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Diggin' In: Popular fall flowers are nectar for beneficial bugs

November 3, 2014
 

Fall asters, goldenrods and black-eyed Susans are the mainstays of fall gardens. An assortment of beneficial bugs comes with them.

Thatís the way itís supposed to work, according to Helen Hamilton. Sheís author of "Wildflowers and Grasses of Virginiaís Coastal Plain" and past president of the John Clayton Chapter, Virginia Native Plant Society.

"These plants with clusters of tiny flowers feed the beetles that hibernate as adults and nourish others that form pupae cases in the soil," she says.

"Monarch and clouded sulphur butterflies have headed south and bumblebees, beetles and hoverflies are preparing to overwinter in leaf litter, under bark or in the stems of goldenrod and asters."

Fall-blooming asters have small heads, 1-2 inches in diameter, with white or bluish rays and usually a yellow center, according to Hamilton. The tiny-flowered disk furnishes nectar to visiting insects.

Aster flowers are often two types ó yellow or white rays surrounding a central disk with disk flowers.

Small white asters bloom late summer-November and even into December. Frost aster (Symphyotrichum pilosum) is one of the last plants in flower before heavy frost, and is seen along roadsides and meadows. The stems and leaves are covered with tiny white hairs, creating a frost-like appearance. The shrub-like aster is a broadly branched perennial with needle-like leaves; it grows 1-3 feet tall.

Another late bloomer is often called calico aster (S. lateriflorum), since the centers are first yellow, then purplish-red, according to Hamilton. 

Big-headed aster (S. grandiflorum) is well named with its yellow disk surrounded by red-purple rays that are 1 Ĺ- inch long. Also shrubby in looks, each flower is solitary at the tip of a branchlet. This aster flowers in dry woods and along roadsides, while New York aster (S. novi-belgii) prefers fresh and brackish marshes, swamps and other wet habitats, she adds.

"All asters are easy to grow and are good additions to the fall garden," Hamilton says. 

"While insects are collecting the flower nectar and pollen, they are transferring pollen from male flower to female flower, ensuring the production of seeds for additional plants next spring."

Tiny flies feed on many garden flowers March through November.

"Often called flower flies, these syphrid flies have dual lives," says Hamilton.

As adults, syrphids collect pollen and nectar for energy and to mature sperm and eggs. Females lay oblong eggs, 1mm in length, usually near aphids or within aphid colonies, which furnish food for the larvae. Not only do these flies perform important pollinator services in gardens and agricultural fields, their larvae are voracious feeders of aphids, scale insects, mealybugs and thrips.

Also known as hoverflies, syrphids hover in flight and can even fly backward. They are true flies with large compound eyes nearly covering their head, two wings and small antennae. Like all flies, they have a complete metamorphosis ó egg, larval, pupal and adult stages. Eggs hatch in three to four days as soft-bodied maggot-like larvae. They feed for seven to 10 days, then fasten to a leaf or twig when ready to pupate, where adults will emerge 10-15 days later. There are several overlapping generations each year.

As predators, hoverflies are as important as ladybird beetles and lacewings. The larvae are legless and wormlike, dull green, less than one-half inch long. During its development, each larvae consumes 100s of aphids. Crawling about on plant surfaces, they grasp their prey, usually an aphid, with their mouth hooks. Holding it over their head, they suck its body contents dry while still alive and discard the skin. When aphids are plentiful, hoverfly larvae can control 70-100 percent of an aphid population, which can seriously damage crops.

"Many species mimic bees or wasps with bands of yellow and black around their bodies, to avoid predatory birds and other insects seeking a meal," says Hamilton.

"Some species of hoverflies feed on fungi, and most are considered beneficial. The adults do not sting and pollinate flowers, and the predatory larvae eat insect pests.

"Itís a win-win situation for gardeners."

 

 


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