Principles of grain condition and
insect pests
Bhadriraju Subramanyam, PhD
Professor
Department of Grain Science and Industry
Kansas State University
Manhattan, KS 66506, USA
Tel: 785-532-4092
Email: [email protected]
http://www.ksre.ksu.edu/grsc_subi
4th Annual SE Asia District Conference
October 8-10, 2013
Ho Chi Minh, Vietnam
Reasons for storing grain
• Harvest occurs only one time
• Storage occurs multiple times after harvest
• Grains are utilized throughout the year for various
purposes
• Grain travels from the farm to the processor and
finally to the consumer
• Export markets
• To obtain the maximum market price
• For food security purposes
• To maintain buffer stocks in case of catastrophes
Stored grain ecosystem
• Ecosystem = combined physical and biological
components of an environment
Physical
-metal bin
-Temperature
-Moisture
Biological – grain
and organisms
associated with it
Grain storage is transient and artificial
Grain storage ecosystem
• Composed of:
• Biotic - living organisms
•
•
•
•
•
•
•
Rodents
Birds
Insects
Mites
Molds
Weed seeds
Other grain
• Abiotic – non-living factors: light, dockage,
temperature, and humidity (moisture)
Stored-grain ecosystem: goal
• Preserve maximum amount of the harvested
seeds/grain in the best possible condition for
the longest time (until used)
• Preserve quantity
• Preserve quality
• Manage biotic and abiotic factors
Biotic factors affecting stored grain
• Vertebrates (birds, rodents)
• direct feeding damage
• fecal contamination
• carry disease-causing
organisms
• Invertebrates (insects, mites)
• direct feeding damage
• frass (insect feces)
• Insect-damaged kernels (IDK)
USDA Insect and Plant Disease Slide Set
Lesser grain borer on a
kernel of wheat
Abiotic factors
• Temperature and moisture
• insect and mold populations, seed germination, and
spoilage by mircroorganisms
– Extraneous materials
• stones, non-grain seeds, metal, dirt
– Dockage
• Chaff, fines from grain
What are stored-grain insects
• Insects associated with cereal grains or commodities
that are harvested and stored are called “storedgrain insects”
• These insects are also called “stored-product
insects” because they are capable of infesting stored
non-cereal commodities and processed cereal or
non-cereal products
• These insects have spread throughout the world
through grain trade
Storage
Farm
Transport
Insects can infest grain and
grain products from the farm
to the consumer
Processing plant
Consumer
Retail store
Proposed Origins
• Thought to be mostly tropical or subtropical in
origin
• Some are seed feeders, others feed on molds
under tree bark, or on decomposing matter
• Some species still inhabit these areas
Present day
• Stored-grain insects have been distributed to
different parts of the world through grain
trade
Stored-grain insects in the marketing
system
Type of study
No. samples
No. species
Reference
Imports into CA
902
37
Olsen (1981)
Imports in CA
3,381
63
Zimmerman (1990)
Imports into UK
3,632
81
Howe & Freeman (1981)
Empty cargo
containers
3,001
22
Stanaway et al. (2001)
Food-handling areas
of ships
1,428
16
Evans & Porter (1965)
Bakeries in CT
290
11
Hankin & Welch (1991)
Packaged food
warehouses
20
24
Highland (1978)
Import warehouses in
CA
18
26
Olsen (1981)
Source: Hagstrum and Subramanyam (2006)
Adaptations of stored-grain insects
•
•
•
•
•
•
Small
Highly mobile
Live in cracks and crevices
Feed on a wide variety of food products
High reproductive rates
Occur in natural or anthropogenic habitats
Postharvest loss assessment
Location
Commodity
Storage period
(months)
Weight loss (%)
Zambia
Maize
7
1.7 – 5.6
India
Paddy
7
4.26
Malawi
Maize
<9
3.2
Nepal
Sorghum
<9
1.7
Tanzania
Maize
3.0 – 6.5
8.7
Cyprus
Barley, wheat
3.5
3.6
Mali
Millet
8.0
1.0
Karachi
Wheat
5.9
4.6
Central stores
Source: Boxall (1991)
Primary vs. secondary feeders
• Primary feeders – develop inside the kernels
of grain
– Five species of beetles and 1 moth
• Secondary feeders – are external, feed from
the outside of the grain. Often need
broken/damaged grains in order to feed. They
can also feed on the germ of kernels
– Many species of beetles and moths
Biology
• Stored-grain insects go
through four life
• stages:
• Egg
• Larva
• Pupa
• Adult
Life cycles of stored-product insects: A, a beetle and B, a moth
Canada. Protection of farm-stored grains, oilseeds and pulses from insects, mites and moulds. Winnipeg, Manitoba: Cereal Research
Centre, 2001. Web.
Rice weevil (Sitophilus oryzae)
Weevil development
Stages of weevil infestation
Grain damage
Quantity and quality loss
Mold and bacterial infection
Weevil infestation effects
Lesser grain borer
Rhyzopertha dominica
Considered the most damaging
pest of wheat in the U.S. and
the world
Small (0.03 inches/0.8 mm)
Dark brown
Head usually held down
http://www.grainscanada.gc.ca/storage-entrepose/pip-irp/lgb-ppg-eng.htm#c
• Body is cylindrical; 2 – 3 mm long
• Head invisible (concealed) from above;
pronotum has rows of teeth
• Antennae with large, loose 3-segmented
club
• Wings have rows of punctures
Immature Stages of Lesser Grain Borer
Larva
Pupa
Stages of lesser grain borer Infestation
100 adults left in grain for 7 days and then removed
86o F (30oC)
0 days
28 days
56 days
76 days
Source: Edmond L. Bonjour, Oklahoma State University, Stillwater, OK
106 days
128 days
Angoumois grain moth (Sitotroga cerealella)
Life cycle
Egg laid on outside of
kernel
Larvae and pupae
develop inside the
kernel
Adult emerges to mate
but have a short
lifespan (few days)
Internal feeders
• Remove energy from kernels
• Create an entry point for external feeding
insects
• Create an entry point for fungi
• Seeds with holes are called insect-damaged
kernels
• Contribute to fragment counts
• Some species penetrate packages
Secondary feeders
Larvae develop on broken kernels, fine material, flour and fungi
•
•
•
•
•
•
•
•
•
•
Red and confused flour beetles
Sawtoothed and merchant grain beetles
Rusty and flat grain beetles
Cigarette and drugstore beetles
Foreign grain beetle
Mealworms
Hairy fungus beetle
Warehouse and carpet beetles
Indianmeal moth
Book lice
Feeding preferences for secondary
pests
•
Animal products
•
•
Warehouse beetle
Broken kernel feeders
• Sawtoothed grain beetle, Red flour beetle, Rusty grain beetle,
Indianmeal moth larvae
•
Germ feeders
• Indianmeal moth larvae, Rusty and Flat grain beetles, Sawtoothed
grain beetles
•
Flour feeders
• Red and Confused flour beetles
•
Mold feeders
• Hairy fungus beetle, Foreign grain beetle
Red flour beetle (Tribolium castaneum)
T. castaneum
Warehouse beetle,
Trogoderma variabile
External feeders
Diagnostic characteristics
• Best characteristic: eyes
• RFB – eyes from beneath
are close together
• CFB – eyes are more
widely separated
Rfb
Cfb
Damage to grain
•
•
•
•
Perform poorly on clean, whole grain
Feed primarily on the germ
Both adults and larvae cause damage
Insects perform better on floury materials
Rusty grain beetle (Cryptolestes ferrugineus)
Sawtoothed grain beetle (Oryzaephilus surinamensis)
Indianmeal moth (Plodia interpunctella)
Damage symptoms: Larva
Webbed food particles
Presence of silk
Moths at rest
Pupa
Pupa
Silk
Larva
Mature larvae can penetrate
packages
Storage molds on grain kernels
Hairy fungus beetle
Typhaea stercorea (L.)
•
•
•
•
•
Order: Coleoptera
Family: Mycetophagidae
Small oval beetle
1/10 in. (2.5-3mm) long
Densely covered with fine hairs
Slightly clubbed antennae
Larvae and adults on molds growing on
grain
• Presence should indicate that portions of
grain are moldy
Foreign grain beetle
Ahasverus advena (Waltl)
• Small (2-3 mm), reddish brown color
• Attracted to damp and moldy grain
• Rounded lobes on the top of the thorax,
behind the head
• Found on a wide range of commodities, or on
mold
Order: Coleoptera
Family: Silvanidae
Book lice (Psocids)
Flow of energy from
grains to insects
Energy loss
•
•
•
•
•
•
Wheat - 1 kernel (34 mg) - 752 J
Red flour beetle Dev 237 J As adult 3111 J
Rusty grain beetle Dev 35 J As adult 311 J
Granary weevil Dev 345 J As adult 1193
Rice weevil Dev 130 J As adult 300 J
Lesser grain borer Dev 33 (88) J As adult 414
(2646)
• Almond moth Dev 605 J As adult (does not feed)
Energy loss
• Corn -1 kernel (225 mg) - 4537 J
• Larger black flour beetle
– Dev. 598 J As adult 8569 J
• Larger grain borer
– Dev. 252 (547) J As adult 4210 (21,383) J
• Indianmeal moth
– Dev. 657 J As adult (does not feed)
Relative weight loss caused by different species
Species
Commodity
Weight loss (mg)
Equivalency
Larva
Adult
Total
C. angustus
Maize
32
453
485
1.00
T. castaneum
Flour
13
315
328
0.68
R. dominica
Wheat
5
149
154
0.32
S. granarius
Wheat
19
67
86
0.18
P. interpunctella
Maize
34
___
34
0.07
S. oryzae
Wheat
7
25
32
0.07
C. ferrugineus
Wheat
1
14
15
0.03
Source: Hagstrum and Subramanyam (2000)
Damage caused by external insects
(1) Weight loss (not as much as internal insects)
(2) Heating
(3) Increase in
– Moisture
– Protein content
– Fatty acid and uric acid content
(4) Contamination of raw and processed foods
(5) Decrease in seed germination
(6) Rejection of infested product by customers
(7) A few species can penetrate packaged food
products
(8) Some species impart odor to food (flour
beetles)
Insects are cold blooded
• Development is dependent on temperature
• Lower, upper, and an optimum limit for
development
• Extreme temperatures can
• be used as a management
• tool
General temperature limits
Response of Stored-Product Insect Pests to Temperature
Temperature
Zone
Range (◦C) Effects
Lethal
> 62
Death in less than 1 minute
50 ― 62
Death in hours to minutes
45 ― 50
Death in a few days
Populations die out, mobile insects seek cooler
35 ― 42
environment
Suboptimum
35
Maximum temperature for reproduction
32 ― 35
Slow population increase
Optimum
25 ― 32
Maximum rate of population increase
Suboptimum
13 ― 25
Slow population increase
Lethal
5 ― 13
Slowly lethal
3―5
Movement ceases
-10 ― -5 Death in weeks, or months if acclimated
-25 ― -15 Death in hours
Source: Adapted from Fields (1992)
Temperature and development
Development curve
160
140
Days
120
100
80
60
40
20
16
18
20
22
24
26
28
30
32
34
Temperature (Degrees Centigrade)
36
Temperature and development time in
days
Temperature (oC)
Rice weevil
Lesser grain borer
17.5
Bean weevil
82.0
20.0
52.9
60.4
22.5
43.2
45.4
25.0
35.9
58.8
35.7
27.5
30.6
49.9
30.2
30.0
27.4
42.4
28.9
32.5
26.7
36.1
35.0
29.1
31.0
37.5
36.7
Source: Subramanyam and Hagstrum (1995)
Life history parameters of some
internal feeders
Common
name
Total adult life
span (days)
No.
egg/female
Optimum
temp. (oC)
Minimum
humidity (%)
Granary
weevil
210-240
50-250
26-30
50
Maize weevil
120-150
Up to 150
25-30
50
Rice weevil
90-185
300-400
27-31
50
Lesser grain
borer
Up to 180
300-500
32-35
30
Angoumois
grain
6-10
100-150
28-30
40
Source: Subramanyam and Hagstrum (1995)
Temperature and egg-to-adult
development in days
Temperature (oC)
Red flour beetle
22.5
Confused flour beetle
56.2
25.0
41.8
44.6
27.5
32.7
35.6
30.0
28.4
28.5
32.5
26.3
23.0
35.0
23.4
20.0
37.5
21.7
34.1
Source: Subramanyam and Hagstrum (1995)
Temperature and total development time in
days for some moths
Temperature (oC)
Species
17.5
20.0
22.5
25.0
27.5
30.0
32.5
35.0
Rice moth
192.0
92.6
57.6
44.8
39.7
37.4
36.1
35.2
Almond moth
108.9
76.7
57.1
45.3
38.3
34.4
32.5
31.8
Raisin moth
129.2
98.7
76.6
60.9
50.8
45.9
46.5
54.1
69.1
56.0
46.5
40.6
39.2
99.3
67.3
48.1
37.9
34.9
38.4
49.1
Mediterranean
flour moth
Indianmeal moth
150.9
Percentage of time spent in egg, larval, and pupal stages is 15, 66, and 19%, respectively.
Source: Subramanyam and Hagstrum (1995)
Percentage of total developmental time spent in
immature stages
Food moisture
Egg stage
Larval stage
Pupal stage
Low (<12%)
15
66
19
High (>12%)
12
72
15
Multiply total development time at any temperature from
previous slide with the proportion given above to get
development time for egg, larval, and pupal stages at
that temperature
Source: Subramanyam and Hagstrum (1995)
Relative Abundance of Insects in Four
Commercial Flour Mills

26 insect species from 2 orders and 12 families were
collected in trap and product samples from all four mills
(7,840 total insects, inside and outside samples)
56.5%
Indianmeal moth
Red flour beetle
Hairy fungus beetle
Foreign grain beetle
Confused flour beetle
Rusty/flat grain beetle
Other
8.0%
12.9%
3.9%
4.5%
8.8% 5.4%
Development and reproduction vary with the
commodity
Granary Weevil
Grain
Development time (days)
No. progeny/20 weevils/4
days
Mean
SD
Range
Mean
SD
Range
Maize
45.5
1.5
32-66
21.0
7.7
10-33
Barley
41.1
1.5
30-62
96.7
17.2
73-126
Oats
40.2
2.0
34-52
9.4
3.8
4-17
Wheat
39.9
0.5
32-60
82.4
17.6
56-112
Rice
35.1
0.6
30-48
12.5
3.4
8-17
Source: Schwartz and Burkholder (1991)
Host range of external beetles
Species
No. hosts
Cigarette beetle
207
Drug store beetle
177
Warehouse beetle
118
Khapra beetle
94
Red flour beetle
246
Confused flour beetle
119
Rusty grain beetle
69
Sawtoothed grain beetle
140
Merchant grain beetle
118
Hairy fungus beetle
73
Foreign grain beetle
120
Source: Hagstrum and Subramanyam (2009)
Host range and reproduction of moths
Species
No. hosts
No. eggs/female
Rice moth
72
160
Almond moth
112
200
Tobacco moth
57
150-200
Mediterranean flour moth
75
100-200
Indianmeal moth
177
150-200
Angoumois grain moth
35
100-150
Source: Subramanyam and Hagstrum (1995)
Some female mating do not produce any eggs; in
some cases, females are capable of laying up to 300-400 eggs.
When exposed to stress (in an environment with carbon dioxide),
Indianmeal moth females lay eggs.
Survival of confused flour beetles in
clean wheat at 26.7oC
Survival of confused flour beetle on
8% moisture wheat with and without
dockage
Survival of rice weevils in wheat at
different moisture contents
Distribution of insect species in the
grain mass
• Data from 23 elevators and
513 bins
• Insect distribution varies by
month
• More insects are found on
the upper grain layers
• Density of lesser grain borer
highest in February
Source: Flinn et al. 2009
Rusty grain beetle numbers decrease
logarithmically from surface of grain in bins
Insect populations grow
logarithmically in grain
Different species grow differently at the same environmental
conditions (Source: Hagstrum and Subramanyam 2006)
Population growth vs. pest
management
• Insect populations at optimum conditions
growth at a 10-fold rate (10x)
• This means that populations reduced by 90% [1log reduction] after pest management
intervention recover to original levels within 1
generation
• After 99% reduction [2-log reduction]
populations will recover after 2 generations
Population growth of different species at
different temperatures and grain moistures
Grain temperature and moisture on lesser
grain borer populations
Source: Hagstrum and Subramanyam (2006)
Aeration slows insect growth
Beneficial effects of aeration (data
from 3 States)
Aeration retards degradation of applied
protectant (chlorpyrifos-methyl) on wheat
(Arthur et al. 1992)
aValues
are in ppm (mg(AI)/kg of grain.
Time of aeration is important
Fumigation and population growth of
lesser grain borer in stored wheat
Source: Flinn and Hagstrum (1990)
Distribution of insects among bins at
elevators
• Highly infested bins (> 2
insects/kg) were located
near other highly infested
bins
• Insects move between
bins
Source: Flinn et al. 2009
Intervening bins
At elevators only 10% of the bins needed
fumigation based on vacuum probe sampling
every 6 weeks
Source: Flinn et al. 2009
Economics of sampling versus treating
all bins
• Fumigating all of the bins at a grain elevator storing
19,048 tons (700,000 bushels) of wheat would cost
US $14,000
• However, when the elevator manager knows that
only 3 out of 30 of these bins are likely to have insect
densities of >2 insect/kg during the next two
months, fumigation of only these 3 bins is the proper
response. This fumigation would cost only US$1,400,
which would reduce the overall cost of fumigation by
US $12,600
IPM Decision Support Software
• Stored Grain AdvisorPro
• http://ars.usda.gov/npa/gmprc/bru/sga
• Uses vacuum probe sampling taken every 6 weeks to decide
whether fumigation is needed
• Population increase (PI) in 30 days (LGB) is predicted by the
following equation:
• PI = (9.2004-1.6898X + 0.0787X2-0.0011X3+0.1841Y)/(10.0197X-0.0161Y)
• X = Temperature of grain in degree Celsius (20-34oC)
• Y = % grain moisture on dry basis (10-13%)
• This software failed to predict when grain was at high risk in 2
out of the 533 bins across 28 elevators in KS and OK (USA)
IPM Practices at Elevators in the US
(OSU Study 1992)
Practice
% that implement
Sanitation
95
Residual insecticide
80
Empty bin fumigation
30
Scout for insect weekly
25
Scout for insects biweekly
29
Scout for insects monthly
36
Permanent thermocouples installed
49
Grain protectants
46
Aeration
82
Dichlorvos strips
9
Top dress (surface treatments)
38
Fumigation
76
Conclusions
• Several species infest stored grain
• Infestations can be carried to the mill
• Different species are associated with raw and
processed grains
• Understand insect biology, ecology, behavior and
response to chemical and nonchemical treatments
• Sampling for insects in critical for management
• Use a combination of chemical and nonchemical
tactics, including sanitation, for reducing insect
numbers in grain bins, mills, and outside your facility
• Insects can never be eliminated completely
Thank you