Effect of Tetranychus urticae and Polyphagotarsonemus latus (Acari: Tetranychidae, Tarsonemidae) at different infestation levels and feeding durations on chlorophyll content of bean plants

Abstract

The study investigated the effects of different initial infestation levels and feeding durations of Tetranychus urticae and Polyphagotarsonemus latus (Acari: Tetranychidae, Tarsonemidae) on the chlorophyll content of the pinto bean plants [Phaseolus vulgaris L. (Fabaceae)]. The experiment was carried out on 3 cm diameter leaf discs and potted plants. To determine the effects of mite feeding on the chlorophyll content of leaf disc, 0 (control), 5, 10, 15, 20, and 25 mated adult females (24-48 hours old) were separately placed on each disc. Chlorophyll measurements were made 5 and 10 days after the initial infestation. For the potted plant bioassay, young plants were infested separately with different densities of P. latus or T. urticae (5, 10, 15, 20, and 25 females per plant) while noninfested plants acted as the control. Data were obtained at intervals of 5 days for a total of 5 times. The chlorophyll contents at infestation levels of 15, 20, and 25 T. urticae per disc were statistically lower than the control discs after exposure for 5 days. The heavily infested discs with 10 or more T. urticae were destroyed until the second measurement. On the other hand, there was no significant difference between the chlorophyll contents of P. latus-infested and noninfested discs 5 days after infestation. However, the content was significantly lower in infested discs at all infestation levels than in noninfested discs 10 days after infestation. According to the potted plant experiment, the chlorophyll contents of T. urticae and P. latus-infested plants were significantly lower than the noninfested plants at all infestation levels from the 10th and 20th days of the infestation, respectively. A highly significant negative correlation was recorded between chlorophyll content and mite density, as well as exposure time indicating that the leaf chlorophyll content of infested bean plants decreased with increasing mite density and time. It was also determined that P. latus required a longer feeding time than T. urticae to affect the chlorophyll content of the bean plants.