The fall armyworm, Spodoptera frugiperda, which destroys many economic crops such as rice and maize, has recently invaded China.  Insect viruses as biological control agents play important roles in killing pests.  One potential viral insecticide is the environmentally highly infective and virulent densovirus.  We successfully rescued Junonia coenia densovirus (JcDV) using its infectious clone in different insect cell lines and larvae of three insect species.  Results showed that the lysate of cultured insect cells transfected by the JcDV infectious clone killed the 2nd instar S. frugiperda.  The LD₅₀ of homogenate from JcDV-infected Spodoptera litura to the 2nd instar S. frugiperda (1.76×10⁸ viral genome copies per larva during 10 d post infection) was higher than that of the 2nd instar S. litura (7.39×10⁷ JcDV genome copies) or Helicoverpa armigera larvae (9.71×10⁷ JcDV genome copies).  The LT₅₀ of the S. litura homogenate (2.60×10⁹ viral genome copies each larva) to the 2nd instar S. frugiperda was 6.96 d, longer than that of the S. litura (6.18 d) or the 2nd instar H. armigera (5.94 d).  JcDV could infect the fat body of H. armigera, but not S. frugiperda or S. litura.  Although JcDV can infect all three lepidopteran species, their susceptibility to the virus differs.  JcDV has great potential as a biological control agent against pests such as S. frugiperda.

 

ATP-binding cassette transporter C2 (ABCC2) is known to be a receptor for Bacillus thuringiensis (Bt) toxins in several lepidopteran insects.  Mutations in the ABCC2 gene have been genetically linked to field-evolved resistance to the Cry1F toxin from Bt in Spodoptera frugiperda.  Here we generated a SfABCC2 knockout strain of S. frugiperda using the CRISPR/Cas9 system to provide further functional evidence of the role of this gene in susceptibility and resistance to Cry1F.  Results from bioassays showed that the SfABCC2 knockout S. frugiperda strain displayed 118-fold resistance to Cry1F compared with the parental DH19 strain, but no resistance to Vip3A toxin from Bt.  These results provide the first reverse genetic evidence for SfABCC2 as a functional receptor for Cry1F.