Predation of two Mediterranean phytoseiid species (Parasitiformes, Phytoseiidae) upon eggs of tetranychid mites (Acariformes, Tetranychidae)

Laboratory trials were carried out to verify the predatory capacity of two generic phytoseiid predators upon eggs of the two most important tetranychids damaging Citrus orchards in Sicily: Tetranychus urticae and Panonychus citri. Both Typhlodromus laurentii and Typhlodromus rhenanoides are autochthonous and common species on spontaneous and cultivated plants. The research aimed at investigating the predatory behaviour of the phytoseiids upon the prey stage considered more vulnerable. The predation rate of the two phytoseiids was different on the two prey eggs, both on each observation day and for the whole observation period. Both phytoseiids clearly preferred T. urticae eggs, on which the predation rate was significantly higher for T. laurentii (12.5±0.28 preyed eggs/female/day), than for T. rhenanoides (9.7±0.21 preyed eggs/female/day). On the contrary, the predation upon P. citri eggs was very scarse, without significant differences for both phytoseiids: 0.5±0.09 and 0.2±0.04 eggs/female/day for T. laurentii and T. rhenanoides respectively. The predatory activity, naturally, influenced the oviposition rate of the two phytoseiids. T. laurentii was the most prolific species with 2.1±0.08 eggs/female/day, when eggs of T. urticae were supplied as food, while upon P. citri eggs only 0.3±0.05 eggs/female/day was layed by the predator. The oviposition rate of T. rhenanoides on T. urticae eggs (1.3±0.06 eggs/female/day) was significantly lower, if compared to that of T. laurentii. However, no significant differences were found when the phytoseiid preyed upon P. citri eggs.