compound known to attract C. sesamiae in a ‘push–pull’
companion cropping system [11], was elevated by egg
deposition in all the maize varieties that exhibited this
trait. This demonstratesthe potential of exploiting maize
plants possessing this trait in biological control of the
stemborer pests.
There was a kind of reverse progression in which the
indirect defence trait we are concerned with is common in
the landraces screened but rare in the hybrid varieties.
This is even more apparent if the wild ancestors of maize
[13
] are considered; we have recently investigated five
teosinte species and found the indirect defence trait
strongly expressed in four of them (Mutyambai et al.,
in press). We also found the trait previously in signal grass
[29] which is less domesticated than maize. Thus, there is
a steady decline in prevalence of the trait going from wild
ancestors to landraces to higher yielding hybrid varieties
favoured by breeders. It is tempting to speculate that
the conditions under which crops have been artificially