The role of natural enemies in controllingIcerya purchasi in South Australia

Abstract

The obscure occurrence of the cottony-cushion scale Icerya purchasi Maskell in its native country Australia is generally attributed to its natural enemies. Twelve natural-enemy-exclusion experiments were conducted at monthly intervals to confirm the role of natural enemies. Each experiment had uncaged, open-caged, and caged treatments. The natural enemies were active throughout the year. The percentage of scales surviving to adults in the cages was significantly higher than in the open-caged treatments, except the April (first) cohort. In both open-caged and uncaged treatments, the percentage of scales surviving to adults was similar and matched the changes in the numbers of natural enemies, thus confirming their importance in controlling L purchasi in South Australia.

Discovery of isolated patches ofIcerya purchasi byRodolia cardinalis: A field study

“…To achieve this, the natural enemy exclusion method (DeBaeh & Bartlett, 1964) was incorporated in the design of the experiment, but many caged patches were accidentally destroyed. However, the influence of natural enemies on the survival of the scales throughout the year was conclusively demonstrated by a series of 12 (monthly) natural enemy exclusion experiments (Prasad, 1989 ). Even in the experiment reported here, within a fortnight of the start of the experiment (table 3), Rodolia adults had found the prey patches also at the isolated location 2, even when all the scales were in I st instar.…”

Observations on the seasonal abundance ofIcerya purchasi onAcacia baileyana in Adelaide, South Australia

“…Both biotic and abiotic factors are known to influence the seasonal abundance of the scale. As in other countries (Bartlett, 1978), the natural enemies keep a check on L purchasi populations from achieving pest status in Adelaide as well (Prasad, 1989). However, the scales are almost immune to attack by natural enemies on some host plants, viz.…”

“…Spartium junceum, Erythrina corallodendrum and Cocculus laurifolius, (Quezada & De Bach, 1973 ;Mendel et al, 1988). On A. baileyana, the most common host plant in Adelaide, isolated scale colonies are easily discovered (Prasad, 1990) and normally attacked by natural enemies (Prasad, 1989). Nonsessile immature scales could be killed by heavy rain (Hale, 1970) and practically all scales were destroyed by a hurricane in Puerto Rico (Wolcott & Sein, 1933).…”

“…Between April, 1982 andOctober, 1983 a series of 12 monthly natural-enemy-exclusion experiments (NEEET) were conducted in the field to provide more detailed data on the seasonal activity pattern of L purchasi and on the role of natural enemies (Prasad, 1989). Each NEEET had 3 replicates in each of 3 treatments for which cohorts of scales were either enclosed in a sleeve cage, enclosed in a sleeve cage open at 1 end or uncaged.…”

Monitoring the effects of Rodolia cardinalis on Icerya purchasi populations on the Galapagos Islands

“…Two experimental conditions were established: (1) controls that were I. purchasi-infested branches enclosed in sleeve cages to prevent access by R. cardinalis (following Luck et al 1998;Prasad 1989;van Driesche and Bellows 1996) and (2) treatment branches that were continuously exposed to foraging R. cardinalis. A preliminary study was conducted to determine the minimum sample size required to estimate scale density.…”