Sunday, January 27, 2013

Dumb cane, ants and aphids

Dumb cane, or Dieffenbachia, is an aroid.

It gets the nickname dum cane because the stem contains crystals of calcium oxalate. They are needle shaped and severely irritating and if they get in the throat they cause swelling and the victim can't talk. It is a defence mechanism by the plant to avoid being eaten.

However aphids and ants live happily on the plant, which also suffers from mealy bug. The aphids manage to avoid the crystals when they feed. They drill into the stem and finds a sap channel and can then drink the sap unaffected by either latex, which exists in separate channels or oxalate spikes which are solid and remain in the stem. Sap is very low in protein however and the aphids need to drink much more sap than they need. The sap is passed out of the body as a waste called honeydew.

This honeydew attracts ants. The ants actually milk the aphids. They will also aggressively defend the aphids against predators.

My original dumb cane was covered in mealy bug and I manged to get rid of most of them, using ethanol. But then the plant outgrew itself, falling over as the stems could no longer give support. So I then cut off the tops, and replanted them, and also replanted a 'blank' piece of stem. They all started sprouting new leaves within a month.

This leaf is only a month old -
New shoots and leaves on the cut stems                                                                                            

I manged to get rid of the mealy bugs. But am fighting a losing battle with the aphids. They reproduce so fast that it is impossible to clear them. And of course they have their bodyguard ants.