Polistes gallicus

Polistes gallicus (also historically referred to as Polistes foederatus) is a fairly common species of paper wasp found in various parts of Europe, excluding England, Denmark, and Scandinavia, from warmer climates to cooler regions north of the Alps.^[1] The distribution of P. gallicus also extends into northern regions of Africa, Israel, Iran, and even parts of China and Russia.^[2] Nests of these social insects are created in these various conditions. The Polistes species uses an oral secretion to construct their nests, which consist of a combination of chewed plant fibers and branches. This structural mixture physically protects the nest from various harsh elements and from weathering over time.^[3]

Description and identification

P. gallicus can be spotted due to its distinct markings of bright yellow and black. Its relatively small in size compared to other native Polistes. Curled antennas are a common characteristic in the genus for males, despite being shorter in length in comparison to wasps of other species. Their faces are also completely yellow in color.^[2] This species of wasps feeds its brood after visiting numerous flowers, collecting nectar in addition to feeding them meat. Due to its dimensions it is still likely that they transfer pollen to the stigma, despite the fact that P. gallicus have bodies that are almost bald which leads to few or no pollen grains stuck on them after foraging. This specific body type can help with identification. ^[4]

Taxonomy and phylogeny

Polistes gallicus is a member of the Vespidae family, further classified under Polistinae (the second largest of the subfamilies) which consists of various social wasps. Within the larger subfamily Polistnae, Polistes are categorized by their independent founding behavior, distinguishing them from swarm founding species.^[5] Furthermore, among the 200 species of wasps in the genus Polistes, P. gallicus is classified.^[6]

P. gallicus is almost indistinguishable from the European paper wasp, Polistes dominula, with which it had long been confused. Nearly every reference to "P. gallicus" prior to 1985 was actually referring to P. dominula; due to the great similarity between species, however, many published studies for which there are no vouchered reference specimens cannot be reliably assigned to either species. Most of the literature that pertains to actual P. gallicus uses the junior synonym, P. foederatus, a name which still occasionally appears in the literature despite the known error.^[1] It is also closely related to P. biglumis and P. hellenicus^[7]

Distribution and habitat

Due to the extensive range Polistes gallicus resides, this species survives in a variety of climates and habitats, although ideally it prefers to nest in warm and dry areas. In Italy, nests are typically built in open areas hanging from branches with the cells opened towards the ground. In the colder conditions north of the Alps, metal scraps such as pipes serve as protective enclosures to P. gallicus nests. When it comes to distribution, these wasps are the most abundant Polistes in Spain. P. gallicus also inhabits parts of Paris, although the farther north, the more rare this species becomes.^[2] It’s conservation status in general has not been evaluated yet, although in it's inhabited regions it is common.^[8]

Nest structure can consist of numerous cells, with some nests reporting as many as 500 cells. These nests are constructed from a mix of oral secretions and plant fibers to make a paper pulp. Bigger nests are more commonly found in southern regions of countries. For example, a study of two wasp nests in Cambridge, Massachusetts found a nest constructed inside a stop sign pole that was 8 cm high and 5 cm wide and consisted of 134 cells. A second nest, that contained 153 cells within the same nest dimensions, was found suspended from a pipe. ^[2] The nests of P. gallicus tend to be smaller than those of comparative Polistes. Nest size also depends on the location, with nests in more sheltered areas tending to be larger. ^[3]

Colony cycle

In the spring, wasps come out of hibernation and several foundresses (potential reproductive females) form nests together.^[9] This group effort is not always the case as nests with multiple founders can be found in southern regions of Germany and also in Italy. Most P. gallicus colonies in Germany are initiated by a single foundress, as well as in other northern areas nearby. In Africa when the reproductive female leaves the nest, accompanied by several other workers, reproduction can occur by swarming.^[2] The cells formed are usually in a hexagonal pattern. The foundress then proceeds to lay eggs directly in the brood cells that are guarded by the foundress and subordinates. The newly hatched larvae are fed throughout their development, and each of the season’s first brood of wasps are exclusively female. These new members of the nest are given worker positions and

serve as subordinates to the foundress.^[10]

In early summer, the first workers tend to emerge, attending to duties such as maintaining the nest and taking care of the brood inside. The females that were assisting in the spring are usually driven off by the foundress at this time, and leave the nest, making room for the new additions. The reproductive phase follows when the female reproductives emerge. Male reproductives then emerge, leading to the start of the intermediate phase. Worker numbers start dropping due to a decline in brood care as the older individuals start dying and replacements no longer exist.^[10]

Behavior

Dominance Hierarchy

Hormones play a role in the establishment of dominance hierarchies among Polistes gallicus. Dominant females tend to have more developed ovaries due to higher activity levels in their endocrine system. A larger corpora allata also influences the determination of dominance. A higher reproductive capacity is indicative of the dominant female.^[9]

Reproductive Suppression

After a hierarchy is established, the dominant wasp remains the sole reproducer in the colony due to the inhibition of endocrine activity within the subordinate wasps. Various factors contribute to the possibility of inhibition, which might also lead to differences in endocrine activity. If subordinates happen to lay eggs after the hierarchy is formed, the dominant foundress will eat the eggs to ensure all laid eggs are of her own genes.^[9]

Kin selection

Genetic Relatedness within Colonies

Colonies of Polistes gallicus have one queen that mates and produces offspring. As a result, the queen to worker male relatedness is 1/2. This is higher than the relatedness of two worker brothers, which is 1/4. On the other hand, worker's relatedness to the offspring of other workers is 3/8. This is true if the queen only mates once. However, in the case that the queen mates more than once, workers are actually more related to their brothers than compared to the offspring of other workers.^[11]

Kin Recognition and Discrimination

P. gallicus reacts to chemical signals within Van der Vecht (VVS) organ secretions. VVS was studied and found to be a composition of hydrocarbons. The exact mixture tended to vary among differing colonies and also between the queen and workers, demonstrating worker specificity. Due to the different composition of the VVS chemicals, workers are able to distinguish these differences and respond with varying degrees of aggressiveness to other wasps who also release these chemicals. These chemicals can allow the wasps to interpret these cues about the presence of a related queen in the colony. While workers are able to discriminate VVS of their own queen and other workers, they are also able to distinguish odors when secreted from alien individuals.^[12]

The foundress of the nest has unicellular glands associated with this organ that peaks in activity around the time when workers start emerging. These chemicals are also hypothesized to serve as repellent secretions in order to defend the nest before it is populated. Also beyond just serving as a means of communication, when the queen deposits VVS on the nest during a particular stroking behavior of the queen, this serves as an indication of ownership tied to the presence of this particular queen. It actually has an inhibitory effect on the ovarian development of other workers within the colony. ^[12]

Worker-Queen Conflict

Queen's Interest

Due to the differences in relatedness within colonies, conflict over sex ratio arises. It would be beneficial for the queen to produce an equal ratio of sons and daughters due to equal relatedness between genders. Fisher’s theory of equal investment supports this 50:50 sex ratio of males and females. This is a stable situation as both males and females have the same expected reproductive success.^[13] In order to maintain balance, queens may eat other workers' laid eggs if she was not successful in preventing workers from laying eggs in the first place.^[11]

Workers' Interest

For workers, the production of males by the queen would be more favorable than to let other workers produce progenies. This would lead to an increased relatedness of around 3/4, compared to the relatedness of worker produced males which is around 2/5.^[11] This might support the worker policing prediction that workers might prevent other workers from laying eggs in support of queen produced progeny when they are multiply mated. ^[14] In addition, in colonies with the presence of a queen, workers will not produce males but instead sacrifice their own interests for the greater good of colony productivity. There has been indirect evidence supportive of matricide within the colony, and queen death has been noted to be high in P. gallicus.^[11]

Interaction with other species

Parasites

Strepsiptera, belonging to the genus Xenos, is known to infect Polistes. Xenos vesparum has been especially documented in these wasps. Younger members of the colony are typically the target and most susceptible to parasitism. It is more difficult to document parasitized adult members due to their departure from the cell, which may play a role in perceived susceptibility. However, parasites are most visible in the neotenic adult or pupal stage. This does not distract from finding of Strepsipteran parasites in all stages of the host, from eggs, to larvae, pupae, and finally the adult stage. Also, nests tended to have more parasites per brood member when there was high parasite prevalence. Xenos tends to infect these wasp either through phoretic transport in which the 1st instars are able to attach to wasps’ abdomens at flowering patches or by infecting masses by releasing close to combs from an infected wasp. Sometimes in brood with high levels of parasitized larval hosts, there might be an adaptation of the parasite to enter the eggs.^[15]

Defense

Polistes are known to use the sting and venom as a means of colony defense. However, this venom seems to be costly to produce as Polistes will only release it after the sting in certain situations. Dangerous stimuli must first be perceived before they go out of their way, leaving a nest unattended, to attack.^[16] In some situations Polistes gallicus are know to exhibit aggressive behavior to wasps of a foreign colony.^[12] While venom from a basic standpoint is used by solitary species to capture prey, it has served a greater purpose of defense in social colonies against colony vertebrate and invertebrate offenders.^[16]

When it comes to alarm systems, Polistes can communicate with others through vibrational and visual signals. It might actually be beneficial for a smaller colony of wasps to switch from alarm pheromones, common with Polistes wasps, to these alternative signals when the colony grows in size. Alarm pheromones mixed in with the composition of the venom can also be released. However, it has yet to be determined if this release occurs following the act of ejecting venom by the signaling wasps or if it’s due to the actual release of the venom during the sting.^[16]

Human importance

Gains from the Study of Polistes Venom

Knowing venom chemistry from these species of wasps can lead to human advantages from a pharmaceutical standpoint. The chemical breakdown of venom allows for synthesis of progress in immunology therapy due to the creation of more reliable and effective treatments for people with allergies. Studies which analyzed the way venom interacts with victims provided a mechanism for drugs to permeate cell membranes. Further studies on wasps could provide a mechanism to control overpopulation through the creation of artificial sex attractants.^[16]

Allergic reaction induced IgE- mediated anaphylaxis is commonly a result of Hymenoptera stings. The composition of venom from a sting can even affect the types of treatment a patient should be given. Differences have been found between the composition of American and European Polistes venoms. Response to different epitope spectrums depends on the type of Polistes that did the stinging. Polistes gallicus venom was found to be a combination of four major allergens: Ag5 (antigen 5), hyaluronidase, phospholipase, and protease. This discovery has led to the addition of these allergens into a standard Polistes mix containing venom from North American species in order to improve diagnosis and therapy for European patients with Polistes allergies. ^[17]

References