Asian Soybean Aphid

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.