Fourth International Bemisia Workshop International Whitefly Genomics Workshop
Nutritional factors influencing whitefly development and flight behavior: The search for a suitable bioassay to test hypotheses
USDA-ARS, Arid-Land Agricultural Research Center, Maricopa, Arizona, USA Correspondence: jblackmer@wcrl.ars.usda.gov
Obtaining adequate nitrogen (N) is considered to be one of the major evolutionary hurdles phytophagous insects had to overcome before they could exploit plants. Phloem feeders, like whiteflies, encounter some of the lowest levels of N, but they have excelled in this niche owing to physiological, morphological and behavioral modifications that suite them well. For most whitefly species, these traits are merely fascinating curiosities; however, for several polyphagous whitefly species, understanding the mechanisms that allow them to be so successful may provide us with insights that could be exploited in their control. One behavioral strategy that these insects use in dealing with inadequate or unbalanced nutrient levels is emigration. However, we know very little about the underlying control mechanisms that lead to the initiation of emigration. Changes in the levels of various amino acids or in the ratio of carbohydrates to amino acids almost certainly play a role in assessing the suitability of a given host for oviposition and feeding, and once host quality declines, may supply the cues that signal that it is time to emigrate. Previously, we showed that various life-history traits of Bemisia tabaci (Gennadius) were correlated with the relative concentrations of essential amino acids that fluctuated during the growing season in Cucumis melo, and that increases in serine and glutamine/glutamic acid during senescence were correlated with increases in flight activity measured in a vertical flight chamber. These findings were interesting, but without a proper bioassay where N concentrations could be manipulated, hypotheses generated from this study could not be tested. This led us to investigate an artificial rearing system for whiteflies where amino acid and carbohydrates could be manipulated. While it was possible to raise whiteflies to the red-eye stage, very few individuals emerged to the adult stage and those that did were too weak to fly in our flight chamber. Currently, we are using TurboGarden™ hydroponic units with rockwool media to grow cotton plants. A top feed dripper manifold supplies varying concentrations of macro and micronutrients. Oviposition, % hatch, developmental time, emergence rates, adult weights and flight behavior of adults were measured. Because whiteflies have the ability to increase their feeding rates to compensate for lower N levels, we also indirectly measured feeding rates on each of the nutrient regimes by counting and measuring honeydew deposited on aluminum foil placed below leaves containing nymphs. It is thought that if nutrients are limiting then the honeydew will lack key amino acids, so after honeydew drops were counted they were collected and analyzed for amino acids.
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