Modeling the effects of climate on date palm scale (Parlatoria blanchardi) population dynamics during different phenological stages of life history under hot arid conditions

The date palm scale (DPS) Parlatoria blanchardi is a serious pest due to the damage it inflicts on its host tree (Phoenix dactylifera). To develop an effective control against DPS in arid regions, it is essential to know its bio-ecology including population dynamics and climatic factors influencing the duration and timing of life history and also the densities of different phenological stages (crawlers, first and second instars nymphs, adult males, and adult females). Monitoring of biological cycle and population dynamics of the pest were achieved through weekly counts of DPS densities on leaflets sampled at different position of date palm trees in an oasis of Ouargla region (Algerian Sahara Desert). Within this hyper-arid region, DPS established four generations per year, the most important was the spring generation. Two overlapping generations occurred in spring–early summer and two in autumn–early winter; these two pairs of generations were interspersed by two phases of high-mortality rates, the first corresponds to winter cold and the second refers to the extreme heat of summer. Statistical analysis of the effects of the studied climatic conditions (minimum, maximum and mean temperatures, precipitation, humidity, wind, rain days, and climatic indices) on the DPS densities at different phenological stages showed great variability from one stage to another. Among these, adult females were the most affected by climate factors. For the total DPS population, high values of minimum temperatures negatively affected population density, while high maximum temperatures, hygrometry, and De Martonne aridity index showed a positive influence.