Outcomes of eradication efforts against Solenopsis invicta Buren in California: Mitigation of bifenthrin insecticide from surface runoff water and increased intercolony aggression between Solenopsis invicta and Linepithema humile (Mayr)

The objectives of this project were to investigate Best Management Practices to prevent bifenthrin runoff and their effectiveness. Studies were conducted to identify bifenthrin sources, remove suspended solids and bifenthrin in runoff, and measure pesticide enrichment in sediment. Monitoring data showed that the BMPs were extremely effective in reducing the runoff of pyrethroids.; Utilization or enhancement of interspecific competition against Solenopsis invicta in California can be an effective tool to improve eradication efforts and minimize the potential of pyrethroid runoff from nurseries and urban homeowners resorting to pyrethroid based ant control products.; Solenopsis invicta display "gaster venom dabbing" behavior during encounters between S. invicta and Linepithema humile. The stinger is extruded and a venom drop is secreted, after which the gaster is moved down to topically apply a drop of venom to the approaching or attacking ant. Studies were conducted to determine the toxicity of S. invicta venom when topically applied to L. humile and Solenopsis xyloni minors, species commonly found in southern California. The LD50 for S. invicta venom applied topically to L. humile was 0.982 mug and the LD95 was 2.659 mug. The LD50 for S. invicta venom applied topically to S. xyloni was 7.734 mug and the LD95 was 690.5 mug. Investigations were then conducted to determine the competitive outcomes between S. invicta pitted against L. humile. In small arenas, populations of S. invicta consisting of major forms or mixtures of major and minor forms killed more L. humile than minors alone or the average mortality ratio observed in colony to colony confrontations. Colonies consisting of 38 S. invicta workers were easily defeated by 1100 L. humile. Colonies consisting of 450 S. invicta workers were defeated after 313 hours. The S. invicta colonies consisting of 1100 S. invicta workers easily invaded the 1100 worker L. humile colony, killed the Argentine ant queens, and removed their brood. To answer the question of whether pyriproxyfen bait treatments give L. humile any competitive advantage against S. invicta, there was no significant difference in percentage mortality between pyriproxyfen treated and untreated S. invicta and L. humile colonies.