Inheritance of Cry1A.105 resistance in fall armyworm (Spodoptera frugiperda)

Resistance evolution in pest populations is a great threat to the sustainable use of transgenic Bt crops. Field resistance due to intensive planting of Bt crops have occurred in at least six cases in the world. The objective of this study is to determine and compare the inheritance of Cry1A.105 resistance in two resistant populations (RR-22 and RR-32) of fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith). Cry1A.105 is a common Bt protein expressed in many Bt corn products for controlling Lepidopteran pests including FAW. Larval mortality of a susceptible strain, RR-22, RR-32, four other populations generated by reciprocal parental crosses and F₁ by F₁ crosses was assayed on Cry1A.105 corn leaf tissue and Cry1A.105 diet. Maternal effect and sex linkage were examined by comparing the mortality between the F₁ populations. Dominance levels of resistance were measured by comparing the mortality of the parental and F₁ populations. Number of genes associated with the resistance was evaluated by fitting the observed mortality of F₂ populations with a Mendelian monogenic inheritance model. The results showed that there might be different genetic bases for the Bt resistance between RR-22 and RR-32 and Cry1A.105 resistance was non-recessive for both resistant strains. In RR-22, the resistance was likely inherited as a single gene, while it might be associated with more than one autosomal gene in RR-32. Information generated from this study will be useful in developing effective resistance management strategies to ensure the long-term success of the Bt crop technology.