Abstract
Simple SummaryThe use of transgenic crops expressing insecticidal proteins from Bacillus thuringiensis (Bt) has been a successful strategy to control the fall armyworm (FAW) Spodoptera frugiperda. However, resistance to many Bt proteins has been observed, which could reduce the effectiveness of this approach as a control strategy. In this study, we compared the reproductive traits of susceptible and resistant FAW males and females to determine if there are costs associated with resistance. Our data provided clear evidence that the development of resistance to the Bt protein affected the reproductive capacity of resistant FAW males.The fall armyworm (FAW) Spodoptera frugiperda is the most significant lepidopteran corn pest in South American countries. Transgenic Bt corn, producing the Cry1Fa toxins, has been used to control this pest, but there is clear evidence that some FAW populations have developed resistance. To determine if there are costs associated with resistance, we compared the mass of adults, the duration of mating, and the mass of the first spermatophore produced, as well as the lifetime fecundity and fertility of once-mated susceptible (SS) and resistant (RR) females. Adult mass was affected by both sex and strain, with SS females being significantly larger than RR ones, while the inverse was true for males. RR pairs took significantly longer to mate than SS pairs, yet the mass of spermatophores produced by RR males was significantly less than those of SS males. The total number of eggs laid did not differ but the fertility of eggs from once-mated RR pairs was significantly lower than that of SS pairs. Our data provided clear evidence that the development of Bt resistance affected the reproductive capacity of resistant FAW.
Highlights
The use of transgenic crops producing insecticidal proteins from Bacillus thuringiensis (Bt) has been a successful strategy for the control of important agricultural lepidopteran pests [1–3], including the fall armyworm (FAW) Spodoptera frugiperda
If there is a fitness cost associated with resistance, susceptible individuals should do better in non-Bt areas, which may reduce the frequency of resistant alleles [16,17]
Santos-Amaya et al [31] reported no apparent fitness cost between control and Cry1Faresistant fall armyworm lines over seven generations when comparing growth rate, larval stage, fecundity and fertility
Summary
The use of transgenic crops producing insecticidal proteins from Bacillus thuringiensis (Bt) has been a successful strategy for the control of important agricultural lepidopteran pests [1–3], including the fall armyworm (FAW) Spodoptera frugiperda E. Smith, 1797) (Lepidoptera: Noctuidae), which is a global pest of corn [4–11]. Resistance to most of the Bt proteins from the Cry group has been observed in numerous S. frugiperda populations in Puerto Rico, the United States, Brazil and Mexico [12–15]. Resistance could reduce the effectiveness of this approach as a control strategy. If there is a fitness cost associated with resistance, susceptible individuals should do better in non-Bt areas (refuges), which may reduce the frequency of resistant alleles [16,17]
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