# Temperature, humidity and pest population growth in cannabis: every major pest compared

> Room temperature is the single biggest lever on how fast cannabis pests multiply: between about 20 and 30 C, most mites, aphids and thrips double every 2-4 days in lab life tables, while mealybugs and fungus gnats double every 6-8 days. Humidity matters mostly through the predators and pathogens that control pests, so set-points should be chosen for the beneficials as much as against the pest.

- Canonical: https://genetixbay.com/knowledge/pests/temperature-humidity-and-pest-population-growth.html
- Category: Pests · Level: Advanced
- Evidence: Supported · Status: Draft: awaiting expert review
- Stage: Any stage · Systems: Any system
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Questions and answers

**Which cannabis pest multiplies fastest?** In lab life tables the fastest-multiplying cannabis pests are [aphids](https://genetixbay.com/knowledge/glossary/aphid.md): cotton aphid reached an intrinsic rate of increase of 0.53 per day at 25 C on cucumber, rice root aphid 0.43 and [cannabis aphid](https://genetixbay.com/knowledge/glossary/cannabis-aphid.md) 0.36 on [hemp](https://genetixbay.com/knowledge/glossary/hemp.md), meaning a doubling every 1.3-2 days. [Broad mites](https://genetixbay.com/knowledge/glossary/broad-mite.md) (0.31) and [spider mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) (0.24-0.30) follow. Mealybugs (0.08) and [fungus gnats](https://genetixbay.com/knowledge/glossary/fungus-gnat.md) (0.11) are among the slowest.

**How much faster do spider mites grow at 30 C than at 20 C?** Two-spotted spider mites grow about twice as fast at 30 C as at 20 C. Lab life tables on apple leaves give an intrinsic rate of increase of 0.161 per day at 20 C and 0.302 at 30 C, doubling every 4.3 versus 2.3 days. Ten mites become about 290 in three weeks at 20 C but about 5,700 at 30 C, with no predators.

**Does lowering the temperature stop pests in a grow room?** Lowering grow-room temperature slows pests but does not stop them, because most cannabis pests have lower developmental thresholds of about 6-13 C, far below any room set-point. Spider mites still double every 4 days or so at 20 C. Cooling from 30 C to 24 C can roughly halve the growth rate of mites and [thrips](https://genetixbay.com/knowledge/glossary/thrips.md), which helps predators catch up, but it never replaces them.

**Why does heat sometimes reduce pest numbers?** Heat reduces some pests because each species has an optimum above which egg-laying and survival fall. Cannabis aphid growth collapsed to 0.019 per day at 30 C on hemp, broad mite growth fell from 0.31 at 25 C to 0.12 at 32 C, and 96% of western flower thrips larvae died at 35 C. Spider mites are the exception: they still grow fast at 30-32 C.

**Does high humidity kill spider mites?** High humidity does not kill spider mites, but it slows them and helps their predators. Greenhouse cucumber trials found up to three times more mites at about 55% [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) than at about 80% RH. The bigger effect is on Phytoseiulus persimilis, whose eggs mostly fail below about 60% RH. Raising humidity is a veg-stage tactic only; in flower it invites bud rot.

**What humidity do [predatory mites](https://genetixbay.com/knowledge/glossary/predatory-mite.md) need?** Most predatory mites need about 60-75% RH around their eggs. Phytoseiulus persimilis egg hatch fell to about 8% at 40% RH versus nearly 100% at 80% RH at 27 C, and [Amblyseius swirskii](https://genetixbay.com/knowledge/glossary/amblyseius-swirskii.md) lost half its eggs at about 63% RH. Neoseiulus californicus tolerates roughly 40-80% RH, which is why it suits drier cannabis rooms and flower.

**What is a [degree-day](https://genetixbay.com/knowledge/glossary/degree-day.md) and how do I use it indoors?** A degree-day is one day spent one degree above a pest's lower developmental threshold. Indoors, divide the pest's degree-day requirement by room temperature minus threshold to get days per stage. Western flower thrips need about 268 degree-days above 7.9 C per generation, so a generation takes about 16 days at 25 C and about 12 days at 30 C.

**Do short days in flower affect pests and [beneficials](https://genetixbay.com/knowledge/glossary/biological-control.md)?** Short days in flower can push some pests and beneficials into diapause. Two-spotted spider mite females may enter diapause under short days and cool temperatures, turning orange and hiding. Some Orius strains entered diapause at 57% at 12:12 and 20 C, and the aphid midge needs about 15.5 hours of light to stay active, so it often fails in 12:12 rooms.

**Why should spray intervals change with temperature?** Spray intervals should change with temperature because development time does. Most contact sprays miss eggs, so the follow-up must land after survivors hatch and before they reproduce. Broad mites go from egg to adult in about 7 days at 18 C but 3.3 days at 28 C on lab leaf discs; a weekly interval that works in a cool room is far too slow in a hot one.

**Which predators work best in hot, dry cannabis rooms?** In hot, dry cannabis rooms, Neoseiulus californicus (active about 8-35 C at 40-80% RH) is the most robust spider mite predator, Amblyseius swirskii suits warm rooms against thrips, whiteflies and broad mites, and Eretmocerus eremicus beats Encarsia formosa against whiteflies above about 27 C. Phytoseiulus persimilis and the aphid midge struggle in hot, dry conditions.

**Short answer.** Temperature sets the speed of every cannabis pest. Between about 20 and 30 C (68-86 F), spider mites, broad mites, thrips and aphids double every 2-4 days in lab life tables, while mealybugs and fungus gnats take 6-8 days. Humidity matters less to the pests directly than to the predators and fungi that kill them. So choose set-points for the beneficials as much as against the pest, and time every repeat treatment from development time at your own temperature. Each pest's article has the full life table; this page puts them side by side.

All life-table figures here are from lab studies at constant temperature, mostly on hosts other than cannabis (bean, apple, cucumber, grape, eggplant). Only the cannabis aphid figures come from hemp. Treat them as the unchecked upper limit of what a pest can do; real rooms with predators, crowding and plant defences run slower.

## How fast does each cannabis pest multiply at 25 C?

At 25 C (77 F), the [intrinsic rate of increase (r_m)](https://genetixbay.com/knowledge/glossary/intrinsic-rate-of-increase.md) of common cannabis pests ranges from about 0.08 per day for citrus mealybug to about 0.53 per day for cotton aphid, a [doubling time](https://genetixbay.com/knowledge/glossary/doubling-time.md) from 8 days down to 1.3 days. Aphids, broad mites and spider mites are the fast group; thrips and whiteflies are intermediate; mealybugs, fungus gnats and moths are slow per day but lay many eggs.

| Pest | Egg (or birth) to adult at 25 C | Eggs or young per female | r_m at ~25 C (/day) | Doubling time | Lower / upper threshold | Favoured RH | Data source |
|---|---|---|---|---|---|---|---|
| Two-spotted spider mite (*Tetranychus urticae*) | ~6.4-10.4 d | 64-141 | 0.231-0.243 | ~2.9 d | 8.4-13.8 C / none published (develops at 35-37 C) | Low (~30-55%) | Apple, eggplant, cotton [3][4] |
| Carmine (red) form of *T. urticae* | 12.8 d at 29.4 C | ~4 per day | 0.183 at 29.4 C | ~3.8 d | as green form | Low | Carnation, 42% RH; see [two-spotted vs carmine](https://genetixbay.com/knowledge/pests/two-spotted-vs-carmine-mite.md) |
| Broad mite (*Polyphagotarsonemus latus*) | 4.4 d | ~44 | 0.31 | ~2.2 d | 9.7 C / ~33-35 C | High (80-90%) | Grape leaf discs [6] |
| [Hemp russet mite](https://genetixbay.com/knowledge/glossary/hemp-russet-mite.md) (*Aculops cannabicola*) | ~5.5 d (proxy) | ~52 (proxy) | 0.286 (proxy) | ~2.4 d | 10.5 C / none published | Contested | Tomato russet mite on tomato, proxy only [7] |
| Western flower thrips (*Frankliniella occidentalis*) | 15.9 d | ~102 | 0.23 | ~3.0 d | 7.9 C / ~31-35 C | No direct effect found | Chrysanthemum, cabbage [8][9] |
| Greenhouse whitefly (*Trialeurodes vaporariorum*) | ~22.8 d | up to ~400 | 0.035-0.072 (poor host) | 10-20 d | 8.3 C / declines from ~26 C | No value found | Bean, degree-day model [11] |
| Silverleaf whitefly (*Bemisia tabaci*) | ~21-23 d | 324 at 20 C | 0.192 | ~3.6 d | 11-13 C / ~35 C | No value found | Eggplant, cotton [10] |
| Cannabis aphid (*Phorodon cannabis*) | 6.4 d to first birth | ~112 | 0.355 | ~2.0 d | ~10-13 C (fitted) / ~30 C | No data (65% RH only) | **Hemp**, lab [12] |
| Green peach aphid (*Myzus persicae*) | ~8.3 d | R0 ~33 | 0.250 (0.356 at 26.7 C) | ~2.0-2.8 d | 3.9-6.5 C / 37.3 C | No value found | Pepper, lab [14] |
| Cotton/melon aphid (*Aphis gossypii*) | ~5 d | ~82 | 0.526 | ~1.3 d | 6.0 C / ~35 C lethal | No value found | Cucumber, lab [13] |
| Rice root aphid (*Rhopalosiphum rufiabdominale*) | ~5 d (estimate) | 63 at 20 C | 0.432 | ~1.6 d | 6.1 C / ~35 C | Lives in the medium | Rice, lab [15] |
| Citrus mealybug (*Planococcus citri*) | ~26-28 d | 300-600 | 0.084 | ~8.3 d | 7.2-10.6 C / ~33.6 C | Not isolated | Grapevine, lab [16] |
| Fungus gnat (*Bradysia impatiens*) | ~17-21 d | ~75 (up to ~200) | 0.111 | ~6.2 d | ~10 C / 32-35 C | Wet medium matters, not air RH | Rice bran, lab [17] |
| Shore fly (*Scatella stagnalis*) | 11.4 d | ~315 | 0.263 | ~2.6 d | 6.4 C / not published | Wet, algae-covered media | Rockwool, lab; see [shore flies](https://genetixbay.com/knowledge/pests/shore-flies.md) |
| Corn earworm (*Helicoverpa zea*) | ~34 d (model) | ~1,500 | no published value | - | 12.6 C / 33.3 C | Indirect (bud rot) | Degree-day model [19] |
| Beet armyworm (*Spodoptera exigua*) | 27.2 d | R0 ~378 | ~0.21 (between 0.149 at 20 C and 0.276 at 30 C) | ~3.3 d | 13.1 C / 32.2 C | No value found | Sugar beet, lab [18] |
| Beet leafhopper (*Circulifer tenellus*) | ~34 d (model) | ~99 | no published value | - | 14.4 C / 35 C | No value found | Degree-day model [20] |

Notes: R0 is the net reproductive rate (daughters per female per generation). A dash means no published value was found. Where a range is shown, values differ by host plant; host quality alone can change r_m by half, as the spider mite data on apple versus peach show (see [spider mites](https://genetixbay.com/knowledge/pests/spider-mites.md)).

## Why does temperature matter so much for pest growth?

Temperature matters because insects and mites cannot regulate their body temperature, so every step of development and egg-laying runs on the heat around them. Between the lower developmental threshold and the optimum, development rate rises roughly in a straight line with temperature, which is the basis of [degree-day](https://genetixbay.com/knowledge/glossary/degree-day.md) models [2].

Heat raises r_m in two ways at once. Generations get shorter, and females start laying sooner. Since r_m is roughly the natural log of R0 divided by generation time, halving generation time doubles r_m even if each female lays the same number of eggs [1].

Above the optimum, the picture flips. Egg-laying and survival fall faster than development speeds up:

- **Cannabis aphid on hemp:** r_m 0.355 per day at 25 C, 0.244 at 28 C, 0.019 at 30 C [12].
- **Broad mite:** 0.31 at 25 C, 0.12 at 32 C [6].
- **Western flower thrips:** 96% of larvae died at 35 C, with development fastest near 31 C [8].
- **Two-spotted spider mite:** still 0.30-0.32 per day at 30 C [3][4]; daughters per female fell sharply only at 35 C [3].

That is why spider mites are the signature pest of hot cannabis rooms. They keep accelerating up to temperatures where aphids and broad mites are already slowing down.

## How much faster do pests grow at 30 C than at 20 C?

Pests with published data grow roughly 1.5 to 2 times faster at 30 C than at 20 C, except those whose optimum is below 30 C. The worked example below starts with 10 females and uses N(t) = N0 x e^(r_m x t), the unchecked exponential model from life tables [1].

| Pest | Temperature | r_m (/day) | Doubling time | After 14 days | After 21 days | After 28 days |
|---|---|---|---|---|---|---|
| Two-spotted spider mite | 20 C | 0.161 | 4.3 d | ~95 | ~290 | ~910 |
| Two-spotted spider mite | 25 C | 0.237 | 2.9 d | ~280 | ~1,450 | ~7,600 |
| Two-spotted spider mite | 30 C | 0.302 | 2.3 d | ~690 | ~5,700 | ~47,000 |
| Broad mite | 18 C | 0.10 | 6.9 d | ~40 | ~80 | ~160 |
| Broad mite | 25 C | 0.31 | 2.2 d | ~770 | ~6,700 | ~59,000 |
| Broad mite | 32 C | 0.12 | 5.8 d | ~50 | ~120 | ~290 |
| Cannabis aphid (hemp) | 20 C | 0.153 | 4.5 d | ~85 | ~250 | ~730 |
| Cannabis aphid (hemp) | 25 C | 0.355 | 2.0 d | ~1,400 | ~17,000 | ~210,000 |
| Cannabis aphid (hemp) | 30 C | 0.019 | 36 d | ~13 | ~15 | ~17 |
| Tomato russet mite (proxy for hemp russet mite) | 20 C | 0.158 | 4.4 d | ~90 | ~280 | ~830 |
| Tomato russet mite (proxy) | 30 C | 0.253 | 2.7 d | ~350 | ~2,000 | ~12,000 |
| Western flower thrips | 25 C | 0.23 | 3.0 d | ~250 | ~1,250 | ~6,300 |
| Citrus mealybug | 25 C | 0.084 | 8.3 d | ~30 | ~60 | ~105 |

**Method.** Doubling time = 0.693 / r_m. Population at day t = 10 x e^(r_m x t). For example, spider mites at 30 C for 21 days: 0.302 x 21 = 6.34; e^6.34 = 568; 568 x 10 = about 5,700. Sources: spider mite [3], broad mite [6], cannabis aphid [12], tomato russet mite [7], thrips [9], mealybug [16].

**What the numbers mean.** These are ceilings, not forecasts. They assume unlimited food, no predators, no crowding and a constant temperature. Their use is comparative: three weeks of neglect at 30 C produces about 20 times more spider mites than three weeks at 20 C. See [intrinsic rate of increase](https://genetixbay.com/knowledge/glossary/intrinsic-rate-of-increase.md) and [doubling time](https://genetixbay.com/knowledge/glossary/doubling-time.md).

## How do developmental thresholds and degree-days help a grower?

Developmental thresholds and degree-days let a grower convert one temperature's life cycle into another's. Days per stage = degree-days required / (temperature minus lower threshold), valid between the lower and upper thresholds [2]. See [developmental threshold](https://genetixbay.com/knowledge/glossary/developmental-threshold.md).

| Pest | Lower threshold | Degree-days (C) | Days at 20 C | Days at 25 C | Days at 30 C | Stage covered |
|---|---|---|---|---|---|---|
| Two-spotted spider mite (apple) | 8.43 C | 172.4 | 14.9 | 10.4 | 8.0 | Egg to adult [3] |
| Broad mite (grape) | 9.71 C | 62.7 | 6.1 | 4.1 | 3.1 | Egg to adult [6] |
| Western flower thrips | 7.9 C | 268 | 22.1 | 15.7 | 12.1 | Generation [8] |
| Shore fly (rockwool) | 6.4 C | 212.8 | 15.6 | 11.4 | 9.0 | Egg to adult; see [shore flies](https://genetixbay.com/knowledge/pests/shore-flies.md) |
| Greenhouse whitefly | 8.3 C | 380.7 | 32.5 | 22.8 | 17.5 | Egg to adult [11] |
| Citrus mealybug (citrus) | 7.15 C | 526.3 | 41.0 | 29.5 | 23.0 | Egg to adult [28] |
| Corn earworm | 12.6 C | 422.3 | 57.1 | 34.1 | 24.3 | Egg to adult [19] |
| Beet leafhopper | 14.4 C | 361.1 | 64.5 | 34.1 | 23.1 | Egg to adult [20] |

The 30 C column for the spider mite and broad mite is close to measured values (about 6-7 days and 3.3-3.5 days), which is a useful sanity check [3][6]. Linear models overestimate speed near the upper threshold, so trust them least above about 30 C.

## How does humidity affect cannabis pests and their enemies?

Humidity affects cannabis pests far less than temperature does, but it decides which predators and pathogens can work. The clearest effects are on predatory mite eggs and on [insect-killing fungi](https://genetixbay.com/knowledge/glossary/entomopathogenic-fungi.md), both of which need high humidity, and on spider mites, which do better in dry air.

**Spider mites prefer dry air.** In greenhouse cucumber, spider mite densities were up to three times higher at about 55% RH than at about 80% RH [5]. Dry air helps mites shed the excess water they take in while feeding; humid air slows feeding and egg-laying. Low humidity is a contributing factor, not a cause.

**Broad mites prefer humid air.** UConn and other extension sources give 80-90% RH at 21-27 C as favourable; see [broad and russet mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md).

**Hemp russet mite is contested.** Extension sources disagree; the tomato russet mite proxy grew fastest at 30-60% RH [7]. See [hemp russet mite](https://genetixbay.com/knowledge/pests/hemp-russet-mite.md).

**Fungus gnats and shore flies respond to substrate moisture, not air RH.** A wet top layer of the medium drives them; see [fungus gnats](https://genetixbay.com/knowledge/pests/fungus-gnats.md).

**Predatory mite eggs need humidity.** Phytoseiulus persimilis egg hatch was about 8% at 40% RH versus nearly 100% at 80% RH at 27 C [22]. The humidity at which half the eggs of persimilis and Neoseiulus californicus die was about 66-70% RH in Wageningen trials [5]. Amblyseius swirskii lost half its eggs at about 63% RH (see [broad and russet mites](https://genetixbay.com/knowledge/pests/broad-russet-mites.md)).

**Insect-killing fungi need humid leaf surfaces** for hours to germinate, which conflicts with flower-room humidity targets. See [entomopathogenic fungi](https://genetixbay.com/knowledge/glossary/entomopathogenic-fungi.md).

## What are the climate windows of the main beneficials?

Each beneficial has a temperature and humidity window, and releasing it outside that window wastes money. The table below summarises extension and research values; supplier technical sheets give similar ranges.

| Beneficial | Target pests | Temperature window | RH window | Notes |
|---|---|---|---|---|
| *Phytoseiulus persimilis* | Spider mites | Above ~20 C; struggles above ~30 C | Above ~60%, optimum >75% | Specialist; starves when prey run out [21][22] |
| *Neoseiulus californicus* | Spider mites, broad mites | ~8-35 C | ~40-80% | Best for warm, dry rooms and preventive use [21] |
| *Neoseiulus fallacis* | Spider mites, russet mites | ~9-29 C | Above ~50% | Cooler rooms [21] |
| *Amblyseius andersoni* | Mites | ~6-40 C | Not well defined | Wide temperature tolerance [21] |
| *Galendromus occidentalis* | Spider mites | ~10-46 C | ~30-60% | Hot, dry conditions [21] |
| *Feltiella acarisuga* (midge) | Spider mite hot spots | Moderate | ~60-95%, optimum ~80% | Flies to colonies [21] |
| *Stethorus* (lady beetle) | Spider mite hot spots | ~16-32 C | - | Needs high prey density [21] |
| *Amblyseius swirskii* | Thrips, whiteflies, broad mites | Develops 11-37 C, optimum ~30 C | Eggs fail below ~63% | Warm rooms [23] |
| *Neoseiulus cucumeris* | Thrips, broad mites | ~24-29 C best | Above ~65%, ideally 75% | Eats first-instar thrips only; see [thrips](https://genetixbay.com/knowledge/pests/thrips.md) |
| *Orius insidiosus* | Thrips | ~20-29 C | - | 57% of females diapaused at 12:12 and 20 C [24] |
| *Encarsia formosa* | Greenhouse whitefly | ~21-27 C; no flight below ~18 C | ~50-80% | Whitefly outpaces it below ~17 C [11][25] |
| *Eretmocerus eremicus* | Whiteflies | ~25-29 C | - | Better than Encarsia in heat [25] |
| *Aphidius colemani* | Green peach and cotton aphids | ~18-25 C; poor above ~30 C | ~60-80% | Match species to aphid [26] |
| *Aphidoletes aphidimyza* (midge) | Aphids | ~16-27 C | ~50-85% | Needs ~15.5 h light or diapauses [26] |
| *Cryptolaemus montrouzieri* | Mealybugs | ~22-25 C best; slows below 20 C | ~70-80% | Needs egg masses to breed [27] |
| *Stratiolaelaps scimitus* | Fungus gnats, thrips pupae | Inactive below ~15 C | Moist medium | Top 2.5 cm of medium [17] |
| *Steinernema feltiae* (nematode) | Fungus gnats, thrips pupae | ~8-30 C, best ~14-26 C | Moist medium | Poor in hot pots above ~30 C; see [fungus gnats](https://genetixbay.com/knowledge/pests/fungus-gnats.md) |

## How do short days and diapause affect a flower room?

Short days can trigger diapause in some pests and beneficials, so a 12:12 flower room is a different biological environment from an 18:6 veg room, not just a different light schedule. See [diapause](https://genetixbay.com/knowledge/glossary/diapause.md).

- **Two-spotted spider mites.** Females reared under short days and cool temperatures can enter diapause, turn orange-red, stop laying and hide in debris and cracks; they are the survivors that restart the next run. Many greenhouse strains diapause weakly. See [spider mites](https://genetixbay.com/knowledge/pests/spider-mites.md).
- **Orius insidiosus.** In a lab study at 20 C, 57% of females entered reproductive diapause at 12:12 and nearly all at 10:14 [24]. Use non-diapausing strains in flower rooms or rely on predatory mites.
- **Aphidoletes aphidimyza.** The aphid midge needs about 15.5 hours of light to avoid diapause [26]. Night-break lighting to prevent it would disrupt cannabis flowering, so the midge is a veg-room tool.
- **Cannabis aphid.** Sexual forms and eggs can appear indoors after the flip to short days; see [cannabis aphid](https://genetixbay.com/knowledge/pests/cannabis-aphid.md).

## How should grow-room set-points be chosen for pest control?

Choose set-points that keep the crop first, then nudge the room toward the predator's window and away from the pest's optimum. The crop's needs win every conflict: late-flower humidity stays at 40-50% RH regardless of what mites prefer, because bud rot costs more [21].

| Stage | Typical set-point | Pests favoured | Beneficials favoured | IPM adjustment |
|---|---|---|---|---|
| Propagation | 22-26 C, 70-85% RH | Fungus gnats, shore flies, broad mites | Persimilis, cucumeris, swirskii, soil predators | Dry the top of plugs; release soil predators |
| Veg | 24-27 C, 60-70% RH | Spider mites (at the hot end), aphids, thrips | Most predatory mites | Keep canopy below ~28 C; hold 60-70% RH where safe |
| Early flower | 23-26 C, 50-60% RH | Spider mites, thrips | Californicus, swirskii | Last window for preventive releases |
| Late flower | 20-24 C, 40-50% RH | Spider mites (dry air) | Californicus, G. occidentalis | Do not raise RH; accept slower mite control |

Leaf temperature matters more than air temperature. A canopy hot spot 3-4 C above the room under a lamp runs spider mites at the 30 C row of the growth table while the thermostat reads 26 C. Check with an infrared thermometer, and see [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) and [leaf VPD](https://genetixbay.com/knowledge/glossary/leaf-vpd.md).

## How do you set re-application intervals from these numbers?

Set the repeat interval of a contact treatment that misses eggs to fall after the eggs hatch and before the survivors become egg-laying adults. Take egg development time as the earliest repeat and egg-to-adult time (plus the pre-oviposition period) as the latest, then aim for the middle. The [IPM programme](https://genetixbay.com/knowledge/pests/integrated-pest-management-program.md) explains the logic.

| Pest | 20 C interval | 25 C interval | 30 C interval | Based on |
|---|---|---|---|---|
| Two-spotted spider mite | ~7 d | ~5 d | ~3-4 d | Egg-to-adult 14.9 / 10.4 / 8.0 d [3] |
| Broad mite | ~3-4 d | ~2-3 d | ~2 d | Egg-to-adult 6.1 / 4.1 / 3.1 d [6] |
| Western flower thrips (foliar stages) | ~7-10 d | ~5-7 d | ~4-5 d | Generation 22 / 16 / 12 d; pupae in medium need a separate tool [8] |
| Aphids (live birth, no eggs) | ~5-7 d | ~3-5 d | ~3-5 d | Birth to first birth ~11 / 6.4 / 5.4 d (cannabis aphid) [12] |

These intervals are calculated from non-cannabis lab data (except the cannabis aphid) and are a starting point to confirm by scouting, not a label instruction. Whatever the interval, follow the label and local law, and rotate mode-of-action groups by pest generation; see [mode of action](https://genetixbay.com/knowledge/glossary/mode-of-action.md).

## What are the common myths about temperature, humidity and pests?

- **"Mites die in winter."** *Myth* for indoor rooms. Rooms never drop below spider mite thresholds of about 8-14 C [3][4]; outdoors, diapausing females survive in debris.
- **"Just raise humidity to beat spider mites."** *Myth* as a cure. High RH slows mites and helps persimilis [5][22], but it does not eliminate them and is dangerous in flower.
- **"Hotter always means more pests."** *Myth.* Cannabis aphid, broad mites and thrips decline above their optimum [6][8][12]; spider mites keep going.
- **"A cold room stops pests."** *Myth.* Cooling slows them; development continues down to thresholds of roughly 6-13 C.
- **"Lab r_m values predict what will happen in my room."** *Myth.* They are upper bounds on non-cannabis hosts, best used for comparisons and timing.
- **"Temperature makes the most difference to pest growth."** *Established* [1][2].

## Common mistakes

- Using air temperature at the thermostat instead of leaf temperature at the canopy.
- Keeping one weekly spray interval all year, whatever the room temperature.
- Releasing humidity-sensitive predators into a dry flower room.
- Relying on the aphid midge or diapausing Orius under 12:12.
- Treating lab r_m values as forecasts instead of upper bounds.

## Evidence

- Temperature-driven development and the degree-day method: *Established* [1][2].
- Pest life-table values: *Supported* from lab studies, mostly on non-cannabis hosts; only the cannabis aphid data are from hemp [12].
- Humidity effects on spider mites and predatory mite eggs: *Supported* by greenhouse trials and lab data [5][22].
- Diapause in Orius and Aphidoletes under short days: *Established* in the cited studies [24][26]; cannabis-specific trials absent.
- Hemp russet mite growth figures: proxy only (tomato russet mite) [7].

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