This is the time of year when folks seem to notice bubble-like galls on the blades of pecan leaves (photo at right). These galls are caused an insect called the pecan leaf phylloxera. At this point during the growing season, the small aphid-like phylloxerans are feeding on plant sap from inside the gall. The seasonal life cycle of the phylloxera starts at leaf burst when spring crawlers emerge from the bodies of over-wintering females and crawl to rapidly growing new leaf tissues. As these wing-less females feed on the leaves, they secrete a growth regulating substance that causes the tree to grow a gall around the insect. Once inside the protective gall, female phylloxera give birth to hundreds of young.
Flip a phylloxera infested leaf over and you might find that some of the galls have developed an opening that almost looks like an exploded volcano (photo at left). A new generation of winged adults will emerge from this hole. The winged adults will mate and impregnated females will migrate to a hiding spot in pecan bark. The phylloxerans will remain dormant until next spring when a new generation of crawlers emerge from the body of the overwintering female.
I cut open a couple of galls with the hopes of photographing phylloxerans inside (photos above). However, what I found in each case was a syrphid fly larvae working to devour all the phylloxerans inside the gall. In photo "A", the syrphid fly larva had cleaned out the gall completely. In photo "B", there were just a few phylloxerans left. Syrphid flies are probably the reason why pecan leaf phylloxera is only a minor pest of pecans.
