Reciprocal crosses and backcrosses

To analyze the mode of inheritance of the resistance allele(s) in the selected strains CpR5M and CpR5S, reciprocal crosses between these two strains and CpS were performed. Resulting pupae were again separated by sex, and further used in two genetic hybrid crosses (Fig 3); in the female crosses, emerging resistant female moths from either CpR5M or CpR5S were mated with males from the sensitive CpS strain. In the hybrid male crosses, resistant male moths were mass crossed with CpS females. Each cross consisted of eight to ten moths with a ratio of 1:1 males to females. Eggs were collected every second day. Neonate larvae of the first generation (F₁) were divided into three cohorts and subjected to artificial diet containing either (i) CpGV-M, or (ii) CpGV-S, each at a discriminating concentration of 5.8 x 10⁴ OB/ml, or (iii) virus free diet as untreated control. Mortality in all three cohorts was scored after one and seven days. The larvae of the control were further reared to adulthood and used for backcrossing experiments (see below).

For backcrosses, hybrid F₁ male moths were crossed with females of the parental strains, CpR5M or CpR5S, respectively. Each backcross consisted of eight to ten F₁ male moths and an equal number of female moths. The neonate offspring were tested for resistance on CpGV-M or CpGV-S at a discriminating concentration of 5.8 x 10⁴ OB/ml after seven days or were reared on untreated diet as described above. Hybrid crosses and backcrosses were independently repeated three to five times.