Polistes Venom: a Multifunctional Secretion
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Ann. Zool. Fennici 43: 488–499 ISSN 0003-455X Helsinki 29 December 2006 © Finnish Zoological and Botanical Publishing Board 2006 Polistes venom: a multifunctional secretion Stefano Turillazzi Centro di Spettrometria di Massa & Dipartimento di Biologia Animale e Genetica “L. Pardi”, Università di Firenze, via Romana 17, I-50125 Firenze, Italy (e-mail: [email protected]fi.it). Received 1 Nov. 2005, revised version received 27 Nov. 2006, accepted 15 Apr. 2006 Turillazzi, S. 2006: Polistes venom: a multifunctional secretion. — Ann. Zool. Fennici 43: 488–499. Polistes venom is a complex secretion that has several functions in the social organiza- tion of a colony. The defensive function as an allomone against vertebrate and inverte- brate enemies is enhanced with antimicrobial properties. Its role in chemical commu- nication is multi-faceted as it contains both alarm and sexual pheromones, but can also have cues which are important both for nestmate and caste recognition, as well as for hibernacula marking. Research on venom chemistry is extremely important for both the establishment of specific immunotherapy for allergic patients and for the discovery of new molecules with pharmacological activity. Venom composition can also provide important characters for taxonomical and phylogenetical studies. Introduction position of Hymenoptera venoms (e.g., Edery et al. 1978, Banks & Shipolini 1986, Nakajima Using weapons that evolved for prey capture 1986, Schmidt 1986, 1990, King & Spangfort as defence against enemies of their own brood 2000); here I focus on the various components was one of the major factors that favoured the of Polistes venom and discuss the possible func- evolution of social life in Aculeate Hymenoptera tions of this secretion. (Hermann & Blum 1981, Andersson 1984, Starr 1985). The stinging apparatus and the secre- tion which it delivers — the venom — became The venom glands more developed in those species (e.g. bees and wasps) whose colonies have aerial nests that are The venomous apparatus of Vespidae, similar to exposed to the attacks of vertebrate predators, that of other Aculeate Hymenoptera, is extremely and reduced or removed in most of the ants. complex and formed by various anatomical parts. The primitive societies of Polistes wasps are It is not my intention to discuss this further as defended by such weapons, and these weapons there are already extensive reviews on this topic represent a harmful deterrent even for humans (for example Spradbery 1973, Hermann & Blum (Schmidt et al. 1983). The venom, however, is a 1981, and references therein). Indeed, a detailed complex secretion whose study is far from com- description of the venom apparatus of Polistes plete and whose properties have not been clari- annularis can be found in Hunt and Hermann fied. Its defensive function seems to be directed (1970). to a broad range of enemies, while its com- Venom is the secretion that comes out of the municative role has not been fully investigated. tip of the sting and originates (perhaps almost There are various detailed reviews on the com- entirely) from the venom reservoir. In wasps ANN. ZOOL. FENNICI Vol. 43 • Polistes venom: a multifunctional secretion 489 and ants, an organ that produces this secretion The quantity of venom available for a single includes two tubular glands, which are external female Polistes dominulus — a medium size and to the reservoir, and one gland that is situated exceptionally common species in the northern inside the reservoir. The last, which is called the hemisphere — is approximately 0.33 µl (E. convoluted gland, is formed by the glandular Francescato pers. comm.). Only a small part epithelia of the tubular glands which infolds like of this can be used during each sting. While a glove finger inside the reservoir (Schoeter & in some polistine wasps the phenomenon of Billen 1995: fig. 1). A recent ultramorphological “venom spraying” is reported (three species in study by Britto and Caetano (2005) shows dif- the genus Parachartergus; see Hermann et al. ferences in the structure and secretory activity 1993, Jeanne & Keeping 1995), it seems that this of the two types of glands in Polistes versicolor: defensive option is not practiced by any Polistes the tubular glands’ cells indicate only a hysto- species. Polistes also do not present sting autot- chemical positive reaction for proteins, while omy which is instead present in other polistine those of the convoluted gland present a posi- wasps belonging to the tribes Epiponini and tive reaction for proteins, and a neutral one for Ropalidiini (Hermann & Blum 1981, Hermann glycoconiugates and lipids. These authors sug- 1984, Sledge et al. 1999). gest that the compounds secreted by the tubular glands could be modified, once in the reservoir, by secretions of the convoluted gland. Powerful Chemical composition of Polistes muscles which coat the reservoir squeeze the venom venom, which spurts through a fissure in the internal edge of one of the two sting lancets (for There is a significant amount of literature on the P. gallicus, Sledge et al. 1999: fig. 2c). chemical composition of venom for other social The use of the sting and venom in Polistes Hymenoptera. The same cannot be said for the wasps is not limited to the defence of the colony, venom of Polistes, which consists of a complex and is modulated by various factors (Turillazzi mixture of compounds that can be grouped in 1984). It is well known that the sting can be used fractions according to their relative molecular as a weapon in fierce intraspecific and interspe- weight (MW): low, medium and high. cific fights (Pardi 1948). In general, the venom is used in very limited amounts, which suggests that the secretion is costly to produce. In addition, the The low MW fraction use of venom against predators is influenced by multiple factors: the parental investment of the This comprises various low molecular weight colony (Judd 1998, 2000), the temperature, the substances and it is probably the least known degree of risk of a given stimulus, the species, etc. fraction of the venom from both its chemical If a stimulus induces a wasp to leave the nest and and functional aspect. It is known that in social attack (and “stinging may in fact be regarded as Hymenoptera, including vespids, this fraction an exceptionally powerful anti-vertebrate tactic”, contains alarm pheromones (Landolt et al. 1998). Starr [1990]), it is important to note that even This has been confirmed for vespine wasps when a wasp lands on a possible target it does not [Vespula vulgaris and V. germanica (Maschwitz necessarily sting it. The venom is released only at 1964), Dolichovespula saxonica (Maschwitz the very end of the complete behavioural sequence 1984), V. squamosa (Landolt & Heath 1987, which includes grasping of the target with legs and Landolt et al. 1999), Provespa anomala (Masch- mandibles and bending the abdomen (pers. obs.). witz & Hanel 1988), V. maculifrons (Landolt et It is evident that the emission of the secretion is al. 1995), Vespa orientalis (Ishay et al. 1965) regulated by complex stimuli and depends on an and V. crabro (Veith et al. 1984)] and in polistine efficient sensorial apparatus of the sting itself (see wasps [Polybia occidentalis (Jeanne 1981, Dani Hermann & Blum [1981], for an extensive bibli- et al. 2000), Polybioides raphigastra (Sledge et ography on the argument). Research on this aspect al. 1999), Ropalidia flavopicta (Fortunato et al. of wasp behaviour is lacking. 2004)]. However, at present, only a few active 490 Turillazzi • ANN. ZOOL. FENNICI Vol. 43 compounds with confirmed alarm pheromone Recently we performed gas chromatographic- function have been reported [N-(3-methylbutyl) mass spectrometric analysis of this fraction on acetamide in Vespula squamosa and V. macu- four species of European Polistes (P. dominulus, lifrons (Heath & Landolt 1988, Landolt et al. P. gallicus, P. nimphus and the social parasite P. 1995), 2-methyl-3buten-2-ol in Vespa crabro sulcifer) and on the South Asian P. olivaceus. (Veith et al. 1984), and the spiroacetal (E,E)- The different species possess a wide range of 2,8-dimethyl-1,7-dioxaspirol[5.5]undecane in compounds, and the mixture of which is par- Polybia occidentalis (Dani et al. 2000)]. Alter- ticular for any species (Table 1) (Bruschini et natively, experiments conducted by Keeping al. 2006c, 2006d), which means that they can (1995) and by London and Jeanne (1996) on be used as systematic characters (Bruschini et the independent founding polistine wasps Belo- al. 2006d). The most common compounds are nogaster petiolata and Mischocyttarus imma- spiroacethals, amides and compounds of acetic rginatus excluded the possibility of chemical and propionic acid. One of the compounds con- alarm communication in these species. sistently present is N-(3-methylbutyl)acetamide, For various species of Stenogastrinae, the which is an alarm pheromone in Vespula squa- most primitive of all social wasps (Carpenter mosa and V. maculifrons (Heath & Landolt 1988, 1982), venom volatiles have been reported but Landolt et al. 1995). The exact pheromone for behavioural experiments failed to demonstrate any Polistes is not yet known, and it may be that var- pheromonal function of the secretion (Dani et al. ious compounds function as an alarm mixture. 1998). After inconclusive experiments by Freis- Communication of alarm in Polistes also ling (1942) on the existence of pheromonal medi- relies on vibrational and visual signals (Turillazzi ation of alarm in the European Polistes nimphus 1984, Starr 1990). A colony of paper wasps with and P. dominulus, Maschwitz (1964) excluded the an un-enveloped nest and relatively small size possibility that P. dubius (= P. biglumis) (subgenus such as those of Polistes, would probably gain Polistes s.s.) had alarm pheromones; this has long advantages by substituting a specific alarm phe- been reported as conclusive evidence that Polistes romone to a vibrational or visual signal only cannot provoke alarm by means of chemical com- when the colony becomes very large.