Although it was first described in 1860, the cannabis aphid (Phorodon cannabis; a.k.a. bhang aphid or hemp aphid) is a very new pest to North America. It was first seen on cuttings originating from Colorado in 2016 and is now widespread throughout that state and Oregon. Its range also includes several other states and parts of Canada. The cannabis aphid closely resembles the hop aphid (Phorodon humuli), to the point that microscopic analysis of the head is required to distinguish them. The hop aphid is common in North American hops production; there have been unconfirmed reports of Phorodon humuli developing on cannabis plants, as well.
Life cycle and appearance of the Cannabis aphid
Adult cannabis aphids are between 1.8–2.7 mm long. They are normally wingless but a winged form appears in late summer. Early in the season, the aphids are nearly colourless to pale yellow, and as the days become shorter, they change to light green or brown with dark green stripes running the length of the body. The winged forms have a dark head and thorax. Cannabis aphids have long antennae (1.1–2.2 mm) and between these are two short knobs (antennal tubercles). Their cornicles (the pair of small, upright, backward-pointing tubes on the aphid's rear end) are white and almost ⅓ the insect’s body length.
Phorodon cannabis usually reproduce asexually; females are essentially born pregnant and give birth to live, genetically identical offspring. Newborn nymphs will typically reach maturity within a couple of weeks, and adults live up to a month.
Outdoors, as the days shorten in late summer/early autumn, winged males and sexually-reproducing females are produced. After mating, the female lays her eggs on leaves, flowers and stems to overwinter and produce the next generation of aphids in the spring. In greenhouses, sexual reproduction is very rare and only triggered if lighting signals a shortening day.
The cannabis aphid is a sap sucker, like all aphids, and affected plants are damaged by the loss of this vital fluid. The following damage symptoms may be observed when plants are infested with Phorodon cannabis:
- Excess sap is excreted on leaves and flowers as a sticky “honeydew” which promotes the growth of black fungal moulds.
- White skin moults visible on the leaves.
- Live aphids may be present in visible colonies; aphids often settle inside buds to feed.
- Slowed plant growth; wilted, yellowing leaves.
- Transmission of viral disease between plants, specifically: hemp streak virus, hemp mosaic virus, hemp leaf chlorosis virus, cucumber mosaic virus, hemp mottle virus and alfalfa mosaic virus.