Distribution, timing of attack, and oviposition of the banana weevil, Cosmopolites sordidus, on banana crop residues in Uganda

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 prostrate 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 experiment, oviposition on standing residues was not significantly affected by residue age. By contrast, oviposition 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 residues. 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 residue 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.