Aphids and aphid mummies on the underside of a nasturtium leaf (smoky gray aphids, tan puffy aphid mummies)
For some gardeners, the mere sight of aphids on their beloved plants is a call to action. They grab the closest bottle of poison and squirt the aphids into oblivion. What many gardeners don’t realize is that aphids are the food of choice for an assortment of beneficial insects. These good bugs are likely hard at work among every aphid infestation, munching, laying eggs for the next generation inside their unsuspecting prey, or sucking the aphid carcasses dry. One squirt from the bottle of insecticide will kill some (not all) of the aphids, and most of the beneficial insects.
If only we could easily tell at first glance that beneficial insects are on the scene! They don’t wear white hats or wave flags to alert gardeners to their presence. Instead, beneficial insects creep, crawl and squirm across our plants, often appearing as if they could be the cause of damage, not the cure.
Take hover fly larvae, for example. As adults, these bee-mimics visit flowers, feeding on nectar and pollen. When the female finds an aphid population, she lays her eggs on the infested plant. Like all flies, the hover fly juvenile stage is a maggot, in this case a small maggot that feeds on aphids. The legless, semi-transparent hover fly larva hardly looks the part of a beneficial insect, but each individual can eat dozens of aphids every day.
Lady beetle eggs (yellow) on a purple leaf plum leaf.
Another aphid-killer that feeds in the larval stage is the lacewing. As adults, these delicate insects with netted wings feed mainly on pollen and nectar. Lacewing larvae, sometimes called “aphid-lions”, are efficient predators, stalking down aphids and piercing them with their hooked jaws. After removing the contents from the aphid’s body, the lacewing larva casts aside the empty aphid carcass, and heads off in search of another victim.
Ladybird beetles are also voracious predators of aphids, feeding in both the adult and the larval stage. Like hover flies, ladybird beetles (also known as ladybugs) will lay their yellow, spindle-shaped eggs on plants that have active aphid colonies. The beetle larvae look nothing like the adult ladybug. They are spiny and elongated, sometimes compared to baby alligators. These active hunters crawl over leaves and across stems to find their next meal.
Parasitic wasps are another group of aphid-eating insects unlikely to be noticed by the uninitiated. The tiny female wasp stings individual aphids, laying an egg inside the aphid’s body. The egg hatches into a wasp larva, which eats the aphid from the inside, killing its victim and causing its body to become papery and swollen. These so-called “aphid mummies” can be seen in aphid colonies; some mummies will have a round hole where the adult wasp emerged to begin the cycle again.
Lady beetle larva
When the gardener rushes for the bottle of insecticide, the predators will likely be killed, but surely not every aphid will die. Since aphids can be born pregnant with their granddaughters, their populations can skyrocket in the absence of beneficial insects.
These aphid predators will in time bring balance to the garden, keeping aphid populations down to a dull roar. If the predators are allowed to complete their lives in the garden – meaning the gardener has provided a habitat with plenty of flowers and a few aphids to feed upon – they are likely to stick around, ready to feed on any future aphid outbreaks.
So the next time you see aphids, grab a magnifying glass and take a closer look. Chances are, the good guys are already on the scene.
Thank You Denise for your Guest Blog!
Denise Ellsworth
honey bee and native pollinator education
OSU Department of Entomology
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