Costs and stability of cabbage looper resistance to a nucleopolyhedrovirus

The goal of this study was to examine the possible costs and the stability of the resistance of cabbage loopers (Trichoplusia ni) to the single (S) nucleocapsid nucleopolyhedrovirus of T. ni (TnSNPV). Resistance to the virus did not appear to incur any measurable fitness costs under laboratory conditions. When reared in the absence of the virus, there was no difference in the number of eggs produced or egg hatch of control and selected individuals. There even was a tendency for selected cabbage loopers to develop faster and to produce heavier pupae. The difference in the pupal weight and developmental time of control and selected T. ni did not covary with the number of generations of selection. Furthermore, the offspring of hybrid crosses (control × selected moths) were as fit as those of pure pairings (control × control or selected × selected adults). Finally, the resistance of cabbage loopers to TnSNPV did not decline when exposure to the virus ceased for nine generations.