explosion of Web-worms

[Frederick W. Schueler]

Everyone,

Back in 2021 -
https://ngtimes.ca/does-mowing-down-the-golden-parsnips-sustain-them/ -
I wrote - "Deliberately introduced biological control agents, like the
tiny Galerucella beetles that have done a good job on Purple
Loosestrife, often bring an introduced weed under control, but the
Parsnip Webworm has been overlooked as a biocontrol agent, because it
was already here. The the control the webworms could provide isn’t
mentioned in the various Parsnip control efforts. The webworms have only
one generation per year, and pupate in the stem of the plant, so control
by mowing, with or without previous herbiciding, results in new leaves
and flowers sprouting from the cut stems, producing a second, smaller
but adequate, crop of seeds, while the webworms are killed off... it
would be more interesting to leave a stand of Parsnips alone, leave the
stems standing through the winters, see how much of a webworm population
builds up, and to what extent it diminishes the Parsnips in subsequent
years."

Since then we have been leaving Parsnips alone around our houses, and
this year checking on consequences of last year's drought. It seems that
the drought didn't inconvenience the Web-worms, because just as the
flowers began to open almost every plant had at least one of its umbels
webbed. We won't be able to estimate the percentage damage for a few
weeks yet, but it is good to see that even with the drought our
leave-them-standing management has promoted a generous population of the
Web-worms (I've tried to take photos, but the stems are so sketchy
against the backgrounds that they're not much use, but there are Aleta's
photos of emerged Web-worm caterpillars in the article).

fred.
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---------Frederick W. Schueler & Aleta Karstad ------------
Fragile Inheritance Natural History - https://fragileinheritance.ca/
6 St-Lawrence Street Bishops Mills, RR#2 Oxford Station, Ontario K0G 1T0
on the Smiths Falls Limestone Plain 44.87156° N 75.70095° W
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[Frederick W. Schueler]

Everyone,

Since this message, the size and number of the Web-worms' webs have
increased through the Parsnips around our houses, and many plants have
almost no remaining flowers or seeds. The big 2m plant outside the front
door here has had most of its minor umbels webbed, and today there are
lumpy webs moving in on the big umbels of green seeds in the centre of
the plant.

I also saw a fair amount of Web-worm activity at Doug & Irene Scott's
place in a small stand of Parsnip at the edge of their lawn, but in
driving the 416 and around Grenville County and Ottawa, all the roadside
Parsnip umbels are flat and yellow, with no evident Web-worm activity,
so it again seems that mowing down the roadside Parsnips has sustained them.

It's possible to get blistered from the foam of Spittlebugs
(Cercopoidea) on Parsnips, but these may be one of the taxa knocked back
by last summer's drought, because I haven't seen any on Parsnips of any
host plants.

fred.
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