Abstract:

【Aim】 The citrus red mite, Panonychus citri, is an important pest of citrus in China where foliar fertilizers are commonly used in citrus orchards. The objective of this research is to assess the influence of two fertilizers, urea and compound amino acid, on the development and reproduction of this mite, and on the growth of citrus seedlings. 【Methods】 Two foliar fertilizers, urea (0.50%) and compound amino acid (0.17%), were applied separately to potted citrus (Citrus reticulata Blanco cv. Shatangju) seedlings in the laboratory, and the seedlings sprayed with water were used as the control. The life-table parameters ［the net reproductive rate (R₀), mean generation time (T), intrinsic rate of increase (r_m), finite rate of increase (λ) and population trend index (I)］ of P. citri, the growth parameters (leaf length, width and area; stem length; plant height; number and length of new shoot leaves) of citrus seedlings and the nutrient (N, P and K) contents in leaves of citrus seedlings were investigated under controlled environment conditions. 【Results】 The duration of immature stages of P. citri was not influenced by the fertilizers, but the survival rate of  deutonymphs on citrus seedlings applied with 0.50% urea (95.40%) was significantly higher than those on the control citrus seedlings (applied with water) (78.26%) and on citrus seedlings applied with 0.17% compound amino acid (75.61%). The fecundity of female mites reared on urea treated citrus seedlings (42.1/♀) was also significantly higher than that of females reared on the control citrus seedlings (33.1/♀). The longevity of females reared on compound amino acid treated citrus seedlings (19.5 d) was significantly longer than that of females reared on urea treated citrus seedlings (14.8 d) and the control citrus seedlings (14.5 d), and the longevity of males reared on compound amino acid treated citrus seedlings (17.6 d) was significantly longer than that of males reared on the control citrus seedlings (13.1 d). Overall, P. citri reared on urea treated citrus seedlings had the highest net reproduction rate (Ro) (17.88) and population trend index (I)(18.08), both significantly higher than that reared on the control citrus seedlings (10.08 and 11.17, respectively). Leaf growth (leaf length, width and area) of citrus seedlings was significantly promoted by both fertilizers. Both fertilizers also significantly increased N, P and K contents, and the ratio of N/K in leaves of citrus seedlings. 【Conclusion】 Urea and compound amino acid as foliar fertilizer both promote the growth of citrus seedlings. Compound amino acid should be recommended in preference to urea because spraying of urea increases P. citri populations in contrast to compound amino acid. However, P. citri population should be also monitored because that although compound amino acid does not facilitate population growth, it does increase the longevity of adult mites.

Key words: Panonychus citri, spider mite, foliar fertilizer, urea, compound amino acid, citrus growth