Brachygastra

Upon its introduction by Perty in 1833, the name Brachygastra was confused with the genus Brachygaster within the family Evaniidae. It was later changed to Nectarina, only to be confused with the genus of birds Nectarinia. Misspellings in publications further compounded the confusion.[2]

In 1991 Carpenter placed Brachygastra in a sister group of Chartergus based on morphological data. In 1993 Wenzel revised this and placed Brachygastra in a sister genus of Protonectarina + Polybia based on nest architecture.[2] Then, in 1994 Carpenter and Wenzel worked together, taking into account a combination of characteristics including adult morphology, nest architecture and larval morphology, and Brachygastra, again, was sister of Chartergus.[3] In 2004 whilst investigating the phylogeny of Epiponini, Noll et al. used discretised morphometric measurements of caste differentiation to reinforced the relationship between Brachygastra and Chartergus.[4] Since then both Arevalo et al. (2004) and Pickett and Carpenter (2010) have placed Barchygastra as a sister genus of Protonectarina after analysing molecular, morphological and behavioural data, however, both groups did not include Chartergus.[5][6]

Phylogeny of the genus Brachygastra according to Carpenter and Wenzel (1994)

The Neotropical realm covers Central and South America

The species of the genus Brachygastra are a common component of neotropical social wasp fauna.[8][7][9] The genus is broadly distributed throughout Central and South America, absent only from Chile, Uruguay and central and south Argentina.[9] One species, B. mellifica, occurs in southwest United States, in Texas and Arizona.[10][7][8]

Humid and forested environments are typical habitat for these wasps, although B. augusti, B. mouleae, B. moebiana and B. lecheguana can inhabit areas with open vegetation.[8] Two species, B. borellii and B. baccaraulea, live in upland areas.[8] The lecheguana group occurs in the Atlantic rainforest and Nearctic region, the scutellaris group lives mostly in the Atlantic forest and the smithii group is confined to the Amazon rainforest.[8] Finally, B. azteca, a sister species to all other species of the genus, occurs in Mexico.[8][2]

The original diversification of Brachygastra probably began about 32 Ma. At that time diverse Amazonian rainforest extended all the way to the Caribbean coast of South America.[11] The Greater Antilles and Aves Ridge land bridge, GAARlandia preceded the formation of the Isthmus of Panama and is thought to have connected the Nearctic and Neotropics, allowing the ancestor of the lecheguana and azteca group to disperse between North, Central and South America.[8]

From 23 to 10 Ma, the Andean uplift accelerated and rapidly changed the Amazonian landscape, with the formation of the vast network of lakes, swamps and wetlands called the Pebas system.[11] It grew to approximately 1 million km² in the northern portion of South America,[11] working to separate populations of ancestral Brachygastra.[8]

Fossils of social wasps are rare in the fossil record, probably due to behavioural characteristics and paper nest structures that do not lend themselves to fossilisation.[8]

Species are easily recognised by the very high scutellum that often projects over the metanotum. The Metanotum and propodeum forms a flat, vertical posterior surface of the mesosoma. The abdomen is often described as truncate due to being wider than it is long (and the genus name means “short-bellied”).[6][3][7] Variation in the size and density of punctures on different parts of the body has been used to describe and identify species, subspecies, and forms of the genus.[2]

Female of Brachygastra cooperi, sp. n. A, lateral view; B, dorsal view. Scale bars = 1.0 mm

There are obvious morphological caste differences in many species with queens being larger than workers. Additionally, larger queens are generally more fecund and dominant that smaller counterparts.[12] Studies on morphological caste differences have been reported for B. augusti, B. bilineolata, B. lecheguana, B. moebiana, B. myersi and B. scutellaris.[10]

Brachygastra mellifica nest in a tree

Nests are always arboreal and sessile.[13] They are made with various plant material consisting of minute chips and long fibres that are chewed and compacted into a paper like material. They are usually a brown or grey colour with a brittle texture. The entrances vary from circular holes or slits, sometimes with multiple entrances arranged chaotically.[13][10] The primary comb is planar or spherical and is usually constructed in a spiral sequence. Nests can contain thousands of individuals and range in size depending on species and colony age or health.[13]

The diet of Honey wasps is made up of carbohydrates from nectar and honey, and protein attained from predation upon various insects such as beetles, weevils, lepidopterans, aphids and various larvae.[14] They have a wide feeding flexibility, probably due to the seasonal availability floral nectar and insect prey.[15][16][17] Floral nectar and insect protein are both stored within the comb of the nest. Brachygastra mellifica and B. lecheguana are well known for their large stores of nectar. B. azteca also stores nectar but in smaller quantities. In addition to nectar, species often collect honeydew from honey-dew producing cercopids and nymphal membracids.[9]

Mexican Honey Wasp (Vespidae, Brachygastra mellifica) collecting nectar from a flower

The nectar gathering activity of these wasp species allows them to provide pollination services to some plant types, such as myrtaceae in the Cerrado,[17] sunflower (Helianthus annuus L., Asteraceae) and mesquite in the Lower Rio Grande Valley of Texas and Avocado.[18] Additionally, honey wasps benefit some plant species by preying upon endophytic herbivorous insects.[15][14] Damaged plants release volatile compounds that act as chemical and olfactory cues for predatory Brachygastra species, attracting them to the source of the grazing herbivorous insect.[19] They have been observed attacking many insect pest species such as Asian citrus psyllid, (Diaphorina citri),[15][16] tomato leafminer (Tuta absoluta),[19] cotton boll weevil larvae, (Anthonomus grandis) and the white coffee leaf miner larvae (Perileucoptera coffeella),[15] suggesting that they have potential to be used as a biological control agent for human crops.

Spiders commonly catch individual wasps in their webs. Opossums and woodpeckers have been observed attacking entire nests.[20]

Conservation of these wasps species is important to allow them to continue providing ecosystem services. Conservation practices include the protection of wasp nests, the maintenance of floral diversity, the preservation of forests and the use to pest control methods that do no harm these wasps.[8]

• Brachygastra azteca
• Brachygastra lecheguana
• Brachygastra mellifica