Vertical Distributions of Potato Leafhopper Nymphs (Homoptera: Cicadellidae) on Potatoes Relative to Leaf Position, Plant Age, and Population Size

Abstract

The vertical distributions of potato leafhopper nymphs, Empoasca fabae (Harris), on potato foliage were monitored over a cropping season. Three treatments were managed with insecticide sprays that allowed nymphal infestations to develop in early, mid-, or late season. The maximum populations ranged from 72 nymphs per 30 mid plant leaves in the early-season infestation to 10 nymphs per 30 midplant leaves in the late-season infestation. The maximum densities of nymphs always occurred within the midplant region, 3-11 leaves from the top, and the frequency distributions of nymphs per leaf generally fit the negative binomial distribution. For a given date, values of the negative binomial’s dispersion parameter, k , did not differ significantly between nymphal infestation levels, but k increased with plant age. Two ratio variables were created by dividing the mean number of nymphs per leaf and the mean number of nymphs per plant by the mean number of nymphs per leaf sampled within the midplant region. The values obtained for these ratios were independent of treatment for a given date, and they each changed with plant age. The ratio of nymphs per leaf to nymphs per midplant leaf increased linearly with increasing plant age, and the ratio of nymphs per plant to nymphs per midplant leaf first increased and then decreased with plant age.