Apple cultivar effects on codling moth (Lepidoptera : Tortricidae) egg mortality following fumigation with methyl bromide

Fumigation experiments with methyl bromide (MeBr) were carried out in New Z ealand over several seasons. In 1988-1989 'Draeburn', 'Fuji', 'Granny Smith ', 'Red Delicious', 'Royal Gala', 'Gala' and 'Splendour' apples were infest ed with freshly laid eggs of codling moth, Cydia pomonella (L), and were fu migated at a range of methyl bromide doses. The concentration-time ct(sum), which estimates the average methyl bromide concentration over the 120 min of fumigation, was used as the measure of exposure. The complementary log-l og of mortality induced by treatment Varied linearly with the ct(sum), with the same equation for all apple cultivars. This relationship allowed accur ate prediction of a 99% lethal value (LC99) for the ct(sum), that was again , the same for all cultivars. Subsequent experiments in 1998-1989 with 'Red Delicious', 'Fuji' and 'Pacific Rose' apples' were conducted in the absenc e of codling moth eggs with the aim of examining the regression of ct(sum), on dose. There were different lines for different cultivars, and different intercepts for different years. The ct(sum) estimates, at an injected dose of 24 g m(-3) could not: however, be distinguished between cultivars. The estimate of ct(sum) for 'Pacific Rose' at 24 g m(-3) cannot be distinguishe d from the ct(sum) estimates for cultivars currently approved for export to Japan. The approved treatment for New Zealand apples exported to Japan inc ludes an injected methyl bromide dose of 24 g m(-3). For acceptance of this treatment for a new variety, it is sufficient to demonstrate that the ct(s um) is maintained at levels which lie within or above the range found for e xisting approved varieties. (C) 2001 Elsevier Science B.V. All rights reser ved.