Orchids, ants and extra-floral nectaries

[wuness]

Howdy! First time poster here.

I've seen several posts, here and on other forums, regarding "honeydew" on various orchid structures outside the flower. I've always assumed this was a genetic phenomenon designed to attract ants. As most of you know, ants have established fascinating relationships with plants in the tropics and elsewhere. They also fiercely defend their territories and food sources. It's easy for me to believe that orchids have evolved the ability to attract ants, using their extra-floral nectaries on stems, leaves and flower stalks, and then rely on the ants to protect the orchid plant, and especially the flower, from herbivorous insects. To me, the extra-floral nectaries of orchids are a holdover from their insect wars of the past. Note that the ants have nothing to do with pollination.

In a similar vein, in my own backyard in Illinois, I've often observed ants interacting with aphids for the same food source. Ants will tap on a feeding aphid and the aphid will release a drop of honeydew which the ant ingests. The ants protect their resources and will repel any insect that approaches. When ant colonies move, they've been known to take aphids with them to a new plant source.

As far as my theory about ants, orchids and extra-floral nectaries, I don't remember whether I read it or just inferred it from other bits of nature trivia. If it is true, I'm surprised that other hobbyists haven't mentioned it. I know there are many who are far more widely read than I am on the subject of orchids. There surely should be some reference to this notion in the literature.

[orchidsal]

Very interesting observations. I have read and seen on my Rose bushes the interaction of ants and aphids and I have seen ants tend mealy bugs almost as if they were cows (very small version there of), but I never thought that they could be beneficial to orchids. If ants stop chewing invaders that is a plus. Now for the orchid grower how do you get the ants to do only what benefits the plant? AL

[Cjcorner]

I have noticed the ants out back tending my orchids. The Encyclia Belizensis has a spike that has more branches and buds than I'd ever been able to grow and it has these tiny ants parading back and forth all the time. My Schomburgkia that has a developing spike is also groomed constantly by ants. The ones on my Schomburgkia are larger than the Encyclia ants too. At first I thought it would be a bad thing. But the plants with ants almost never have bugs on them and the buds are more numerous and healthier. Just my opinion...the ants do something for the plant overall. Maybe that is why when I sit a bug infested plant on the ground under a tree...the bugs mysteriously disappear. Hmm....

[panam]

Interesting - but as I keep my orchids in the house, I hope to never observe this in my plants, ha, ha!

[swtheory1986]

I also have observed ants doing this on my pepper plants, farming aphids and mealy bugs alike. There is an article in one of the newer nat geos, that talks about weaver ants being one of the first forms of biological insect control. As far as orchids go, I have a bunch of little black ants patrolling my B. Little Stars daily, I also have a few dendrobiums that spiders have made nest on. Usually I will stop spraying these plants with insecticide, unless my insect buddies can't maintain.

[wuness]

Anyone who grows peonies is familiar with the ants crawling over the buds and ingesting the nectar droplets long before the buds open. I presume the peony is doing the same thing I've suggested the orchids are doing. They, and the orchids, have managed to evolve a system where they sacrifice minimal amounts of their sugar resources for the greater good (i.e., enticing ants to protect the plant from even greater losses of sugar from aphids and scale insects and also from structural damage from herbivorous insects). It's a clear case of quid pro quo.

When I've read the several posts where individuals report droplets of nectar on their orchids (outside the flowers), they are invariably concerned about the possibility or disease or insect damage. Normally the advice given is that there is nothing to be concerned about. The ensuing discussion then centers on how to remove the secretions. My point is that these secretions are a normal part of the orchid plant, just like the stems, leaves, and flowers. As someone has said before, "nothing happens in nature without a reason."

[swtheory1986]

Couldn't be more true on your last statement Dave!

[catttan]

I agree with you, Dave. Exactly what I was thinking.

[Halloamey]

It depends on ants also. I don't want the farmer ants with aphids like their flock of sheep anywhere near my orchids, also some ants like to nest in the bottom of my orchids and during repotting, it can become a painful experience for me or a lethal one for them, thats why I try not to have them around.

[TwoStems]

All of my plants are indoor, so my main concern is fungus gnats since those are the only thing that seem to bother any of the plants I have (orchids or otherwise). Would this nectar attract them? Since I've repotted most of my orchids in s/h I haven't noticed them as much so I'm less worried about removing the sap than I used to be. Interesting how nature is so harmonious, we as humans have so much to learn (or we've forgotten so much?)