Seasonal Phenology and Developmental Biology of Amorbus obscuricornis (Westwood) and Gelonus tasmanicus (Le Guillou)(Hemiptera : Coreidae)

Abstract

Detailed studies of the seasonal phenology and developmental biology of two eucalypt-feeding coreid species,Amorbus obscuricornis and Gelonus tasmanicus, were undertaken over three years in Tasmania. Both species are univoltine, their active season being from spring to autumn, with the adults being the overwintering stage. Adults of A. obscuricornis andG. tasmanicus emerge during spring to feed, mate and oviposit. Periods of peak copulatory activity and gravidity of females in both species correspond to times when the proportion of males to females is slightly male biased. Eggs of A. obscuricornis did not hatch at temperatures below 15˚C while the number of eggs of G. tasmanicus hatching at 13˚C remained high. The minimum developmental threshold temperature and number of degree-days (DD) required for hatching by eggs of A. obscuricornis and G. tasmanicus were estimated to be 11·8 and 10·8˚C and 147 and 136 DD, respectively. Embryonic developmental rates are considered to reflect differences in the evolved temperature preferences of each species. During spring and summer the nymphs develop through five instars to eclose in autumn just before overwintering. Second-instar mortality for both species was high, suggesting that the initiation of feeding may be a crucial developmental stage.