Dual Cry2Ab and Vip3A resistant strains of Helicoverpa armigera and Helicoverpa punctigera (Lepidoptera: Noctuidae); testing linkage between loci and monitoring of allele frequencies.

Considerable attention has been given to delaying the evolution of insect resistance to toxins produced by transgenic crops. The major pests of cotton in Australia are the Lepidoptera Helicoverpa armigera (Hubner, 1805) and Helicoverpa punctigera (Wallengren), and the toxins deployed in current and imminent transgenic cotton varieties are Cry1Ac, Cry2Ab and Vip3A from Bacillus thuringiensis. In this study, lines that carry alleles conferring resistance to Cry2Ab and Vip3A were isolated using F2 tests. Extensive work on the Cry2Ab resistant lines, and preliminary work on the Vip3A resistant lines, suggested a single common resistance to each toxin in both species thereby justifying the use of more efficient F1 tests as the primary means for monitoring changes over time. A potential further efficiency could be gained by developing a single resistant line that carries both types of Bt resistance. Herein we report on work with both H. armigera and H. punctigera that tests whether dual Cry2Ab-Vip3A resistant lines can be developed and, if so, whether they can be used to effectively monitor resistance frequencies. Furthermore, the creation of dual resistant lines allowed linkage between the Cry2Ab and Vip3A resistances to be investigated for H. punctigera. We show that dual resistant lines can be used to increase the efficiency of the F1 screen for recessive alleles, and that in H. punctigera there is no linkage between Cry2Ab and Vip3A resistance.

Frequency of familial colorectal cancer.

Familial clustering of cancer is not uncommon. The frequency of familial colorectal cancer was estimated by taking family histories from 100 patients presenting with apparently sporadic colorectal cancer. Compared with controls, the relative risk of a positive family history for colorectal cancer was 4.6. Life-table methods were used to examine the observed to expected mortality from colorectal cancer. Overall there was a fourfold increase in mortality rate (P less than 0.0001), which was greatest in female relatives of patients with colonic cancer (P less than 0.001). Three families with dominant inheritance of colorectal cancer and one family with Lynch type II syndrome were identified. Nine per cent of patients had siblings who had developed colorectal cancer a median of 4 years before the diagnosis of the index patient (range 1-17 years). It is recommended that a careful family history should be obtained from all patients with colorectal cancer. Where a positive history is obtained a geneticist may determine empirical risks for the development of colorectal cancer and the appropriate method of surveillance may be selected.