ABSTRACT
Yam beetles are one of the most damaging soil insect pests to yam and have caused considerable set back to yam farmers in the yam growing area of Niger Delta. A one year study to determine the potential threshold level of Heteroligus meles damage on yam farm was conducted at the Faculty of Agriculture Teaching and Research Farm, Delta State University, Anwai, Asaba Campus, Delta State, Nigeria in 2004. The variety of yam used was Dioscorea rotundata (white yam) cv. Adaka. The experiment was laid out in a randomized complete block design (RCBD) with three replications. The treatments used were: 1, 2, 3, 4 and 5 beetles per stand respectively. No beetle was in the control plot. Beetles were artificially introduced into yam planted in nylon net cages/bags six weeks after sprouting and vine establishment. Results showed that plots infested with various populations of H. meles had more number of feeding holes, depth, diameter and size than uninfested control plots. Severity of beetle damage was highest at 4 and 5 beetles/ yam stand and was significantly different (p<0.05) from other treatments. Damage scoring ranged from mild to severe damage in beetle infested treatments while no symptom was recorded in the control. Tuber yield was highest in the uninfested control plots which were significantly different (p<0.05) from the beetle infested plots. Percentage yield reduction over control was dependent on beetle population while the yield index and multiplication ratio had best results on control plots. The result therefore suggests that the economic threshold level of the insect may be lower than one adult beetle per yam heap under field condition considering the degree of damage. |
KEYWORDS: |
Yam, Yam beetle, damage severity, feeding holes, populations, yield index. |
