Seed Pod Damage
Hendersonville, North Carolina
This article is being written to alert the reader to what was until now a relatively obscure insect pest that destroys the seed of our native azaleas. This article gives a brief history of personal observations and what is currently being done to identify and neutralize this pest.
Brief History, 1991-1996
Since moving to Western North Carolina in the fall of 1991 and being bitten by the native plant bug I have visited many native azalea sites in the Western North Carolina region. These trips took me to places like the Blue Ridge Parkway, Pilot Mountain, Pisgah Forrest, Burrels Ford, Copper Bald. Gregory Bald, Wayah Bald, Roan Mountain, Jane Bald, Curtis Creek and many others.
Superior forms were selected, photographed and tagged. A return trip to collect seed from these plants was made each year. It was on these seed collecting trips that I noticed a tiny, barely perceptible hole in the side of the seed capsules. Opening the capsules revealed that there was no viable seed. Since these were few in number there was no need for alarm.
Chapter member Dorothea Turlington, owner of what was the Henry Skinner property, graciously offered seed from some of Henry's spectacular native azalea hybrids. I was elated when I arrived in late October to find the heaviest seed set I have ever seen. The branches were covered with huge clusters of seed pods. I then noticed the hole in the pods. Breaking the pods open revealed a dark mass like wet peat moss. I collected a bag of seed pods the size of a ½ gallon milk container, returned home and inspected each seed pod for holes. Only about 5 percent had no hole.
I sent the bag of pods to the Entomology Department in Raleigh to no avail. They couldn't find any insect or insect part and with out this material proper identification was impossible. They did say that they thought the hole was an exit hole. That an egg had been inserted in the flower and the seed pod developed around it.
Some time in mid September, Rob Eisenberg, Bob Stelloh and I went to one of our favorite sites to see if the seed was ripe. It became evident that we were much too early and there was very little seed set; however, the first pod I looked at was bright green, smooth and had no holes. When I broke it open to check the seed I saw something move. There was a ¼ inch long larva thinner than a pencil lead.
At last we had a sample to aid in identification. We opened several more and found larva and pupa. We then collected about 30 pods. When we returned home Rob contacted a friend at the Entomology Department at the University of Delaware. He said it sounded like a Eurytomid seed chalid. This is a tiny wasp with parasitic ancestry that has become a seed specialist. He recommended we contact Dr. Christine Nalepa at NCDA in Raleigh. I contacted Dr. Nalepa, relayed our findings, and to say she was interested is an understatement. She wanted to see plants that had the pod damage and volunteered to drive here the following week.
Meanwhile, chapter member Don Johnson gave me a seed pod with a hole that came from a large leaf rhododendron hybrid. After the meeting I checked some of my rhodos and found the critter there also. The problem is worse then I thought.
Dr. Nalepa arrived on Thursday, Sept. 24, and she, with Rob Eisenberg and I, toured my property. We found a number of damaged seed pods. Dr. Nalepa wanted to inspect as many native azalea species as possible so we went to the North Carolina Arboretum to see the native azalea collection. We found infestation on all but Rhododendron vaseyi. My theory is that the seed pods of R. vaseyi is so small that the insect wouldn't survive.
We also found infestation on Rhododendron maximum, Kalmia latifolia and Leucothoe axillaris. Again the problem worsens.
It appears that ericaceous plants are the insects favorite. Dr. Nalepa said she may be able to identify the insect but further study would be impossible because of scheduling conflicts and lack of funding. The next day I received a message from Dr. Nalepa that her colleagues are guessing that the insect may be some type of fly. Further study is under way.
Dr. Nalepa sent the following message: "Here is a brief report...All of the samples I collected had damage. However there may be more than one culprit. The only live insects to emerge were hemipterans in the family Coreidae: Arhyssus lateralis. These are generalized plant feeders; however, we can't find any records of them being found in association with Rhododendron spp., or feeding specifically on seeds. They were fairly abundant. These were identified by NCDA taxonomist Ken Ahlstrom. Dave Stephan (NCSU) and I dissected pods and found the head capsule of a weevil and the dead larvae of a tortricid moth (like the green one you collected). Weevils are known borers (think boll weevil), and tortricids also bore into fruit. The pupae that emerged from the Copper Bald site (that you gave me) were flies. I have some incubating in the hopes that some will emerge so that we can identify them, but the chances are slim. If you follow up on the project next year, the collections need to be made earlier in the season, so that live weevils and tortricids may be collected for identification. Looks like there is not going to be an easy answer."
There goes my hope for a quick solution.