CSIRO Entomology, GPO Box 1700, Canberra, ACT 2601, Australia.
J Econ Entomol. 2010 Apr;103(2):472-81. doi: 10.1603/ec09225.
F2 and F1 tests to detect resistance to Cry2Ab in Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) were performed during the 2007-2008 summer. F2 tests indicated a resistance frequency of 0.006, which is similar to the published resistance frequencies for this species during the summers spanning 2002-2006. In contrast F1 tests indicated a resistance frequency of 0.033. Thus, F1 tests isolated Cry2Ab resistance alleles almost six-fold more frequently than the F2 method. A discrepancy might be expected if the F2 tests detected resistance conferred by more than one locus because F1 tests identify only the form of resistance present in the tester resistant colony. However, if so, F2 tests would detect more, not fewer, cases of resistance. In addition, complementation tests on 10 separate isolates indicate that there is only one common form of resistance. We hypothesized that some "resistance alleles" are homozygous lethal if autozygous (as generated in F2 tests) but not as allozygous homozygotes (as generated in F2 tests). The hypothesis was extended to accommodate the possibility that alleles at linked loci may be homozygous lethal. Neither of two tests of the hypothesis provided evidence that any alleles that confer resistance are associated with severe fitness costs. Thus we are presently unable to explain the basis of the difference in frequencies between the methods. Because of the simplicity of the F1 tests, it is difficult to imagine that it overestimates the frequency of resistance and we therefore accept that this test should provide a more robust method to estimate the frequency of Cry2Ab resistance in H. armigera.
2007-2008 夏季期间，对棉铃虫（鳞翅目：夜蛾科）Cry2Ab 抗性进行了 F2 和 F1 测试。F2 测试表明抗性频率为 0.006，与 2002-2006 年夏季公布的该物种抗性频率相似。相比之下，F1 测试表明抗性频率为 0.033。因此，F1 测试分离 Cry2Ab 抗性等位基因的频率几乎是 F2 方法的六倍。如果 F2 测试检测到由多个基因座赋予的抗性，可能会出现差异，因为 F1 测试仅识别在测试抗性品系中存在的抗性形式。然而，如果是这样，F2 测试将检测到更多而不是更少的抗性病例。此外，对 10 个单独分离株的互补测试表明，只有一种常见的抗性形式。我们假设，如果是纯合的（如在 F2 测试中产生的），则某些“抗性等位基因”是纯合致死的，但不是杂合纯合子（如在 F2 测试中产生的）。该假设被扩展到可能的情况，即连锁基因座上的等位基因可能是纯合致死的。该假设的两个测试均未提供证据表明任何赋予抗性的等位基因与严重的适合度成本相关。因此，我们目前无法解释两种方法之间频率差异的基础。由于 F1 测试的简单性，很难想象它会高估抗性的频率，因此我们接受该测试应该提供一种更可靠的方法来估计 Cry2Ab 抗性在棉铃虫中的频率。
