The Carolina Buckthorns are once again under attack by Asian
Soybean Aphids, Aphis glycines. I first
encountered the aphids last year when they were found on a few Carolina
Buckthorns. This plant that I found
yesterday is typical of the worst condition I found in July of 2011. There are some yellowed leaves and a few
tightly curled leaves.
The aphid damage is much more severe and widespread this
year. Entire branches are showing curled
leaves. Carolina Buckthorn is an
uncommon plant in Ohio
with a range that just catches the southern edge of the state. Its primary threat has always been extreme
low winter temperatures. I frequently
monitor the plants to see how they are growing, so I am certain that the aphids
were not a problem before last year.
This is what’s inside the curled leaf. Aphids busily feed and reproduce within the
protective folds of leaf. Ants visiting
the aphids to collect honeydew, provide another measure of security. Asian Soybean Aphids are a non native species
that was first discovered in the United States about 12 years
ago. They became a species of concern
because of their use of Soybeans as a summer host plant. Large populations of these aphids can cause
severe damage to soybean plants and devastate yields.
Soybeans are annual plants that only exist for a limited
time each year. In order to sustain
themselves during the non soybean season, the aphids utilize a second host for
the winter. Non-native Buckthorns,
Rhamnus species, were the original preferred winter host. It became a case of one invasive species
damaging another. Now it’s obvious that
at least one native Buckthorn is a suitable host for the Asian Soybean Aphid.
Aphids feeding on the buckthorn cause the distorted, curled
leaf formation. Judging by what I found,
it appears that the leaves curl prior to being invaded by the aphids. The leaves remain green even after intensive
feeding has taken place, so the leaf functions may continue to provide
nutrients to the plant.
Aphids on the buckthorn come from eggs laid the previous
fall. These aphids are all females that
reproduce by giving live birth. The
youngsters begin producing their own young when about a week old, so it doesn’t
take long for a population explosion to occur.
Eventually, winged females are produced and these fly off to find
soybean plants on which to start a summer colony.
The aphid spends most of its time attached to leaf veins by
way of its tubular mouth. Consuming sap
and producing babies is the life of the aphid.
After producing many generations of aphids on soybean plants, male and
female winged adults search out buckthorns where mating occurs and eggs are
laid. Aphids in the wind may travel
hundreds of miles, so the proximity of soybean fields is not an indicator of
whether or not the buckthorns will be found by aphids. The eggs overwinter and the whole cycle
begins anew.
The winged individuals apparently don’t all develop on the
same schedule. This population looks to
have everything from winged adult to newborn infant. I’ll have to wait to see what level of
survival threat the aphid poses to the Carolina Buckthorn. Since the aphids will leave the buckthorn in
early summer, the buckthorn may have time to regrow with minimal ill
effects. What I’m expecting next is to
find the aphids on local native legumes.
I’m afraid that won’t be a fun discovery.
Isn't it amzing the amount of variety within each kind of a critter in our world. I remember the very first time I ever saw the brightly coloured yellow-orange Aphid which parasitizes Oleander bushes. At first I thought, no way ? But then realize, why not!
ReplyDeleteIn parts west of you, soybean aphids have triggered an explosion of Asian variable ladybird beetles Harmonia axyridris. What could be wrong with a bunch a ladybugs? They leave the fields (probably forest canopies, too) by the billions in fall, bite when they bump into you, swarm into wall spaces on south walls of buildings, where many die and stink. I also worry that reduction of native aphid populations may impact their parasites, predators and mutualists, which constitute abundant and diverse links in the food chain.
ReplyDeleteOn a positive note, Steve, these are stunning photos of these tiny insects! (and of the acrobat ants Crematogaster cerasi visting them)
You're so right, Kevin.
ReplyDeleteThanks James. It's been several years since we've had a large population of the beetles. One year they were so thick in the air that it was like being in a hail storm. Except that the beetles started chewing on you as soon as they landed.