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Tarnished Plant Bug and Other Stinging Insects
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IntroductionThe "stinging bug" complex consists of a number of true bugs (Hemiptera) including: the mullein bug (Campylomma verbasci), the tarnished plant bug (Lygus lineolaris), the apple red bug (Lygidae communis), the green stink bug (Acrosternum hilare). The apple seed chalcid (Torymus druparum), is a small wasp and, although not a "stinging bug", is included here. Stinging bugs have sucking mouth parts that are inserted into plant tissues to extract juices. During this process a toxin is released into the fruit, blossom of leaf axle. This toxin kills cells in the immediate vicinity of the wound, resulting in some deformation in the fruit as it continues to grow. Fruit stung after petal fall often remains on the tree into the harvest period. Tarnished plant bug and mullein bug are the only two insects in this complex which are considered of economic importance in Ontario apple orchards. The latter is reviewed in the Mullein Bug page. | Top of Page | Apple Red Bug and Green Apple BugThese insects belong to the Miridae family and are about 5 cm long. They resemble tarnished plant bugs in shape but are distinctive in their colours, as their names imply. 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. Apple red bug injury appears as areas of smooth russeting on the fruit surface (Figure 1). Green apple bug injury appears as raised, russeted bumps on the fruit. These insects, considered pests of economic importance in the Maritimes, are not generally a problem in Ontario. no monitoring or special sprays are necessary. Figure 1. Apple red bug feeding injury on fruit.
| Top of Page | Green Stink BugThese shield-shaped green insects belonging to the Petatomiidae family, are occasionally a concern in hot, dry summers when alternate food sources such as broadleaf weeds are scarce. 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 2). Cutting the 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 (Figure 3). Since injury from stink bugs usually occurs later in the summer, fruit tends to hang on though the harvest period. Figure 2. Green stink bug "sting"
Figure 3. Cross-section of stink bug sting.
No specific monitoring methods or chemical control are recommended. Weedy areas along headlands should by kept mowed to prevent migration of stink bugs into orchards in dry, droughty summers. | Top of Page | Apple Seed ChalcidThis insect, a small wasp, is an occasional problem in some orchards, but is usually controlled by insecticides applied for other pests. The larva of this insect overwinters in seeds of apples. it pupates in late May and emerges as an adult wasp in mid-June. Adult damage fruit by stinging the surface and ovipositing and egg into the seeds of the apple. At harvest the injury appears as a depression on the fruit surface. Cutting the apple open shows a brown, narrow tunnel running though the flesh right to the core (Figure 4). Figure 4. Apple seed chalcid sting - note tunnel to core.
| Top of Page | Tarnished Plant BugThe tarnished plant bug has a broad host range, feeding also on peach and other stone fruit, pear, raspberry, strawberry, crucifer crops, peppers, celery, alfalfa, tobacco, broadleaf weeds (including chickweed, clovers and dandelion), and many other plants. DescriptionAdult tarnished plant bug are 5-6 mm long with segmented antennae and brown bodies. A diagnostic feature is the buff or yellow Y on its thorax (Figure 5). Nymphs are greenish with black spots (Figure 6). Figure 5. Tarnished plant bug adult.
Figure 6. Black spots on tarnished plant bug nymph.
| Top of Page | BiologyAdult tarnished plant bug 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 insect migrates to herbaceous weeds, flowers and vegetables where they lay eggs into stems and stalks. Nymphs progress through five instars before moulting to adults. The final three instars have wing pads. There are three to five generations of tarnished plant bug per year.
DamageAdults begin feeding on apple buds on warm days in early April by inserting their piercing-sucking mouth parts into plant tissue. Buds that have been stung exude a clear liquid ooze, which becomes amber after several hours (Figure 7). Affected buds do not set and subsequently abort (Figure 8). Figure 7. Tarnished plant bug injury to fruit cluster.
Figure 8. Aborted fruit clusters due to plant bug sting.
Adults continue to feed on developing flowers from pink through the petal fall period. Flowers attacker prior to petal fall will abort. Fruitlets stung after calyx will often drop during the June drop, but some will hang on through to harvest (Figure 9). Figure 9. Fruitlets with plant bug injury.
In general, early season damage tends to be near the calyx end. Later season damage can be anywhere on the apple.
Feeding injury to fruitlets is often superficial, with small localized areas of dead cells due to a toxin injected while feeding. Egg laying punctures are deep and often near the calyx end (Figure 10). Damage that occurs after fruit set appears at harvest as small surface scars, or as deep conical depressions (dimples) with a narrow central hole. Longitudinal sections cut through the depressions show a narrow tube extending to the core or calyx (Figure 11). Figure 12 illustrates different injury patterns by stinging insects. Figure 10. Mature fruit with plant bug injury.
Figure 11. Cross-section of fruit showing plant bug sting.
Figure 12. Distinguishing Injury of Seed Chalid, Plant Bug and Stink Bug.
The amount of injury is dependent on numbers of adults which have successfully overwintered and on spring temperatures. Warm weather in early April, prior to broadleaf emergence, often results in adults moving into trees. Cool springs usually result in less damage. Some studies indicate that tarnished plant bug injury is often heaviest on lower branches. While damage to bearing orchards is minimal after June, nurseries and newly planted blocks are suseptible throughout the summer. | Top of Page | Monitoring and ManagementInjury from this pest at harvest normally ranges from 0.25 - 1.00%. At this level it is not economical to target specific pesticide applications at the pest. Occasionally injury levels do increase to 2% or more, but unless tarnished plant bug is a perennial problem in an orchard, treatments are not recommended due to the unpredictability of pest activity. Trapping with white sticky boards, recommended in some other provinces and states, gives irregular, and often unreliable results and is therefore not recommended in Ontario. Adult insects are wary and quick to take flight and there not easily seen. Walking through the orchard every few days in early spring and looking for ooze near or on flower buds can give an indication of adult feeding activity. Pre-bloom and petal fall insecticide applications, targeted at other early season pests (i.e., caterpillars, tentiform leafminer, mullein bug, plum curculio), normally suppress tarnished plant bugs. However, narrow-spectrum insecticides, such as B.t. (Dipel) and tebufenozide (Confirm), have no activity on plant bugs. Cultural management techniques can be important in reducing risk of tarnished plant bug injury. The following practices are recommended:
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