Coupling Feeding Effects of Potato Leafhopper, Empoasca fabae (Homoptera: Cicadellidae), Nymphs to a Model of Potato Growth

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Abstract
Effects of potato leafhopper, Empoasca fabae (Harris), feeding were coupled to a simple potato growth model that accumulates and partitions dry matter into leaves, stems, roots, and tubers. Feeding effects of leafhopper on potato were modeled in two ways: as a temporary and reversible reduction in the plant's potential net crop growth rate, and as leaf area lost to hopperburn. Daily reductions in potential net crop growth rate were determined by an exponential relationship of leafhopper feeding activity, which was defined as number of nymphs per 30 midplant leaves multiplied by daily degree-day increment. Rate of hopperburn development was determined from a modified logistic equation. Values for the model's parameters were derived with data from 8 or 13 sequential, within-season harvests of plant dry matter and counts of leafhopper nymphs from infested and uninfested field plots collected over 2 yr. Partitioning responses of the modeled crop were similar to those observed for field-grown plants. Model output was also verified against nymphal counts, hopperburn readings, and final yields from an independent field experiment, which resulted in a one-to-one correspondence between predicted and final yields. Computer simulations with nymph infestations at different times of the season indicated that reductions in final tuber yield were differentially effected by leafhopper feeding at different stages of growth.