Degree-Days & Project the Grain-Insect Bloom
Projects rice weevil
Pick the species and enter your bin temperature and storage period to get the degree-days per day, days per generation, generations and population multiplication over storage — plus the cool-to-arrest temperature that stops them.
Bin conditions
Cool below the species base of 13°C to arrest development; below 15°C suppresses nearly all stored-grain insects.
Next: aerate to cool the grain toward 15°C now — at 28°C a generation completes every 24.9 days, so the population reaches 7.9×10^3 before you sell. Cooling below the 13°C base stops the clock.
DD/day = max(0, grainTemp − base) · days/gen = K ÷ DD/day · generations = days × DD/day ÷ K · population = (offspring/female)^generations.
Stored-grain insect growth — key facts
- DD per day
- grain temp − base (≥ 0)
- Days per gen
- K ÷ degree-days per day
- Generations
- days × DD per day ÷ K
- Population
- (offspring/female)^generations
- Arrest below
- the species base temperature
- Safe target
- ≤ 15°C suppresses most species
- Very slow below
- 18°C
- Privacy
- Runs in your browser; nothing uploaded
Stored-grain insect development thresholds
Each species has a lower developmental threshold (base) below which it cannot grow, and a thermal constant — the degree-days needed for one egg-to-adult generation. Cool the grain below the base of your pest and its population stops climbing.
| Species | Scientific name | Base (°C) | Optimum (°C) | DD / generation | Notes |
|---|---|---|---|---|---|
| Rice weevil | Sitophilus oryzae | 13 | 28 | 374 | Internal feeder of whole grain; one of the most damaging primary pests. |
| Maize weevil | Sitophilus zeamais | 13 | 28 | 380 | Flies; attacks maize and other cereals in store and the field. |
| Granary weevil | Sitophilus granarius | 11 | 26 | 360 | Flightless; tolerant of cooler temperate stores. |
| Lesser grain borer | Rhyzopertha dominica | 18 | 34 | 420 | Strong internal feeder; reduces grain to dust, thrives in hot grain. |
| Red flour beetle | Tribolium castaneum | 18 | 35 | 300 | Secondary feeder on broken grain/flour; very fast at warm temps. |
| Confused flour beetle | Tribolium confusum | 15 | 30 | 320 | Secondary feeder; tolerates cooler mills than red flour beetle. |
| Sawtoothed grain beetle | Oryzaephilus surinamensis | 16.5 | 31 | 230 | Secondary feeder; cosmopolitan, very short generation time. |
| Khapra beetle | Trogoderma granarium | 18 | 35 | 290 | Quarantine pest; diapausing larvae survive harsh, dry, hot stores. |
| Angoumois grain moth | Sitotroga cerealella | 12 | 30 | 340 | Larvae develop inside single kernels; primarily a surface-grain moth. |
| Indianmeal moth | Plodia interpunctella | 12 | 30 | 360 | Webs the grain surface; the most common stored-grain moth. |
| Cigarette beetle | Lasioderma serricorne | 17 | 35 | 320 | Attacks pulses, spices, tobacco and stored seeds. |
| Cowpea weevil (bruchid) | Callosobruchus maculatus | 17 | 32 | 300 | Devastates stored pulses; very rapid build-up in warm stores. |
Sources: Howe (1965) J. Stored Prod. Res.; Fields (1992) extreme-temperature control; Kansas State & Oklahoma State Extension stored-grain entomology; Throne (USDA-ARS) development models. Values are representative published mid-points; field development varies with grain moisture, kernel condition and strain.
Warm grain is a breeding incubator
A grain bin held warm is, to a weevil, an endless warm meal. Because stored-grain insects develop on accumulated heat above a base temperature, a few degrees of grain warmth decide whether a generation takes three weeks or three months — and because each generation multiplies the population, a small starting infestation can explode into thousands over a single storage season. The degree-day model turns your bin temperature into the rate of that bloom: degree-days per day, days per generation, and the generations stacking up over the time you hold the grain.
The same model points straight to the cure. Drop the grain temperature below the species base and the degree-days stop accumulating — development is arrested. Holding grain at or below about 15°C suppresses nearly every stored-grain species, which is why aeration cooling is the backbone of stored-grain pest management. This tool shows where your grain sits on that curve and the temperature you must reach to flatten it.
How to use it in five steps
- 1Pick the species
Choose the stored-grain insect of concern; its base temperature and degree-days per generation load automatically.
- 2Measure the grain temperature
Enter the steady grain-mass temperature — probe the grain, not the headspace air.
- 3Set the storage period
Enter how many days the grain will be held before sale or use.
- 4Read the projection
Read the degree-days per day, days per generation, generation count and population multiplication, with a growth verdict.
- 5Cool to arrest
If growth is active or explosive, aerate toward the cool-to-arrest temperature to stop development.
Frequently Asked Questions
How does grain temperature drive insect multiplication?+
Stored-grain insects are cold-blooded, so their development is driven by heat accumulated above a species lower developmental threshold (the base temperature). At a steady bin temperature the degree-days gained per day are simply the grain temperature minus the base. The warmer the grain above that base, the more degree-days per day, the shorter each generation, and the faster the population multiplies. Below the base, development stops entirely.
What is a degree-day in this model?+
A degree-day is one degree of temperature above the species base, sustained for one day. If rice weevil has a base of 13°C and your grain sits at 28°C, it accumulates 28 − 13 = 15 degree-days per day. Each generation needs a fixed thermal constant (K) of degree-days — about 374 for rice weevil — so days per generation = K ÷ degree-days per day = 374 ÷ 15 ≈ 25 days.
How many generations can occur over a storage season?+
It depends on the temperature and the length of storage. At 28°C a rice weevil generation takes about 25 days, so a 90-day storage allows roughly 3.6 generations. Because each generation multiplies the population — a single mated female can leave a dozen or more offspring — three or four generations can turn a handful of insects into thousands. The tool projects both the generation count and the multiplication factor for your inputs.
What temperature stops stored-grain insects?+
Cooling the grain below the species base temperature arrests development — no degree-days accumulate, so the population cannot grow. As a practical rule, holding grain at or below about 15°C suppresses nearly all stored-grain species, and below roughly 18°C development is very slow. That is exactly why aeration cooling is a cornerstone of stored-grain pest management: cool the grain and you stop the clock.
How does aeration cooling control insects?+
Aeration moves cool ambient air through the grain mass to lower its temperature. Once the grain drops below a species base temperature, that species cannot develop; below about 15°C almost none can. Cooling does not kill existing adults quickly, but it halts reproduction, so the population stops climbing while you decide on further action. On cool nights even a modest aeration fan can pull grain into the safe range over a few weeks.
Which stored-grain insects are the most damaging?+
Primary internal feeders that attack whole, sound grain do the most direct damage: the rice weevil, maize weevil, granary weevil and lesser grain borer bore into kernels and hollow them out. Secondary feeders such as the red flour beetle, sawtoothed grain beetle and flour moths follow on broken grain and dust. The lesser grain borer and the flour beetles are also among the fastest to multiply in warm grain.
What is the base (developmental threshold) temperature?+
The base, or lower developmental threshold, is the temperature below which an insect species does not develop. It varies by species — around 11°C for the cool-tolerant granary weevil, 13°C for the rice and maize weevils, and 18°C for the heat-loving lesser grain borer, red flour beetle and khapra beetle. The base is the temperature you must cool the grain below to arrest a given species.
Does grain moisture affect these figures?+
Yes. The degree-day model captures the temperature effect, but development is also faster at higher grain moisture and slows or stops when grain is very dry. The figures here assume favourable moisture, so they represent something close to a worst-case rate for the temperature you enter. Keeping grain dry as well as cool is the complete strategy; this tool focuses on the temperature lever.
Why is the population shown on a log scale?+
Because geometric (multiplicative) growth quickly produces enormous numbers. After four generations at a multiplier of, say, 18 offspring per female, the population is around 18⁴ ≈ 100,000 times its start. A linear axis would compress everything except the final spike into a flat line, so the growth curve uses a logarithmic vertical axis to keep every generation visible and readable.
Is this a worst-case or typical estimate?+
The development thresholds and thermal constants are representative published mid-points, and the model assumes steady temperature and favourable moisture, so it leans toward a rapid, planning-conservative estimate. Real bins have temperature gradients, drier pockets and natural mortality. Treat the result as a decision aid that tells you when temperature alone makes the grain unsafe — then confirm with trapping and inspection.
When should I act on the result?+
If the tool projects more than about one generation over your storage period, the population is set to climb and you should cool the grain toward the arrest temperature, monitor with traps, and consider treatment of hot spots. An 'arrested' or 'slow' verdict means temperature is on your side — keep it there and watch for warm pockets that could restart development.
Is anything uploaded?+
No. The whole calculation runs locally in your browser from the degree-day model and the built-in species table. Nothing you enter leaves your device.