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Insects of the Month - True Bugs - Plant Bugs vs Stink/Shield Bugs

 
  Hort Snacks - December 2018
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 True Bugs | Plant Bugs | Stink / Shield Bugs | Tarnished Plant Bug | Brown Marmorated Stink Bug

True Bugs

The order Hemiptera contains about 50,000 to 80,000 different species of insects, all of which have some form of sucking mouthparts. Among the members of this order you’ll find many different insect pests which are common to Alberta, including aphids, shield bugs, spittle bugs, leafhoppers, thrips, etc.

Plant bugs and stink bugs are both part of this larger True Bug order. Plant bugs are a part of the Family Miridae and stink bugs are in the Family Pentatomidae.

Insects in these groups vary in their host ranges, feeding habits and level of pest status. Some are plant pests and others are beneficial predators/parasites.

Plant Bugs (Miridae)

These insects are smallish insects, typically being oval or elongate in shape, and often less than a centimetre in length. Many of them have a hunched look, because of the shape of the prothorax, which carries the head bent down. Their mouthparts have four segments. Some are brightly coloured and patterned, while others are drab or dark; most are inconspicuous.

One useful feature in identifying members of the family is the presence of a cuneus, which is a triangular-shaped area at the tip of the horny part of the forewing.

Example insects:
Lygus Bugs (Lygus lineolaris (& other species))

Tarnished Plant Bug adult on strawberry – note the distinctive “cuneus” (triangular area) on the upper part of the forewing
Photo by Robert Spencer

Stink / Shield Bugs (Pentatomidae)

Stink and shield bugs are larger insects with broad, flattened, shield-shaped bodies, small, narrow heads and fairly short legs. They range in colour, generally being green to brown. They have long, four to five-segmented antennae and large, compound eyes. They have a three to four-segmented piercing/sucking "beak" for mouthparts. The beak is held below the body when not in use. Their forewings have the front half leathery and the back half membranous. Eggs are laid in clusters. Nymphs (the immature stage) resemble the adults, but have no wings.

The stink bug derives its name from a pungent unpleasant odor from a glandular substance released from the thorax when disturbed or crushed. The smell is used to protect themselves and discourage predators.

Example insects:
Green stink bug (Chinavia hilaris)
Twice-stabbed stink bug (Cosmopepla lintneriana)
Brown marmorated stink bug (Halyomorpha halys)

Adult Twice-stabbed stink bugs on strawberry – one example of the stink/shield bug group
An adult stink/shield bug of some sort
Photos by Robert Spencer

Tarnished Plant Bug

Lygus lineolaris (& other species)

Crops Affected: Wide host range – many fruit, vegetable, field and forage crops and weed species

Life Cycle:
  • One of the most serious & widespread of strawberry pests
  • Sucking insects that pierce flower buds, blossoms, and developing fruits and plant parts
  • Adult has distinctive triangle or “V” mark on back; strong fliers
  • Overwinter as adults in leaf litter or under debris and migrate into fields in spring or fall to feed on weeds and crops
  • Lay eggs in spring in plant tissues
  • Young (nymph) resemble aphids without cornicles (tail pipes) and move more quickly; hatch & feed on developing blossoms & fruit
    • Nymphs feed through May and June, maturing in late June to early July
    • Most of damage results from nymphal feeding
  • Adults feed on developing fruit
    • Leave with fruiting complete in June or July (strawberries)
    • May have 2-3 generations per year (depending on season length)
  • Due to the fact that day neutral strawberries are flowering when TPB numbers are high, damage potential is higher
Tarnished Plant Bug damage
Tarnished Plant Bug damage - catfacing
Photos by Robert Spencer

Symptoms:
  • Presence of insect life stages
  • Range of damage to vegetables: reduced fruit set in bean, pepper & eggplant; blemishes on tomato fruit; necrotic spots on florets & curd of broccoli, cauliflower and heads of lettuce; dead leaves on potatoes; foliar injury on cucumbers; gummosis on zucchini
  • Raspberries (most damage occurs after petal fall)
    • Feeding on flower blossoms & developing fruit = crumbly berry
    • Reduced plant vigour
  • Saskatoon berries
    • Yellow, aborting flower buds; droplets of brownish liquid may exude from newly pierced buds
    • Fruit deformation
  • Strawberries
    • Feeding by nymphs – Nubbins or deformed fruit / Apical seediness
    • Adult feeding – CATFACING
      NOTE: Catfacing can be caused by other factors, producing identical symptoms
  • Feeding also reduces plant vigour due to removal of plant nutrients
Monitoring:
  • Be aware of neighbouring crops that might be a host or that might release a large number of adults when cut (e.g. alfalfa or canola)
  • Crop should be monitored for the number of nymphs in flower blossoms. Sweep nets can determine adult numbers
    • Scout the field perimeter in new fields or entire established fields
    • Start monitoring in overwintered fields when they are uncovered onward
  • Blossoms may be sampled from across the field, counting the number of nymphs and adults present
    • Survey the field from pre-bloom until green fruit stage (strawberries)
      • Tap plants or shake fruit clusters over a non-metallic pie plate
      • Count the number of nymphs per 100 clusters
  • Strawberry Economic threshold = 1 nymph or adult per 8 blossoms
Management:
  • Careful monitoring of TPB populations
  • Remove weeds (especially leguminous species)
  • Ensure alternate host crops are not planted too close (e.g. alfalfa)
  • Make careful and timely chemical control applications
    • Controls are available with application timing restrictions
    • Chemical control is challenging due to continuous flowering and fruiting of day neutral strawberries
    • Only products with short Pre-Harvest Intervals (PHI) may be used
    • Do not apply products when bees are actively working
Tarnished Plant Bug – A Major Pest of Strawberry – OMAFRA article

Brown Marmorated Stink Bug

Holyomorpha halys

Crops Affected:
Wide host range (over 300 plants) – berry crops, grapes, stone and pome fruit, peppers, tomatoes, corn, ornamental tree and shrub plants, etc.

Life Cycle:
  • In northern areas, overwinter in buildings or structures (e.g. houses, woodpiles)
  • In some regions where they are established, they can “gather” indoors in fall/winter
  • Typically a single generation per year
  • Tend to hitchhike from other regions in containers, vehicles, etc.
    • NOTE – BMSB was detected in a shipment of RVs in central Alberta in 2012
  • Adults are large insects, 12-17 mm long and 8mm wide
    • Emerge in May to June as it warms up (if overwintered)
    • Marbled brown/grey backs (dorsal) and pale undersides (ventral)
    • Pinkish forewings (when extended) – hidden
      • Distinctive identifying characteristics of BMSB adults
        • Two white bands on antennae
        • Smooth “shoulders” that don’t protrude forward
        • Inward-pointing white triangles alternating with dark areas that run along the edge of the abdomen
  • Pale-green, barrel-shaped eggs are laid in clusters of 20-30 on leaf undersides from early June until late July / early August
  • Multiple (5) instars of nymphs develop
    • Each instar is somewhat different – ranging from red and black early instars to grey/brown later stages
  • May move between different host crops – highly mobile
Brown Marmorated Stink Bug adult
Photo by Jennifer Read - NRCan

Symptoms:
  • Nymphs and adults can cause injury through insertion of piercing/sucking mouthparts
  • Feeding results in necrotic spots at the initial site
  • Other damage symptoms might include
    • Discoloured/deformed fruit
    • Abortion/abscission of berries
    • Death of buds
    • Stippled leaves
    • Missing, shrivelled or punctured seeds/kernels
    • Sap flow or discoloured bark in trees
Monitoring:
  • Regular monitoring for tell-tale signs
  • Watch for signs of the insect or symptoms
  • Watch for winter aggregations (mass groupings of adults) in/on structures
Management:
  • Monitoring for early detection and monitor throughout season into fall/winter
  • Ensure clean, pest-free plant material
  • Pesticide application (broad-spectrum) can be somewhat effective in the short term
  • Most new pesticides are less effective as they don’t have long residual times
Additional Sources of Information
Brown Marmorated Stink Bug - OMAFRA info
BMSB – OMAFRA – ID Postcard
Brown Marmorated Stink Bug – Penn State info
BMSB “Have You Seen This Bug” – British Columbia Ministry of Agriculture
 
 
 
 
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For more information about the content of this document, contact Robert Spencer.
This information published to the web on November 28, 2018.