Numerical host plant relationships of Bemisia tabaci MEAM1 (Hemiptera: Aleyrodidae) within and among major Australian field crops

Abstract

The within-plant, vertical (internodal) distribution of the silverleaf whitefly (SLW), Bemisia tabaci (Gennadius) MEAM1 (biotype B) adult, large nymph (3rd and 4th instar) and egg stages was quantified in relation to four major Australian field crops, viz., cotton, mungbean, soybean and sunflower in 2003. The objective was to identify suitable sampling locations within the crop canopy. Ovipositional preference of SLW among the four crops under field conditions was also determined to gauge potential susceptibility and support crop choice and configuration decisions in multi-crop systems. SLW abundance at main stem leaf nodes within each crop was characterised in a two-stage analysis of the proportion of infested nodes and the number of SLW at the node if infested. The vertical distribution profiles of adults and nymphs from the experimental plots were validated for cotton using scouting data collected in the 2002–2003 growing season and for mungbean from an agronomic comparison of commercial germplasm conducted in 2003. Vertical distributions of adults and juvenile stages differed among the four crops. Based on their distribution profiles, the optimal sampling locations in cotton, mungbean, soybean and sunflower are leaf nodes 3–5, 2–3, 3–4 and 5–7 for adult SLW and 7–10, 4–5, 5–6 and 17–21 for large nymphs, respectively. A comparison of egg density per unit area of green leaf among the four host plant species indicated that soybean is the most attractive to ovipositing females, mungbean the least, and cotton and sunflower intermediate. The potential of each crop as a source for SLW on the basis of nymph abundance is discussed. Low preference combined with a low source potential makes mungbean the crop of choice in broad acre cropping areas in which SLW is endemic.