Effects of plant nutrition on the expression of abdominal discoloration in Phytoseiulus persimilis (Acari : Phytoseiidae)

The effect of plant nutrition on the expression of abdominal discoloration in Phytoseiulus persimilis Athias-Henriot was investigated. Phytoseiulus persimilis were fed spider mites, Tetranychus urticae Koch. (Acari: Tetranychidae), that were reared on bean, Phaseolus vulgaris L. (Fabaceae), plants treated with distilled water or one of three concentrations of 20-20-20 fertilizer (0.6, 2.4, and 3.8 g/L). Symptoms observed in P persimilis included white stripes along the sides of the body in the region of the Malpighian tubules, white coloration of the rectum, or a combination of these symptoms. The proportion of observations of white symptoms in P. persimilis increased in an asymptotic curvilinear fashion as fertilizer concentration increased. There was no significant difference in life-history characteristics of R persimilis from the four treatments, including total fecundity, mean daily oviposition, oviposition period, post-oviposition period, or adult survival. Peak oviposition for mites from all treatments (4.9 eggs per female per day) occurred 2-3 days following mating. Thereafter, mean fecundity was greater than 4 eggs per female per day until day 11, and greater than 3 eggs per female per day until day 15, followed by a sharp decline. Following death, individual mites were examined for microsporidia, but none were detected. Results suggest that the expression of white. abdominal discoloration in R persimilis is related, at least in part, to plant nutrition; symptoms are an expression of normal excretory function in P. persimilis; and white abdominal discoloration does not necessarily affect predator performance.