Many studies are under way in order to identify
new insecticidal products. One strategy is to
screen new sources for potential insecticidal
proteins in a random fashion. Sources for screening
include plant samples, particulary tropical
plants with well-known insecticidal properties,
and bacteria at different physiological stages. Results
in this latter field of research are particularly
interesting. During their vegetative growth, some
Bacillus species become the source of insecticidal
activities: B. thuringiensis produces a protein,
Vip3A, active against lepidopteran insects such as
the black cutworn (Agrotis ipsilon), a corn pest
[60]. Streptomyces cultures secrete a cholesterol
oxydase active against the boll weevil (Anthonomus
grandis) [61,62]. These proteins are
highly toxic (within the same range as B.
thuringiensis toxins) and could be new interesting
sources for engineering resistance. Because of the
bacterial origin of these genes, synthetic genes
may have to be constructed to reach high enough
levels of expression, as it is the case for B.
thuringiensis genes.