Egg Production and Population Growth of the Citrus Red Mite (Acari: Tetranychidae) on Differentially Irrigated Citrus Trees

Abstract

We determined the effect of moderate (20%), continuous water stress of citrus trees on the egg production and population growth of the citrus red mite, Panonychus citri (McGregor). We also measured differences in individual and total free amino acids, soluble protein, total nitrogen, and percentage of soluble nitrogen to determine if water stress influenced the concentration of soluble nitrogenous compounds. Although this level of water stress can reduce yield directly, we observed no consistent effect of irrigation on concentrations of nitrogenous compounds. Temporal or ontogenetic variation among trees more strongly affected concentration of plant nitrogenous compounds than irrigation. The three citrus cultivars examined— Citrus limon (L.) Burman f. cv. Eureka, and Citrus sinensis (L.) Osbeck cv. Valencia and cv. Washington Navel—also varied in sensitivity to differential irrigation; lemon was least sensitive and ‘Washington Navel’ orange was most. Egg production rates were independent of irrigation level. Mite population growth on commercial, differentially irrigated ‘Washington Navel’ trees also was independent of irrigation level. When P. citri activity is expected to be greatest, differential irrigation is expected to have minimal influence on P. citri populations. The direct effects of suboptimal irrigation on yield probably are of more economic importance than any indirect effects of altering host tree suitability to mites.