Study of two forms of the adult Stenocranus minutus



  • 1In studies on Stenocranus minutus, two winged forms of adults have been observed, macropterous and sub-macropterous. Macropterous individuals, with extra-long wings, have not been previously observed or described. Probably only the macropterous form disperses by flight.
  • 2The two forms differ in their wing lengths, intensity and extent of pigmentation.
  • 3The rate of maturation differs in the two forms. In macropters, maturation is delayed; the period of oviposition is shorter and they are less fecund.
  • 4Macropters do not live as long as sub-macropters.
  • 5The macropters weigh less than the sub-macropters.
  • 6Under laboratory conditions, both forms can hop but the macropterous forms fly for a longer time than the sub-macropters.
  • 7At 25°C, more macropterous forms were produced on wilting Dactylis than on green, succulent Dactylis.
  • 8Dispersal of field population was inferred from changes in proportions of the two forms and by simultaneous occurrence of macropters in aerial suction traps.
  • 9The macropterous forms of S.minutus migrate a few weeks after emergence while still immature and migration coincides with drying up of host plant, Dactylis glomerata L.
  • 10Relatively high temperature, low wind speeds and a small number of hours of sunlight seem to favour dispersal by flight in S.minutus.