Community Ecology of Two Pest Ant Species in Hawaiʻi and a Potential Advancement in Microbial Ant Biocontrol

Abstract

Many invasive ant species have become pests of global status and have had an enormous suite of economic and ecological impacts. In Hawaiʻi, one of the few places on Earth thought to completely lack native ants, these impacts are especially severe. Four species present, Pheidole megacephala, Anoplolepis gracilipes, Linepithema humile, and Wasmannia auropunctata, are on the IUCN-GISD list of the 100 worst invasive species. While P. megacephala established in the late 19th century, W. auropunctata arrived in the late 1990s. Despite this comparatively recent introduction and proactive treatment regimes, W. auropunctata continues to spread throughout the archipelago and has become a serious economic, ecological, and public health hazard. There are concerns that W. auropunctata could expand into the range of P. megacephala, either through competitive displacement or by moving into vacated treated areas. To test this possibility, I evaluated intraspecific aggression between 16 P. megacephala nesting sites on Oʻahu to better understand its social structure. Upon discovering that P. megacephala displays nonsignificant levels of intraspecific aggression, I performed laboratory confrontations between P. megacephala and W. auropunctata to determine whether numerical superiority and lack of intraspecific competition could enable P. megacephala to resist encroachment from W. auropunctata. Interspecific laboratory confrontations revealed that W. auropunctata overwhelmingly dominated P. megacephala.This finding suggested the need to develop flexible pest ant treatment technologies to account for potential shifts in the community composition of ants. To address this need, I attempted to integrate +ssRNA ant viruses identified within P. megacephala and W. auropunctata populations into alginate hydrogel beads. The detection of integrated hydrogels revealed that a P. megacephala-associated virus could be successfully integrated into hydrogels. Detection attempts using a W. auropunctata-associated virus were inconclusive. As ants are necrophobic insects, the palatability of gels conditioned using a homogenate of 25% sucrose solution and ant tissue was examined. Despite the presence of ant tissues within the hydrogel beads, both species exhibited attraction to these tissue-integrated beads. While additional work is needed to better understand how to efficiently integrate viruses into hydrogels and whether the consumption of integrated hydrogels leads to infection, these results suggest that hydrogels are a potential vehicle for the microbial biocontrol of pest ants.