| Population densities and spatial distribution patterns of threecornered alfalfa hopper, Spissistilus festinus (Say), instars on soybean (Glycine max (L.) Merrill) were estimated by two ground-cloth methods, whole-plant inspection, and an absolute sampling method. Population size and age structure were more reliably estimated by whole-plant inspection than by ground-cloth methods. Parameters for Taylor's power law were influenced by instar, sampling method, and sample size.;Vertical distributions of nymphs and girdles, and plant-part and girdle associations of nymphs were examined by inspecting randomly selected whole-plants. Most nymphs were on the lower stems of stage V2 to V7 plants, and in the lower plant canopy of more developed plants. Most main-stem girdles occurred on the lower stems and most petiole girdles occurred in the lower parts of the canopy. Plant-part associations changed with changing plant phenology. The degree of girdle association varied with girdle type and instar.;Diel patterns in vertical distribution, intra- and interplant movement, molting, ant tending, and attrition of nymphs were examined in the field. Periodicity was observed in intra- and interplant movement, molting, and attrition. Differences between instars were observed in intra- and interplant movement, ant tending, and attrition.;Temporal effects of 1-, 7-, and 14-d old petiole girdles on translocation were investigated using the herbicide glyphosate as a tracer. Girdles initially blocked translocation, but translocation was resumed within 7 d of girdling.;Temporal effects of 1-, 3-, 7-, and 10-d old petiole girdles on leaf starch, free sugars, free amino nitrogen, specific leaf weight, and leaf percent moisture were examined. Specific leaf weight was increased by girdling. Leaf starch was initially increased and percent moisture was decreased by girdling, but returned to normal levels by 10 d after girdling. Free sugars were decreased at 1, 3, and 7 d after girdling. When corrections were made for increased starch, girdling did not affect free sugars. Effects of girdling on amino nitrogen were similar to effects on free sugars, except amino nitrogen was decreased at 3 and 10 d after girdling when corrections for increased starch were made. The amino nitrogen: free sugar ratio was decreased at 10 d after girdling. |
