Study of two forms of the adult Stenocranus minutus

SUMMARY In 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. The two forms differ in their wing lengths, intensity and extent of pigmentation. The rate of maturation differs in the two forms. In macropters, maturation is delayed; the period of oviposition is shorter and they are less fecund. Macropters do not live as long as sub‐macropters. The macropters weigh less than the sub‐macropters. Under laboratory conditions, both forms can hop but the macropterous forms fly for a longer time than the sub‐macropters. At 25°C, more macropterous forms were produced on wilting Dactylis than on green, succulent Dactylis. Dispersal of field population was inferred from changes in proportions of the two forms and by simultaneous occurrence of macropters in aerial suction traps. The 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. Relatively high temperature, low wind speeds and a small number of hours of sunlight seem to favour dispersal by flight in S.minutus.