Response to purified Cry IB protein in lab-wild type crosses of lightbrown apple moth.

A survey for genetic variability in response of Epiphyas postvittana to a purified Bacillus thuringiensisδ-endotoxin (Cry IB) was conducted in order to assess the risk of development of resistance, prior to the deployment of transgenic apple trees. Tethered laboratory colony female moths were mated to feral males at sites in the North Island in 1993 and 1994. The progeny of iso-female lines were tested for response to two concentrations, or to a range of concentrations of purified toxin. The LC50s varied by a factor of 4.3 fold in six iso-female lines from the 1993 collection. The lines were significantly more susceptible to Cry IB toxin than 14 iso-female lines originating from the second collection (7.2 fold range in LC50). The range in LC50s of 20 field populations was 14 fold. This level of variation is similar to that reported for other species.