Biological control of the fruit-spotting bug Amblypelta lutescens using weaver ants Oecophylla smaragdina on African mahoganies in Australia

1 African mahogany Khaya senegalensis is a high-value timber tree. Pilot plantings showed that the fruit-spotting bug Amblypelta lutescens causes severe damage of the tree in the wet-dry tropics of northern Australia. The weaver ant Oecophylla smaragdina is an efficient biocontrol agent in some horticulture crops. To investigate whether the ants control this pest, field experiments were conducted from April 2006 to January 2009 at two study sites in the Darwin area, Australia. A laboratory experiment was carried out in March 2007 at Berrimah Farm. 2 During the experimental period, in the weaver ant treatments, the overall percentage of trees damaged by the pest was 0-8% at both sites, and the damaged trees were attacked once only. In the treatments without weaver ants, however, the damage level was > 80% at Berrimah Farm and 31-100% at Howard Springs, and the damaged trees were attacked more than once. 3 The mean percentage of trees damaged per monitoring occasion was 0-2.6% in the weaver ant treatments at both sites, whereas, in the treatments without the ants, the damage percentages were 14.2-27.0% at Howard Springs and 28.2-48.6% at Berrimah Farm. 4 Extrafloral nectar of African mahoganies is attractive to weaver ants. Fruit-spotting bugs only damage the tender parts of flushing shoots and growing tips. Weaver ants live on sugar solution and meat, and they frequently harvest extrafloral nectar on growing shoots, on which they catch nymphs of the pest for their meat supply. The aggressive behaviour of the ants also repels the pest away from flushing shoots. 5 The data suggest that weaver ants were effective biocontrol agents of fruit-spotting bugs, and the ants can be used to manage the pest on African mahoganies. 6 The present study demonstrates that the introduced African mahogany comprises another major host of the fruit-spotting bug.