Observations on soil-inhabiting insect populations of improved pasture in nelson province, with particular reference to costelytra zealandica (white) (col., scarabaeidae)

Abstract

Observations were made on populations of four species of soilinhabiting insects at two sites near Nelson in 1968-70. The species were Thyreocephalus chloropterus (Staphylinidae), Conoderus (Mollcrepidus) exsul (Elateridae), Wiseana cervinata Walk. (Hepialidae ), and Costelytra zealandica (White). Fluctuations in population density over the period were recorded, and probable factors affecting mortality were examined. The first two species were predators on C. zeal andico, hut their importance in this role was unknown. The last two species fed on the foliage and roots respectively of pasture plants. The major part of overall mortality in these species was apparently associated with adverse climate and management practices.

The rate of growth of C. zealandica larvae was reduced during summer drought and in pastures treated with herbicide. The effects of poor larval nutrition on larval mortality and adult fecundity are discussed. It is concluded that the results indicate a good prognosis for the control of grass grub populations by the use of resistant pasture plants.