - may suppress tarnished plant bugs. Many newer narrow-spectrum insecticides have no activity on plant bugs. Cultural management techniques are important in reducing risk of tarnished plant bug injury. The following practices are recommended:

• practice good sod management by reducing or eliminating alternate weed hosts, particularly chickweed, dandelion, clovers, pigweed and lamb's-quarters
  
• avoid mowing of sod from bloom through petal fall period to prevent adult plant bugs from flying into trees
  
• maintain clean herbicide strip
  
• control weeds at headlands, these act as alternative hosts and resting sites
  
• avoid situations where orchards are adjacent to hay (alfalfa) fields, strawberry patches or other susceptible crops
  

Stink bugs

Stink bugs can occasionally cause fruit damage in orchards.

Description

Green stink bugs, Acrosternum hilare (Say), are the most common pests of the insect family Pentatomiidae found in Ontario apple orchards. Stink bugs are relatively large insects with well-developed shield shaped bodies and small, narrow heads. They have five-segmented antennae and a four-segmented "beak" for mouthparts. Eggs are laid in clusters and have a somewhat barrel shape with a circular pattern of raised bumps on top. Nymphs are oval, predominantly black, and become green as they age. Later instar nymphs have obvious wing pads. The green stink bug adult is, as the name implies, green (Figure 4-70). There are other stink bug species present in orchard habitats, some of which are beneficial predictors.

Figure 4-70. Green stink bug adult

Biology

Stink bugs have a wide host range including ornamental and fruit trees, vines, weeds and other cultivated crops. They overwinter as adults in protected areas, becoming active when temperatures increase in the spring. They are usually present in orchards following bloom.

Damage

Injury to fruit occurs when adult stink bugs pierce the fruit skin to extract plant juices. The injury consists of slightly indented areas with a light brown corky area just under the fruit surface (Figure 4-71). Cutting fruit open shows a feeding tube rarely more than half way to the core. This characteristic helps distinguish stink bug damage from other stinging insects. Injury from stink bugs usually occurs later in the summer, and fruit tends to hang on though the harvest period.

Figure 4-71. Stink bug injury (Peter Jentsch, Cornell University, Hudson Valley Laboratory, NY)

Monitoring and threshold

There are no established thresholds or monitoring techniques. Keep in mind that predatory stink bugs may also be present in the orchard.

Management

Stink bugs are not considered economically significant in Ontario. They are occasionally a concern during hot, dry summers when alternate food sources such as broadleaf weeds are scarce. Keep weedy areas along headlands mowed to prevent migration of stink bugs into orchards during dry, droughty summers.