SEASONAL PHENOLOGY AND DEVELOPMENTAL BIOLOGY OF AMORBUS-OBSCURICORNIS(WESTWOOD) AND GELONUS-TASMANICUS (LE-GUILLOU) (HEMIPTERA, COREIDAE)

Detailed studies of the seasonal phenology and developmental biology o f two eucalypt-feeding coreid species, Amorbus obscuricornis and Gelon us tasmanicus, were undertaken over three years in Tasmania. Both spec ies are univoltine, their active season being from spring to autumn, w ith the adults being the overwintering stage. Adults of A. obscuricorn is and G. tasmanicus emerge during spring to feed, mate and oviposit. Periods of peak copulatory activity and gravidity of females in both s pecies correspond to times when the proportion of males to females is slightly male biased. Eggs of A. obscuricornis did not hatch at temper atures below 15 degrees C while the number of eggs of G. tasmanicus ha tching at 13 degrees C remained high. The minimum developmental thresh old temperature and number of degree-days (DD) required for hatching b y eggs of A. obscuricornis and G. tasmanicus were estimated to be 11.8 and 10.8 degrees C and 147 and 136 DD, respectively. Embryonic develo pmental rates are considered to reflect differences in the evolved tem perature preferences of each species. During spring and summer the nym phs develop through five instars to eclose in autumn just before overw intering. Second-instar mortality for both species was high, suggestin g that the initiation of feeding may be a crucial developmental stage.