Today’s emphasis: A bird’s-eye view of insects that feed on spring oak leaves.
Link to Don Hunter’s Facebook album for this Ramble. Photos that appear in this report were taken by Don [DH], Heather [HL] & Bill [BS].
Announcements: Heather: Piedmont Gardeners 30th Garden
Tour of Athens, Saturday April 15 from 10 am to 4 pm.
Number of Ramblers
today: 30
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| Preparing to seek what we find [DH] |
Today’s Route: From the Right of Way parking lot to the Blue Trail and back.
We first gathered around the low-hanging branches of the large Water Oak by the parking lot. Everyone was encouraged to look for insects and bring interesting leaves to a picnic table for discussion. After that we rambled across the street to Compost Pile Row (where there are accessible hickories), up to the Blue Trail and to the left for several hundred yards (where there are saplings of Water Oak, White Oak and Southern Red Oak along the trail). Thanks to Gary Crider for suggesting the Blue Trail for its oak saplings!
INTRODUCTION
Bill read two of his favorite quotes about nature and provided some factual prose from Doug Tallamy’s delightful 2021 book, The Nature of Oaks.
- "It is fortunate perhaps, that no matter how
intently one studies the hundred little dramas of the woods and meadows, one
can never learn all the salient facts about any one of them"
-- Aldo Leopold - “It’s the small things that run the world. … The
truth is that we need invertebrates but they don’t need us. If human beings
were to disappear tomorrow, the world would go on with little change. … But if
invertebrates were to disappear, I doubt that the human species would go on for
more than a few months.”
— E O Wilson, 1987
Why focus on oaks when
looking for insects?
As Tallamy puts it, “oaks support more forms of life and more fascinating interactions than any other tree genus in North America.” There are more oak species in North America (91), and in the world, than in any other genus of trees.
- There are far more moth and butterfly species that feed on oaks than feed on any other tree species. “The number of caterpillars hosted by North American native plants varies in anyone location from well over 500 caterpillars species (oaks) to no caterpillars at all.” “Oaks represent less than 2% of our woody plant diversity but support at least 30% of our moth species.”
- There are nearly 800 species of plant-feeding gall wasps in North America, and most of these have specialized relationships only with oaks. And most of these species have two different generations each year, one with both females and males, the other with only females – and both wasps and the galls usually look quite different!
What do birds eat?
“Most songbirds in North America are primarily insectivores, particularly during the all-important nesting season, with seeds and berries, only supplementing their diet. Their nestlings are unable to digest seeds at all; thus, most of our bird species cannot reproduce without a ready supply of insects.”
- Tallamy found that one chickadee family fed their babies 350 to 570 caterpillars every day. That's 6,000 to 9,000 caterpillars to raise one family of baby birds.
Plants have developed numerous strategies to avoid being eaten by herbivorous insects. And herbivorous insects have developed a vast range of strategies to avoid being eaten by birds or parasitized by parasitoids. The goal of today’s walk was to adopt a bird’s-eye and parasitoid’s-antenna’s view of the insects that feed on spring oak leaves – and think about what strategies the insect herbivores might be using to evade birds and other predators.
The notes below are organized by tree species since most of the insects we saw are tree specialists.
Oak
Leaf Rolling Weevils
(Homoeolabus analis). These fascinating little critters feed on several
species of oak. The adult weevils measure and cut with their mandibles strips
of the leaf tip into what looks like a tiny egg roll that hangs from the
midvein. The beetles are careful to leave the midvein intact so it supports the
leaf roll. When done, the adult female inserts an egg, which hatches into a
larva and eats the leaf roll. It is not uncommon to see three or four egg rolls
on a branchlet. How fascinating can you get?
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A little egg roll carefully cut and rolled by mama weevil, and left dangling from the midvein. [HL]
- There’s a good account of the biology with great photos from the Univ of Florida.
- Also check out this time lapse video of a related Asian species.
Oak Treehopper (Platycotis
vittata). Treehoppers are plant sucking insects. Both nymphs and adults are
strikingly beautiful but look different. Tallamy describes the maternal
care behavior of this species, which is highly unusual among nonsocial insects.
The mother stays with her young –- lined up along a twig or branch -- and
protects them for weeks until they reach adulthood. There’s a spring brood and
a fall brood. Tallamy claims that these insects can only thrive when the oak
tree sap is flowing up in the spring or back down in the fall, and that it is
therefore adaptive for the mother to invest in guarding her young rather than
laying more eggs elsewhere.
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RED OAK GROUP
Dryocosmus Gall Wasps. We saw galls of two species of Dryocosmus gall wasps that look entirely different. Both are found on a variety of oaks in the Red Oak Group; we saw them on Water Oak and Southern Red Oak.
Dryocosmus floridensis (no common name) induces a rosette
gall which looks inverted.
Succulent Oak Gall Wasp (Dryocosmus
quercuspalustris)
induces a green ball which contains a free rolling cell inside. The cell
contains a larva which will complete its development inside the rolling cell
before chewing its way out of both the inner cell and the outer gall. Perhaps
the unattached nature of the cell makes it difficult for an insect predator
or parasitoid to grasp and penetrate the structure.
Inverted rosette gall (contains one chamber) [DH]
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| Gall wasp develops inside the free-rolling cell (note emergence hole in cell).[BS] |
Amphibolips
melanocera
(no common name). This gall has a green ball like
the Succulent Oak Gall Wasp above, but the small
chamber in the middle is attached with radiating fibers, making a beautiful mandala-like
structure in cross section.
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| Inner wasp chamber suspended by radiating fibers.[DH] |
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| Multiple tiny wasps develop in separate chambers.[DH] |
SOUTHERN
RED OAK
Fusiform Oak Apple Gall Wasp (Amphibolips
acuminata). This
is a large and striking fleshy gall, pointed and speckled on the outside and
juicy wine-purple on the inside. It forms on just a few Red Oaks; we found it on
Southern Red Oak. Interesting that this gall wasp is in the same genus as Amphibolops
melanocera, but looks so different.
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| This huge gall nourishes a tiny wasp (cell in lower right of bottom photo) [BS] |
Wool
Sower Gall Wasp gall (Callirhytis
seminator). These are the insect
equivalent of charismatic megafauna – beautiful and hard to miss. We saw a White Oak sapling on the Blue Trail with four large balls. We pulled down the
crown of the flexible sapling to take a closer look. The gall is composed of
several dozen capsules, each containing one wasp larva. Each red spot on the
surface corresponds to one capsule. We cut a gall in half to see the layout.
Sometimes you will see a gall that has been torn open. This is actually one of
the few galls large enough for birds and perhaps squirrels to bother attacking.
%20041323SBGRamble_0113.jpg)
%20041323SBGRamble_0128.jpg) |
| A large gall producing many wasps, each in a small kernel near the center. [DH] |
Oak Petiole Gall Wasp (Andricus quercuspetiolicola). This gall is solid with the consistency
of a hard apple. It contains many cells each of which will produce a tiny wasp.
%20041323SBGRamble_0112.jpg)
%20041323SBGRamble_0117.jpg) |
| Kind of like an apple? [DH] |
Phylloxera
galls. Hickories
and oaks are the trees that host the greatest diversity of galls in our area. Hickories
(including pecan and walnut) host galls of phylloxerans (tiny aphid-like
sucking insects), as well as gall midges, which, like gall wasps, induce a mind-boggling diversity of gall structures. We didn’t see gall midge galls today, but we did see
Phylloxera galls on hickories in Compost Row.
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| The fundatrix (upper right) has already given birth to hundreds of young'uns. [DH] |
Phylloxera
complex life history from the Internet: Eggs hatch in spring. Feeding by the newly-hatched
immature fundatrices induces galls on young twigs, on petioles, or at bases of
leaflet main veins, sometimes in clusters. The galls are globular, pale
yellowish green tinted with red before opening, but afterwards becoming
leathery and black. On reaching maturity the fundatrix reproduces
parthenogenetically inside the gall, depositing up to a thousand eggs. The eggs
hatch into nymphs that feed and eventually develop wings. Finally, the galls
split open and the (all female) phylloxera emerge to lay eggs on leaves. These
eggs hatch male and female phylloxera that mature and then mate. Mated females
lay eggs that overwinter.
BOX
ELDER
Box
Elder gall midge
(Contarinia negundinis). This little fly larva feeds in the buds and
makes swollen chambers at the bases of the leaves.
Erineum
Gall Mites.
Some tree species that don’t have beautiful wasp or midge galls
nonetheless sport specialist mites -- trees like Box Elder, Beech and Gum (Nyssa).
The galls all look fairly similar: a wart-like protrusion on the top of the leaf
with a hairy pouch underneath. Don’t expect to see the mites, though, even with
a 10x hand lens. They are sometimes too small to be seen with a dissecting
microscope (45x)!%20041323SBGRamble_0059.jpg)
Swollen petiole base made by gall midge (a true fly) [DH]
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| Mite galls are tree specific but most look similar: warts on top, hairy depression below. [DH] |
Puss Caterpillar/ Southern Flannel Moth cocoon (Megalopyge opercularis). These cocoons are made of extremely tough material. I had trouble cutting one with a razor blade. But when the adult moth is ready to exit the chamber he/she simply opens the circular door on one end (left side in this photo).
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| Kevlar of the insect world... [HL] |
LEAF RAMBLING MEDITATION
Leaf rambling can be a form of meditation. Stand in front of a branch at eye level and just look until things start to appear.
Mornings are usually best for observing insects because
it’s cooler (insects move less) and there’s often less breeze. But you don’t
need live insects. You’ll probably first notice places where leaves have been
eaten, from tiny pin pricks to big chunks. Who ate that and where are they now?
Could the hole have been made when the leaf was just emerging out of the bud
and enlarged as the leaf grew? You’ll notice leaves tied together; is the
caterpillar still there? The longer you look the more you’ll notice smaller and
smaller things. A 10x hand lens is a good investment, as is a dissecting
microscope. When you notice something interesting you may notice more of them
wherever you look. That’s how many predators forage: by developing search
images.
Leaf rambling uncovers
a hundred little dramas. Every part of every plant — leaf, petioles, stem,
flower, fruit, even roots — is a potential food source for the rest of us
living creatures, created out of sunlight and thin air by plants.
RESOURCES
Dough Tallamy, The
Nature of Oaks. (2021)
Gives a good ecological overview of Oaks and presents, month by month,
fascinating accounts of the birds and insects that interact with and oaks.
For gall identification:
Start at the free website Gallformers.org, which was created by avid citizen
scientists and links to iNaturalist. If you post your finds to iNaturalist you
can tag an expert from Gallformers and they will usually get back quickly with
helpful information. WARNING: You must learn tree identification to get good at
gall identification: most gall makers are host plant specific, so the first question on Gallformers is, ‘What is the host
plant species?’ Native
Trees of the Southeast is a good guide.
Plants make galls to
accommodate foreigners: some are friends, most are foes.
Marion O. Harris and Andrea Pitzschke, New Phytologist, 2020. A good overview of all kinds of galls. It’s
surprisingly well written for an academic review paper. https://pubmed.ncbi.nlm.nih.gov/31774564/
