The leafminer Phyllocnistis citrella (Stainton, 1856) (Lepidoptera: Gracillariidae), is considered a potential serious pest of citrus in Algeria. The aim of this work was to investigate the relationship between the ecophases of the citrus leafminer and the leaf surface of the Washington navel citrus variety. Practically all the examined leaves of the young shoots were occupied by at least a developmental stage of this insect. More than 80% of the leafminer ecophases were distributed on the lower surfaces of the leaves. A relationship is highlighted between the leaf surfaces and the stages evolution of citrus leafminer. The choice of area laying by females is decisive for the survival and evolution of stages of development of the insect in relationship with leaf age. The analysis of the eggs distribution revealed that young leaves, with leaf surface smaller than 2 cm², were significantly preferred by females for oviposition. However, the larvae were abundant on leaf surfaces smaller than 6 cm² which provide a favorable environment for the development of larvae in order to realize their respective gallery. The pupal stage was observed almost uniformly on all the analyzed area classes. These results could contribute to the guidelines for pest risk assessment highlighting the intervention for the protection of citrus orchards against heavy infestations of Phyllocnistis citrella.
The zoophytophagous mirid Pilophorus clavatus has been recently identified inhabiting citrus orchards in the Mediterranean region, where it feeds on several important citrus pests. In this work, we investigated whether the plant feeding by P. clavatus could induce defensive responses in citrus plants.Here, we show for the first time that the P. clavatus herbivory triggers the accumulation of the stressrelated hormones salicylic acid (SA) and jasmonic acid (JA) in citrus plants. Moreover, the SA and JA pathways enhanced plant defence mechanisms as the expression of genes encoding enzymes from both biosynthetic and responsive pathways were upregulated in P. clavatus punctured plants. We also investigated whether the induced defences could affect the plant host selection of Tetranychus urticae and the predatory mites Phytoseilus persimilis and Neouseiulus californicus. Neither T. urticae nor N. californicus preferred the odour source emitted by intact or P. clavatus-punctured plants in a Y-tube olfactometer assay. However, P. persimilis were significantly attracted to P. clavatus-induced plants.The performance of T. urticae was also compared when mites were released on control or previously P. clavatus-induced plants. Compared to the control, the infestation of T. urticae was significantly reduced up to 70% on those citrus plants previously activated by P. clavatus. Our results show for the first time that feeding of P. clavatus on citrus plants can have a dual beneficial effect due to its known predatory action and, at the same time, by inducing the plant's immune system.
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