Dominance of Cry1F resistance in Spodoptera frugiperda (Lepidoptera: Noctuidae) on TC1507Bt maize in Brazil

Abstract

Resistance to Cry1F in TC1507 maize is incompletely recessive in S. frugiperda. TC1507 maize is not high dose for S. frugiperda. Additional or alternative resistance management strategies, such as the replacement of single-trait Bt maize with pyramided Bt maize, which produces multiple proteins targeting the same insect pests, should be implemented wherever this technology is in use and S. frugiperda is the major pest.

Frequency of Cry1F resistance alleles in Spodoptera frugiperda (Lepidoptera: Noctuidae) in Brazil

“…The efficiency of the F 2 screen at higher R allele frequencies was examined using published methods, and was compared with other possible discriminating concentration assays. We calculated the minimum number of insect samples necessary to detect one R allele on average, using the heterozygosity known for resistance in S. frugiperda ( h = 0.15) . Previous work assumed that h = 0, and for h > 0 the number of required samples is reduced for many of the detection methods.…”

“…Successful insect resistance management (IRM) for Bt crops requires a low initial frequency of resistance whether or not the Bt crop is high dose . In Brazil, field‐evolved resistance to Cry1F was recently reported from western Bahia during 2011, and was based on a single resistance allele from one locus that was partially recessive, with about 8% of heterozygotes expected to survive on Cry1F maize . Because the frequency of the resistance allele is a key element for predicting the rate of resistance evolution, it was imperative to estimate the frequency of resistance throughout the major maize production regions of Brazil.…”

Is a larger refuge always better? Dispersal and dose in pesticide resistance evolution

“…For example, resistance of Spodoptera frugiperda has high dominance, $h=0.15$, and selection survival of susceptible individuals is also significant (Farias et al. 2016). The larger value of s (lower selection pressure/lower efficacy) allows the treated patch population to maintain a sufficiently large population size, which diminishes the effect of migrants on the mating population in the treated patch.…”

Molecular characterization of fall armyworm (<em>Spodoptera frugiperda</em>) resistant to Vip3Aa20 protein expressed in corn

“…no movement, ). Most of the Cry proteins are not "high dose" for FAW (Santos-Amaya et al 2015, Farias et al 2015 and the potential of late instar survivorship is very high, accelerating resistance evolution. Assuming 50% of cporn plants are infested at with 1 larvae, and planted at 65,000 plants per hectare, around 32,500 larvae per hectare in the first generation can be produced.…”

“…However, expectations suggest that compliance is at or lower than 20%. In addition, resistance for Cry proteins launched since 2008 are not consistently recessive (Cry1F - Farias et al 2015, Cry1Ab -Jakka et al 2016, thus not adhering to the high dose/refuge strategy. Vip3Aa20 expressed in Agrisure Viptera ® hybrids is a unique Bt corn event that adheres to high dose concept for FAW .…”