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Re: Aquatic Plants Digest V4 #706

Dwight wrote:
>  Thus, whenever a leaf broke
>  the surface....aphids!
>  I have a terrarium for emersed growth Ludwigia acuata, grandelosia and a
>  few others... no aphids.  Yet the terrarium is side - by - side w/ an
>  opened top tank who's emersed growth got hit w/ aphids.  The terrarium is
>  opened to the air w/ a 1/4" crack that allows any aphid to enter.   It
>  seemed so obvious that high leavels of Co2 gas in the terrarium kills all
>  the aphids!  Talk about a natural insecticide!  

    I reply:
     Perhaps this "obvious" reason for a lack of aphids is correct, but has 
this hypothesis been tested?  If someone had asked me what the obvious anti- 
aphid agent in the example was, I would have guessed "higher humidity," or 
perhaps "airborne aphids are few and far between and 96% tank coverage 
typically excludes enough to prevent formation of a population."
    A very preliminary test of your hypothesis would be to add aphids to the 
terrarium onto a plant of identical species and see how they do. 
    Pierre Gagne
    Kensington, MD