Performance of chlorantraniliprole against beet armyworm populations from the Florida Panhandle, 2024

Beet armyworm (BAW) has increased its economic impact associated with vegetables and field crops in the southeastern United States with reports of increased tolerance to chlorantraniliprole. In the 2024 crop season, reports of outbreaks in peanut fields in the Florida Panhandle were followed by control failure of Vantacor (FMC). A field-derived colony from collections in commercial fields in the region was established at the West Florida Research and Education Center, UF, Jay, Florida. The collected larvae were placed in 2.5 ml plastic cups containing a multispecies lepidopteran diet (Southland Products, Lake Village, Arkansas) and kept until adult emergence. Emerged moths were placed in rearing cages (W30 × D30 × H30 cm) and fed with 10% honey. The eggs were collected and transferred to 473-ml polypropylene containers (Fabri-Kal Corp. Kalamazoo, Michigan) until hatching. The colony was maintained at 25 ± 5 ºC, 70 ± 10% relative humidity, and 14L:10D photoperiod. The concentration-mortality of BAW to the commercial formulation of chlorantraniliprole was estimated. The bioassay was conducted with ten insecticide concentrations, prepared with tap water, and included a control. The dilutions were prepared considering the label rate (469 mg/l) as a middle point and then making serial dilutions using a 3 dilution factor in the insecticide concentration. The leaf-dip technique recommended by the Insecticide Resistance Action Committee (Method n. 007) was used. Fresh leaves of peanut were collected from the upper portion of the plant canopy during the vegetative to initial reproductive stage, dipped into insecticide solution for 5 s with gentle agitation, and then placed on paper towel for 5 min to allow to dry. The leave was transferred to 250 ml polypropylene containers (Fabri-Kal Corp. Kalamazoo, Michigan, USA) using a tweezer to avoid touching the surface of the treated area and infested with one-third instar larva. The bioassays were replicated two times using 30 larvae per treatment. Larval mortality was recorded in 24, 48, 72, and 96 h intervals, and larva was considered dead if they did not move when prodded with a fine paintbrush. The percentage of larval mortality was estimated and adjusted and subjected to ANOVA using the Kaplan–Meier survival analysis (Log-rank) using Sigma Plot 14.

The results are presented in Table 1 and indicate tolerance of the BAW population from Florida Panhandle in the 2024 crop season, considering larval mortality approximately 75% at the label rate, under laboratory conditions. Continuing monitoring of the insecticide performance in populations of BAW is necessary, considering their potential impact on the economic production of peanut and other host plants in the region. The region under this study represents a potential source of migratory populations carrying alleles genes for resistance to other higher latitudes in the southeastern United States.¹

Footnotes