INFLUENCE OF EMBRYONIC DEVELOPMENT AND HEAT ON POPULATION TREND OF THREE GRASSHOPPER SPECIES (ORTHOPTERA: ACRIDIDAE) IN SASKATCHEWAN

Abstract

The study examined quantitatively the effects of embryonic development in the preceding fall and cumulative heat units from 1 April to 31 July in the current year on density trends of three major grasshopper species (Melanoplus sanguinipes (Fabr.), M. bivittatus (Say), and Camnula pellucida (Scudder)) in Saskatchewan. The influence of adult density of the previous year, embryonic development, heat units, and their interactions were examined by multiple regression analyses for each of the three species to determine their contribution to next year’s adult populations. The models tended to underestimate density during a population increase and to overestimate during a population decline. Combined heat units during the preceding fall and following spring indicated that a general increase in density should occur when heat units were equal to or greater than 1600 °D₅₀.