No abstract

Khaya senegalensis (African mahogany or dry-zone mahogany) is a high-value hardwood timber species with great potential for forest plantations in northern Australia. The species is distributed across the sub-Saharan belt from Senegal to Sudan and Uganda. Because of heavy exploitation and constraints on natural regeneration and sustainable planting, it is now classified as a vulnerable species. Here, we describe the development of microsatellite markers for K. senegalensis using next-generation sequencing to assess its intra-specific diversity across its natural range, which is a key for successful breeding programs and effective conservation management of the species. Next-generation sequencing yielded 93,943 sequences with an average read length of 234 bp. The assembled sequences contained 1030 simple sequence repeats, with primers designed for 522 microsatellite loci. Twenty-one microsatellite loci were tested with 11 showing reliable amplification and polymorphism in K. senegalensis. The 11 novel microsatellites, together with one previously published, were used to assess 73 accessions belonging to the Australian K. senegalensis domestication program, sampled from across the natural range of the species. STRUCTURE analysis shows two major clusters, one comprising mainly accessions from west Africa (Senegal to Benin) and the second based in the far eastern limits of the range in Sudan and Uganda. Higher levels of genetic diversity were found in material from western Africa. This suggests that new seed collections from this region may yield more diverse genotypes than those originating from Sudan and Uganda in eastern Africa.

1 African mahogany Khaya senegalensis is a high-value timber tree species widely grown in central Africa, south-east Asia and northern Australia. Pilot plantings show that the tree grows well in the wet-dry tropical areas of northern Australia, and the shoot borer Hypsipyla robusta (Lepidoptera: Pyralidae) is a potential pest of the tree. The weaver ant Oecophylla smaragdina is an efficient biocontrol agent in some horticulture crops. To investigate whether the ants control shoot borers, field experiments were conducted at two sites near Darwin, Australia from April 2006 to January 2009. 2 In the weaver ant treatments, the overall percentage of trees damaged by shoot borers was 0-2.7% at Berrimah Farm and 0-4.2% at Howard Springs, and the damaged trees were attacked once only. In the treatments without weaver ants, however, 9.9-52.1% trees were damaged at Berrimah Farm, and 6.3-64.6% at Howard Springs, and the damaged trees were generally attacked more than once. 3 At both sites, significantly fewer trees on each monitoring occasion were damaged in weaver ant treatments than in treatments without weaver ants. 4 The mean percentage of overall flushing shoots damaged by the pest at both sites was significantly lower in weaver ant treatments compared with treatments without weaver ants. 5 Fewer shoots were damaged per damaged tree in weaver ant treatments compared with treatments without weaver ants. 6 The data obtained suggest that weaver ants were effective biological control agents of the shoot borer, and that the ants can be used to manage the pest on African mahogany trees.

African mahogany, Khaya senegalensis, is a high quality timber tree that grows well in the wet-dry tropical areas of Australia. Most trees grown in the latter regions are branched at lower levels on the trunk (a symptom known as 'low-branching'), which limits timber production per tree. Inferring that it may be caused by herbivorous insects, we sought to establish whether low-branching can be reduced by the presence of predatory weaver ants, Oecophylla smaragdina. Two field experiments on young African mahoganies were conducted at two sites in the Darwin area of Australia from 2006 to 2008. Each experiment had two treatments: trees with weaver ants and trees without the ants. Pest damage was found to be the most important correlate of the multiple branching, and weaver ants were effective in limiting the formation of multiple leaders. In 3-year-old mahoganies at Berrimah Farm, the percentage of trees with pest-caused multiple leaders was 4.8% in the weaver ant treatments (WAT) but 45.5% in the treatments without the ants (TWWA). In 2-year-old mahogany coppices at Howard Springs, no trees developed multiple leaders in WAT, but 22% developed such leaders in TWWA. The average pest damage on flushing shoots at both sites was significantly lower in WAT (1.8-2.5%) than in TWWA (22.9-24.9%).

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.