Insects
A Bt susceptible strain of H. armigera (GR), originally obtained
from CSIRO Entomology was used as the susceptible strain for
these studies. This strain has been in culture in CSIRO’s Canberra
laboratory since the mid 1980s.
The resistant strain (BF) was established in the following manner.
H. armigera were collected in January 2006, as eggs, from both
Bollgard II and conventional cotton at Breeza, NSW (an area where
there had been considerable survival of H. armigera on Bollgard II
cotton in the 2005/2006 cotton growing season). The strain was
maintained on a diet which uses heat-denatured soybean flour,
in the laboratory for 12 months without selection and was then selected
once on Bollgard II cotton (Sicot 289b), expressing both
Cry2Ab and Cry1Ac. Neonate, first instar larvae were sealed into
vented, air tight, polystyrene 5 cm diameter petri dishes (Falcon)
(4 larvae per petri dish), and allowed to feed on the cotton leaf
discs (5 cm diameter) for 3 days (25 C). Surviving larvae were
transferred to artificial diet. Mortality continued to occur up to
10 days after exposure to Bt cotton. In all, there was approximately
90% larval mortality. Survivors were reared to form the ‘BF’ strain,
which was maintained in the laboratory without further selection