POTATO LEAFHOPPER (HOMOPTERA, CICADELLIDAE) LIFE-HISTORY TRAITS ON WATER-STRESSED ALFALFA IN THE EARLY REGROWTH AND BUD STAGE

In controlled environment studies the effect of plant water stress on the life history characteristics of the potato leafhopper, Empoasca fabae (Harris), was examined for insects on early regrowth and bud stage alfalfa (Medicago sativa L.). On both plant growth stages, the developmental period of male and female nymphs increased with the increase in plant water stress. Although the differences were relatively small, the stressed treatments were significantly longer than the well-watered control. Plant water stress did not influence nymphal mortality at either plant growth stage. Adult survivorship was lower on the water-stressed treatments, except for females on early regrowth alfalfa. Fecundity declined with the increase in plant water stress, particularly for insects reared on bud stage alfalfa. Oviposition rates during the first half of adult life declined with the increase in plant water stress, but this relationship was not found for the gross reproductive rate. The long-term effect on reproduction of nymphal development on water-stressed alfalfa was examined by switching recently emerged adults from stressed to well-watered hosts. The oviposition rates of these females remained below that of the control for most of the subsequent six 2-d oviposition periods. These changes in the life history traits of the potato leafhopper indicate that water-stressed alfalfa is unfavorable for leafhopper population growth. This decline in suitability may result from the lower nitrogen content of water-stressed alfalfa or to changes in other components of host quality.