Resistance to Bacillus thuringiensis Cry1Ac toxin in three strains of Heliothis virescens: Proteolytic and SEM study of the larval midgut

In a previous study, We demonstrated that resistance to Bacillus thuringien sis toxins in Heliothis virescens might be related to differences in the co mposition of the proteolytic extracts from insect midgut. There, we found s pecific proteolytic bands present in the gut extracts of the resistant stra in and absent from the susceptible one. sere we report related facts using a new resistant strain (KCB) and a cross between the two strains used in ou r previous study, As would be expected, no quantitative differences in tota l proteolytic activity were found between the strains, although qualitative differences related to the presence or absence of specific proteolytic act ivity bands using SDS-PAGE could be responsible for the observed resistance phenomenon. Moreover, an SEM study made at different time intervals after intoxication shows that in the initial hours following intoxication, both t he susceptible and the resistant strains show significant damage to the mid gut epithelium. In the interval between 3 and 48 h, however, the resistant strain recovered such that by 48 h it had fully recovered whereas the susce ptible strain did not. (C) 1999 Wiley-Liss, Inc.