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Mulch on, and don't fear the aphids

“Listen

With faint dry sound,

Like steps of passing ghosts,

The leaves, frost-crisp’d, break from the trees

And fall.”

— Adelaide Crapsey, “November Night” in “Verses,” 1915

American poet Adelaide Crapsey (1878-1914) did not enjoy a long life — she died in New York at the age of 36 from tuberculosis. Although her poetry is not widely remembered today, Crapsey left an important legacy in the form of her unrhymed, five-line, 22-syllable poems, inspired by her love of Japanese haiku.

Her style has become known as the American cinquain, adopted and modified by many poets of the 20th and 21st centuries. In his 1918 collection of poems “Cornhuskers” (for which he won a Pulitzer Prize), Carl Sandburg published a tribute to Adelaide Crapsey in a section of the book called “Persons Half Known.”

Speaking of the “half known,” I received an email from a reader who wanted to know more about using fall leaves for mulch in the garden (the topic of my column Nov. 8). Donna wrote, “I appreciate the benefits of mulching. However, no one seems to include aphids in these discussions, only beneficial insects. What is the life cycle for aphids and does mulching encourage their overwintering?”

I replied to Donna that aphids do, indeed, overwinter in our garden, usually in the egg phase of their development. Although leaf litter provides shelter for aphids, most of the approximately 5,000 known species of aphids lay eggs on the leaves and stems of specific host plants. For example, Donna’s aphid nemesis is the lupine aphid (Macrosiphum albifrons), and my roses are sometimes plagued by a different species called rose aphids (Macrosiphum rosae).

Other aphids prefer vegetable crops for their host plants, such as cabbage aphids (Brevicoryne brassicae) and turnip aphids (Lipaphis erysimi).

In the spring, only female aphids hatch from overwintered eggs, and they begin reproducing one week later. During most of the year, female aphids reproduce asexually through a process called parthenogenesis, whereby they give birth to miniature replicas of themselves rather than laying eggs. During one season, some aphid species can produce up to 41 generations of offspring, each insect living 20 to 40 days and producing between 50 and 100 babies.

Most aphids live out their lives on their host plants. Later in the summer, some adults will develop wings and fly off to visit other plant species, but subsequent generations of females will return to their host plant species in the fall. By then, some aphids have developed into males, so females find a mate and then lay their fertilized eggs on the host plant, or in leaf litter, to start the process all over again.

By layering garden beds with leaf mulch, it seems like gardeners are practically ensuring aphids will not only survive but remain comfortable all winter. However, scientists have found that 70% to 80% of overwintering aphids die before spring due to predation or cell damage. (Keep in mind that leaf mulch also provides shelter to aphid predators.)

Aphids that do survive the winter are an excellent source of nutrition for hungry birds, as well as many kinds of beneficial insects: parasitic wasps, ladybugs, lacewings, hover flies and soldier beetles.

In fact, aphids are not just sap-sucking, disease-spreading garden pests; they’re also an important part of the food chain in a balanced ecosystem. In order to attract our pollinator friends to the garden, we must provide food for them, and aphids and other insects we consider pests fit that bill quite nicely.

Aphid infestations occur when the garden doesn’t have enough aphid predators or when weakened plants are unable to ward off insect pests; thus, aphid invasions tell us that the garden ecosystem is off-balance in some way. We might say aphids are “food for thought” for gardeners just as they are food for wildlife.

Leaf mulch is an efficient use of fall leaves to provide habitat for overwintering wildlife, including aphids. When we see overwintering birds foraging in the garden, we may even be thankful the aphids are there!

In response to another reader’s email, the leaf mulch saga continues next week with “What about oak leaves?”

Rhonda Nowak is a Rogue Valley gardener, teacher and writer. Email her at Rnowak39@gmail.com. For more about gardening, check out her podcasts at https://mailtribune.com/podcasts/the-literary-gardener and her website at www.literarygardener.com.