Location: Southern Insect Management ResearchTitle: Effect of two Bacillus thuringiensis proteins on the development of the fall armyworm after a seven-day exposure
Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/28/2020
Publication Date: 6/23/2020
Citation: Portilla, M., Blanco, C.A., Arias De Ares, R.S., Zhu, Y. 2020. Effect of two Bacillus thuringiensis proteins on the development of the fall armyworm after a seven-day exposure. Southwestern Entomologist. https://doi.org/10.3958/059.045.0208.
Interpretive Summary: The present study is the first attempt that studied the resistance of S frugiperda to Cry1Ac and Cry1Fa by bioassay of the insect throughout their life cycle. The trade-off between Bt resistance and fitness was caused by severe growth disruption after the fifth instar as well as low population growth rates in the survival adults. This demonstrated that resistance of S. frugiperda is incompletely recessive to both Cry1Ac and Cry1Fa toxins. Autosomal inheritance of resistance is questionable, but resistance inheritance from the mother may occur. Our findings illustrated that if S. frugiperda responded to the Bt toxins in the field as it did in the laboratory, the mating of resistant insects and susceptible insects will produce susceptible offspring, easily controlled by GE crops. When the fall armyworm acquires resistance to B. thuringiensis, these insects are not as ‘fit’ as their susceptible counterparts, are less competitive in the environment, would produce less progeny, or may be totally eliminated.
Technical Abstract: The fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuide) is one of the most economically important pests of maize, Zea mays L. and it has become resistant to a number of different insecticides. The susceptibility of Cry1Ac and Cry1Fa of three suspected resistant populations native to Puerto Rico, along with their crosses with a susceptible colony was evaluated. Variation in LC50 values was found in all three populations and in their backcrosses with the susceptible colony. Highest mortality was observed when insects reached sixth instar, and all treatments produced high mortality in the pupa and adult stages. A linear trend was similar for all treatments and showed a correlation between the resistance ratio and the stage of insect development. The three colonies had higher tolerance to both Cry toxins in their earlier instars of development than did their crosses.Crosses between a resistant female and a susceptible male produced offspring with significantly higher net reproductive rates, intrinsic and finite rates of increase, mean generation time and doubling time as compared with the colonies. Our data confirmed the existence of resistance to Cry1Fa and Cry1Ac in S. frugiperda from Puerto Rico, however, the high tolerance to Bt toxins did not persist to the adult stage.