Euonymus scale (Homoptera: Diaspididae) effects on plant growth and leaf abscission and implications for differential site selection by male and female scales

Effects of infestation by Unaspis euonymi on leaf abscission and growth of Euonymus fortunei were measured. During summer 1985, leaf abscission by infested plants significantly increased in August and September, coinciding with development of the 2nd generation of scale insects. Infested plants suffered relatively greater winter injury than did uninfested plants, so that by spring 1986, they supported significantly lower stem and leaf weights. Reduction in root weight of infested plants was not evident until July of the 2nd growing season. Proportionately more mortality of leaf tissue than of stem tissue occurring during winter, so that the probability of plant tissue bearing overwintering females surviving until spring was nearly 3 times higher for stems than for leaves. The characteristic distribution of U. euonymi with males mainly on leaves and longer-lived females on stems probably reflects the relatively greater risk to females of mortality from leaf abscission and from winter injury to leaves. -from Authors