Behavioural and chemical evidence for multiple colonisation of the Argentine ant, Linepithema humile, in the Western Cape, South Africa

<p>Abstract</p> <p>Background</p> <p>The Argentine ant, <it>Linepithema humile</it>, is a widespread invasive ant species that has successfully established in nearly all continents across the globe. Argentine ants are characterised by a social structure known as unicoloniality, where territorial boundaries between nests are absent and intraspecific aggression is rare. This is particularly pronounced in introduced populations and results in the formation of large and spatially expansive supercolonies. Although it is amongst the most well studied of invasive ants, very little work has been done on this ant in South Africa. In this first study, we investigate the population structure of Argentine ants in South Africa. We use behavioural (aggression tests) and chemical (CHC) approaches to investigate the population structure of Argentine ants within the Western Cape, identify the number of supercolonies and infer number of introductions.</p> <p>Results</p> <p>Both the aggression assays and chemical data revealed that the Western Cape Argentine ant population can be divided into two behaviourally and chemically distinct supercolonies. Intraspecific aggression was evident between the two supercolonies of Argentine ants with ants able to discriminate among conspecific non-nestmates. This discrimination is linked to the divergence in cuticular hydrocarbon profiles of ants originating from the two supercolonies.</p> <p>Conclusions</p> <p>The presence of these two distinct supercolonies is suggestive of at least two independent introductions of this ant within the Western Cape. Moreover, the pattern of colonisation observed in this study, with the two colonies interspersed, is in agreement with global patterns of Argentine ant invasions. Our findings are of interest because recent studies show that Argentine ants from South Africa are different from those identified in other introduced ranges and therefore provide an opportunity to further understand factors that determine the distributional and spread patterns of Argentine ant supercolonies.</p

Host-plant species conservatism and ecology of a parasitoid fig wasp genus (Chalcidoidea; Sycoryctinae; Arachonia)

Parasitoid diversity in terrestrial ecosystems is enormous. However, ecological processes underpinning their evolutionary diversification in association with other trophic groups are still unclear. Specialisation and interdependencies among chalcid wasps that reproduce on Ficus presents an opportunity to investigate the ecology of a multi-trophic system that includes parasitoids. Here we estimate the host-plant species specificity of a parasitoid fig wasp genus that attacks the galls of non-pollinating pteromalid and pollinating agaonid fig wasps. We discuss the interactions between parasitoids and the Ficus species present in a forest patch of Uganda in context with populations in Southern Africa. Haplotype networks are inferred to examine intraspecific mitochondrial DNA divergences and phylogenetic approaches used to infer putative species relationships. Taxonomic appraisal and putative species delimitation by molecular and morphological techniques are compared. Results demonstrate that a parasitoid fig wasp population is able to reproduce on at least four Ficus species present in a patch. This suggests that parasitoid fig wasps have relatively broad host- Ficus species ranges compared to fig wasps that oviposit internally. Parasitoid fig wasps did not recruit on all available host plants present in the forest census area and suggests an important ecological consequence in mitigating fitness trade-offs between pollinator and Ficus reproduction. The extent to which parasitoid fig wasps exert influence on the pollination mutualism must consider the fitness consequences imposed by the ability to interact with phenotypes of multiple Ficus and fig wasps species, but not equally across space and time

Parasitic Cape honeybee workers, Apis mellifera capensis, evade policing

Relocation of the Cape honeybee, Apis mellifera capensis, by bee-keepers from southern to northern South Africa in 1990 has caused widespread death of managed African honeybee, A. m. scutellata, colonies. Apis mellifera capensis worker bees are able to lay diploid, female eggs without mating by means of automictic thelytoky (meiosis followed by fusion of two meiotic products to restore egg diploidy), whereas workers of other honeybee subspecies are able to lay only haploid, male eggs. The A. m. capensis workers, which are parasitizing and killing A. m. scutellata colonies in northern South Africa, are the asexual offspring of a single, original worker in which the small amount of genetic variation observed is due to crossing over during meiosis (P. Kryger, personal communication). Here we elucidate two principal mechanisms underlying this parasitism. Parasitic A. m. capensis workers activate their ovaries in host colonies that have a queen present (queenright colonies), and they lay eggs that evade being killed by other workers (worker policing)—the normal fate of worker-laid eggs in colonies with a queen. This unique parasitism by workers is an instance in which a society is unable to control the selfish actions of its members

Controlling invasive Argentine ants, Linepithema humile, in conservation areas using horizontal insecticide transfer

CITATION: Buczkowski, G. & Wossler, T. C. 2019. Controlling invasive Argentine ants, Linepithema humile, in conservation areas using horizontal insecticide transfer. Scientific Reports, 9:19495, doi:10.1038/s41598-019-56189-1.The original publication is available at https://www.nature.comInvasive ants are major agricultural and urban pests and a significant concern in conservation areas. Despite long history of control and eradication efforts, invasive ants continue to spread around the globe driven by a multitude of synergistic factors. Lack of effective management tools is one of the biggest challenges in controlling invasive ants. The goal of the current study was to improve the efficacy and safety of ant management and to develop effective control strategies for sensitive conservation areas. We utilized the Argentine ant (Linepithema humile) as a model system to evaluate a target-specific pesticide delivery system that exploits the interconnected nature of social insect colonies to distribute a toxicant effectively within the colony. The approach, based entirely on horizontal transfer, takes advantage of various levels of social interactions in ant colonies to disseminate a toxicant throughout the colony. Results of laboratory studies coupled with LC/MS/MS analysis demonstrate that fipronil is toxic to Argentine ants in extremely small (nanogram) quantities and is efficiently transferred from a single treated donor to multiple recipients, causing significant secondary mortality. A field study was conducted in native fynbos plots invaded by Argentine ants. The study consisted of collecting naïve workers, treating them with fipronil, and releasing them within invaded plots. Results show that the release of fipronil-treated ants reduced Argentine ant abundance by >90% within 24 h. The horizontal transfer approach offers environmental benefits with regard to pesticide use in ecologically sensitive environments and appears ideally suited for ant management in conservation areas.https://www.nature.com/articles/s41598-019-56189-1Publisher's versio

Honeybee queen tergal gland secretion affects ovarian development in caged workers

The inhibitory effects of honeybee queen tergal gland secretion on worker ovarian development was studied using a laboratory bioassay with the honeybee races Apis mellifera capensis and A. m. scutellata. Glass pseudoqueens were treated with daily doses of tergal gland extracts from virgin queens and exposed to queenless experimental groups of caged workers. The control groups of queenless caged workers were exposed to solvent controls. Analysis using loglinear models showed that there were no interactions between treatment, race and cage, with respect to the frequency of developing ovaries. The response was homogeneous among cages and among the two races. The virgin queen tergal gland extracts of both A. m. capensis and A. m. scutellata inhibited ovarian development in their own workers (χ2 = 8.28; df = 1; P = 0.004). These results indicate that the secretion from the tergal glands can operate as a primer pheromone. © Inra/DIB/AGIB/Elsevier, Pari

“You are not always what you eat”: diet did not override intrinsic nestmate recognition cues in Argentine ants from two supercolonies in South Africa

Nestmate recognition in ants is based on cuticular hydrocarbons (CHCs), which are heritable and may also be acquired from the environment (i.e. diet and nest environment). In Argentine ants (Linepithema humile), diet and a homogenous environment have been shown to affect nestmate recognition by altering the CHC profile and consequently intraspecific aggression. In our study, Argentine ants were collected from field nests representing two supercolonies in South Africa. Individuals were paired in aggression assays and their CHC profiles analysed. The same nests used in the aggression assays were maintained in the laboratory for five months on a shared diet of crickets and sugar water, in soil-free nests. We predicted that aggression between previously aggressive paired individuals from different nests would decrease over time through the homogenisation of CHCs as a consequence of the shared diet and similar nesting environment. Our data showed that ants maintained in the laboratory readily absorbed prey-derived hydrocarbons and experienced a loss in the number of cuticular compounds compared with their original CHC profiles. However, the changes in CHCs did not impair nestmate recognition with non-aggressive paired interactions maintained while previously aggressive paired interactions persisted. The persistence of aggression between previously aggressive pairs despite environmental homogeneity supports the notion that intrinsic nestmate recognition cues are not overridden by extrinsic cues in the recognition system of Argentine ants.Keywords: cuticular hydrocarbons, intraspecific aggression, Linepithema humile, nestmate recognition, supercolonie

How queen-like are the tergal glands in workers of Apis mellifera capensis and Apis mellifera scutellata?

Tergal gland morphology was investigated for Apis mellifera capensis and A. m. scutellata virgin queens and workers. Workers exhibit two types of tergal glands. Type-A glands consist of single cells, are located along the anterior edge of the tergites II-V, characterised by numerous mitochondria and rough endoplasmic reticulum, and closely associated with fat cells and oenocytes. Type-B tergal glands are bicellular and found predominantly in capensis queens and workers and in scutellata queens. These type-B glands occur along the posterior edge of tergites II-V and are characterised by secretory cells with numerous mitochondria, end apparatuses, and secretory vesicles. There were no differences in gland location or structure in the honeybee queens of both races. However capensis workers possess more glands of both types and larger type-A gland cells than scutellata workers. This result further emphasises the distinctiveness of Cape honeybees.Les glandes tergales des ouvrières d'Apis mellifera capensis et d'Apis mellifera scutellata ressemblent-elles à celles des reines ? L'ultrastructure des glandes tergales des reines vierges et des ouvrières d'A. m. capensis et d'A. m. scutellata a été étudiée au microscope optique et au microscope électronique à balayage. Les reines et les ouvrières des deux races possèdent des glandes tergales sur les bords antérieurs et postérieurs des tergites II à IV (Fig. 1a). Elles sont de deux types (type A et type B, Fig. 1b). Les glandes tergales de type A sont présentes le long du bord antérieur du tergite et seulement chez les ouvrières. Elles sont unicellulaires et associées à des cellules adipeuses et des oenocytes (Figs. 3c, 3d et 2a) et semblent former un complexe glandulaire qui pourrait avoir une fonction de synergie dans la synthèse des sécrétions de surface à base protéique. Du point de vue de l'ultrastructure, les cellules des glandes de type A sont riches en mitochondries et en réticulum endoplasmique rugueux (RER), ce qui caractérise les glandes synthétisant des protéines. Les glandes de type B sont présentes chez les reines vierges et les ouvrières d'A. m. capensis et chez les reines vierges d'A. m. scutellata, mais elles sont réduites ou absentes chez les ouvrières d'A. m. scutellata (Figs. 1e, 1f). Ces glandes comportent une cellule conductrice et une cellule sécrétrice. Cette dernière se caractérise par un appareil terminal spectaculaire, un grand nombre de vésicules sécrétrices, des mitochondries en forme de bâtonnets et du réticulum endoplasmique lisse (SER) (Fig. 2b). Les mitochondries et le SER sont des constituants du cytoplasme largement répandus chez les glandes de l'épiderme des insectes qui produisent des molécules non protéiques. D'après l'analyse des images vidéo, le diamètre moyen des cellules sécrétrices était significativement plus grand ($p = 0,003$) chez la reine vierge d'A. m. capensis que chez celle d'A. m. scutellata, mais il n'est pas possible de tirer de conclusions, une seule reine de chaque race ayant été examinée. La comparaison de l'ultrastructure et de la localisation des glandes n'a fait apparaître aucune différence nette entre les deux races capensis et scutellata. Néanmoins la comparaison des ouvrières âgées de huit jours montre que les ouvrières d'A. m. capensis possèdent significativement plus de glandes de type A et de type B ($p < 0,001$, Tab. I, Fig. 3) que les ouvrières d'A. m. scutellata. Elles possèdent aussi des glandes de type A plus grandes ($p < 0,0001$, Tab. II). Ces deux différences pourraient être responsables du fait que la sécrétion de phéromone chez les ouvrières d'A. m. capensis se situe au-dessus du seuil à partir duquel elle devient fonctionnelle, ce qui permet aux ouvrières d'A. m. capensis de dominer les ouvrières des autres races

Data from: The behavior and reproductive physiology of a solitary progressive provisioning vespid wasp: evidence for a solitary-cycle origin of reproductive castes

The emergence of queens and workers from solitary antecedents mark a major evolutionary transition in the history of life. The solitary progressive provisioning wasp Synagris cornuta, a member of the subfamily basal to eusocial vespid wasps (Eumeninae), alternates between behavioral states characterized as queen-like and worker-like. Akin to a queen in eusocial wasps, a S. cornuta female initiates construction of a cell into which she oviposits, and then, similar to a worker, she cares for the brood as it develops. The Ovarian Groundplan (OGP) hypothesis for caste origins predicts that these behavioral states are associated with cyclical changes in ovarian status, where females performing queen-like tasks have eggs and those performing worker-like tasks possess only small oocytes. Our findings show strong support for the OGP hypothesis: the ovaries of S. cornuta females undergo differential oogenesis depending on the behavioral phase: the largest oocyte in the ovaries of females building a cell progress faster compared to that of females attending brood. Yet contrary to the OGP hypothesis, neither juvenile hormone nor ecdysteroids are associated with the reproductive cycle. Finally, the cuticular hydrocarbon profile showed no link with ovarian status, suggesting that fertility signals evolved subsequent to the emergence of group living

Datasheet - Investigating hygienic behaviour and AFB resistance of Apis mellifera capensis colonies: are Cape honey bees hygienic and how well do they cope with the disease?

This is the raw data for "Investigating hygienic behaviour and AFB resistance of Apis mellifera capensis colonies: are Cape honey bees hygienic and how well do they cope with the disease?" paper. The dataset presents results obtained at 14 inspections after infecting colonies with AFB spores. The hygienic behavior of the colonies was evaluated prior to this experiment.</p