Influence of temperature on the population dynamics of Parlatoria ziziphi and potential for biological control by the parasitoids Aphytis and Encarsia in citrus orchards

The black scale, Parlatoria ziziphi (Lucas, 1853), is a significant citrus pest that weakens trees, reduces fruit quality, and significantly lowers production, thereby affecting profitability. Parasitoids play a key role in its biological control, parasitizing P. ziziphi at different developmental stages. This study aimed to examine the population fluctuations of P. ziziphi in citrus orchards in the Kadiria region (Bouira, Algeria). Additionally, we investigated the influence of temperature on its development and mortality and identified potential biological control agents. Weekly monitoring was conducted in a citrus orchard to assess P. ziziphi populations on orange and mandarin trees. Leaf and fruit samples were collected for identification. The pest was also reared under controlled laboratory conditions to determine its life cycle. The study found that P. ziziphi was more frequently present on leaves and fruit, and laboratory observations identified two parasitoids from the genera Aphytis and Encarsia, though the parasitism rate was low. Moderate temperatures favored P. ziziphi infestations, particularly during the citrus harvesting phase. Regression analysis showed that temperature variations significantly influenced the pest development and mortality. For mandarin orchards, temperature accounted for 33% of the variation in P. ziziphi development/mortality (R² = 0.330, p = 0.020). For orange orchards, the correlation was stronger, with temperature explaining 48.5% of the variation (R² = 0.485, p = 0.001). The findings highlight the role of temperature in influencing P. ziziphi population dynamics. While the natural parasitoids were identified, their impact on controlling the pest remains limited. These insights contribute to understanding the pest behaviour and improving management strategies for sustainable citrus production.