Behavior, Distribution, and Population Dynamics of Cottony-Cushion Scale,lcerya purchasi, inDesmodiumFields in Hawaii

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Abstract
Distribution studies of Iccrya purchasi Maskell (Homoptera: Margarodidae), on Desmodium sandwicense E. Meyer in the field showed that 59% of the scales settled on the leaves and 41% on the stems. The 1st instars settled predominantly on the leaves near the apex of the plant. The 2nd instars occurred in about equal numbers on stems and leaves of the whole plant. However, higher numbers settled on the leaves near the apex and on the stems near the base of the plant. The seasonal abundance of I. purchasi was high during July through November 1967, and low during December 1967 through June 1968. Scale mortality in the field decreased as the scale reached maturity, with the highest mortality occurring in the crawler and egg stage. The suppressive abilities of the predator Rodolia cardinalis (Mulsant) and the parasite Cryptochactum iceryae (Williston) on field populations of I. purchasi were studied. No parasitism of the 1st instar of I. purchasi was found. The percent parasitism of susceptible nymphs and adults in Desmodium fields was: 2nd instar 3.5–5.2%; 3rd instar 10–18.5%; and adults 14.8–25.2%. There was a lag between the peaks of predator and prey populations which occurred during October and November. The sharp decline in the scale populations during October and November was primarily a result of predation by R. cardinalis.

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