Cabbage looper resistance to a nucleopolyhedrovirus confers cross-resistance to two granuloviruses

Previously we showed that cabbage loopers(Trichophsia in Hubner) can evolve >20% resistance to the single (S) nucleocapsid nucleopolyhedrovirus (NPV) of Trichoplusia ni (TnSNPV). In this study, we investigate one potential cost that resistant cabbage, loopers may incur, increased susceptibility to other mortality agents. Contrary to expectation no such cost was observed with any of the six mortality agents tested. In fact. the LD50 of selected larvae was always greater than that of control caterpillars for each agent tested. However, the differences were never significant for permethrin or Bacillus thuringiensis subsp kurstaki (Berliner). The differences in the LD50 of control and selected T. ni for the wild-type multiple (M) nucleocapsid NPV of Autographa californica Speyer (AcMNPV), clone C6) and the recombinant AcMNPV (AcMNPV-AaIT) were small (approximate to2X) and significant in only one of three denerations. Surprisingly, the highest level of cross-resistance was to the granuloviruses fo Pieris rapae L. (4-5X; significant in two of three generations) and T. ni (20-30X; significant fit three of three generations). This suggests that the infection pathway of TnSNPV may be more similar to TnGV than to that of AcMNPV.