Paper wasps of the species Polistes satan (whose common name is marimbondo-cavalo in Brazil) behave in ways that intrigue scientists who study social insects. In modified environments such as farms, these wasps build nests near each other instead of forming independent nests in separate locations, as they do in natural landscapes. P. satan is an endemic Brazilian species found in the Southeast region and part of the Center-West.
A group of researchers at the University of São Paulo (USP) in Brazil, in collaboration with colleagues at the University of Bristol in the United Kingdom, discovered that wasps fly to and fro between neighboring nests, sharing food and other resources, collaborating, and functioning as a supercolony.
The study was conducted with FAPESP’s support under the aegis of an agreement with the Natural Environment Research Council (NERC), the leading funder of independent environmental science in the UK.
“We found that this species of wasp uses all the space available in modified environments to form a single colony and extract everything it needs from the area,” said Fábio Santos do Nascimento, a professor at USP’s Ribeirão Preto School of Philosophy, Science & Letters (FFCLRP) and principal investigator for the study, in an interview given to Agência FAPESP.
To map the flow of wasps between nests, the researchers attached radio-frequency identification (RFID) tags to the thoraxes of 515 insects that circulated among 15 nearby nests forming a supercolony on a farm in Pedregulho, a small town in São Paulo State.
Radio antennae installed at nest entrances automatically detected the passage of inbound and outbound wasps with RFID tags. The wasps were monitored 11 hours per day for six days.
Analysis of the data collected showed that 20.9% of the tagged female wasps visited more than one nest during the 66 hours of RFID monitoring. “The wasps flew a lot and visited the different nests very frequently,” Nascimento said.
To find out whether this intense traffic occurred because wasps were unable to identify their natal nests or did not detect invading wasps, the researchers tested their ability to identify kin and the extent to which they accepted or rejected “foreigners”.
To this end, wasps were removed from their natal nests and then reintroduced there, and wasps from one nest were placed in another inhabited by kin or non-kin. The nests concerned were at varying distances from each other.
Observation of the resulting interactions showed that during the first two minutes, a wasp removed from a natal nest (resident) and then reintroduced was attacked less than a non-resident, proving the species’ ability to identify kin.
Surprisingly, wasps near nests where they were introduced suffered a significantly higher level of aggression than kin in distant nests. “It’s as if these wasps near the nest where they were introduced but not kin were considered disagreeable neighbors,” Nascimento said.
To find out whether foreign wasps that visited a non-kin nest bringing resources such as food were less rejected by residents, the researchers performed an experiment in which they introduced wasps with honey into a non-natal nest. The results confirmed that they were attacked less.
“They were accepted by residents of neighboring nests precisely because they brought resources. It wouldn’t make sense to reject outsiders if they bring something good for the nest,” Nascimento explained.
The experimental findings were corroborated by field observations. In-depth analysis of the resources carried by the wasps that traveled most among nests in the supercolony showed they were transporting caterpillars, the main food source for these insects. “We found generalized sharing of food among nests of these insects,” Nascimento said.
The changes observed in the behavior and social structure of P. satan, with a large number of nests forming a single cooperative network, represent a form of adaptation to the transformation of natural landscapes into urbanized areas, he surmised.
Colonies of these wasps, comprising between 50 and 70 individuals, do not form such large clusters in natural environments as the researchers observed in the study area in Pedregulho, which has recently been classified as a remnant or fragment of Cerrado, Brazil’s savanna biome.
“We’ve observed that because social insect species such as Polistes satan have relatively plastic phenotypes, in tropical environments, they can modify their biology, as it were, by adapting to anthropogenic [human-caused] environmental impacts,” Nascimento said.
Until now, the only social insects known to have supercolonies were ant species such as Linepithema humile (Argentine ant) or leafcutters.
“L. humile was introduced into Europe in the last century and became a pest by building monumental nests, each with a unique gene set,” Nascimento said.
In the case of P. satan, supercolony formation may have agricultural applications, including biological control – the regulation of crop pests by natural enemies – since the caterpillars on which these wasps feed are pests that attack corn, coffee and sugarcane, among other crops.
“Each colony of P. satan needs hundreds of caterpillars to feed its brood. Our idea is to construct vespiaries near plantations so that the wasps can serve as pest biocontrol,” Nascimento said.
The researchers plan to use these wasps to control larvae of the sugarcane borer Diatraea saccharalis, the main pest that attacks sugarcane.
“We’ll do a number of experiments this year to see whether these wasps can wipe out the borers in the early larval stage,” Nascimento said.
Source : By Elton Alisson | Agência FAPESP