Around 20 million years ago, Cannabis and Hops diverged from a shared ancestry, and spread throughout Eurasia and other parts of earth. When a speciation event like this happens in plants, other organisms like microbes and even insect herbivores associated with the ancestor may split as well and follow the new species gradually over time.
Aphids are an extremely common group of insects that predate flowering plants, and it is thought that many of their species developed by following their hosts as they branched out and diversified. The aphid genus Phorodon contains a species that feeds on hops—Phorodon humuli, the Damson-Hop Aphid—as well as a closely related species that feeds on only Cannabis: Phorodon cannabis, the Cannabis Aphid. Existing since around the divergence of these two plants, the Cannabis Aphid has been a faithful companion.
Undoubtedly, the first Cannabis plants humans encountered and began cultivating contended with them for several millennia until they were documented and described scientifically a little over 200 years ago in Italian Hemp of 1860.
Pale-green in color, Cannabis Aphids have a somewhat teardrop-shaped body a few millimeters in length with two conspicuous structures on their rear abdomen called cornicles which dispense alarm compounds when threatened. Aphids have one pair of antennae located on their head like other insects, but they curve back around the length of the body, distinguishing them from other insects that may be found on the same plant.
Cannabis Aphids have two main body types as adults: wingless forms called “apterae” and winged forms called “alates”. Aphids generally produce winged forms in response to various factors like crowding, seasonal changes associated with autumn and winter, and plant maturation or senescence which they can taste during feeding, whereas the wingless forms are more commonly encountered. Egg laying may occur in tandem with winged forms, presenting as white oblong structures that darken with age, but this is not always the case.
As a colony organism, aphids are often found near others of their kind, and immature stages usually concentrate near their mother. Because most aphids are female, born pregnant, and livebirth their daughters, there is no need for sexual reproduction and populations rapidly expand from a single individual when undisturbed in foliage.
Feeding in the same localized area maximizes the immune-suppressing effects that aphids inflict on their healthy plant hosts, making life easier for the colony in aggregate to expand. These localized effects eventually interfere with the plant body at large, even if these effects are not apparent upon visual inspection as they happen at the cellular level inside the tissues by disabling or interfering with cellular signaling.
Sugary sap is the lifeblood of aphids and other piercing-mouthpart insects, and aphids shunt the liquid they process through their bodies very quickly, producing prodigious puddles called “honeydew” which can be an additional sign of aphid presence. This sticky substance is the substrate for a special black fungus that lives on the surface called “sooty mold” that, while not pathogenic, can foul the plant tissues, especially flowering tissues.
Scouting is imperative for successful treatment, and quarantine of new plants is effective for limiting spread to established plants as a preventative measure. The most common manner by which aphids disperse in cultivated settings is through the unrestricted movement of plant tissue, and this is a major issue in Cannabis biosecurity currently. As growers at all scales from home to commercial increase their production, the chances of encountering these aphids increases proportionally.
There are several options for treatment. Spray applications must obtain good coverage in order to be effective. This is difficult when the canopy is dense, so marking plants that are colonized and pruning plants can be a viable strategy to increase spray efficacy. Safe compounds derived from plants are popular choices but treatment during flower is more contentious.
The use of biocontrol agents like green lacewing larvae or even fungi that kill aphids are frequently applied especially after knocking down a significant portion with a botanical insecticide.
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