Tuesday, August 3, 2010

Hackberry Galls Revisited

July's hot and humid weather has created the perfect storm for mosquitos.  They're everywhere.  Bzzt.

They're most active at dawn and dusk, so I've modified my schedule.  I head outdoors around mid-day.  It's not the best time to watch wildlife - so I've modified my viewing targets: plants.

Today's plan:  find and photograph galls - what happens to plants when they're "bitten" by insects.

Hackberry Nipple Galls

Galls are distinctive growths in plants caused by parasites (insects, mites, bacteria and fungi).  The parasites actually take control of the growth of plant tissues.

Hackberry Nipple Galls are formed by jumping plant lice (psyllids).  These insects overwinter as adults and mate in the spring.  I first noticed the adults this spring, when one landed on my arm.  (They're harmless).

Females lay eggs on the underside of Hackberry leaves.  When the eggs hatch, the nymphs, feeding on the leaves, cause the leaf tissue to grow galls around them.   The nymphs feed on these tissues through out the summer and then emerge as adults in September.

 Hackberry Nipple Galls in November

I first noticed these galls last November when the Hackberry leaves littered the Chippewa River Trail.
Crunch, crunch.

 Hackberry Nipple Galls in July

The Hackberry leaves I saw today were literally weighted down with these galls.  But they don't harm the tree.   Amazing how that works. 

Hackberry Nipple Galls and a Hackberry Petiole Gall

I spotted another gall associated with Hackberries:  Hackberry Petiole Galls.  Much larger than the Nipple Galls, they're also created by a psyllid.   Petiole galls are multi-chambered with up to a dozen or more nymphs inside.  The psyllids overwinter in these galls as nymphs and emerge as adults in the spring, leaving behind an empty woody husk.

Hackberry Petiole Gall in the winter

Petiole galls are easy to spot during the winter, providing a quick clue for identifying Hackberry trees when their leaves have dropped.

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