Lengthening of Insect Development on Bt Zone Results in Adult Emergence Asynchrony: Does It Influence the Effectiveness of the High Dose/Refuge Zone Strategy?

Abstract

The “High Dose/Refuge” strategy (HD/R) is the currently recommended Insect Resistance Management strategy (IRM) to limit resistance development to Bacillus thuringiensis (Bt) plants. This strategy requires planting a “refuge zone” composed of non-Bt plants suitable for the target insect and in close proximity to a “Bt zone” expressing a high toxin concentration. One of the main assumptions is that enough susceptible adults mate with resistant insects. However, previous studies have suggested that the high toxin concentration produced by Bt plants induces slower insect development, creating an asynchrony in emergence between the refuge and the Bt zone and leading to assortative mating between adults inside each zone. Here, we develop a deterministic model to estimate the impact of toxin concentration, emergence asynchrony and refuge zone size on the effectiveness of the HD/R strategy. We conclude that emergence asynchrony only affects resistance when toxin concentration is high and resistance is recessive. Resistance develops more rapidly and survival of susceptible insects is higher at lower toxin concentration, but in such situations, resistance is insensitive to emergence asynchrony.

Performance of Sesamia nonagrioides on cultivated and wild host plants: Implications for Bt maize resistance management

“…This is because even if these plant species are present and abundant near or within (i.e. Johnsongrass) Bt maize fields in Spain and they coincide with maize in both space and time, they do not comply with other requirements that must be met by unstructured refuges, that is, that they are able to host a large population of high‐quality moths, and that no asynchrony exists between these moths and those emerging from Bt fields 70–72 . For some polyphagous target pests, natural refuges can be very effective, if the host plants in the refuge can produce sufficient numbers of high‐quality moths 71 .…”

Performance of Field-Collected Spodoptera frugiperda (Lepidoptera: Noctuidae) Strains Exposed to Different Transgenic and Refuge Maize Hybrids in Argentina

“…Therefore, if this situation would develop in the field, in natural conditions, the susceptible adults would not likely encounter nor mate with the emerging adults from resistant strains. This behavior will affect the random mating between moths emerging from a Bt crop and refuge areas (Gryspeirt and Gregoire 2012, Jakka et al 2014).…”

“…All these information are relevant since Cry1F-resistant individuals may be frequently found in refuges instead of purely susceptible insects. If there are differences in the performance between susceptible and Cry1F-resistant larvae in the refuge (including developmental delays), it may affect random mating between moths emerging from the Bt crop and refuge areas, and significantly decrease the efficacy of the refuge (Gryspeirt and Gregoire 2012, Jakka et al 2014). The objectives of this study were to 1) determine the performance of fall armyworm collected from various Bt maize hybrids in the field after continuous rearing on the same collected hybrid and 2) evaluate the performance of fall armyworm resistance to Cry1F when continuously reared on non-Bt and Bt maize hybrids grown in the field.…”

Fitness of Bt‐resistant cabbage loopers on Bt cotton plants

“…An asynchrony between adult stages of susceptible and resistant insects has been reported when the insects were grown on secondary host plants or on plants expressing a single Cry toxin (Bird and Akhurst, ; Gryspeirt and Gregoire, ; Wang et al ., ). In this study, the developmental delay in the GLEN‐Cry1Ac+Cry2Ab‐BCS on Bollgard I leaves was observed to be 1.5 days.…”