Action: Isolate colonies of beneficial ants
Natural enemies: One replicated, controlled study from Australia found predatory ants occupied more cashew trees when colonies were kept isolated.
Pest damage and yield: The same study found lower pest damage to cashews and higher yields.
The crop studied was cashew.
This intervention involves pruning perennial crop trees to isolate ant colonies living in the tree canopy. Where ants act as natural predators, this action may improve pest control by reducing the time, energy and ant population losses incurred when rival ant colonies interact and viciously fight each other. This differs from the action 'Exclude ants that protect pests' for managing ants that limit rather than benefit natural pest control (for inclusion in a future synopsis).
Supporting evidence from individual studies
A replicated, controlled experiment in 1996-1997 in Northern Territory, Australia (Peng et al. 2001) found predatory green ants Oecophylla smaragdina occupied more cashew Anacardium occidentale trees when their colonies were kept isolated from each other (100% of trees occupied) than when left to interact normally (52-66%). Damage by tea mosquito bugs Helopeltis pernicialis, mango tip-borers Penicillaria jocosatrix and fruit spotting bugs Amblypelta lutescens was 1% in the colony isolation treatment compared to 23%, 8% and 14% (for these pests respectively) in the non-isolation treatment. Yields were higher in the colony isolation treatment (10.5 and 14.5 kg/tree, in 1996 and 1997 respectively) than the non-isolation treatment (4.6 and 3.9 kg/tree). Ant colonies were isolated by pruning tree branches that linked a colony to other trees occupied by rival colonies. Four colonies in 14 trees were isolated from April onwards in 1996, and five colonies in 16 trees were isolated from March onwards in 1997 (at the same site). In nearby parts of the plantation, 9-12 colonies were identified but not manipulated, creating non-isolated controls. The percentage of flower shoots damaged by pests was recorded fortnightly from June to November, in the bottom and middle of the tree canopy.