Figure 1

Diagram of crosses and backcrosses between flea beetles. The first Aa males used in the initial backcrosses were the F1 from a cross between one field-collected female from Ejby and a male from the ST-line, in each of the two lines. Expected frequencies of offspring when reared on two different plants (radish, Barbarea vulgaris ssp. arcuata) are given under the assumption that AA and Aa genotypes survive equally well on B.v. ssp. arcuata. The aa genotype is unable to survive on B.v. ssp. arcuata. Aa females (*) used in the analytical crosses originated from the initial backcrosses used for maintenance of the heterozygous lines.