| dc.description.abstract | One of the major constraints to maize production in East Africa is attack by lepidopteran stem
borers, including Chilo partellus and Sesamia calamistis. Stem borer control by conventional
methods has had variable success. The use of transgenic (Bt) maize is being attempted as a
novel stem borer control option but the biosafety issues surrounding its use need to be
addressed. Studies were conducted at the Kenya Agricultural Research Institute (KARl),
Biotechnology Centre, to investigate the effects ofBt maize (Event 216) on these two important
stem borers in East Africa, their oviposition preference and development as well as the impact
of this GM maize on host finding by and biology of selected stem borer parasitoids (Cotesia
jlavipes, Cotesia sesamiae and Xanthopimpla stemmator). The isogenic non-Bt maize (CML
216) was used as a control in all the experiments. The oviposition preference experiments,
exposing stem borer pupae or moths to Bt and non-Bt maize under both choice (only one plant
line) and non-choice (Bt + non-Bt plants) situations, indicated no significant effects on
oviposition behaviour, moth fertility or fecundity. Different stem borer instars were also
exposed to Bt maize for 5 days. Earlier instars were more susceptible to Bt maize than later
ones. The effect of transient exposure to Bt maize on stem borer development was studied by
. rearing third, fourth and fifth larval instars on Bt maize stems for 24h; before and after this
exposure, they were reared on non-Bt maize. Bt maize prolonged stem borer development time
at the instar during which exposure took place but had no significant effect on subsequent
developmental stages. The effects of C. partellus and S. calamistis partially exposed to Bt
maize on host finding by C. flavipes, C. sesamiae and X stemmator was determined by
exposing female parasitoids to Bt vs. non Bt infested and uninfested plants in a Y-tube
olfactometer and information obtained in the choices made. Bt maize had no significant effect
in host finding behaviour of C. flavipes and C. sesamiae but was deterrent to X stemmator.
Effects of stem borer hosts partially fed on Bt maize on development of C.jlavipes, C. sesamiae
and X stemmator was evaluated by obtaining information on parasitoid life table parameters
and fluctuating asymmetry. The response to the Bt maize varied between host and parasitoid
species. The results alongside previous studies indicate that the existing database on parasitoid
exposure to Bt-intoxicated hosts was insufficient to predict the reaction of these important
parasitoids to two African stem borers. This underlines the importance of enhancing the
empirical database. The generally used "test species approach" that is taken over from pesticide
testing regimes, is only a first, imperfect step, to be followed by selecting locally or regionally
important natural enemy species for biosafety tests. These should also be combined with at least
semi-field studies before we can form a reasonable prediction about possible consequences of a
profound technological innovation such as growing transgenic crops in African countries. | en |
