Influence of cold temperature and exposure time on egg overwintering survival in the white-whiskered grasshopper (Orthoptera: Acrididae)

The effect of cold temperatures and exposure time on egg survival and hatching success were examined in the white-whiskered grasshopper, Ageneotettix deorum. Temperature treatments ranged from 4°C to -35°C, with treatment times ranging from 48 to 240 hours. Both decreasing temperatures and exposure time negatively affected egg survival, with a temperature below -25°C being lethal. Similar lethal temperatures are known for several North American grasshopper species. The relatively shallow location of A. deorum egg pods would result in increased vulnerability of eggs to cold temperatures in the absence of snow.

TEMPORAL VARIATION IN RANGELAND GRASSHOPPER (ORTHOPTERA: ACRIDIDAE) COMMUNITIES IN THE STEPPE REGION OF MONTANA, USA

A study was conducted to evaluate changes in rangeland grasshopper communities over a 5-year period in the Agropyron spicatum (Pursh) Scribn. and Smith and Bouteloua gracilis (H.B.K.) Lag. provinces of the steppe region of Montana, USA. Results showed that it was possible to categorize years into outbreak, non-outbreak, and transitional based on rangeland grasshopper intensity. Nearly twice as many species were observed in outbreak versus non-outbreak years. Of the 57 total grasshopper species collected over the entire study period, 16 species were found only during outbreak years and only two were found exclusively during non-outbreak years. Of the remaining 39 species collected during outbreak and non-outbreak years, 27 species showed no significant differences in the percentage of the community that they represented and 11 species showed significant increases. The only species that made up proportionately less of the community as densities declined from outbreak to non-outbreak was Melanoplus sanguinipes (F.). Although M. sanguinipes, Ageneotettix deorum (Scudder), and Aulocara elliotti (Thomas) were the three top-ranked species in both outbreak and non-outbreak years, M. sanguinipes contributed most to overall shifts in grasshopper intensity. Results support the hypothesis that grasshopper communities overall are sensitive to temporal changes in resources, even though responses of individual species differed.

IMMEDIATE AND 2ND-YEAR EFFECTS OF INSECTICIDE SPRAY AND BAIT TREATMENTS ON POPULATIONS OF RANGELAND GRASSHOPPERS

Two, 1400-ha blocks of rangeland in western South Dakota were treated aerially with malathion liquid spray or carbaryl – bran bait in early July 1986 to determine the immediate and 2nd-year impact of treatments on grasshopper populations. Total grasshopper populations were reduced by 92 and 47% in the malathion and carbaryl – bran bait treatment plots, respectively, within 48 h after treatment and remained at a low level throughout the summer. Populations did not change in the control plots. Populations of the two most abundant species, Ageneotettix deorum (Scudder) and Melanoplus sanguinipes (F.), declined by 65 and 87%, respectively, in the carbaryl – bran bait plots but populations of bran "rejectors" (predominantly Trachyrhachys kiowa [Thomas]) did not change.Densities of the bran "acceptors" (Melanoplus spp., Phoetaliotes nebrascensis [Thomas], and A. deorum), as a group, did not change significantly in the control plots between the pre-treatment and July 1987 sampling dates. Densities within both sets of treatment plots were significantly lower in the 2nd year of the study than on the pre-treatment sampling date. Although 2nd-year populations of bran acceptors, as a group, did not increase to pre-treatment levels in the treated plots, populations of M. sanguinipes did increase to pre-treatment levels in both sets of treatment plots. Populations of bran rejectors generally remained low in treatment and control plots.Analysis of covariance of the densities of 2nd-year populations of total grasshoppers and bran rejectors indicated that treatment had no significant effect on populations of these grasshoppers, but the covariable, pre-treatment density, was significantly correlated with 2nd-year densities. Densities of 2nd-year populations of bran acceptors were also significantly correlated with pre-treatment densities.It was concluded that both the insecticidal spray and bait were effective in controlling most economically important species of rangeland grasshoppers. Although both treatments may have suppressed populations of bran acceptors, as a group, in the 2nd year of the study, neither suppressed populations of M. sanguinipes which increased to pre-treatment levels regardless of treatment. The effect of treatments on 2nd-year populations of bran rejectors could not be determined because populations of this group also declined in control plots.

SPECIES RICHNESS, DENSITY, AND DIVERSITY OF GRASSHOPPERS (ORTHOPTERA: ACRIDIDAE) IN A HABITAT OF THE MIXED GRASS PRAIRIE

An assemblage of 24 grasshopper species inhabited a mixed grass prairie site near Livermore, Colorado. Ten species were gomphocerines, 9 melanoplines, and 5 locustines; the gomphocerines represented ca. 80% of total density, melanoplines 15%, and locustines 5%. Grass feeders, gomphocerines and most locustines, made up 85% of total density. The dominant species was Ageneotettix deorum which contributed 52% of the grasshopper density in 1981 and 37% in 1982. The grasshopper population was at outbreak density both years, 60/m2 in 1981 and 36/m2 in 1982. The pasture had never been treated with insecticide or herbicide. The Shannon-Wiener index of ca. 2.00 indicated a high grasshopper diversity.