Insects Attacking Stored Grains, Seeds, and Grain Products
Dr. Ayanava MajumdarExtension Entomologist
Alabama Cooperative Extension SystemGulf Coast Research & Extension Center
8300 State Hwy 104, Fairhope, Alabama 36532Cell phone: 251-331-8416
front corners of pronotum not pointed
rounded or irregular punctures
Maize weevil orSitophiluszeamais
oryzae
molitor
Oryzaephilus
Key pest types:
Beetles & weevils
Moths
Mites (non-insectan)
Insect Attacking Stored GrainInsects: hard exoskeleton, three part body (head thorax, abdomen), jointed appendages, legs never >3 pairs
Arachnids: two body regions (head+thorax fused, large abdomen), jointed appendages but >3 pair legs normal
HEAD
PROTHORAX
ABDOMEN
How insects respire?
Insect blood doesn’t carry O2
Tracheal system: a system of tubes and fine tracheoles that forms respiratory system
Spiracles: are external openings of tracheal system
Tracheoles: are fine internal tubes that directly supply oxygen to muscles; this makes oxygen abundant inside but also makes them highly susceptible to fumigants.
BEETLES/WEEVILS IN STORED GRAIN
Granary weevil vs. Rice WeevilCommon characters:• Most destructive grain insects in world• Thrive in undisturbed grain• Adult beetles and legless grubs destroy grain• Mouthparts located at the end of a prominent snout• Antennae at the base of snout• Eat out kernel of grain, larvae live inside seeds
Granary weevil, Sitophilus granarius
S. oryza
Granary weevil vs. Rice WeevilDistinguishing characters:• Granary weevil: cylindrical,
wings with ridges, pits on prothorax are oval, snout very long, does not fly and moves slowly
• Rice weevil: smaller than granary weevil, smoother wings with lighter patches, short snout, pits on prothorax round, good flyer & attracted to light
Granary weevil, Sitophilus granarius
S. oryza
Feeding injury from weevils
Feeding injury: • Female weevil lays 300-400 eggs one in a cavity• Larva dev. internally at high growth rate (egg hatch in 3 d at 13% RH, 27C)• Attack whole grain, on farm storage bins• Raise grain temp. and moisture to cause germination
Sawtooth vs. Merchant grain beetles
• Sawtoothed grain beetle: Oryzaephilus surinamensis• Merchant grain beetle: O. mercator
Important characters:
• Flattened beetles & larvae (mouthparts directed forward)
• Prothorax with saw-like projections
• Forewings with ridges
• Females can lay 250 eggs on grain
• Pupation in grain by binding damaged seeds
• Saw-T beetle is flightless
• Common in grocery stores, storage warehouses, homes
• Adults penetrate packaged products
• Rapid lifecycle of 3 to 4 wk
• Larvae do not enter seed, feed externally as they go (secondary pest?)
• Serious heating of stored grain
Damage from grain beetles
Red flour beetle (RFB) Tribolium castaneum
Identification:
• Head is visible from above
• Adult beetles very active, strong flyers
• Antennae abruptly enlarged at the terminal segments
• Eyes close to each other
• Side of thorax curved
• Long-lived (3 yr) adult female, ~1000 eggs
• Sticky eggs laid on sacks, in cracks or on food
• 3 to 4 months per generation
Confused flour beetle (CFB)Tribolium confusum
Identification:• Flat, shiny beetles with visible head• Adult beetles slower, poor flyers compared to
RFB• Antennae gradually enlarged at the tip (club-
shaped)• Eyes widely separated from each other• Side of thorax rounded• Larvae flattened, creamish, forked terminal
Feeding injury by RFB & CFB
• First reported as pests in USA in 1893
• RFB serious in farm storage bins
• CFB in retail grocery stores, serious pest in flour mills, warehouses
• Extended feeding life stages causes more damage
Lesser grain borer (LGB)Rhyzopertha dominica
• AKA Australian wheat weevil, more southern distribution
Identification:• Dark brown cylindrical beetles, head
tucked beneath the prothorax• Larva is thick-bodied, head is
retracted, mandibles visible• Females lay 300 to 500 eggs on or
around grain• Larvae live inside grain and emerge
as adult
Lesser grain borer feeding injury
• Adults and larvae feed on grain• Extremely active insect with one to
two month lifecycle (temp. and food dependent)
• Larva develops within seed, so injury is difficult to assess
• Adults can eat into wood and paper boxes
• Larger grain borer (Prostephanus truncatus) may look similar to the LGB >>>>>>>>>>>>>>>>>>>>>>
Drugstore beetle vs. Cigarette beetle
Identification:
• Beetle forewings with ridges or striations, fine body hair
• Feed on a wide variety of retail products, incl. medicines
• Symbiotic yeast in stomach aid in digestion
• Larvae bare and pupate by making a cocoon using food particles
Identification:
• Cylindrical brown beetles have “hump-backed” appearance
• Velvety appearance of adults
• No ridges on forewings
• Larvae very hairy or fuzzy, darker head (unlike drugstore beetle larvae)
• Larvae pupate in thin cocoons made from food debris
Stegobium paniceum Lasioderma serricorne
Feeding injury by drugstore & cigarette beetles
• Drugstore beetle: major problem in retail stores & dry processed food; can bore through packaging, cardboard and tin cans
• Cigarette beetle: narrow host range - tobacco & spice factories; damage more under warm temp. (70+ degrees) and high humidity
Cigarette beetle damage
CadelleTenebroides mauritanicus
General feeder on stored grain and seed
Identification:• One of the largest stored grain insect (0.5 in)• Adult beetle is black, flattened with
mouthparts ahead of the head• Loose joint between prothorax & abdomen• Single female may lay >1000 eggs in
protected places• Larvae are fleshy cylindrical grubs, prolonged
lifecycle• Pupation away from food, hidden (e.g.,
wooden containers)…carry over infestation
Feeding injury from cadelle• Wide range of stored grains may be attacked• Adult and larvae attack grain to feed on the germ or
embryo (soft-portions)• Move rapidly from seed to seed destroying produce• Adult beetles could be predaceous but prefer seeds
MealwormsYellow mealworm = Tenebrio molitor
Dark mealworm = T. obscurus
Identification:• Beetles are ½ to 1 inch long, shiny• Beetles may look like ground beetles (predatory)• Grubs are cylindrical, sold as fish bait• Adults and larvae prefer dark, damp places in spoiled grain• Larvae can remain alive for >600 d in unfavorable conditions
Insect is native of Europe.
1 23
4
Ground beetle
1 2 3 4 5 5 tarsal segments
Dermestid beetles• Scavengers by habit• Very wide host range/habitat• Khapra beetle (Trogoderma
granarium) – strict quarantine has reduced spread or eliminated local infestations
• Adult beetles are oval, 2 mm, reddish brown
• Larvae are fuzzy, plump shape
• Recent detections in spice warehouses
Carpet beetle, Anthrenus sp.Khapra beetle,
Trogoderma
MOTHS IN STORED GRAIN
Angoumis grain mothSitotroga cerealella
• First site of infestation in USA was North Carolina
Identification:• Adult moth is small (2/3 inch), brownish
gray with long fringes of hair on wings• Hindwings extended at the apical angle
(arrow)• Larval and pupal stages remain inside
seed
Grain moth damage• First reported from France in 1736• Most destructive insect of grain in
USA, esp. corn• May also attack developing wheat
grain in field• Adult moths do not feed on grain• Eggs laid in clusters on
grain>>produces larvae that feed in masses
• Larvae feed on starchy portions of seed, adult escapes from a circular exit hole
• There could be 6 generation
Indian meal mothPlodia interpunctella
• Has European origin• Moth with a natural parasite (Bracon
hebetor)• Identification (moth): base of forewings
gray, half of the wing is reddish brown; black legs; conical head
• Identification (larva): creamish with pinkish tinge and light brown head, make extensive webbing
• Lifecycle: 4 to 6 weeks
Bracon hebetor Meal moth larvae
Damage by Indian meal moth
• Pest with a wide host range
• Rapid lifecycle (4 wk)
• Destroys stored grain by
– Directly feeding on grain
– Producing silken tunnels
– Contaminating grain with excreta
Mediterranean flour mothEphestia kuhniella
• First reported from NA in 1889
Identification:• Moth had gray wings with zigzag
line that may not be very clear• Hindwings are white with hairy
margin• Eggs are laid in clusters on food or
sacks or cracks• Larva is damaging: whitish or
pinkish with hardened head capsule, spin silken tubes in flour
• Pupate in silken cocoons • Lifecycle: 9 to 10 weeks
• Modern fumigation methods have reduced pest status
• Caterpillars web together flour and live inside
• Flour is favorite but whole grain may be attacked
• Moths may be monitored using pheromone traps
Feeding injury by mediterranean flour moth
Sto
rage tem
p. vs.
Insect activity
0
150
300
450
0 1 2 3 4
No.
of I
nsec
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Months
The number of insects present at the start of storage is critical
Treat the storage areas and harvest at the right time to cut postharvest losses!
Back to basics…• In USA, stored product losses have been enormous due to rice or maize weevils.
Reduction of losses:
• By sanitation or hygiene – need of good plant design, stacking, sweeping, vacuum cleaning, and efficient disposal of infested debris
• Use of monitoring devices – light traps (cigarette beetle, med. flour moth), pheromone traps (delta traps for Angoumois grain moth, Indian meal moth), floor traps (sawtooth grain beetle, drugstore beetle, etc.)
• By using fumigants & contact insecticides
• By improved storage/packaging: more research??Source: Page & Lubatti (1963), Parkin (1956), Fields & White (2002)
Back to basics…
• Mode of action: fumigants intervene ATP formation, upset enzyme systems, action is rapid
• The rate of uptake of fumigant by insects depends on the rate of fixation in tissues
• Insects that may seem to recover can have sublethal effects
• Success of fumigation depends largely on even distribution of fumigant and on penetration.
Source: Page & Lubatti (1963), Parkin (1956), Fields & White (2002)
QUESTIONS?
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