Bugs only bug unhealthy plants? (fwd)

Allyn Weaks allyn at u.washington.edu
Sat Aug 9 16:03:11 EST 1997

In article <taguebw-0908970909490001 at taguebw.winston.wfu.edu>,
taguebw at wfu.edu wrote:

> In article <allyn-ya02408000R0808971643200001 at news.u.washington.edu>,
> allyn at u.washington.edu (Allyn Weaks) wrote:
> [SNIP]
> In this interesting thread, this was mentioned:
> periodical cicadas (with periods that are prime
> > numbers, which makes it harder for the predators to synchronise :-)). 
> Is this really true -- are the cycles usually prime numbers and does this
> make it harder for predators? Or is that emoticon pulling my leg?

Well, I read it somewhere.  But since I don't remember where, that doesn't
help much!  I just checked in Borror & White (the Peterson field guide to
insects) and they don't specifically say anything about prime numbers, but
they do say that periodical cicadas (Magicicada) come in 13 and 17 year
varieties with three species each, and most emerging broods contain two or
three species.  Other cicadas do have periods of 2-5 years depending on
species, but even within a spcies, the cycles overlap; some are present
every year so it isn't an impressive event when they show up.

13 and 17 seem pretty big numbers for an insect life cycle. They're well
out of the range of the smaller periods of 2-5 years and not a multiple of
them, so they should be independent of any regular boom/bust cycles of the
predators on those other cicadas.  If the long periodical cycles were 12,
14, 15, or 18 years, it does seem that they would be more likely to match
boom/bust cycles of one or another of the regular cicadas, which might
encourage a specific predator just for them.  All of which isn't proof of
anything, of course...

The emoticon was intended more as 'isn't biology fun, and see, there's a
use for those useless math things they made us learn in school'.
Allyn Weaks  allyn at u.washington.edu
PNW Native Wildlife Gardening:  http://chemwww.chem.washington.edu/natives/
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