Lepidoptera (Crambidae, Noctuidae, and Pyralidae) Injury to Corn Containing Single and Pyramided Bt Traits, and Blended or Block Refuge, in the Southern United States

Abstract

Fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae); corn earworm, Helicoverpa zea Boddie (Lepidoptera: Noctuidae); southwestern corn borer, Diatraea grandiosella Dyar (Lepidoptera: Crambidae); sugarcane borer, Diatraea saccharalis F. (Lepidoptera: Crambidae); and lesser cornstalk borer, Elasmopalpus lignosellus Zeller (Lepidoptera: Pyralidae), are lepidopteran pests of corn, Zea mays L., in the southern United States. Blended refuge for transgenic plants expressing the insecticidal protein derivative from Bacillus thuringiensis (Bt) has recently been approved as an alternative resistance management strategy in the northern United States. We conducted a two-year study with 39 experiments across 12 states in the southern United States to evaluate plant injury from these five species of Lepidoptera to corn expressing Cry1F and Cry1Ab, as both single and pyramided traits, a pyramid of Cry1Ab×Vip3Aa20, and a pyramid of Cry1F×Cry1Ab plus non-Bt in a blended refuge. Leaf injury and kernel damage from corn earworm and fall armyworm, and stalking tunneling by southwestern corn borer, were similar in Cry1F×Cry1Ab plants compared with the Cry1F×Cry1Ab plus non-Bt blended refuge averaged across five-plant clusters. When measured on an individual plant basis, leaf injury, kernel damage, stalk tunneling (southwestern corn borer), and dead or injured plants (lesser cornstalk borer) were greater in the blended non-Bt refuge plants compared to Cry1F×Cry1Ab plants in the non-Bt and pyramided Cry1F×Cry1Ab blended refuge treatment. When non-Bt blended refuge plants were compared to a structured refuge of non-Bt plants, no significant difference was detected in leaf injury, kernel damage, or stalk tunneling (southwestern corn borer). Plant stands in the non-Bt and pyramided Cry1F×Cry1Ab blended refuge treatment had more stalk tunneling from sugarcane borer and plant death from lesser cornstalk borer compared to a pyramided Cry1F×Cry1Ab structured refuge treatment. Hybrid plants containing Cry1F×Cry1Ab within the pyramided Cry1F×Cry1Ab blended refuge treatment had significantly less kernel damage than non-Bt structured refuge treatments. Both single and pyramided Bt traits were effective against southwestern corn borer, sugarcane borer, and lesser cornstalk borer.

Fall armyworm migration across the Lesser Antilles and the potential for genetic exchanges between North and South American populations

“…Describing the magnitude of flying insect migration across the Caribbean region as exemplified by fall armyworm has important ramifications for assessing risks and predicting the spread of both invasive pests and deleterious traits throughout the hemisphere. Fall armyworm itself provides a real world example with the discovery of naturally occurring resistance to the Cry1F Bt -toxin in fall armyworm populations in Puerto Rico [ 31 , 47 , 48 ] and subsequent reports of this resistance trait in populations in Brazil [ 49 ], Argentina [ 50 , 51 ], and the United States [ 52 , 53 ]. The simplest scenario is that the observed resistance stems from a single origin, which then became more widely dispersed by natural migratory behavior.…”

Pollen contamination in seed mixture increases the dominance of resistance to Bt maize in Spodoptera frugiperda (Lepidoptera: Noctuidae)

“…In the whorl stage, larvae feed on unfurled leaves and the whorls . Larvae of S. frugiperda also behave in a manner similar to H. zea , penetrating into the ear and feeding on kernels . In this study, we used S. frugiperda and Cry1F‐maize plants as a model to examine if pollen contamination in seed mixtures increases the dominance of resistance.…”

Frequency of Cry1F Non-Recessive Resistance Alleles in North Carolina Field Populations of Spodoptera frugiperda (Lepidoptera: Noctuidae)

“…The relatively low frequency of resistance alleles in this single location also confirmed the observations of previous investigators, who characterized corn hybrids expressing Cry1F as effective to manage S . frugiperda in the mainland US north of Florida [ 14 , 15 ]. It should be noted that this estimation is conservative because it did not estimate the frequency of recessive alleles in the heterozygous form.…”

“…In the U.S. mainland north of Florida, S . frugiperda has been effectively managed using corn hybrids expressing Cry1F [ 14 , 15 ]. The number of resistant and susceptible S .…”

“…Pyramided Bt corn hybrids (second generation) are being planted more frequently and are more effective for S . frugiperda management than single Bt protein hybrids (first generation) [ 14 , 15 , 28 , 29 ]. One reason pyramided Bt maize products are becoming more prevalent in North and South America is to manage Cry1F- resistant populations of S .…”