Damage byCylas formicariusFab. to sweet potato vines and tubers, and the effect of infestations on total yield in Papua New Guinea

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Abstract
In a series of four trials on sweet potato (Ipomoea batatas (L.) Lam.) four parameters relating to sweetpotato weevil (Cylas formicarius Fab.) population and damage levels were recorded. These were the numbers of adult weevils per m2 of foliage, the numbers of weevil life stages in 15 cm vine sections immediately above the tubers, the percentage of damaged vines and the percentage of damaged tubers. Strong positive correlations were found between the various parameters. Infestations of vines by weevils reduced the vigour of surface foliage and resulted in reduced yields. It was not possible to establish a spray threshold because reduced yields and damage to tubers occurred at low population levels. The number of rainy days between 60–90 days from planting was negatively correlated with the percentage of damaged tubers at 175 days from planting.