The four Amblyseius swirskii lines used in the experiments derived from two origins, each reared in two different ways. Two lines were founded with specimens from a commercially mass-reared population obtained from Koppert B.V. (The Netherlands) while the other two lines were founded with free-living specimens collected on citrus trees in Israel. No specific permission was required to collect the mites on the citrus trees because those trees were located on public grounds and A. swirskii is not an endangered or protected species. In the laboratory, all four lines were reared on separate artificial arenas for about 11 months (~30 generations) before conducting the experiments. One line of each population origin was reared with cattail pollen Typha angustifolia (Nutrimite; Biobest, Belgium), and the other line with two-spotted spider mites, Tetranychus urticae (Tetranychidae). Each rearing arena consisted of an acrylic plate (200 x 200 mm) placed on top of a water-saturated foam cube in a plastic box half-filled with tap water. Wet tissue paper was wrapped around the edges to establish a border between the acrylic plate and the surrounding water, and to prevent the predatory mites from escaping. Additionally, cotton wool fibres under coverslips served as shelters and oviposition sites for the predatory mites. Pollen was dusted onto arenas twice per week. Tetranychus urticae was reared on whole common bean plants Phaseolus vulgaris grown at room temperature 23 ± 2°C and 16:8 h L:D photoperiod. The spider mites were brushed from infested leaves onto glass plates, using a mite brushing machine (BioQuip®, USA), and then from glass plates onto the rearing arenas. Depending on the population origin (KO for Koppert; IL for Israel) and rearing food (PO for pollen; SM for spider mites), the henceforth-used acronyms of the four lines are KO-PO, KO-SM, IL-PO and IL-SM.
Prey used in the experiments were Western flower thrips Frankliniella occidentalis (Thripidae) and two-spotted spider mites T. urticae. Frankliniella occidentalis was reared on detached primary leaves of common bean P. vulgaris placed upside down on a 1% agar solution in a closed petri dish (140 mm Ø, 20 mm height). The lid of the petri dish had a hole (10 mm Ø) covered with gauze for ventilation. Only first instar larvae were used as prey in the experiments. To obtain first instar larvae, adult thrips females were randomly taken from the stock population, reared on whole green beans inside glass jars, and placed on detached bean leaves inside petri dishes for oviposition. After 24 h, the females were removed and after another ~70 to 80 h the first instar larvae hatched [40 (link)].
Predator rearing arenas, thrips rearing units and experimental cages were kept in climate chambers at 25±1°C, 65±5% relative humidity and 16:8 h L:D photoperiod.
Prey used in the experiments were Western flower thrips Frankliniella occidentalis (Thripidae) and two-spotted spider mites T. urticae. Frankliniella occidentalis was reared on detached primary leaves of common bean P. vulgaris placed upside down on a 1% agar solution in a closed petri dish (140 mm Ø, 20 mm height). The lid of the petri dish had a hole (10 mm Ø) covered with gauze for ventilation. Only first instar larvae were used as prey in the experiments. To obtain first instar larvae, adult thrips females were randomly taken from the stock population, reared on whole green beans inside glass jars, and placed on detached bean leaves inside petri dishes for oviposition. After 24 h, the females were removed and after another ~70 to 80 h the first instar larvae hatched [40 (link)].
Predator rearing arenas, thrips rearing units and experimental cages were kept in climate chambers at 25±1°C, 65±5% relative humidity and 16:8 h L:D photoperiod.
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