Virginia Berg Virginia.Berg at uni.edu
Mon Feb 14 12:10:54 EST 2000

As amazing at it seems, I am not currently interested in getting rid of the
whiteflies on my small greenhouse-grown bean plants.  They have become much
more interesting as a result of a chance observation, and I was wondering if
others had seen (consciously or unconsciously) the same phenomenon.

While installing a sticky yellow card (whose surface roaming whiteflies
prefer to leaves--a one-way trip to whitefly heaven), I had great difficulty
persuading the flies to, well, fly, and make a choice of substrates. The
flies could be persuaded to leave their feeding sites only be pretty
vigorous (keeping the scale in mind) physical perturbation. The beans were
well watered.

Then the weekend presented many activities that made me forget to water the
beans, which had wilting leaves by Monday morning..  The whiteflies were
exceedingly easy to perturb:  When I brushed the leaves, the area around
plants looked like a blizzard. When I think about it, it seems that the
whitefly storms in our greenhouses were mostly common on hot days. Obviously
the phloem wouldn't be so attractive when stomata are closed and pressures
down.  I had always ascribed the invasion to increased temperature for
faster fly development, but I wonder if this is a major dispersal-promoter.
There are obvious issues here for control (or loss thereof).  A vacuum or
even exhaust fans present control possibilities, and dispersal would be a
lot greater during drought. Have you seen this? [My n=1 at this point.] Any

And after I check a couple of more wet/dry cycles, my interest in the
whiteflies will no doubt diminish.

--Gini Berg

Truth comes out of error more readily than out of confusion.  
-- Francis Bacon (1561-1626)

Virginia Berg  (bergv at uni.edu)
Biology Department 0421
University of Northern Iowa
Cedar Falls, IA 50614
(319) 273-2770 (phone), 273-2893 (fax)


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