Oviposition and oogenesis in virgin fire ant females Solenopsis invicta are associated with a high level of dopamine in the brain

In the fire ant Solenopsis invicta Buren, virgin females are capable of shedding their wings (dealation) and laying haploid eggs. However, dealation and reproduction are inhibited by a queen primer pheromone that depresses the release of Juvenile Hormone by the corpora allata. In an attempt to identify other neural signals that trigger the reproductive system, we measured the effect on brain biogenic amines of separation from the queen. Dopamine in the brain of virgin females increased from 552 +/- 42 to 971 +/- 65 fMol/brain when reproduction and dealation were stimulated by 15 days of separation. Octopamine and 5-hydroxytryptamine did not change significantly after the separation. Isolated virgin females fed with a tyrosine hydroxylase inhibitor 3-iodo-L-tyrosine mixed in sucrose for 15 days laid significantly fewer eggs and had fewer chorionated oocytes in their ovarioles than females fed with sucrose only. Restoring dopamine biosynthesis by adding L-dopa to the food also restored oogenesis and oviposition. Dealation was not affected by 3-iodo-L-tyrosine or L-dopa. The possible role of dopamine as the neural target of the queen pheromone regarding, its potent allotoregulatory effect in other insects is discussed.