HIPV-mediated indirect defences following larval feeding
are well known in maize (e.g. [13,24,25]). HIPV
emission after oviposition of the stemborer C. partellus
was recently discovered in certain maize landraces [26,27]
but not in the commercial hybrids we examined initially.
In the last two years, we screened for egg induced HIPV
emission in a much wider range of maize germplasm
(25 landraces, 30 hybrids and 22 inbred lines;Figure 1). This was to determine whether HIPV emission
after stemborer oviposition could be found in improved,
higher yielding maize varieties and to enable ongoing
genome wide association studies (GWAS) [28] mapping
single nucleotide polymorphisms (SNPs) linked to the
egg induced indirect defence trait. We collected headspace
samples of volatiles from plants with and without C.partellus eggs, analysing the volatiles by gas chromatogra-
phy and exposed the parasitoid C. sesamiae to the volatiles
in an olfactometer bioassay (Methods as in [26]). Plants
were grown under insect free conditions; treated plants
were caged overnight with five gravid naı¨ve female
stemborer moths and volatiles were then collected for
48 h. Egg hatch occurs five days after oviposition which
meaning that the plants were only exposed to eggs and
not to larvae.