Susceptibility of Fall Armyworms (Spodoptera frugiperda J.E.) from Mexico and Puerto Rico to Bt Proteins

Abstract

Fall armyworm is one of the main pests of conventional and Bacillus thuringiensis (Bt) corn in many countries in the Americas, Africa, Asia and in Australia. We conducted diet-overlay bioassays to determine the status of susceptibility to four Bt proteins (Cry1A.105, Cry2Ab2, Cry1F and Cry1Ac) in three different populations of fall armyworm from Mexico, and one population from Puerto Rico. Bioassays showed that fall armyworms from Puerto Rico were resistant to Cry1F with a resistance ratio 50 (RR50) higher than 10,000 ng/cm2 and to Cry1Ac with a RR50 = 12.2 ng/cm2, displaying the highest median lethal concentration (LC50) values to all Bt proteins tested. The effective concentration 50 (EC50) values further confirmed the loss of susceptibility to Cry1F and Cry1Ac in this population. However, LC50 and EC50 results with Cry1A.105 and Cry2Ab2 revealed that fall armyworm from Puerto Rico remained largely susceptible to these two proteins. The Mexican populations were highly susceptible to all the Bt proteins tested and displayed the lowest LC50 and EC50 values to all Bt proteins. Our results suggest that Cry1F and Cry1Ac resistance is stable in fall armyworm from Puerto Rico. However, this population remains susceptible to Cry1A.105 and Cry2Ab2. Results with Mexican fall armyworms suggest that possible deployment of Bt corn in Mexico will not be immediately challenged by Bt-resistant genes in those regions.

Large genomic deletion linked to field-evolved resistance to Cry1F corn in fall armyworm (Spodoptera frugiperda) from Florida

“…However, while the FL39 strain is highly resistant to Cry1F (> 270-fold), it presents low levels of cross-resistance (4.8-fold) to Cry1A.105 9 . The FL39 phenotype is similar to S. frugiperda collected in Puerto Rico, which displayed high resistance to Cry1F while remaining relatively susceptible to Cry1A.105 26 . This discrepancy may be suggestive of multiple resistance alleles present in strains resistant to both Cry1F and Cry1A.105 13 , or that Cry1A.105 and Cry1F may recognize physically close but distinct sites in SfABCC2 that are differentially affected by resistant mutations.…”

Genetic Screening to Identify Candidate Resistance Alleles to Cry1F Corn in Fall Armyworm Using Targeted Sequencing

“…Based on similar mutations in knockout and resistant strains of S. frugiperda [ 8 , 9 , 11 , 13 ], these homozygotes would display a Cry1F-resistant phenotype. The relatively high frequency of mutations predicted to result in resistance to Cry1F through SfABCC2 truncation is in line with the high levels of resistance to Cry1F maintained in Puerto Rico [ 18 , 43 ] and the lack of relevant fitness costs in disruptive SfABCC2 mutants [ 15 , 44 ]. Our targeted approach does not allow us to identify additional Cry1F-resistant individuals carrying alternative resistance genes, which could potentially increase the frequency of Cry1F-resistant individuals.…”

Invasiveness, biology, ecology, and management of the fall armyworm, Spodoptera frugiperda

“…Starting in about 2000, spinosyns, avermectins, oxadiazines, insect growth regulators (chitin synthesis inhibitors and ecdysteroid agonists) and diamides have been used intensively in the Americas (Bolzan et al 2019;Kaiser et al 2021;Lira et al 2020;do Nascimento et al 2016;Okuma et al 2018). Bt-based insecticide formulations have also been used in the region (Blanco et al 2014;Gutierrez-Moreno et al 2020).…”