Phytoecdysteroids and Related Sterols Isolated from Mexican Cacti: their Potential Use as Natural Insecticides - Natural Antioxidants and Biocides from Wild Medicinal Plants - page 167

11 Phytoecdysteroids and Related
Sterols Isolated from Mexican Cacti:
their Potential Use as Natural Insecticides

Juan R. Salazar 1 * and Carlos L. Céspedes 2
1 Facultad de Ciencias Químicas, Universidad La Salle, Hipódromo Condesa,
México; 2 Departamento de Ciencias Básicas, Universidad del Bío-Bío, Chillán, Chile

11.1 Introduction

The nature of the relationship between
phytophagous insects and the plants they eat
has been studied extensively but, even today,
many questions still remain unanswered.
Some points that remain are: (i) knowledge of
the quantity and nature of the sterols present
in plants; (ii) the exact mechanisms through
which the insects use such mixtures of ster-
ols in their diets; and (iii) the possible uses of
sterols in the context of plant-insect relation-
ships and as pharmaceuticals, and so on.
In this chapter we review some aspects
of the chemistry of ecdysteroids, relating it
to the chemistry of the sterols present in the
family Cactaceae.

The chemistry and structural diversity of
sterols is very rich. Because sterols have
been recognized in several biochemical reac-
tions, research in the field is still growing.
In recent years several novel structures and
biological activities have been published,
and new functions are now being recognized
for those 'old molecules' sometimes even
ignored in the past.
Sterols are present in fungi, plants and
animals. Campesterol and sitosterol are the
major end-products of the sterol pathway in
higher plants (Schaller, 2003). Most insects
require sterols in their diets; cholesterol is the
major sterol found in insects. It serves as a
structural component of cell membranes and
as the precursor of the insect moulting hor-
mones, ecdysteroids. Cholesterol has been
shown to support normal development in
most insects and it will satisfy the dietary
need for sterol in most insects (Canavoso
et al ., 2001). Although most plant material
contains little or no cholesterol, most phy-
tophagous insects are capable of obtaining
adequate cholesterol by converting C 28 and
C 29 phytosterols to cholesterol via dealkyla-
tion of the C-24 alkyl group (Svodova, 1999).

11.2 Ecdysteroids: a Family

of Peculiar Sterols

Ecdysteroids are a group of polyhydroxy-
lated steroids that act as hormones in all
arthropods, studied primarily in insects.
These steroids are present at all stages of
insect development, regulating many bio-
chemical and physiological processes such
as embryonic and post-embryonic develop-
ments, moulting and metamorphosis, repro-
duction and diapause (Dinan, 2001).

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