Investigation of bioactivity and variations in alkaloid and hydrocarbon profiles of Solenopsis invicta Buren minim workers in relation to their age

Abstract

Red imported fire ant, Solenopsis invicta Buren, is a significant invasive pest introduced into the United States in the early 1930s. Venom alkaloids and hydrocarbons play important roles in the social life of the red imported fire ant. The minim is a unique caste in the fire ant colony development. However, the information on venom alkaloids and hydrocarbons of minims is very limited. In this study, alkaloid and hydrocarbon profiles of minims were examined from eclosion up to eight days after eclosion. Unlike the normal workers, the venom alkaloid component of the minim is dominated by a single piperidine alkaloid, 2-methyl-6- tridecenylpiperidine (C 13:1 ). The hydrocarbon profile of minims is very similar to that of normal workers, which was dominated by 5 hydrocarbons (heptacosane, 13-methylheptacosane, 13,15- dimethylheptacosane, 3-methylheptacosane, and 3,9-dimethylheptacosane). Heptacosane was the most dominant within five days after eclosion. Squalene, a triterpene, was also detected in minims. Both hydrocarbons and squalene were detected at one day after eclosion. Alkaloids were detected at one day after eclosion in ten out of the thirteen colonies. Alakloids, cuticular hydrocarbons and squalene varied quantitatively among different colonies and different ages of the minims from the same colony. This study also investigated the biological activity of heptadecane and squalene on fire ant workers. A behavioral bioassay demonstrated heptadecane was attractive to workers, while squalene was attractive at low concentrations (<=0.5%) but repellent at higher concentrations (>=2.5%).