Discovering New Links in the Garden Food Web

I made a commitment to spend more time in the garden this summer simply looking, peering under leaves, turning over stones, peering into the heart of flowers, walking slowly around the garden with no other purpose than to discover something new, to learn more about the garden ecosystem.  I do this in the early morning on some days, at dusk on others, and occasionally stop in the middle of a day’s work, dropping spade or fork to simply stroll the garden paths.

I have learned much about the garden food web.  With each new discovery comes late evening or rainy day research into the lives of the creatures discovered.  I’ve come to realize that the garden ecosystem is far more complex than any of us imagine.

The American Pelecinid Wasp

In many of my talks and writings I have found it convenient to speak about the garden ecosystem as separate from the soil ecosystem, one direct link being plant root systems.  Recently, resting on a bean leaf, I discovered another direct link between these two ecosystems.

The American Pelecinid wasp

Take a look at this creature, the American Pelecinid wasp, Pelecinus polyturator, the only member of its genus in North America.  Suddenly coming across it while harvesting beans for supper, what would be your first response?  Friend or foe?

I agree, she does look menacing – and it must be a female, for the male is much smaller and rarely seen – particularly if that long ovipositor is presumed to end in a stinger.  And it does, although the sting is reported to be mild, like a pin-prick, and seldom experienced except by those attempting to pick her up.

It is the long ovipositor that connects this member of the above-ground garden ecosystem with the soil ecosystem.  The female Pelecinid wasp probes the soil with it, searching for the larvae of a specific scarab beetle.  When she finds a grub, she lays a single egg on it.  The Pelecinid larvae hatch and burrow into the host grubs, killing them.  The larvae feed on the remains of the grubs until they pupate.

Because this sequence of events ends in the death of the host, we call the Pelecinid wasp a parasitoid rather than parasite.  Parasites prefer long-term relationships with their hosts.

The host larvae selectively victimized by the Pelecinid wasp are those of the Junebug, the grubs that devour the roots of lawn grasses and vegetable transplants.  Instead of being terrified by this slender black wasp, gardeners should be protecting it.

The life cycle of the Pelecinid wasp must, therefore, be synchronized with that of the Junebug.  Because male Pelecinid wasps are rare, females reproduce primarily by parthenogenesis, each female laying unfertilized eggs that develop into replicas of their mother.  Like the wasp in my photo, these adult females emerge in mid-summer when the Junebug larvae are feeding in the soil.

When she is not probing the soil for beetle grubs, the female Pelecinid wasp feeds on nectar.  Is it possible my wasp was resting just after sipping the nectar of a bean blossom?

Treehopper Nymphs and the Ants that Protect Them

Passing close to a bed of sunflowers, I noticed a lone ant crawling across a leaf.  What was the ant doing six feet off the ground?  I turned the leaf over and, sure enough, there were two other ants at work, tending a herd of tiny insects.  The ants seemed to have divided the herd into two groups and each ant was stroking one of their charges with its antennae.  I turned over other sunflower leaves and found more of the same.

I often see ants “milking” aphids for honeydew, a sugary waste product that aphids and related sap-sucking insects secrete, but these little insects were clearly not aphids.  Excited by the prospects of adding yet another species to my growing list of garden biodiversity, I grabbed my camera and began shooting, hoping that at least one photo would be useful in solving the mystery.

Ants “herding” a group of treehopper nymphs

I poured over Internet images of nymphs, assuming that the unknown insects were immature stages in the life cycle of a species closely allied with aphids, i.e. a member of the insect order Homoptera.  Persistence paid off and I finally found an image that looked exactly like the creatures in my photographs.  My mystery nymphs were treehoppers, Entylia carinata.

Like aphids, treehopper nymphs and adults typically do little damage to garden plants.  And while they are often found on oaks, walnuts, black cherries, and other tree species, E. carinata also feed on several herbaceous garden annuals and perennials, including joe-pye weed, calendulas, artemisias, achilleas, rudbeckias, goldenrods, and, of course, sunflowers.

We grow several of these perennials in our garden, yet this is the first time I have run across E. carinata.  No doubt this is because I’m spending more time turning over leaves.

Intent on creating a garden in tune with nature, I am always excited when I can add yet another link to the garden food web.  One discovery leads to another.  Who eats Pelecinid wasps?  Who feeds on treehopper nymphs?

Meanwhile, if I leave well enough alone, fewer grubs will be chewing transplant roots in Marjorie’s Garden next spring.

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About Reeser Manley

I was born in Laramie Wyoming but moved to the southeast at an early age. I was educated through my B.S. in Biology in the Columbus, Georgia area, then crossed the Chattahoochee River to earn my M.S. in Botany at Auburn University. For the next ten years, I worked as Horticultural Manager for the George W. Park Seed Co. in Greenwood, S.C. At 40 years of age, I decided to return to graduate school and in 1994, I earned a Ph.D. in Horticultural Science from Washington State University, Pullman, Washington. Fast forward through 10 years at university (7 at UMaine, Orono) and you find me teaching high school science in Eastport, Maine, the edge of the world, and writing a weekly garden column for the Bangor Daily News. My new book, The New England Gardener's Year, a Month-by-Month Guide for Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut, and Upstate New York”, will be published later this year by Cadent Publishing. You can learn more about the book by visiting its Facebook page: http://www.facebook.com/pages/The-New-England-Gardeners-Year/187285218055676.)