Life-History Traits of Spodoptera frugiperda Populations Exposed to Low-Dose Bt Maize

Abstract

Exposure to Bacillus thuringiensis (Bt) toxins in low- and moderate-dose transgenic crops may induce sublethal effects and increase the rate of Bt resistance evolution, potentially compromising control efficacy against target pests. We tested this hypothesis using the fall armyworm Spodoptera frugiperda, a major polyphagous lepidopteran pest relatively tolerant to Bt notorious for evolving field-relevant resistance to single-gene Bt maize. Late-instar larvae were collected from Bt Cry1Ab and non-Bt maize fields in five locations in Brazil, and their offspring was compared for survival, development, and population growth in rearing environment without and with Cry1Ab throughout larval development. Larval survival on Cry1Ab maize leaves varied from 20 to 80% among the populations. Larvae reared on Cry1Ab maize had seven-day delay in development time in relation to control larvae, and such delay was shorter in offspring of armyworms from Cry1Ab maize. Population growth rates were 50–70% lower for insects continuously exposed to Cry1Ab maize relative to controls, showing the population-level effect of Cry1Ab, which varied among the populations and prior exposure to Cry1Ab maize in the field. In three out of five populations, armyworms derived from Bt maize reared on Cry1Ab maize showed higher larval weight, faster larval development and better reproductive performance than the armyworms derived from non-Bt maize, and one of these populations showed better performance on both Cry1Ab and control diets, indicating no fitness cost of the resistance trait. Altogether, these results indicate that offspring of armyworms that developed on field-grown, single-gene Bt Cry1Ab maize had reduced performance on Cry1Ab maize foliage in two populations studied, but in other three populations, these offspring had better overall performance on the Bt maize foliage than that of the armyworms from non-Bt maize fields, possibly because of Cry1Ab resistance alleles in these populations. Implications of these findings for resistance management of S. frugiperda in Bt crops are discussed.

Managing fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae), with Bt maize and insecticides in southern Brazil

“…24,25 However, the survival of FAW on Cry1Ab maize is also a consequence of resistance evolution. 13,26 Similarly, Herculex maize also presented effective control of FAW during the first few years of its commercial use in Brazil. 23 Since 2011, severe damage by FAW of this Bt maize has been reported as a consequence of field-evolved resistance to the Cry1F protein.…”

“…The damage by FAW of Cry1Ab maize is attributed to the low natural susceptibility to this Bt protein, which has low affinity and degrades rapidly in the midgut of this species . However, the survival of FAW on Cry1Ab maize is also a consequence of resistance evolution . Similarly, Herculex maize also presented effective control of FAW during the first few years of its commercial use in Brazil .…”

Laboratory and field survival of Spodoptera frugiperda (Lepidoptera: Noctuidae) on Bt and non‐Bt maize and its susceptibility to insecticides

“…These results corroborate previous studies that reported lack of strong fitness costs associated with resistance of FAW to Bt maize expressing Cry1, Cry2, or Vip3A proteins . Only the progeny from reciprocal crosses between H‐R × Sus survived on Herculex maize leaves, showing that plant expression of Cry1F protein does not meet the high‐dose concept, as demonstrated in previous studies . In contrast, progeny from Y‐R × Sus and P‐R × Sus did not survive on YieldGard VT PRO and PowerCore, respectively, showing that resistance is functionally recessive and Bt proteins expressed in these events meets the definition of high dose …”

Chromosome level draft genomes of the fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae), an alien invasive pest in China

“…Although many pesticides are less harmful to the environment and humans, all these factors can lead the sublethal effects, which possibly help the FAW to evolve resistance against the pesticides 25-27 . An effective compensating management for insecticides is the use of Bacillus thuringiensis (Bt) toxins produced by the by the bacterium.Bt plants have been proved fatal to many insect pests, including the FAW 28-30 . The Bt toxin provides much longer protection than insecticides and less harmful to the environment and humans.…”