Field evaluation of predacious mites (acari: Phytoseiidae) for biological control of citrus red mite, panonychus citri (trombidiformes: Tetranychidae)

Abstract

We evaluated 3 species of predacious mites (Acari: Phytoseiidae), Galendromus occidentalis (Nesbitt), Phytoseiulus persimilis Athias-Henriot and Neoseiulus californiens (McGregor), as biological control agents for citrus red mite, Panonychus citri (McGregor) (Trombidiformes: Tetranychidae), on citrus in southern Alabama. Three separate experiments were carried out during 2008 and 2011 to evaluate various factors (i.e. release rate, release frequency and initial prey density) that may impact the performance of the predacious mites. In the first experiment conducted in 2008 on trees with moderate initial prey densities (i.e. < 4 P. citri motiles per leaf), one single release of P. persimilis or G. occidentalis at a rate of 100 or 200 per tree effectively prevented the prey from exceeding the economic threshold (5 motiles/leaf) for the entire duration (35 d) of the experiment. The result of the second experiment in 2008 on trees with high initial prey densities (i.e. ≥ 5 motiles per leaf) showed that 2 releases of P. persimilis or G. occidentalis at a rate of 100 or 200 per tree per release could not provide adequate suppression of P. citri below the economic threshold. In both experiments, P. citri densities were significantly lower in most predacious mite treatments compared to the control (no release). Also, lower P. citri densities were recorded at the higher release rate (200 per tree) compared to the lower rate, but this was only significant in a few cases. The third experiment conducted in 2011 in large plots on trees with low initial P. citri densities (i.e. < 1 motile per leaf) showed that 2 releases of N. californiens or P. persimilis at a rate of 200 per tree per release effectively maintained P. citri at low densities (< 1.5 motiles per leaf) throughout the duration (56 d) of the experiment. Limited observations in spring 2012 confirmed the establishment of the predacious mites released in the 2011 study. These results showed that all 3 phytoseiid species were effective in reducing P. citri densities on citrus. However, initial prey density may be an important factor influencing their performance.