Ground cover management does not influence densities of key Iridomyrmex species (Hym., Formicidae) in Australian citrus groves
Ants in the genus Iridomyrmex cause extensive problems for citrus producers in southern Australia by disrupting the biological control of honeydew-producing Hemiptera. We used baited pitfall traps to survey ant communities in 20 commercial citrus groves and test the hypothesis that populations of Iridomyrmex rufoniger gp spp. and Iridomyrmex purpureus can be reduced by conserving volunteer inter-row vegetation. Nine groves (five in the Murrumbidgee Irrigation Area, New South Wales, and four in the Sunraysia area, Victoria) were classified as bare groves, where inter-row vegetation was routinely eliminated using herbicides and cultivation. The remaining grassed groves (five in the MIA, six in Sunraysia) had inter-row vegetation controlled only by intermittent mowing. All groves had been managed consistently for between 9 and 22 years. MIA groves were trapped on three occasions (October 1997, January 1998 and April 1998), and Sunraysia groves once (March 1999). Over 190 000 ants were recovered, with I. rufoniger gp spp. accounting for 74% of overall captures and dominating collections in both bare and grassed groves. A linear mixed model analysis showed that ground cover management history had no significant effect (P > 0.05) on captures of I. rufoniger gp spp., I. purpureus, other Dolichoderinae, Ponerinae, Formicinae or Myrmicinae. High variability between ant populations in groves under the same management regime in each region suggests that aspects of grove management may be affecting ant community composition, however, our results indicate that suppression of pest Iridomyrmex species cannot be reliably achieved simply by altering the management of volunteer inter-row vegetation.