Functional response of Phytoseiulus macropilis under different Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae) population density in laboratory
Juarez Ferla, NoeliMarchetti, MarlaJohann, LianaHaetinger, Claus
We tested the functional response of the phytoseiid predator Phytoseiulus macropilis (Banks, 1904) to different population densities of Tetranychus urticae Koch, 1836 (the two-spotted spider mite - TSSM) in the laboratory. We evaluated the curve that best fits the data obtained, based on the reduced X². The predators were obtained from leaves of Oso Grande strawberries at the municipality of Bom Princípio, state of Rio Grande do Sul, Brazil. Fifteen seemingly healthy females of P. macropilis were randomly chosen and individualized in each of the arenas with different TSSM densities. The following prey densities were tested: 1, 2, 3, 5, 10, 20, 30, 35, 45, 55, 70 and 125 females. The tests were performed in a germination chamber with photoperiod of 12 hours at 28 ± 1ºC per day and 22 ± 1ºC at night and 80 ± 5% relative humidity. In all tests with up to three prey items, P. macropilis showed low functional response, whereas higher rates were observed when more prey items were offered. There was a strong positive correlation between increased prey numbers and daily prey consumption (r = 0.84 and p = 0.0006). A significant correlation was found between prey consumption and total oviposition (r = 0.70, p = 0.01). The daily oviposition rate was lower when few prey items were offered, increasing significantly with increased prey availability. The results showed a positive correlation between the number of prey items offered to the predator and its oviposition rate (r = 0.66, p = 0.01). Nevertheless, a strong correlation was observed between the daily consumption of prey and eggs/female/day (r = 0.92, p 0.0001). A shorter oviposition period was reported when up to three prey items were offered. The oviposition period and the increase in prey numbers were positively correlated (r = 0.30, p = 0.34), but the difference was not statistically significant. Nevertheless, the longer the egg-laying period, the greater the oviposition rate (r = 0.90, p 0.0001). The curve that best fits the data obtained in each case was also calculated, based on the least square method.
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