What's Bugging You? Aphids

Aphids are soft-bodied, pear shaped, sap sucking insects that are very tiny

I have a love hate relationship with aphids.  While I realize they can be very destructive in large numbers, I also find them one of the most fascinating insect groups to study because of their complex life cycle.  They are also coveted by ants who protect them in return for free food!  More about that later. 

Aphids are soft-bodied, pear shaped, sap sucking insects that are very tiny - 2-10 mm long. There are over 1300 species in North America that damage herbaceous plants, shrubs and trees.  They thrive in hot weather and dry conditions.  Aphids come in many colors; green, brown, black, yellow, pink and white. The excess sticky plant sap an aphid consumes is released by the cornicles (tubelike projections) on their abdomens.  This residue is called honeydew.  When the aphid is threatened, these cornicles also emit a quick hardening liquid called cornicle wax.  This wax will gum up a predator’s mouth rendering it useless. Aphids also produce a pheromone ‘alert’ to warn other aphids of impending doom.  It is interesting to note that ladybugs have learned the aphid pheromone language and will track it to the tasty aphid colony.

Life Cycle

Aphids have a complex life cycle to say the least.  Each species of aphid has its own life cycle which may involve one or sometimes two host plants.  This is the Reader’s Digest condensed version- my apologies to my entomologist friends!

Stem mothers hatch from eggs on the winter host plants in spring.  They may be winged or wingless.  The winged females will migrate to a summer host plant.  These winged stem mothers will begin to bear live winged and wingless females on the summer host.  The bearing of live aphid young without male fertilization is called parthenogenesis.

A baby female aphid becomes a reproducing adult within one week.  You do not need to be an expert in math to see what this leads to ; a mass of live bearing female aphids within a short period of time! 

This massing of aphids eventually leads to overcrowded housing conditions and when this occurs some of the winged females (called alates) will fly to start a new colony on other host plants. 

As fall approaches, both males and females are produced.   Winged males will mate with special egg producing females (oviparae) on the winter host plant. The eggs are deposited on the winter host plant and wait for spring.

Signs of Aphids

The signs of aphids on your plants are many.  If you look very closely you may actually see them – especially on the new growth tips.   Their saliva causes stunted, twisted shoot growth and the plant may develop a dark sooty mold that feeds on the honeydew.  Quite often aphids will feed on plant tips only and then leave for greener pastures.  This leaves the homeowner puzzled as to what has caused the damage.  Fortunately, this tip damage does not negatively affect the rest of the plant.

Aphids are also found on the undersides of leaves.  The leaves will develop spots, wilt, curl or yellow.     

Adelgids or woolly aphids produce hard plant galls mainly on conifers.   

Aphids can also transmit viral diseases through their saliva to host plants such as potato, raspberry and rhubarb.  Some signs of a viral disease are a mosaic pattern on the leaves, leaf spot and stem blight. 

Ants and Aphids

Ants and aphids have a special relationship.  Aphids supply ants with food while ants play the role of aphid bodyguards.    The ants will ‘farm’ the aphids and obtain the honeydew by stroking the abdomens of the aphids.  This is called milking.  Ants will also go so far as to carry aphids further up a a tree or plant to better feeding areas.  They will protect aphids from the weather, natural enemies and transfer them from wilted to healthy plants. Some ants will even take aphids back to their nest during the winter months to keep them safe until spring.

Control

I do not recommend using insecticides to control aphids as this will kill beneficial bugs as well.  

If you catch an aphid outbreak early on, cut the affected shoot(s) off and washing the plant down with water.  This applies to houseplants as well.  Isolate the affected houseplant until you are sure the aphids are gone.  Check plants daily, repeat the trimming and wash down the leaves again if necessary.   

Surprisingly, the best aphid control outdoors is to hit them with a sharp spray of water, knocking them to the ground.   This will kill some of them and the wingless females cannot climb back up the plant.  They will eventually starve. 

Keep the weeds down in your garden.  Weeds are often host plants.

Thoroughly inspect all new plants you bring into the garden or your home.  Keep checking your plants weekly to catch any outbreaks early on. 

Plant herbs that repel aphids such as basil, coriander, catnip, chives and dill.

Photo: Ladybug larvae

Encourage predators to take up residence in your yard.  In Saskatoon, the main predator of aphids is the seven spotted ladybug and their voracious larvae. 

Photo: Lacewing

Other predators include the green lacewing and their larvae (aphid lions), parasitic and stinging wasps, damsel bugs, pirate bugs and hoverfly larvae. 

Aphids will not go down without a fight.  They will beat their enemies with strong hind legs and feet and stab the eggs of predators. 

Here are just a few of the aphid species known to frequent Saskatoon gardens.

Apple Aphid – Yellow green with a dark head and legs.  Overwinters as a black egg on its only host – the apple tree.  Mainly an eastern insect but has been found in Saskatchewan and Manitoba.

Cabbage Aphid – Grey green, small with a powdery waxy coating.  It is found on the underside of the leaves of cabbage, radish, cauliflower and brussels sprouts.

Cooley Spruce Gall Adelgid – This aphid’s saliva triggers a reaction in spruce causing the formation of cone- like galls about 3 inches long on the tips of twigs.  In mid summer the galls open, and adults migrate to nearby Spruce or Douglas Fir to lay eggs.  When possible, remove galls. 

Green Peach Aphid – Most common species of aphid.  Likes to feed on many types of plants.  Can transmit many plant mosaic diseases. 

Honeysuckle Aphid – Very tiny green body covered with a whitish powdery coating.  The saliva can cause weird dense twig deformities on a honeysuckle.  Branch tips will curl.

Caragana Aphid – Can defoliate a large caragana shelterbelt.  If shrubs are healthy, they can recover. 

Woolly Elm Aphid – Bluish black flattened oval, soft bodied insect that emerges from eggs laid on elm bark. In early spring they will feed on elm leaves.  In mid summer winged females will fly to Saskatoon bushes where they feed on the fine roots of the shrub.