Evaluation of different marking and trapping methods for Spodoptera frugiperda used to assess structured refuges in Bt maize

The fall armyworm (Spodoptera frugiperda) is an important pest of maize, and a key target of transgenic crops expressing Bacillus thuringiensis (Bt) insecticidal proteins. These exert a strong selective pressure, so susceptible plants (refuges) are planted together with the transgenic seed to lower such pressure. The system favored in North America is to mix Bt and non-Bt seed (refuge-in-a-bag, or RIB). However, South American farmers favor structured refuges, interplanting rows of Bt and non-Bt seed. Yet, the proportion of susceptible maize must be minimized to prevent yield losses, and flight distance before mating is considered the best way to gauge the adequate distance between non-Bt rows in structured refuges, which has been estimated through mark–release–recapture experiments. The aim of this study was to compare three marking techniques and three trapping systems in laboratory and field experiments. Results suggest conventional marking techniques were not completely innocuous to the moths. UV traps drastically overrode the effect of synthetic and natural pheromones, suggesting they may not reflect normal dispersion behaviors. Marking experiments may not provide reliable measures of flight distance, and although farmers tend to resist the RIB option the data suggests it should be enforced.