There were no consistent morphological and biochemical characters available as genetic markers to distinguish the three biotypes of the BPH (biotypes 1, 2 and 3) at the IRRI, except for the significant variations in the sucking response to various amino acid-sucrose solutions. Biotypes 2 and 3 appeared to have a wider acceptability to those artificial dietary substrates.
Biotypes were found to differ significantly in their host preference and feeding responses as well as nymphal development and fecundity on the resistant varieties. In particular, the average amount of honeydew excreted on resistant varieties differed among biotypes despite a wide range of individual variations. The different ability of biotypes to suck the resistant varieties was considered to be a crucial factor responsible for their different performance on the resistant varieties. Different reproductive potentials were also found among them not only on resistant varieties but also on susceptible ones. A reproductive disadvantage was loaded by biotype 3.
Hybridization experiments showed that physiological characters of biotypes 2 and 3 were inherited in a recessive or intermediate manner when these were crossed with biotype 1, indicating that the host resistance-breaking biotypes 2 and 3 were not stable in the conditions which allow the coexistence of biotype 1. It could not be clearly demonstrated whether the indefinite segregations in the F₂ and back cross progenies were due to the polygenic nature of the traits examined or to the genetic heterogeneity of the biotype populations used.