Oviposition and oogenesis in virgin ®re ant females Solenopsis invicta are associated with a high level of dopamine in the brain RAPHAEL BOULAY*, LINDA M. HOOPER-BUI* and JOSEPH WOODRING ² *Department of Entomology and ²Department of Biological Sciences, Louisiana State University, Baton Rouge, Florida, U.S.A. Abstract. In the ®re 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 6 42 to 971 6 65 fMol/brain when reproduction and dealation were stimulated by 15 days of separation. Octopamine and 5-hydroxytryptamine did not change signi®cantly after the separation. Isolated virgin females fed with a tyrosine hydroxylase inhibitor 3-iodo-L-tyrosine mixed in sucrose for 15 days laid signi®cantly 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. Key words. Biogenic amines, dealation, ®re ant, ovarian development, oviposition, Solenopsis invicta. Introduction In colonies of eusocial hymenoptera, females unequally share reproductive tasks and only queens (or the gamergates in some ponerine ants) reproduce. Other females living in the same nest are not necessarily sterile, but in many species functionally reproductive females use behavioural or chemical cues to signal their ovarian activity and to prevent their nestmates from reproducing. Despite the increasing number of observed instances of queen control in ants, the neuroendocrine system that triggers reproduction in ants is not well understood. In the ®re ant Solenopsis invicta Buren, workers are completely sterile but winged virgin females are capable of dealating and laying haploid eggs. However, the queen produces an as yet unidenti®ed primer pheromone that inhibits virgin female dealation and reproduction until they have left the parent nest (Fletcher & Blum, 1981). Several lines of evidence indicate that the pheromone may in¯uence the corpora allata (CA) to produce less Juvenile Hormone (JH), a gonadotropin in many insects, to a level below that necessary for vitellogenin incorporation into oocytes and wing-shedding (see review by Robinson & Vargo, 1997; Vargo, 1998). Neurosecretions that may be produced in the brain and exercise this control are not yet identi®ed. The insect CNS contains large quantities of biogenic amines, some of which are known to mediate learning and memory (Hammer, 1993; Pribbenow & Erber, 1996; Hammer & Menzel, 1998; Neckameyer, 1998), arousal (Robinson et al., 1999) and division of labour (Schulz & Robinson, 1999; Wagener-Hulme et al., 1999). In workers of the carpenter ant Camponotus fellah octopamine affects social behaviour and reverses isolation-induced need for trophallaxis (Boulay et al., 2000). This biogenic amine also stimulates the biosynthesis of JH in Locusta migratoria (Lafon-Cazal & Baehr, 1988) and in both larvae and adult workers of the honeybee Apis mellifera (Kaatz et al., 1994; Rachinsky, 1994). In the cricket Gryllus bimaculatus and in the cockroach Diploptera punctata octpamine inhibits CA activity (Thompson et al., 1990; Woodring & Hoffmann, 1994). Oviposition is also increased Correspondence: Raphae Èl Boulay, Dipartimento di Biologia Animale e Genetica, Universita Á di Firenze, Via Romana 17, Firenze, I-50125, Italy. Tel.: +39 (0) 55 2288 218; fax: +39 (0) 55 222565. 294 ã 2001 Blackwell Science Ltd Physiological Entomology (2001) 26, 294±299 Physiological Entomology (2001) 26, 294±299