Seasonal variations in foraging by ants (Hymenoptera : Formicidae) in two New South Wales citrus orchards

Pitfall traps were used to monitor the seasonal activity of ants in 2 citru s orchards in the Murrumbidgee Irrigation Area of south-western New South W ales for 22-24 months (November 1992-August/October 1994). Twenty-four spec ies were recorded (22 species at Yanco and 18 species at Cudgel), with Irid omyrmex rufoniger group species being numerically dominant at both sites (6 3 and 59% of total captures at Yanco and Cudgel respectively). Meat ants, I ridomyrmex purpureus (F. Smith), were a significant (9%) component of trap captures at Yanco where regular soil cultivation was practised, but were le ss common (<1% of captures) at Cudgel. Sample species richness was generall y greater at the Yanco site (mean 9.3 species per trapping interval compare d with 6.6 at Cudgel). Total ant captures and sample species richness showe d a positive correlation with mean daily temperatures over trapping interva ls. Variations in seasonal activity were shown by the numerically dominant species, with 2 distinct patterns being evident. Whilst all taxa were less active during winter, some species [I. rufoniger group sp. 2, Pheidole sp., Rhytidoponera metallica (F. Smith)] continued to forage, albeit at reduced levels. Other species of Iridomyrmex including I. rufoniger group sp. 1 an d I. purpureus ceased foraging almost entirely during June-September. Irido myrmex species are known to interfere with the biological control of honeyd ew-producing insects in citrus orchards, and our results indicate that ant control programs in southern New South Wales should be initiated in late Au gust-early September to achieve optimal results.