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Field trips are full of opportunities to exercise and develop skills
in observation, and to answer queries which the outdoors stimulates.
There is a variety of inquiries centered around biological and
physical interrelationships, which are fine subjects for broadening
understanding of the science of the outdoor world.
One of the interesting features in vacant lots, along streamsides,
and in brush patches are plant galls formed by insects, mites, fungi
and viruses. On the oaks in the foothills of the Great Basin,
numerous kinds of galls are produced, generally by tiny wasps.
During the laying of the eggs on oak leaves, stemms and buds, the
irritation caused by chemicals, usually of a hormonal nature produced
by the wasp or the larvae, stimulates the plant to surround the area
with a large mass of tissue. Within this mass are found the
developing larvae of the wasps feeding on the plant tissue.
When the larvae have matured, they enter a seeming quiescent pupal
stage, during which there is a radical reorganization of the materials
in the tissues to result in the adult. Upon emerging from the pupal
stage, the adults start the cycle again of eggs, larvae, pupae, and
adults.
Oaks are not the only plants which have galls on their stems and
leaves. One of the best sources of galls for study are the wild
roses. Several kinds, each formed by a different species of insect,
are to be found. If conditions are right, galls gathered in the field
and brought to the laboratory in plastic bags may release the insects,
which will present a challenge of identification.
Sagebrush, goldenrod, willows, wild cherry, and rabbitbrush almost
invariably yield some galls. The sense of inquiry can run to great
depths. The life histories of the wasps, flies, moths and others
can be determined. Some of these are unknown to science.
Historically, oak bark was used extensively as a cource of tannic acid
in the leather tanning industry. Early settlers found the oak bullet
galls a rich source of tannin, and whole families made excursions into
the hills to gather these insect-formed structures. This would be a
rich field of research for alert students and teachers. Thus, field
trips can be rewarding in many ways.
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