Temperature-dependent development of the broad mite Polyphagotarsonemus latus (Acari: Tarsonemidae) on Rhododendron simsii.

The broad mite, Polyphagotarsonemus latus (Banks), is one of the major pests causing severe economic damage in Rhododendron simsii Planch hybrid production in Belgium. In order to optimize biological control programs and to parameterize warning programs, we studied the effect of environmental temperature on the development of P. latus on R. simsii leaves. In combination with a photoperiod of 16:8 h (L:D) and a relative humidity of 80 ± 5 %, six constant temperatures (15, 17, 20, 25, 30 and 33 ± 1 °C), were studied. Total developmental times of 13.3, 10.5, 6.6, 4.2, 3.5 and 4.0 days were measured, respective to each of the aforementioned temperatures. Development of females took significantly longer than that of males at 15, 17, 20 and 30 °C. Survival rates observed between 17 and 30 °C varied between 43.5 and 96.9 %. Lower survival rates were found at 15 and 33 °C, i.e. 31.8 and 23.6 %, respectively. The lower, optimal and upper developmental threshold (t min , t opt and t max , respectively) and thermal constant (K) of the pest were estimated for each life stage by a linear and two non-linear models. Based on measurements of total development of P. latus thermal thresholds of 10.0, 30.1 and 36.0 °C were calculated for t min , t opt and t max , respectively. The number of degree-days needed to complete immature development when feeding on R. simsii was 66.7.