Stored Grain Insect Pests

1. Insects Attacking Stored Grains,
Seeds, and Grain Products
Dr. Ayanava Majumdar
Extension Entomologist
Alabama Cooperative Extension System
Gulf Coast Research & Extension Center
8300 State Hwy 104, Fairhope, Alabama 36532
Cell phone: [phone]

2. front corners of pronotum not
pointed
rounded or
irregular punctures
Maize weevil or
Sitophilus
zeamais
oryzae
molitor
Oryzaephilus

3. Key pest types:
Beetles & weevils
Moths
Mites (non-insectan)
Insect Attacking Stored Grain
Insects: 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

4. How insects respire?
Insect blood doesn’t carry O
2

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.

5. BEETLES/WEEVILS IN
STORED GRAIN

6. Granary weevil vs. Rice Weevil
Common 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

7. Granary weevil vs. Rice Weevil
Distinguishing 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

8. 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

9. 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

10. •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

11. 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

12. 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

13. 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

14. 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

15. 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 >>>>>>>>>>>>>>>>>>>>>>

16. 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

17. 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

18. Cadelle
Tenebroides 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

19. 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

20. Mealworms
Yellow 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
2
3
4
Ground beetle
12345 5 tarsal
segments

21. 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

22. MOTHS IN STORED GRAIN

23. Angoumis grain moth
Sitotroga 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

24. 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

25. Indian meal moth
Plodia 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

26. 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

27. Mediterranean flour moth
Ephestia 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

28. •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

29. Storage temp. vs.
Insect activity

30. 0
150
300
450
0 1 2 3 4
No. of Insects
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!

31. 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)

32. 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)

33. QUESTIONS?