Posts Tagged ‘beneficial insects’

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!

Fans are invited to join the OSU BeeLab contact list for updates and workshop offerings. Follow my bee blog at www.OSUpollination.com
Denise Ellsworth
honey bee and native pollinator education
OSU Department of Entomology

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It’s my pleasure to introduce Denise Ellsworth honey bee and native pollinator education from The Ohio State University Department of Entomology. She’s doing a very special Guest Blog today. Please leave any comments or questions for her below and sign up for her blog at the bottom of this piece. Take it away Denise……

in bloom at Toledo Botanical Garden

March days with temperatures in the 80’s brought many of our native bees out of their winter hiding places. On a visit to the Toledo Botanical Garden a few weeks ago to teach a class of new OSU Master Gardener recruits, I was lucky enough to find an area with hundreds of soil mounds created by ground nesting native bees.

hundreds of native bee nests under oak tree

At first glance, the soil mounds resemble ant hills. but they are larger and have a hole in the center about a half-inch in diameter. As I crouched down to observe the mounds, I saw dozens of adult bees flying across the area from one hole to another. These solitary bees aren’t aggressive and rarely sting (unless handled), so I spent several minutes crouched over the nests to capture the bees on film. When I could keep very still, a bee head would slowly start to emerge from the hole at the center of each mound. Once I moved or created a shadow, the individual bee would quickly pull back into the soil nest.

Digger bees, plasterer bees and polyester bees are all native solitary bees that make this kind of soil mound in spring. Typically found in sandy soils on south-facing slopes, the nests are made by the adult bee. She removes sandy soil particles from the nest as she excavates new chambers for her young to grow. The soil is piled up around the nest exit, forming chimney-like mounds. On sunny, warm spring days, the bees are active, emerging from their nests to mate.

ground bee nest, with acorn for scale

chimney-like soil mound from ground bee

Females fly off to forage on blooming plants (lamium, crocus, azaleas, magnolias and cornelian-cherry dogwood were in bloom that day at the Botanical Garden), then bring the pollen and nectar back to the nest. She lays an egg in the chamber she’s excavated and leaves a loaf of pollen and nectar food (also called bee bread) behind for her yet-to-emerge larva to eat. As a solitary bee, this adult doesn’t tend the nest, but instead provisions the chamber with enough food to bring her offspring from egg to adult.

willow flower offers early food source

These ground-nesting bees aren’t the only bees active in early spring. Carpenter bees have just emerged from their tunnels in wood, and will be starting this year’s generation of baby bees. On a visit to the Holden Arboretum in Kirtland, OH, last week, I witnessed dozens of carpenter bees foraging on flowers of the three-flowered maple. This native bee is large like a bumble bee, but has a shiny abdomen. The male carpenter bee buzzes menacingly around the nest opening, but can’t harm you because he doesn’t have a stinger. The female can sting, but she’s reclusive and non-aggressive. Instead, she’s busy chewing out galleries in wood for this year’s brood. Like the ground nesting bee, this mother bee will gather pollen and nectar, then bring it back to the chamber she’s chewed with her strong jaws. She lays a single egg in each chamber and provisions the egg with bee bread.

carpenter bee on three-flower maple

The larval carpenter bees develop inside the wood galleries until late summer, when they emerge as adults. Their mother and father have already died; this new generation will spend the winter in the galleries, emerging to mate next spring. Carpenter bees can cause significant structural damage to wood structures, and can be difficult to evict. Adults return to the same galleries from which they emerged, and will continue to tunnel and cause damage. I once had carpenter bees take up residence in a porch area — they were still a problem even after I added vinyl siding to the home. Read more about carpenter bees, and how to keep them from damaging decks, porches and lawn furniture.

adult bee near nest

Even though they can cause damage to wood, carpenter bees are important pollinators. By leaving dead trees standing or providing brushy habitat, our landscapes can be a haven for native bees. These bees play an important role in pollination of garden crops and native plants. Encourage native bees by planting flowers to bloom from spring through fall and reducing or eliminating pesticide use. Early bloomers, like maples and willows, can be especially helpful to emerging spring bees. Gardeners and homeowners can make a big difference in the conservation of these vital insects.

Cornus mas -- corneliancherry dogwood in bloom

Bee fans are invited to join the OSU BeeLab contact list for updates and workshop offerings. Follow my bee blog at www.OSUpollination.com
Denise Ellsworth
honey bee and native pollinator education
OSU Department of Entomology

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