Population studies of the potato leafhopper, Empoasca fabae (Harris), on alfalfa, Medicago sativa L.

Abstract

The potato leafhopper, Empoasca fabae (Harris), is a primary pest of alfalfa grown in Virginia. Sampling techniques and sampling programs for each growth stage (egg, nymph, and adult) were developed to study the population dynamics of this insect. Distribution patterns exhibited by each stage have been used to determine sample unit size and optimum number of samples. The sampling technique was also evaluated in field population studies. The egg sampling technique, which used an acid fuchsin stain and lactophenol clearing solution, was efficient in estimating egg densities within 20 to 30% C.V. about the mean based on 100 single stems collected on each sample date. The nymphal sampling technique using 0.946 liter ice cream containers with dichlorvos squares (ca 1.2 cm²) glued in the bottom of the container was efficient in estimating nymphal densities within 20 to 30% C.V. based on 100 three-stem bouquets collected on each sample date. The adult sampling technique was efficient within 10 to 20% C.V. about the mean based on sixty 0.92 m² samples collected with a vacuum backpack insect collector (D-Vac ® manufactured by D-Vac Co., Riverside, Calif.). Developmental rates for eggs and nymphs and ovipositional rates of adult females in laboratory studies were determined at several temperatures. Egg and nymphal development rate increased with increasing temperatures from 13 to 32°C. The development followed a linear relationship between upper and lower threshold levels. Oviposition rate was consistent between 18 to 29°C, but ceased above and below these temperatures. Developmental rates and maximum-minimum daily temperatures were used to study the effect of alfalfa harvest on egg and nymphal abundance. Mortality was high after harvest, and harvest time was important in reducing potato leafhopper abundance. Clean harvest practices were also important in reducing egg and nymphal survival, and in reducing population buildup of potato leafhoppers on early regrowth of alfalfa.