Cannabis aphid (Phorodon cannabis): ID, life table, overwintering and control

Short answer. The cannabis aphid (Phorodon cannabis) is a pale yellow to light green aphid that develops only on Cannabis ^[3]. On hemp at 25 °C (77 °F) it starts breeding 6.4 days after birth and doubles every 2 days (r_m 0.355 per day) ^[4]. Short days trigger males and egg-laying females, outdoors in September and indoors after the flip ^[2][3]. Quarantine clones, release natural enemies early, and keep sprays out of flower. General aphid biology and the other species are in Aphids.

Cannabis aphid numbers at a glance

What is the cannabis aphid, and where did it come from?

The cannabis aphid (Phorodon cannabis Passerini), also called hemp aphid or bhang aphid, is an Old World aphid that develops only on Cannabis ^[1][3]. It is the aphid most consistently reported as a pest of hemp worldwide, and McPartland, Clarke and Watson's Hemp Diseases and Pests reviews it among the insects of the crop ^[11].

First North American records. Cranshaw and colleagues reported it in 2018 as a newly recognised pest in North America, observed in Colorado hemp since 2015, when significant outdoor production began ^[1]. Halbert (2016) recorded it as new to the Western Hemisphere (as cited in ^[4]).

Pest status. In Colorado it has produced high late-summer populations in some fields every season since 2016 ^[2]. Cranshaw and colleagues name it, with hemp russet mite, one of the two most damaging sap-feeding pests of US hemp ^[2]. See Hemp russet mite.

Indoors. It can be a common pest wherever hemp has an indoor phase, such as clone propagation or transplant production ^[2]. In Canadian licensed production it is described as quickly becoming one of the most prevalent pests on cannabis crops ^[7].

How do I identify the cannabis aphid?

Identify the cannabis aphid by a pale yellow, soft-bodied aphid on Cannabis leaf undersides and stems, often with a pale stripe along the back, plus honeydew droplets and cast skins on the leaves below ^[3][6]. Confirming the species needs a microscope.

Colour forms. Pale yellow forms predominate; light green is less common ^[3]. Pale pink and light brown forms occur indoors after the shift to short-day lighting and outdoors late in the season ^[3]. NC State describes early-season aphids as light cream to pale yellow, and late-season ones as light green, pale pink or light brown ^[5].

Colour and reproduction. Colorado State suspects the pale yellow form is the normal asexual one, and that coloured forms (pink, brown, green) may be sexual forms, including egg-laying oviparae ^[3]. Contested: this is a stated hypothesis, not a measured result.

Stripes and spots. Wingless forms may carry a pale yellow stripe beside a thin green stripe along the back; winged forms have some dark spotting ^[3][6]. Greenhouse Canada describes winged forms as mostly brown and green, with harder bodies ^[7].

Eggs. Yellow-green at first, turning black as they harden ^[5].

Microscope ID. The cannabis aphid is very similar to the hop aphid (Phorodon humuli). Separating them needs a microscope to see the horn-like projections at the base of the antennae and the bulb-tipped hairs on the head, thorax and antenna bases ^[5]. Use 40-60x or send a sample to an extension lab.

Commonest mix-up. A green, unstriped cannabis aphid can be mistaken for green peach aphid, which leads growers to Aphidius colemani; one trade article calls that a less effective choice for cannabis aphid than A. matricariae ^[14] (page blocked)being reviewed.

Where on the plant does it live, and what damage does it do?

The cannabis aphid lives on leaf undersides and stems, and late in the season infests maturing flowers and nearby leaflets ^[2][3]. It feeds on phloem, so it leaves no stippling or scarring; damage comes from sap loss, which at high, sustained numbers causes slowed growth, wilting and yellowing ^[3].

Buds at harvest. Large numbers of aphids and their eggs can be incorporated into harvested flower, and the aphid produces abundant honeydew ^[2]. Effects on yield are unknown ^[2].

Honeydew as a sign. Honeydew falls as tiny droplets that show as small shiny spots on leaves below the colony, together with white cast skins; both are excellent diagnostic signs ^[3]. See honeydew.

Viruses. The cannabis aphid can transmit cucumber mosaic virus and alfalfa mosaic virus to hemp ^[5]. Colorado State notes the main viruses described from Cannabis are mechanically transmitted and cannot be spread by aphids ^[3]. See Hop latent viroid and viruses.

What is the cannabis aphid life cycle in numbers?

The cannabis aphid life cycle under long days is clonal: females give live birth to genetically identical daughters, nymphs moult through four instars, and at 25 °C (77 °F) they begin reproducing 6.4 days after birth ^[3][4]. The only published life table is Durak and colleagues' 2021 study on hemp ^[4].

Study conditions. Hemp cultivar Henola, 6-week-old plants, 20, 25, 28 and 30 °C, 65 ± 5% RH, 16L:8D, 50 aphids per temperature ^[4]. Values are lab means, not field rates.

Source: ^[4]. 15 and 35 °C were not tested; no published values found.

Extension estimates. Colorado State gives a looser field picture: maturity within one to two weeks of birth, 1-5 young per day, and a likely maximum adult life of 3-4 weeks ^[3]. The lab figure of 7.5 nymphs per day at 25 °C ^[4] is higher, as expected on young plants without enemies.

Thresholds. No published lower developmental threshold or degree-day requirement was found for the cannabis aphid. A linear fit of the pre-reproductive times at 20, 25 and 28 °C ^[4] gives roughly 10 °C and 100 degree-days; a two-point fit at 20-25 °C gives 13 °C and 77 DD. Both are GenetixBay calculations from very few points. See developmental threshold.

Proxy for missing temperatures. For 15-18 °C and 32 °C, the closest well-studied relative is the green peach aphid. Proxy only, a different species on pepper: green peach aphid reached adulthood in 12.4 days at 18 °C and 13.0 days at 32 °C, with r_m 0.189 at 18 °C and -0.097 at 32 °C ^[9].

Why do temperature and humidity matter for the cannabis aphid?

Temperature sets how fast the cannabis aphid multiplies: on hemp its r_m more than doubled from 0.153 per day at 20 °C to 0.355 at 25 °C, then fell to 0.244 at 28 °C and almost zero at 30 °C ^[4]. Of the common cannabis aphids, it is the least heat tolerant.

Heat stress. At 30 °C (86 °F) the reproductive period shrank to 2.1 days, females produced 2.4 nymphs each, and 57% of nymphs died before maturity ^[4].

Grow-room set-points. Veg rooms at 24-28 °C (75-82 °F) and flower rooms at 22-26 °C (72-79 °F) sit in or near the cannabis aphid's 25 °C optimum. Mother and clone rooms at 20-22 °C slow it, but do not stop it.

Humidity. No published effect of RH on cannabis aphid development was found; the only life table used 65% RH ^[4]. Humidity matters through control agents: entomopathogenic fungi need relatively high humidity ^[3], and aphid parasitoids prefer about 70-85% RH ^[10]. See VPD.

Day length. Short days are the trigger that matters. Declining day length triggers males and egg-laying females outdoors in September and October ^[3]. Indoors, the switch to short-day lighting can do the same ^[3]. Short days may also raise the share of winged forms ^[3].

How fast can a cannabis aphid colony grow? A worked example

A cannabis aphid colony unchecked by enemies grows as N(t) = N0 × e^(r_m × t). Ten aphids at 25 °C (r_m 0.355 per day ^[4]) become about 120 in one week, 1,440 in two and 17,300 in three. At 20 °C (r_m 0.153) they reach only about 250 in three weeks.

Method. N0 = 10; r_m from ^[4]; t in days. Example at 28 °C, 21 days: 10 × e^(0.244 × 21) = 10 × 168 ≈ 1,680.

Upper bound only. The model assumes unlimited food, no predators, no disease and no winged emigration. Real colonies slow as plants decline and aphids crowd. The lesson holds: at 25 °C, three weeks without scouting turns a few aphids into thousands.

Where does the cannabis aphid hide, how does it spread, and how does it get in?

The cannabis aphid gets into a clean indoor facility almost only on Cannabis plant material carrying live aphids, because it develops on no other host and starves within a few days without one ^[3]. Clones, mother plants and transplants are the main vector.

Hiding places. Leaf undersides, stems, and later maturing flowers and leaflets ^[2][3]. Eggs, when laid, go on stems, flower buds and seed capsules ^[3][5].

Winged dispersal. Winged forms disperse over long distances and most readily colonise new plants ^[3]. They are weak fliers carried by winds above about 3 mph (1.3 m/s); greenhouse airflow largely controls where they settle ^[3].

Outdoors to indoors. Outdoor fields and volunteer hemp carry the aphid into nearby propagation areas. Overwintering eggs survive on crop debris and hatch onto volunteer seedlings in spring ^[2][3].

Clothing and pets. No published data were found. Because the aphid starves quickly and walks slowly, people moving from infested outdoor plants to clean rooms are a plausible but minor route (Grower practice: visit clean rooms first).

Quarantine. Hold new plant material separately for several weeks and inspect it for honeydew droplets, cast skins, live aphids and winged aphids on sticky traps before it joins clean stock ^[3].

How do I scout for cannabis aphid?

Scout for cannabis aphid by looking for honeydew droplets and cast skins on leaf tops, then inspecting leaf undersides and stems directly above them ^[3]. Check mother plants and clones weekly at minimum, and twice weekly in rapid growth (Grower practice; UC IPM gives twice weekly for aphid-prone plants, see Aphids).

Lens. 10-20x to confirm aphids, cast skins and mummies; 40-60x microscope to separate cannabis aphid from hop aphid ^[5].

Sticky traps. Yellow sticky traps capture winged cannabis aphids and show when winged forms disperse; distinguishing them from fungus gnats and parasitoid wasps needs magnification ^[3]. Place cards near, not touching, plants ^[7].

After the flip. Watch for colour change to pink or brown and for winged males: they signal sexual forms and possible eggs ^[3].

Threshold. No action threshold has been researched for hemp ^[5]. Indoors, act on the first confirmed colony (Grower practice).

How do I control the cannabis aphid by life stage?

Control the cannabis aphid by attacking nymphs and adults with contact tactics and natural enemies under long days, and by removing eggs and debris once short days have produced sexual forms ^[3]. Indoors under long days, there is no egg stage to shelter survivors.

Nymphs and adults. Remove infested leaves into a bag; squash small colonies. Insecticidal soaps (potassium salts of fatty acids), pyrethrins and azadirachtin are among the materials with aphid activity allowed on cannabis in some US states ^[3]. Greenhouse Canada reports insecticidal soap as the most effective registered option in Canadian production, needing thorough coverage of leaf undersides ^[7].

Re-application interval. Newborn nymphs that survive a spray begin reproducing in 6.4 days at 25 °C and 11 days at 20 °C ^[4]. Re-spray every 5-6 days at 25-28 °C, or every 7-9 days at 20-22 °C, for at least three applications, in veg only.

Eggs. No published data on egg mortality from sprays were found. Remove all plant debris after harvest, because eggs are laid on Cannabis tissue ^[3].

Room clear-out. Removing all Cannabis plants from a room should kill all remaining aphids within a few days, since both winged and wingless forms starve quickly ^[3].

Resistance. No published insecticide resistance data were found for the cannabis aphid. Its clonal reproduction means any resistant female founds a uniform resistant colony. Rotate modes of action by IRAC group, and see Aphids for the resistance record of green peach aphid. Registrations on cannabis vary by jurisdiction; follow the label and local law.

Fungi. Isaria fumosorosea and Beauveria bassiana infect aphids; relatively high humidity is essential to their effect ^[3].

What biological control works on the cannabis aphid?

Biological control of the cannabis aphid outdoors comes mostly from native lady beetles, lacewings, hover flies and the midge Aphidoletes, which in Colorado built up enough to control late-season outbreaks ^[2][3]. Indoors those enemies are absent unless released, and no parasitoid has yet been proven in peer-reviewed trials ^[3][8].

Field enemies. Convergent lady beetle (Hippodamia convergens) and multicoloured Asian lady beetle (Harmonia axyridis) were most important in Colorado, with at least four other lady beetle species, three green lacewings, at least four syrphid species and Aphidoletes aphidimyza ^[2]. Braconid parasitism and fungal infection were observed only infrequently ^[2].

Purchased predators for indoor use. Colorado State lists green lacewings (sold as eggs), the aphid predatory midge and convergent lady beetle as among the more effective ^[3]. Field-collected lady beetles arrive semi-dormant and may take weeks to lay eggs ^[3]. Greenhouse Canada reports that green lacewings did not control infestations and that Aphidoletes is not recommended in Canadian cannabis production ^[7]. Contested.

Parasitoids: what the evidence says

Bottom line. Is Aphidius colemani effective against cannabis aphid? Industry sources disagree, and no published trial settles it ^[7][14]. A. matricariae has the stronger trade-press support ^[14]. A mixed release of both, made early and checked by counting mummies after 10-14 days, is the cautious choice (Grower practice).

Release rates. No cannabis-aphid-specific rates are published. Biocontrol supplier technical sheets for A. colemani give 0.25 wasps/m² every 1-2 weeks preventively, and 0.5-2 wasps/m² weekly for at least three releases after detection ^[13]. Greenhouse Canada reports weekly or biweekly re-releases being needed when prey is scarce ^[7].

Climate. A. colemani works from 15 °C, best at 18-25 °C and 60-80% RH (supplier sheet ^[13]); parasitoids generally prefer 70-85% RH ^[10].

Aphidoletes and 12/12. Aphidoletes larvae need about 15.5 h of light to avoid diapause ^[10]; one strain did not diapause at 25 °C or above at any day length ^[12]. Night-break lighting is not an option in a flowering room. See Aphids.

Predator:prey ratio. No published ratio for cannabis aphid was found.

How can the environment be used against the cannabis aphid?

The environment slows the cannabis aphid most in propagation, where cooler rooms at 20-22 °C stretch its doubling time from 2 days at 25 °C to about 4.5 days at 20 °C ^[4]. That buys scouting time but does not replace control.

Mother and clone rooms. Keep them at 20-22 °C and 60-70% RH: slower aphids, better parasitoid humidity ^[4][10].

Do not run hot. Lab data show the cannabis aphid collapsing at 30 °C ^[4], but plants, parasitoids and beneficials suffer there too, and cotton aphid thrives. See Heat and light stress.

Airflow and screening. Winged aphids ride air above about 3 mph ^[3]; filtered intakes and positive pressure keep outdoor migrants out.

Break the host chain. The aphid lives only on Cannabis. Remove volunteer hemp near outdoor plots, clean up crop debris after harvest, and avoid overlapping old and new crops ^[2][3][5].

Nitrogen. USU advises avoiding excess nitrogen ^[6] (Grower practice for aphids generally).

Flower trade-off. Do not raise flower humidity above 45-55% RH to help fungi or parasitoids; botrytis risk outweighs the gain.

What should I not do about cannabis aphids in flower?

In flower, do not spray soaps, oils, pyrethrins or neem products onto buds; residues stay on harvested flower and wet buds invite bud rot. Release beneficials before or at the flip, remove infested branches, and cut out honeydew-coated buds.

Expect sexual forms. After the flip to 12/12, the cannabis aphid can produce winged males and egg-laying females ^[3]. Eggs on stems and buds can end up in harvested flower ^[2].

Clean thoroughly after harvest. Remove all plant debris and leave the room empty for several days before restocking ^[3].

No systemics, no night-break lights. Systemic insecticides are not registered on cannabis in most places. Night-break lighting disrupts flowering.

What are the common myths about the cannabis aphid?

Common cannabis aphid myths are about identity, reinfestation, parasitoids and eggs.

• "Cannabis aphids are just green peach aphids." Myth. It is a distinct, Cannabis-only species ^[1][3]; mistaking it can lead to a less suitable parasitoid ^[14].
• "Weeds outside will reinfest a clean room." Myth. It develops only on Cannabis and starves within days without it; reinfestation comes from Cannabis plant material ^[3].
• "Aphidius colemani is proven against cannabis aphid." Contested. One industry report names it among the most successful ^[7], another calls it less effective than A. matricariae ^[14]; no peer-reviewed greenhouse trial was found, and Colorado State could not name the parasitoid species seen in the field ^[3].
• "Eggs only happen outdoors." Myth. Short-day lighting indoors can trigger sexual forms and eggs ^[3].
• "Indoor eggs survive indefinitely." Contested. USU states eggs survive better indoors ^[6]; Colorado State says egg survival indoors at warm temperatures is unknown ^[3].

Common mistakes

• Treating it as green peach aphid and buying the wrong parasitoid ^[14].
• Skipping quarantine on clones from another facility ^[3].
• Leaving plant debris and old mother plants in the room after harvest ^[3].
• Waiting for numbers to build: doubling time is 2 days at 25 °C ^[4].
• Missing the colour change to pink or brown after the flip ^[3].

Evidence

• Host specificity, Colorado biology, holocycle on the crop: Established in extension and review literature ^[1][2][3][5].
• Life table on hemp at 20-30 °C: Supported, one lab study ^[4].
• Short-day sexual forms indoors: Supported, extension observation ^[3].
• Parasitoid efficacy: Grower practice and industry reports ^[7][14]; peer-reviewed data minimal ^[8].
• Action threshold: none researched ^[5].