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  • From: "Lawrence F. London, Jr." <lflj@intrex.net>
  • To: permaculture <permaculture@lists.ibiblio.org>
  • Subject: [permaculture] Ecology of bugs and plant "defenses"
  • Date: Wed, 20 Feb 2008 08:40:43 -0500



-------- Original Message --------
Subject: Re: [SANET-MG] Ecology of bugs and plant "defenses"
Date: Wed, 20 Feb 2008 08:03:26 -0500
From: Douglas Woodard <dwoodard@BECON.ORG>
Reply-To: Sustainable Agriculture Network Discussion Group
SANET-MG@LISTS.IFAS.UFL.EDU>,
Douglas Woodard <dwoodard@BECON.ORG>

As a partial reply:

It seems that healthier or thriftier plants with more available surplus
production over what we might call subsistence, are better able to put
energy and materials into strong cell walls which are resistant to
chewing insects and possibly to penetration by sucking insects; and also
into a larger supply of defensive chemicals. A similar effect is seen in
the improved coldhardiness of thriftier plants due to higher soluble
solids and sometimes higher concentrations of chemicals which
specifically produce resistance to freezing.

It is known that fertilization with high levels of nitrogen produces
plant sap containing more free amino acids which sucking insects can
more readily use, while moderate levels of nitrogen favour complete
proteins, presumably more usually non-mobile rather than dissolved in
the sap, and in any case requiring more effort at digestion.

Mammals for understandable reasons prefer healthier organic-grown
plants; perhaps they find them more flavourful as we do.

Doug Woodard
St. Catharines, Ontario, Canada


David wrote:
I wonder if anyone has any information about a question which has been rattling around in my three brain cells recently:

Ecologically speaking, it seems that within the limits of their abilities to sense such things, most creatures will choose the most healthful food/fodder in order to gain the best advantage for their genes (as it were). Predators without substantial numeric advantages choose weak/sick animals, however (presumably because healthy adults are harder to bring down), in spite of the fact that presumably these sick animals do not provide optimum nutrition. (Young animals are also often chosen, but these would probably provide very good nutrition. In this instance, I'm focusing on weak/ill.)

But whereas the reasons for carnivores under most circumstances to choose sub-optimal animals seem fairly clear, what seems less clear is why (speaking generally) bugs would apparently prefer plants with unbalanced mineral nutrition, plants that are already stressed, etc. Whereas a parallel proposition may be made-- i.e. that healthy plants are somehow better able to resist attack by insects-- I am not familiar with research that elucidates the mechanisms that exist only in healthy plants which enables them to protect themselves from such attacks, where those mechanisms do not exist or fail in exactly the same plants when stressed.

In other words, whereas experience tends to validate the proposition that healthy plants are not as often or as successfully attacked, in spite of the presumably superior nutrition that they would provide to insects, I am unfamiliar with the literature which supports this idea in any depth (i.e. beyond simply demonstrating the truth of the proposition). Further, whatever the mechanisms are that plants have developed to avoid such attack, it seems odd that insects do not appear to be able to evolve a response thereto, since it would seem to confer considerable advantage. Finally, if such mechanisms are known, does anyone know if artificial forms thereof have been proposed or are being used to protect plants which are under stress?





  • [permaculture] Ecology of bugs and plant "defenses", Lawrence F. London, Jr., 02/20/2008

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