Inheritance And Fitness Costs Of Resistance To Transgenic Bt Maize Expressing Cry1Ab Toxin In Ostrinia Furnacalis (Lepidoptera: Crambidae)

Asian corn borer, Ostrinia furnacalis (Guenee), (ACB), is the primary insect pest targeted by transgenic Bt corn in China. Bt corn can provide season long protection from this insect, but its success will be short-lived if ACB adapt to Bt corn. The effective implementation of insect resistance strategy depends on well research on the biology of resistant colony and inheritance of resistance, which can provide a powerful tool for facilitating progress in understanding, monitoring, and managing resistance to Bt crops.Inheritance of resistance in the field and the fitness cost of a laboratory-selected CrylAb resistant population of ACB to transgenic Bt corn event MON810 and Btll, the resistant gene dominant level, maternal effect, the cross resistance of to CrylAh and Cry l Ie, and molecular cloning of APN gene , comparison of the flight capability and field calling males by females effect between the Cry1Ab resistant and susceptible ACB, mating attractiveness between resistant and susceptible populations were investigated . The main results are as follows:The genetic inheritance of resistance to Bt corn was examined in ACB CrylAb resistant colony, progeny of Fl reciprocal crosses and backcross between F1 larvae and resistant population were assayed at different tissue of Bt corn, Including the silks in the field and whorl leaf in the laboratory.The genetic inheritance of resistance in the whorl-stage of Bt corn event Btl 1 was also examined in Cry1 Ab resistant colony, also including RS, SR, BC1, BC2, BC3 and BC4 colonies in the laboratory. After 14 d infestation, the survival rate in the whorl leaf of Bt corn was 1.3%, 15.7%, 8%, 8.5%, 6.5%, 10%, 31.5% and 2.5%, separately. The Dlc values of RS and SR colony was 0.47 and 0.50, respectively. The resistance to the whorl leaf of Bt corn, the laboratory colony of ACB resistant to Cry1Ab, was determined as an incompletely dominant inheritance.The neonates (less than 24 h) from different colonies of ACB (RR, SS, RS, SR, BC1 and BC2 colonies) were infested in the silk of MON810 in field. The results show that: the survival rate in the silk of Bt corn event MON810 expressing CrylAb toxin was 38.3%, 21.0%, 28.6%, 37.9% and 29.5% respectively. The Dominant level of RS and SR colony was 0.55 and 0.75. It demonstrates that the resistance to the silk of Bt corn in the field, the laboratory colony of ACB resistant to CrylAb, was determined as an incompletely dominant inheritance. These results show that the ACB CrylAb resistant colony can establish reproducing populations in the tested silk of MON 810. The expression of CrylAb protein in the silk of event MON810 was 4.18μg /g (fresh weight) according to enzyme-linked immunosorbent assays.Cross resistance of CrylAb resistant colony was evaluated by determining the susceptibility to Crylle and CrylAh, respectively. Based on LC₅₀, CrylAb resistant colony evolved 16.87 fold resistant to CrylAb protein, 176.4 fold to CrylAh protein, but 0.42 fold to Crylle protein. This indicates that there is a high cross resistance between CrylAb and CrylAh, but no cross resistance between Cry1Ab and Crylle in ACB.Three sequence of cDNA of aminopeptidase N from the fourth instars larvae midgut of ACB susceptible and resistant to CrylAb are cloned and sequenced. Sequence 1 from susceptible colony, have 587 nucleotides, and sequence 2 and 3 from resistant colony, have 587 and 566 nucleotides. All the three deduced proteins share the consensus zine binding /gluzincin motif HEXXH and GAMEN sequence common to gluzincin aminopeptidases. It was considered that sequence 1 and 2 are belonging to APN3, and sequence 3 is belonging to APN1 by blast in Genebank. The sequence 2 from resistant colony has 2 amino acid changes in consensus zine: Leu-*Ile, Ala-"Val.The survival rate, average pupal weight, sexual ratio, and the number of eggs per female of susceptible colony were significantly higher than that of resistant colony, respectively. The larval developmental time of resistant colony was significantly longer 4 d than susceptible. There was no significantly difference in longevity of the adults between resistant and susceptible colonies. The capacity of female moth calling effect from CrylAb resistant colony is lower significantly than that of susceptible colony. No significantly difference was observed in flight capacity between the resistant and susceptible colony. Among four type of mating combinations (RRxSS/RR, SS*SS/RR, SS/RRxSS, SS/RRxRR), no significantly difference was observed between the inter-population and intro-population mating and the capacity of reproducing.The studies for inheritance mode and fitness of resistant to Bt in ACB, can provide strategies for pest control and transgenic Bt corn management.