Bemisia tabaci MEAM1 population surveys in soybean cultivation

Abstract

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.

Distribution of Bemisia tabaci within soybean plants and on individual leaflets

“…As a consequence, in the lower third of the soybean plant the pattern of aggregate distribution is no longer visually or statistically significant, due to the gradual emergence of adults and consequent abandonment of the leaflets by them. Czepak et al () also state that exuviae of B. tabaci are found most frequently in the lower third, and least in the upper parts of the soybean plants, assigning this to the accumulation of cuticles from two or more generations in the older leaves of the plants.…”

“…Regarding the quantification of whitefly nymphs in the soybean leaflets, the pattern of aggregation in the middle and bottom areas of the leaf surface denotes a preference of the insect for this site, as explained above. This distribution pattern, statistically significant for the leaflets of the middle third of the soybean plants, was not taken into account by the quantification methodologies proposed to date, which suggest, for instance, sampling areas of 1 cm 2 on a random point of the leaflet (Czepak et al, ). Therefore, it is possible to delimit a reduced area of the soybean leaflet in which to quantify the number of whitefly nymphs, as long as it covers both this preferential region of nymph aggregation and the adjacent regions of the leaflet, thus avoiding quantification errors and increasing the uniformity and efficacy of the evaluation method for B. tabaci in soybean plants.…”

“…The randomness in the distribution of whitefly nymphs on the leaflets from the upper third can be attributed to the behavior of adult B. tabaci females, which feed and oviposit mainly in the upper parts of the soybean plant (Czepak et al, 2018). This preference of B. tabaci adults for younger leaves was also observed by Gusmão (2000) in tomato and by Moura et al (2003) in cucumber plants and may be explained by the nutritional value of these leaves, which present a higher concentration of nitrogen and sugars (van Lenteren & Noldus, 1990;Walker & Perring, 1994).…”

“…Sampling plans are a key factor in the integrated pest management (IPM) approach. There are suggested methods for the sampling of B. tabaci in soybean, as recently proposed by Czepak et al (2018); however, they do not take into account variation in the distribution of the pest over soybean leaves and between leaflets of a single trifoliate leaf, and they only consider different parts of the plant. Therefore, the aim of this study was to evaluate the concentration of B. tabaci nymphs in the top, middle, and bottom thirds of soybean plants under field conditions and their distribution pattern on leaflets under both greenhouse and field conditions, aiming at optimizing sampling plans for whitefly populations in this crop.…”

What makes an insect invasive? An introduction

“…Czepak et al. () investigated the distribution of several developmental stages of whiteflies on soybean plants during harvest. They find clear differences in the locality of eggs, larvae, pupae, and exuviae, depending on the maturation stage of the plant.…”