Bionomics and the predicted distribution of the aphid Brachycaudus rumexicolens (Hemiptera : Aphididae)

Development rates of the aphid, Brachycaudus rumexicolens (Patch), a recent arrival in Australia and a potential biological control agent against weed s in the family Polygonaceae, were measured over a range of constant temper atures. The theoretical lower limit for development is 6.4 degrees C and th e upper limit 32 degrees C. Maximum fecundity per day was reached at 19 deg rees C. The rate of increase peaked at about 28 degrees C giving a populati on doubling time of less than two days. These values were used with the cur rent distribution to develop a CLIMEX model to predict the potential world distribution of the aphid. The model predicts that the aphid has suitable p eriods of population growth in autumn and spring, and that survival is unli kely over summer in most of south-western Australia where the aphid has the potential to contribute to the biological control of the polygonaceous wee ds, Emex and Rumex species. The model predicts that years with cool summer temperatures and late summer rains in south west Australia, such as in 1990 when the aphid was first abundant, will be particularly suitable for aphid development. These conditions occurred twice between 1985 and 1995. To inc rease the effectiveness of the aphid as a biological control agent of weeds in other years, augmentation by provision of alternative hosts and/or the release of mass reared individuals during autumn is proposed.