Fruit gall, New Caledonia Minimize

March 2009. An unusual symptom from guava growing in New Caledonia. What is it?

It was said to be a gall induced by an insect, and the mostly like cause was aphids/Hymenoptera/psyllids.  The photo shows a very well developed gall, and so the insects may have departed. Look at the younger galls to get a better chance of finding the insect. A physiological condition and Eriophyid mites were also suggested, but thought less likely to be the cause.