Costs and stability of cabbage looper resistance to a nucleopolyhedrovirus

Genetic variation in fitness parameters associated with resistance to Bacillus thuringiensis in male and female Trichoplusia ni

“…The heritability for female pupal weight was also low and non-significant. This result is consistent with the expectation that characters closely associated to fitness have the lowest heritabilities (Falconer and MacKay, 1996), considering that in T. ni, female pupal weight is proportional to fecundity (Milks et al, 2002). However given the rapid loss in resistance observed in the original unselected line (Janmaat and Myers, 2003) and continual losses of resistance in the absence of selection, we had expected to find a positive correlation between Bt susceptibility and fecundity.…”

Sex linkage of CpGV resistance in a heterogeneous field strain of the codling moth Cydia pomonella (L.)

“…However resistance decreased in both strains when they were released from selection pressure indicating that there are fitness costs related to resistance (Fuxa and Richter, 1998). Similar to the case of a cabbage looper strain resistant to Trichoplusia ni single nucleopolyhedrovirus (TnSNPV) described by Milks et al (2002), there were no fitness costs for resistance that would have selected for susceptible insects in CpR, at least under laboratory conditions. There is thus an urgent need to determine whether the CpGV resistance allele of codling moth suffers a fitness cost in the field in the absence of virus selection pressure.…”

High stability and no fitness costs of the resistance of codling moth to Cydia pomonella granulovirus (CpGV-M)

“…Though this could be a potential disadvantage for the fitness due to the linear correlation between pupal weight and number of eggs (Zwölfer, 1933), the fecundity was not affected. Milks et al (2002) found, that resistance of laboratory selected cabbage looper T. ni to Trichoplusia ni single nucleopolyhedrovirus (TnSNPV) did not decline when exposure to the virus was stopped for nine generations. Similarly to our findings, the resistance to TnSNPV did also not incur any measurable fitness costs under laboratory conditions.…”