Model Insect Species and Experiments

The beetle Chrysolina fastuosa was used as a model insect species because (1) it occurred in great numbers at the study site and (2) our previous experiments, proving insect attachment ability on various plant surfaces, have been carried out with this insect species [28]. An insect was allowed to walk on the tested surface for 1 min. The beetle was transferred on a clean glass plate, and its legs (foreleg, midleg, and hindleg of one side) were immediately cut off with a sharp razor blade and mounted on SEM holders using conductive carbon double-sided adhesive tabs. On each plant surface, at least five insects were tested. Insects demonstrating cleaning behavior of the tarsi were excluded from the further microscopic procedures. Preparations were air dried, sputter coated with gold-palladium (10 nm), and examined in a Hitachi S-800 scanning electron microscope at 20 kV. Only males were used in the experiments because their pads bear mushroomlike hairs having round or oval-shaped flat tips, and this facilitated quantification of the contamination.

A portion of the contaminated area of the setal tips was quantified from digital images. At least 10 setae having flat, round, or oval-shaped tips were taken for measurements. For this purpose, the most contaminated part on the ventral surface of the third tarsomere (the most distal attachment pad) was selected. Since the tarsomere was not regularly contaminated, portion of setae covered with wax crystals and dust particles were evaluated from three to five SEM images of the central part of the pad (120 ^m x 100 ^m each) taken at low magnification. For measurements, SPSS was used.

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