© 2005 The Netherlands Entomological Society Entomologia Experimentalis et Applicata 117: 119–126, 2005 119 Blackwell Publishing, Ltd. Distribution, timing of attack, and oviposition of the banana weevil, Cosmopolites sordidus , on banana crop residues in Uganda M. Masanza 1,2 , C.S. Gold 1, * & A. van Huis 2 1 International Institute of Tropical Agriculture, PO Box 7878, Kampala, Uganda; 2 Laboratory of Entomology, Wageningen University, PO Box 8031, Wageningen, 6700 EH, the Netherlands Accepted: 16 June 2005 Key words: crop sanitation, cultural control, highland banana, oviposition, Coleoptera, Curculionidae, pest management Abstract Crop sanitation (removal and chopping of residue corms and pseudostems following plant harvest) has been recommended as a ‘best bet’ means of reducing banana weevil, Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae), populations. However, it has been unclear when such practices should be carried out and what types of residues should be destroyed. Therefore, trials were conducted in Uganda to determine C. sordidus distribution, timing of attack, and oviposition on crop residues and growing plants. Assessments were performed in on-station trials on different aged standing and pros- trate residues by destructive sampling. Similar data were collected from farmers’ fields maintained at low, moderate, and high levels of sanitation. In the on-station trial, oviposition occurred on up to 120- day-old residues, although most occurred within 30 days of harvest. In a second on-station experi- ment, oviposition on standing residues was not significantly affected by residue age. By contrast, ovi- position on prostrate residues was two times higher on 4-week-old than on 2-week-old residues, while the number of larvae on 8-week-old residues was three times higher than on 2-week-old resi- dues. The number of adults was twice as high on 16-week-old residues as that on 2-week-old residues for both prostrate and standing residues. Farmers’ fields maintained at high sanitation had 50% fewer eggs per residue than farms with low sanitation levels. In general, the number of immatures per res- idue was 50% higher on banana corms than on pseudostems. Numbers of larvae per residue were three times more abundant at low than at high sanitation levels. Residues in fields with high sanitation supported 50% fewer adults than residues in low sanitation fields. The results suggest that removal and splitting of corms after harvest is effective and practical in destroying immature growth stages of the pest and that such practices should be carried out soon after harvest. Introduction The banana weevil, Cosmopolites sordidus (Germar) (Coleo- ptera: Curculionidae), is an important pest of East African highland banana (Musa spp. (Musaceae), genome group AAA-EA) (Sebasigari & Stover, 1988; Gold et al., 1999). Damage is caused by the larvae, which tunnel in the corm and pseudostem. Cosmopolites sordidus attack interferes with water and nutrient uptake resulting in plant loss, delayed maturation, reduced bunch weights, and shortened plantation life (Rukazambuga et al., 1998; Gold et al., 2004a). Damage also weakens the plant base leading to snapping and toppling. In severe attacks, yield losses can reach 100% (Sengooba, unpubl.). This pest has been implicated as a principal cause of highland banana decline in central Uganda (Gold et al., 1999). Bananas are rhizomatous herbaceous plants (Stover & Simmonds, 1987). A mat consists of an underground corm from which one or more plants (shoots) emerge. The shoot consists of a pseudostem, comprised of leaf sheaths, and a true stem that grows through its center and bears the flower and fruit. New plants (ratoons) are produced by suckers emerging from lateral buds in the corm. Normally, a banana mat consists of three or more plant generations (ratoons or crop cycles) at any one time. Plant density is *Correspondence: IITA, PO Box 7878, Kampala, Uganda. E-mail: c.gold@cgiar.org