There is no sampling methodology defined for the whitefly Bemisia tabaci MEAM1 (Hemiptera: Aleyrodidae) in soybean crops. We optimized a plan, through the minimization of total sampling variance, to evaluate population density of various whitefly stages, based on a feasible sample size. The sampling plan proposed for N1–N4 immature stages consists of four random sampling points in a field. Per point, four leaflets are collected per third of a plant's height (one leaflet per plant), evaluating 1 cm2 per leaflet.

No abstract

Helicoverpa armigera (Hübner) is one of the most important agricultural pests in the world. This historically Old World species was first reported in Brazil in 2013 and has since spread throughout much of South America and into the Caribbean. Throughout North America, H. armigera surveys are ongoing to detect any incursions. Each trap is capable of capturing hundreds of native Helicoverpa zea (Boddie). The two species cannot be separated without genitalic dissection or molecular methods. A ddPCR assay is currently used to screen large trap samples, but this equipment is relatively uncommon and expensive. Here, we optimized a newly designed assay for accurate and repeatable detection of H. armigera in bulk samples across both ddPCR and less costly, and more common, real-time PCR methods. Improvements over previously designed assays were sought through multiple means. Our results suggest bulk real-time PCR assays can be improved through changes in DNA extraction and purification, so that real-time PCR can be substituted for ddPCR in screening projects. While ddPCR remains a more sensitive method for detection of H. armigera in bulk samples, the improvements in assay design, DNA extraction, and purification presented here also enhance assay performance over previous protocols.

Recently, a sampling method was proposed to estimate the population of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) in soybean, Glycine max (L.) Merr. (Fabaceae), by counting its immature stages on 1 cm² leaf surface as a sampling unit to reduce the effort required. However, no study has verified whether this sampling unit could accurately estimate the immature stages similar to counting individuals in the total area of a soybean leaflet. Thus, we studied the correlation between the counts performed in 1 cm² and those in the total area of a leaflet to validate the 'squared centimeter' method as a sampling unit for immature stages of the whitefly. The research was carried out in two commercial soybean crops during the 2018/2019 harvest in Brazil. Each sampling was conducted by four individuals at 12 random collection points in the field. A plant was divided into three parts: apical, middle, and lower thirds, where a trifoliate leaf was removed from each of these plant thirds. For the evaluation, the trifoliate leaf was divided into left, central, and right leaflets. The immature whitefly population on its abaxial face was evaluated using two methods: counting in 1 cm² and counting in the total area of the leaflet. The four stages of immature B. tabaci quantified and identified were egg, crawler, nymphal stage 1-4 (N1-N4), and pseudo-pupa. Significant positive correlations were detected between the mean counts in 1 cm² and in the total area of the soybean leaflet for the four whitefly stages. However, the correlation was weak for the crawler stage. Therefore, this study elucidates that 1 cm 2 as sampling unit is suitable for estimating the population densities of eggs, N1-N4, and pseudo-pupa stages of B. tabaci in soybean plants.

No abstract