A depression in BPH feeding, as measured by honeydew
production, has been observed when the protein is fed in
artificial diet (Powell et al., 1995a), and a similar result on
GNA1 transgenic plants was indicated in these bioassays
(Figure 6c). Studies of BPH feeding patterns by the electrical
penetration graph method (unpublished results) have
shown that GNA strongly inhibits active ingestion of diet
in vitro, but does not deter the insect from probing behaviour.
If this is duplicated in vivo, transgenic rice may still
be vulnerable to viral transmission by probing activity.