Survival and development of <i>Spodoptera frugiperda</i> (Lepidoptera: Noctuidae) strains in different hosts: implication for resistance management

The fall armyworm Spodoptera frugiperda (J. E. Smith, 1797) has evolved resistance to different Bt maize technologies carrying Bacillus thuringiensis genes. One hypothesis for the rapid evolution of resistance may be associated with the species' ability to multiply and survive on alternative host plants, especially during the off-season of the main crops. The aim of this study was to evaluate the biological parameters and fertility life table of susceptible (SS), heterozygous (RS) and resistant (RR) strains of S. frugiperda to Bt YieldGard VT PRO maize when kept in summer-winter cover crops. Based on the results, S. frugiperda did not survive on weeds Barnyardgrass (Echinochloa crus-galli). SS, RR, and RS larvae fed on white oats (Avena sativa), ryegrass (Lolium multiflorum), maize (non-Bt isoline) showed an egg to adult generation of approximately 30 d. The RS strain performed better than both the SS and RR strains, this is consistent with the individuals' high heterosis index. In addition, the insects reared on these hosts showed the highest reproductive rates (Ro = 496.2 to 578.1) and growth rates (rm = 0.143 to 0.185). In contrast, sorghum (Sorghum bicolor) or Persian clover (Trifolium resupinatum) prolonged the cycle by 4 d and reduced egg-to-adult viability parameters by 13%, larval weight (0.057 to 0.74 mg), pupal weight (0.36 to 0.86 mg), Ro (196.4 to 324.0), and rm (0.104 to 0.122). However, it is worth noting that all the host plants evaluated, except for Barnyardgrass, can serve to multiply S. frugiperda in the field and favor the reestablishment of the insect during the corn off-season and, consequently, accelerate the evolution of the pest's resistance.