Abstract
AbstractFor electrical penetration graph (EPG) recording from a piercing insect, attachment of the insect to an electrode of thin wire is needed. The effects of tethering on the probing behaviour of the greenhouse whitefly Trialeurodes vaporariorum (Westwood) were studied by comparing free (not wired) whiteflies with tethered whiteflies, using gold wire of 10 and 20 μm diameter. As an additional group, whiteflies with silver paint contact but without wiring were used to accomplish discontinuous EPG recordings. The total probing time and the total time spent with the stylets in phloem sieve elements (phloem phase) differed between these treatments. Probing time of free insects was significantly longer than that of whiteflies wired with 20 μm, but not with 10 μm wires. Time spent in phloem phase was considerably shorter for 20 than for 10 μm wired whiteflies. These differences decreased over the 8 h experimental time. In an additional 12 h experiment, a free/tethered comparison was made on the basis of honeydew excretion, using ‘honeydew clock’ recording. By comparing the simultaneous EPGs with honeydew recordings of wired insects, a highly positive correlation was found between total duration of phloem phases and periods of honeydew excretion. Free insects spent longer time in phloem sieve elements than wired ones and shorter intervals occurred before reaching the phloem phase, which always includes phloem feeding. However, when a 2 h adaptation period was given to the wired whiteflies, an improvement could be observed in shortening the interval to the 1st phloem phase and increasing the total time of phloem phases. Although there is still an effect of a 10 μm gold wire on probing behaviour, EPG recording seems an acceptable method for investigating probing behaviour of whiteflies, as long as control whiteflies in behavioural and ecophysiological studies are tethered as well. Using an adaptation procedure to reduce the wire stress is recommended.
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