Wooly Apple Aphids (Eriosoma lanigerum)¬†are a common, and often serious pest, on apple, pear and other trees. Aphids are a piercing sucking insect that feeds on plant sap, which can weaken trees’ roots or limbs, and can be particularly damaging to young, developing trees. Wooly Apple Aphids also secret honeydew, a sticky substance which can attract other pests or coat the fruit before harvest.
Aphids are typically controlled with chemical pesticide sprays, but options can be limited for organic orchards. Also since organo-phosphates and other harsher chemicals have begun to be phased out in many regions, growers are looking to other options to effectively, and efficiently control aphids.
Researchers at Washington State University, recently found that flowers, specifically sweet alyssum flowers (Lobularia maritima), can be a very effective tool in reducing aphid populations.  These flowers, inter-planted into orchards, attracted a range of spiders, hoverflies, and other predators that feed on Wooly Apple Aphids. These predators were able to greatly reduce the amount of aphids. Just one week after introducing the sweet alyssum flowers, aphid populations decreased, compared to control plots, and the results maintained for most of the season.
Six different types of flowers were screened for this study, but sweet alyssum was the most attractive to syrphids, or hoverflies, an important predator of aphids. Syrphid fly adults mainly eat pollen and nectar, and are attracted to these flowers, but syrphid larvae prey on aphids and can be an effective control against them, allowing growers to avoid, or reduce, chemical sprays.
Syrphid Fly larvae attacking aphids. Photo: Good Fruit Grower
Syrphid Fly larvae attacking aphids. Photo: Good Fruit Grower

However, in this study, syrphid fly populations were not necessarily higher in instances where aphid population densities showed decreases. This surprising result was explained by researchers using protein markers to see which insects visited the alyssum flowers. They found that spiders, and several other generalist predators, had visited the flowers are were likely responsible for the aphid control.

The results found in this study suggest that introducing sweet alyssum flowers into an orchard, can be an effective, low cost, tool in reducing aphid populations and should be considered as a part of any grower’s integrated pest management program, whether organic or not.