Survival, growth and gall formation by Phytolyma lata on Milicia excelsa established in mixed-species tropical plantations in Ghana

1 Milicia excelsa (Moraceae) is an important timber tree in much of Africa and when grown in monocultural plantations has been subject to nearly complete destruction by gall-forming psyllids in the genus Phytolyma. 2 We tested the impact on susceptibility to Phytolyma spp. of planting Milicia excelsa in various densities and species mixtures. Replicated plantings consisting of 11, 25, 50 and 100% Milicia in mixtures with Terminalia superba (Combretaceae) were established at a site surrounded by natural forest and in an agricultural area. 3 In addition at the agricultural site, 50–50 mixtures of Milicia excelsa with Albizia adianthifolia (Mimosaceae), Tectona grandis (Verbenaceae), Khaya ivorensis. (Meliaceae), Ceiba pentandra (Bombacaceae) and a mixture combining all species were planted. 4 Two months after planting, gall numbers were significantly lower in the 11% Milicia mixtures at the forest site. Gall numbers were also significantly lower at the forest site than at the agricultural site, for all densities of Milicia. At 6 months, dieback of Milicia resulting from gall formation had taken place equally on all seedlings, but survival of seedlings at the forest site was 40% higher than at the agricultural site.