Icerya aegyptiaca (breadfruit mealybug)

Sap depletion may lead to leaf drop and stunted growth. As with most sap-sucking insects, the production of honeydew leads to the growth of sooty mould.

Introduction

Sprays containing white oil or some of the modern synthetic pesticides will control I. aegyptiaca, but these are expensive and difficult to apply to large trees (Waterhouse, 1991). In addition, all life stages of I. aegyptiaca are covered with wax, which reduces the effectiveness of most chemical insecticides. However, natural enemies have proved to be effective in most areas where the pest has been introduced. Serious damage is rare in the range of I. aegyptiaca.

Biological Control
 

Waterhouse (1993) provides a table of the main natural enemies of I. aegyptiaca and discusses the use of some of these species as biological control agents.

The dipteran parasitoid Cryptochetum grandicorne parasitizes I. aegyptiaca at levels of up to 90% in India and up to 10% in Pakistan (Waterhouse, 1991). However, colonization trials in Israel showed that the related species C. iceryae did not parasitize I. aegyptiaca (Mendel and Blumberg, 1991).

The ladybird Rodolia cardinalis is indigenous to Australia. After its well-known success in regulating the cottony cushion scale, I. purchasi, on citrus in 1888-89, it was considered for the control of other Icerya species. It has established successfully in Egypt on I. aegyptiaca, but despite introductions into Micronesia, does not appear to have persisted in this region (Waterhouse, 1991).

A related ladybird R. pumila, presumed to be an accidental introduction from the Orient, had become established on most of the high islands of Micronesia by the 1950s (Beardsley, 1955; Chapin, 1965) and I. aegyptiaca is no longer regarded as a pest on these high islands (Schreiner, 1989). However, R. pumila does not appear to persist for more than a few years on atolls, despite repeated introductions (Waterhouse, 1991). It has been suggested (Schreiner, 1989) that on small atolls, R. pumila died of starvation once populations of Icerya scales were reduced to low levels. Being specific predators of Icerya scales, R. pumila would find it difficult to find alternative prey on most atolls which have a limited fauna compared with that of high islands. Waterhouse (1991) suggested that biological control of I. aegyptiaca with R. pumila on Pacific atolls would require regular re-introductions every few years.

After trials in Israel, a related ladybird, R. iceryae was found to be unable to complete its development on I. aegyptiaca (Mendel and Blumberg, 1991).

An unidentified species of the predator Scymnus has been recorded clearing the leaves of I. aegpytiaca on mulberry in India (Siddpapaji et al., 1984).

I. aegyptiaca has been recorded as a serious pest of citrus, fig and shade trees in Egypt, although it is now largely controlled by natural enemies (Clausen, 1978). It is also a pest of breadfruit, avocado, banana, citrus and ornamentals in the South Pacific (Williams and Watson, 1990); annona, jackfruit, sapote (Pouteria sapota) and guava in India (Rao, 1951), mulberry in India (Siddpapaji et al., 1984) and breadfruit in the Maldive Islands (Watson et al., 1995).Damage to the plant is caused by sap depletion; shoots dry up and die, and defoliation occurs. In addition, copious quantities of honeydew are produced by the scales; this results in the growth of sooty moulds over the surfaces of the leaves, reducing photosynthesis.Heavy infestations of breadfruit on Pacific atolls have been reported to kill even mature trees but, more often, trees are partially defoliated and the crop reduced, sometimes by more than 50% (Waterhouse, 1991).