Aphids

With their shockingly high reproductive rates, aphid populations can quickly get out hand if not properly understood and respected. If you choose to control aphids using biocontrols, there are two keys to success:

Start Early and Act Swiftly

Many of the commercially-available aphid predators take days or weeks to reduce aphid populations, which all happens while the aphids continue to reproduce, making existing issues difficult to handle. Trying to handle an outbreak that is already at crisis levels with biocontrols is not recommended. You need to start early!

Properly Identify the Aphid

Aphid parasitoids like Aphidius colemani only attack a few aphid species; they are ‘host specific’. Other aphid predators, such as Chrysoperla (lacewing larvae) and Aphidoletes aphidimyza, have a broad host range, feeding on dozens of different aphid species. So, when using host specific parasitoids like Aphidius it is critical that we match the species of aphid with the proper parasitoid.

Identification

There are over 5,000 known species of aphid in the world. Fortunately, only a handful of species are currently known to feed on cannabis. As cultivation of this plant expands, the list of aphids attacking it will also continue to expand.

Features used to Identify Aphids in the Field

• Head -The shape of the head in adult aphids is a key feature.
Cornicles/Siphunculi - Oftentimes referred to as the ‘tail-pipes’, the shape and color of the cornicles can be used to distinguish between species. 
Antennae -The length of the antennae relative to the body, and its shape can be an important factor.

Life History

• Aphids are built to survive, and their reproduction can be extremely complicated.
• Most aphid reproduction happens via parthenogenesis; i.e. females do not need to mate with males in order to reproduce. 
• Females reproducing via parthenogenesis give birth to live young. This is known as vivipary.
• Nymphs reproduced by this manner are clones of their mother.
• Nymphs developing inside their mother may have their own embryos developing inside of them, giving rise to telescopic generations of aphids.
• The newly born nymphs generally undergo 4 to 5 molts before reaching adulthood. Their shed skins are a very visual indication of aphid presence.
• Occasionally, winged forms may develop. Known as alatae, these winged aphids are normally female and serve the purpose of spreading the colony.
• Alatae may also appear in the autumn months, when outdoor aphid populations prepare for winter. Winged females (and sometimes winged) males mate, with the mated females laying eggs as a means to overwinter. In the spring, the process repeats itself.

Biology

Aphids have piercing/sucking mouthparts, which they use to feed on plant sap.
A large amount of the sap ingested by the aphids is expelled. This sugary waste-product is called ‘honeydew’.
The iconic cornicles on each aphid are used to excrete an 'alarm' pheromone, warning nearby aphids of danger.

I see Aphids, now what?... 

As previously noted, the quickness with which you act will be the primary determining factor your success using biocontrols to control aphids and their damage. If the problem is too far gone, biocontrols are a poor choice. If you are catching the problem in the early stages, the next most important factor in your success is to properly identify which species you are dealing with. In general, the species of aphid will dictate the species of predator you choose.

I don't see any Aphids, but I'd like to act preventatively...

Although small populations of aphids are not typically a concern on their own, their propensity to reproduce quickly, and at extremely high rates, should not be underestimated. Prevention is the best way to ensure these pests never become an issue. In outdoor operations, during spring and late summer months, it is a good practice to introduce aphid predators preventatively. For example, low numbers of parasitic wasps and/or lacewing larvae can be released with the intention of nipping aphids in the bud, before they can increase to problem-levels.

Additional Notes

• Ants will ‘farm’ aphids for their honeydew, oftentimes protecting the aphids from predators. 
• If ants are present, they must also be controlled in order for the biocontrol program to be successful.
• Over-fertilization with nitrogen can increase the size and severity of aphid infestations by increasing the amino-acid content of the plant sap.