|Galls on Pongamia leaves|
Here are some Pongamia pinnata leaves I found not so long ago. One usually finds little outgrowths on the leaves. These are mostly insect galls, but galls may also be formed by fungi. If you cut an insect-gall you will likely find a central hollow, perhaps an exit hole on the base or tip and if you are lucky, a tiny larva somewhere. That could most likely belong to one of numerous wasps or flies and you will surely be hard-pressed to find anyone who can identify the species. Galls are not always shaped like this - they can be spherical, formed at the tip of a branch and botanists have been known to sometimes describe the gall as the characteristic fruit of a new found tree species. What exactly is happening is something to consider - is the plant trying to isolate the insect like a cyst forms to engulf a foreign body or is the insect manipulating the biochemistry of the plant to make it produce tasty tissue around it ? Turns out that the latter is often the case and sometimes the gall-inducer seems to be capable of inducing galls with very specific shapes, colours and structures (this article with illustrations is particularly worthy of reading).
|Ficus at Hebbal with leaves eaten away|
|Leaf mine - note widening with age of miner|
|The caterpillars on the Ficus (unidentified)|
So, next time you have something to ponder over when you see a fallen leaf...
Turns out that some studies suggest that leaf dropping does not kill many leaf-miners and so seems unlikely while others point out that gall infestation induces early leaf shedding.
Also discovered Huitlacoche caused by Ustilago maydis
- Pritchard, I. M.; James, R. (1984) Leaf fall as a source of leaf miner mortality. Oecologia 64():140-141
- Stromgren, ES & CA Lanciani (2001) Early abscission in hackberry leaves bearing Pachypsylla galls (Homoptera: Psyllidae). Florida Entomologist 84(4):727-728
- Graham N. Stone and Karsten Schonrogge (2003) The adaptive signiﬁcance of insect gall morphology. TRENDS in Ecology and Evolution 18(10):512-522