Variation in Life History Parameters of California Red Scale on Different Citrus Cultivars

Abstract

We measured survival, growth rate, and initial egg complement of California red scale, Aonidiella aurantii, when reared on foliage and bark of four citrus cultivars in order to detrmine the extent that variation among citrus cultivars may introduce variation in the number and quality of scale for utilization by the introduced parasitoid Aphytis melinus. Among bark substrates, lemon (Citrus limon) and grapefruit (Citrus paradisi) were most suitable for scale survival and growth. Bark of mandarin (Citrus unshiu) was nearly unsuitable for California red scale survival, and bark of sweet orange (Citrus sinensis) was intermediate in suitability. Foliage was a more uniformly suitable substrate for California red scale in that variation in survival and adult sizes was generally insignificant when scale were reared on different cultivars. Substantial differences in concentrations of free animo acids and soluble protein occurred in foliage and bark among citrus cultivars, but these differences were not correlated with differences in scale performance. The more uniform densities and sizes of scale on leaves across cultivars may have contributed to the development of A. melinus' propensity to search the leaves on the tree's exterior more frequently and regularly than the bark on the tree's interior for individual scales suitable for the reproduction of female progeny.