The rice root aphid is native to southeast east Asia, but now has worldwide distribution. Populations have been found as far north as Finland living in greenhouses. As its name suggests, the rice root aphid is commonly found feeding on the roots of rice plants. However, as ths aphid’s geographic distribution has expanded, so too has its host range. The rice root aphid is recognized as feeding on a wide variety of crops, including cereals, tomatoes, potatoes and peppers (solanacea), and now cannabis.
Like other aphids, the rice root aphid feeds on a plant’s vascular system. And while it primarily feeds on roots, this aphid will also climb up the stem to feed on that, as well. The tough periderm of mature cannabis plants probably prevents feeding during later stages of production, however.
The reproductive cycle of the rice root aphid is important for growers to understand. There are two populations of these aphids in the world: those that reproduce solely through parthenogenesis (females that reproduce asexually by ‘cloning’ themselves), and those that are able to fully complete their life cycle sexually and produce eggs. In order to fully complete their life cycle via sexual means, the rice root aphid must have its primary host plant, in this case plants in the genus Prunus. Instances of sexual reproduction have been documented in Asia, and now northern Italy.
With eggs as their sole means of overwintering, rice root aphids must find their primary host plant. Without this host, the aphids cannot survive cold winter temperatures.
This primary host is critical for the aphids’ ability to overwinter: sexual reproduction means the creation of eggs, and the eggs are their only way of surviving freezing temperatures. If they cannot overwinter as eggs, the rice root aphid can survive harsh winters by overwintering in greenhouses or a grow room.
What to look for:
Diminished yields, leaf chlorosis, wilting, plant stunting, and ants.
Life Cycle of Root Aphids
As state above (and elsewhere), aphid reproduction can be complex. Aphids are capable of reproducing two ways: sexually and asexually. In the case of the rice root aphid, most (if not all) cannabis growers are dealing with aphids that are reproducing asexually via parthenogenesis. This means all of the aphids are female. They survive the winter in temperate regions living in protected areas such greenhouses and grow rooms, spreading from plant to plant.
When reproducing asexually, the rice root aphid life history is comprised of four nymphal stages, and the wingless adult stage (known as the aptera). A winged form may also be present. These are known as alate, and serve to spread the colony if it is threatened, or a new host must be found. These winged adults can also give birth to live young, which they sometimes do when stuck to cannabis flowers.
- Optimum temperature range for rice root aphids is 68˚-77˚F. - In lab conditions, adult females can live up to 30 days at 50˚F, and 10 days at 86˚F. - The aphids are most active in dry soil conditions.
I see root aphids, now what?
The rice root aphid is small in size, and is normally a mottled green color, making detection difficult on the soil surface. They can also be found on plant stems, crawling on the rim of containers, near container drain holes, and on tables, trays and floors. They are especially visible on white plastic tables. Root aphids develop wings when their population density necessitates a new host environment, which is usually when growers first detect them. At this point, the use of biocontrols may not be the best option, as reproduction rates of root aphids far outpace the rates of other beneficial insects. That being said, there are predators that can provide some relief, if drenching and/or dunking treatments are not an option.
I don't see any root aphids, but I'd like to act preventatively...
Because root aphids are notoriously difficult to deal with once populations establish in your garden, acting preventatively is crucial. Regular releases of Atheta (Rove) beetles, in combination with Stratiolaelaps scimitus (soil mites). Alternatively, there has been some success using the predatory nematode, Heterohabditis bacteriophora, as a preventative treatment.
Root Aphid Predators
Stratiolaelaps scimitus (formerly H. Miles)
Stratiolaelaps scimitus (formerly called Hypoaspis miles) is a soil dwelling, generalist mite that feeds on fungus gnat larvae, pupating thrips, pathogenic nematodes, immature root aphids, and small insects in your substrate. Preventative applications will protect against many of the most common pests that feed on your roots or have a life stage in the soil. They can also be released onto the floors and corners of room and greenhouses.
Dalotia (Atheta) is a soil dwelling rove beetle. It is an effective predator of fungus gnat larvae, shore fly eggs, pupating thrips, as well as other small, soft bodied arthropods in and around your rooting system.
Dalotia are capable of flight and adapt well to various growth media including rock wool and coconut fiber. Results have been impressive when used in conjunction with Stratiolaelaps to help prevent root aphids.