Theresa Wossler - Academia.edu (original) (raw)

Papers by Theresa Wossler

The invasive Argentine ant, Linepithema humile, is widespread and has been introduced into the Ca... more The invasive Argentine ant, Linepithema humile, is widespread and has been introduced into the Cape Floristic Region (CFR) of South Africa. It has successfully established and spread into both urban and natural environments. Even with its potential negative effects on the CFR, a biodiversity hotspot, very few studies have focused on this ant in South Africa. Even less is known about the indigenous ants to the CFR highlighting the paucity in our knowledge of resident ant community structure and the threat of L. humile on our native ants and ultimately the CFR. In the Fynbos biome, L. humile occupies distributions mutually exclusive to those of many of the dominant native ants, as well as to Pheidole megacephala which occupies the eastern escarpment of the country. We investigated resource exploitation: i) under controlled laboratory conditions, ii) floral nectar utilisation in the field and iii) diet switching in response to levels of L. humile invasion, as well as interspecific inte...

Background: The Argentine ant, Linepithema humile, is a widespread invasive ant species that has ... more Background: The Argentine ant, Linepithema humile, 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. Results: Both the aggression assays and chemical data revealed that the Western Cap...

Apidologie, 2020

The Cape honey bee (Capensis) is unusual in that workers can produce viable female offspring via ... more The Cape honey bee (Capensis) is unusual in that workers can produce viable female offspring via thelytokous parthenogenesis. In contrast, mated queens never reproduce thelytokously, even though they could benefit from doing so when generating daughter queens. Nonetheless, virgin Capensis queens induced to lay without mating by CO 2 narcosis produce a high proportion of thelytokous eggs, and instrumentally inseminated queens produce triploid offspring as the result of the fusion of two egg pronuclei and a sperm nucleus. We show here that thelytoky/triploidy in Capensis queens is not a consequence of CO 2 narcosis per se because narcosis of laying queens does not induce thelytokous or triploid progeny. We also show that in artificially inseminated queens, the frequency of thelytoky/triploidy declines with age and is absent 10 months post-insemination. We confirm that the presence of semen in the spermatheca is not the mechanism that prevents thelytoky/triploidy in mated queens.

Apidologie, 2017

Haplodiploid insects reproduce both sexually and asexually; haploid males arise from unfertilized... more Haplodiploid insects reproduce both sexually and asexually; haploid males arise from unfertilized eggs, while diploid females arise from fertilized eggs. Some species can also produce female offspring by thelytokous parthenogenesis. For example, queenless workers of the Cape honey bee, Apis mellifera capensis , of South Africa can produce diploid female offspring from unfertilized eggs. Genetic evidence suggests that in A. m. capensis , diploidy is restored in zygotes by the fusion of two maternal pronuclei, the haploid descendants of the two alternate products of meiosis I. Here, we confirm this genetic evidence by direct cytological observation of pronucleus fusion. We also provide a description of how the fusion occurs at 4.5-5 h post oviposition and describe the meiotic events that lead up to and follow the fusion. Finally, we document numerous departures from the typical meiotic patterns, which likely explain some of the anomalous A. m. capensis individuals that have been previously identified genetically.

Journal of Apicultural Research, 1999

ABSTRACT

Behavioral Ecology, 2014

Eusocial insects undoubtedly evolved from solitary ancestors, but how this occurred is not well e... more Eusocial insects undoubtedly evolved from solitary ancestors, but how this occurred is not well established. The Ground Plan hypothesis suggests that gene networks that once regulated the oviposition and foraging phases of an ancestral solitary insect's life cycle have been co-opted to establish the queen-worker dimorphism in extant eusocial insects; queens permanently express genes that were once expressed during the oviposition phase, whereas workers express genes that were once associated with foraging. An extension of the Ground Plan hypothesis, the Reproductive Ground Plan-forager hypothesis, proposes that foraging specialization by worker honey bees for either pollen or nectar is controlled by the same reproductive gene networks. According to the Reproductive Ground Plan-forager hypothesis, workers with more ovarioles forage early in life and specialize in pollen collection. Here we find that among workers of a highly reproductive honey bee subspecies, Apis mellifera capensis, there is a positive correlation between ovariole number and age at onset of foraging, and no association between ovariole number and foraging preference, thus contradicting key aspects of the Reproductive Ground Plan-forager hypothesis. We also find a negative association between ovariole number and ovary activation, suggesting that high ovariole number is not directly related to reproductive potential as previously assumed.

Apidologie, 1999

The inhibitory effects of honeybee queen tergal gland secretion on worker ovarian development was... more 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 (χ 2 = 8.28; df = 1; P = 0.004). These results indicate that the secretion from the tergal glands can operate as a primer pheromone. ©

Apidologie, 2007

Note scientifique sur la période de vol des mâles d'Apis mellifera capensis et d'A. m. scutellata... more Note scientifique sur la période de vol des mâles d'Apis mellifera capensis et d'A. m. scutellata. Eine wissenschaftliche Notiz über die Drohnenflugzeit von Apis mellifera capensis und A. m. scutellata

Fire potentially plays an important role in minimising the impact of biological invasions through... more Fire potentially plays an important role in minimising the impact of biological invasions through its ability to change habitat structure, particularly resource availability; generating unsuitable environments that may prevent the spread of invasive species. The invasive Argentine ant, Linepithema humile has been introduced into the Cape Floristic Region (Fynbos) of South Africa and has negative impacts on this biodiversity hotspot. Understanding both the abiotic and biotic factors that reduce its spread into pristine areas are important. Fires may limit the invasion of L. humile and play an important role in controlling its population dynamics, and consequently be a potential mechanism that prevents the spread of L. humile into pristine Fynbos environments. Short and long term effects of fire on L. humile abundance and distribution were measured using a combination of bait surveys and pitfall trap sampling pre-and four years post-fire that swept through the Jonkershoek Nature Reserve, South Africa in 2009. The fire changed the plant community structure and soil condition along the distribution range of L. humile dominated by large stands of nectar producing Protea nitida and Protea repens. Native ant species, especially the displaced dominant ants Pheidole capensis and Anoplolepis custodiens, recolonised burnt areas soon after the fire while 80% fewer L. humile workers were sampled four years post-fire. The invasion front receded by 92 m after the fire owing most likely to a deficiency in floral carbohydrate resources and drier soil conditions , limiting L. humile currently to areas dominated by P. nitida stands. More studies are needed to understand the role of fire in regulating invasion success of introduced species.

Invasive ants opportunistically form mutualistic associations with plants and arthropods that pro... more Invasive ants opportunistically form mutualistic associations with plants and arthropods that produce carbohydrate exudates such as nectar and honeydew. Argentine ants, Linepithema humile, shows ecological plasticity in resource use and behaviour which is thought to enhance its invasion success. The ability of L. humile, to utilise temporarily available floral nectar was compared to that of the dominant native ant, Anoplolepis custodiens, within the Cape Floristic Region (CFR), South Africa. The abundance and species composition of ground foraging ants as well as floral arthropod visitors in inflorescences of two Proteacea species were assessed, as well as comparing the foraging activity of the two ant species on the Proteacea nectar, during different flowering periods. Elemental Stable-isotope analysis of Carbon and Nitrogen, as well as the ratio of Carbon to Nitrogen (C:N), was used to investigate patterns of resource assimilation in L. humile and A. custodiens, and how they respond to increased carbohydrate resource availability. Compared to A. custodiens, L. humile showed strong dietary flexibility, showing a trophic position similar to that of herbivores during the flowering period, and a higher trophic position when floral nectar was depleted. Linepithema humile presence altered the composition of floral visitors by 29% compared to the dominant native ant A. custodiens, and negatively affected species abundance and composition of epigaeic native ant species. The CFR is rich in floral resources, providing ample opportunity for L. humile to spread further in this biodiversity hotspot. Through the effective utilisation of this fluctuating and temporarily available carbohydrate resource abundant in the CFR, coupled with the lack of competition from native ant species, L. humile has the potential to expand into more pristine areas, which may exacerbate its negative impacts in this biodiversity hotspot.

Apidologie, 2011

We artificially inseminated queens of Apis mellifera scutellata and A. m. capensis with equal num... more We artificially inseminated queens of Apis mellifera scutellata and A. m. capensis with equal numbers of drones of both subspecies to determine the effects of sperm genotype on rates of sperm utilization. Contrary to a previous study we did not find a consistent overrepresentation of workers sired by A. m. scutellata males in the first four months after insemination. Interestingly, our study does suggest that there is a significant interaction between drone and queen genotype in both subspecies, with queens of each subspecies producing more workers sired by drones of the same subspecies. Apis mellifera scutellata / Apis mellifera capensis / sperm competition / Africanization / hybrid zone

Entomologia Experimentalis et Applicata, 2014

Argentine ants, Linepithema humile (Mayr) (Hymenoptera: Formicidae), are a significant pest in va... more Argentine ants, Linepithema humile (Mayr) (Hymenoptera: Formicidae), are a significant pest in various agricultural systems around the world, and are often associated with outbreaks of phloem-feeding hemipteran insects. Previous research has evaluated a number of active ingredients and management approaches for controlling Argentine ant populations in agricultural systems, but various regulatory and economic issues have limited the development of effective management tools. Current chemical controls rely on residual sprays or toxic baits, each one posing unique disadvantages that limit their usefulness and efficacy. This study evaluated the potential of water-storing crystals to effectively deliver liquid baits to Argentine ants. The efficacy of bait crystals containing 0.007% thiamethoxam was first evaluated in laboratory colonies. In addition, field studies were performed in a commercial plum orchard to determine the efficacy of the bait crystals. Protein marking was used within the orchard to examine the distribution of the bait in Argentine ant populations when delivered via water-storing crystals. Results of laboratory tests showed that water-storing crystals containing 0.007% thiamethoxam are highly attractive and effective against Argentine ants and require ca. 3-5 days to kill all castes and life stages. Results of the protein-marking study demonstrated that the percentage of ants carrying protein-labeled sugar water decreases sharply with increasing distance from the bait station. Bait movement was limited to within 17 m of the bait dispenser. Furthermore, bait efficacy tests in the field showed that Argentine ants can be effectively controlled using liquid thiamethoxam baits deployed via water-storing crystals. The bait was highly effective and ant densities throughout the baited plots declined by 94 AE 2% within 14 days. The results of this study demonstrate that (1) thiamethoxam is highly effective for Argentine ant control in fruit orchards when used in low concentrations (0.007%), and (2) water-storing crystals are an effective tool for delivering liquid baits to Argentine ants in agricultural settings.

Apidologie, 2011

Honey bee colonies are characterised by well-developed reproductive division of labour between th... more Honey bee colonies are characterised by well-developed reproductive division of labour between the queen and workers. Here, we test whether this reproductive division of labour is evident in both the socially parasitic workers that invade a colony as well as in their offspring generation. We infected six Apis mellifera scutellata host colonies with pseudo-clonal socially parasitic Cape honeybee workers (Apis mellifera capensis). We show that the first generation of socially parasitic workers can monopolize reproduction within host colonies. Of the initially invading parasites, 94.4% became reproductive pseudoqueens with activated ovaries and produced queen-like pheromones. Their offspring, however, had much lower levels of ovary activation (3.1%), yet 89% showed fatty acid synthesis typical of the queen substance (9-oxo-2(E)-decenoic acid) biochemical pathway. However, in these second-generation workers, the last oxidation step from the precursor (9-hydroxy-2(E)-decenoic acid) to the queen substance was interrupted and appears to be required for reproductive dominance in honeybee workers. Our data show that despite the absence of genetic diversity, residual queen mandibular pheromone (QMP) variation is sufficient to establish reproductive dominance hierarchies among parasitic workers. Consequently, QMP produced by a group of workers can maintain reproductive division of labour in queenless honeybee colonies.

Apidologie, 2002

Thelytokous Apis mellifera capensis workers recently brought into regions occupied by the arrkeno... more Thelytokous Apis mellifera capensis workers recently brought into regions occupied by the arrkenotokous African bee A. m. scutellata, parasitise these colonies, causing colony death. These capensis workers are genetically almost identical and are referred to as a 'pseudo-clone'. We surveyed 120 scutellata colonies, 27 in detail, at various stages of usurpation by the pseudo-clone. The scutellata queen could co-exist with egg-laying pseudo-clones for 50+ days in one case but disappeared 1-15 days in three other cases. Despite the presence of emerged queen cells no new adult queens of either race were observed in usurped colonies. Only 11 ± 13% of the pseudo-clone population had fully active ovaries, suggesting ovarian development is inhibited in the majority of the pseudo-clones. Only 2.7 ± 1.7% of the foraging force were pseudo-clones. The data were modelled and showed the rapid (56-105 days) growth of the pseudo-clone population and colony death over a wide range of initial conditions.

Proceedings of the Royal Society B: Biological Sciences, 2008

The Cape bee ( Apis mellifera capensis ) is unique among honeybees in that workers can lay eggs t... more The Cape bee ( Apis mellifera capensis ) is unique among honeybees in that workers can lay eggs that instead of developing into males develop into females via thelytokous parthenogenesis. We show that this ability allows workers to compete directly with the queen over the production of new queens. Genetic analyses using microsatellites revealed that 23 out of 39 new queens produced by seven colonies were offspring of workers and not the resident queen. Of these, eight were laid by resident workers, but the majority were offspring of parasitic workers from other colonies. The parasites were derived from several clonal lineages that entered the colonies and successfully targeted queen cells for parasitism. Hence, these parasitic workers had the potential to become genetically reincarnated as queens. Of the daughter queens laid by the resident queen, three were produced asexually, suggesting that queens can ‘choose’ to produce daughter queens clonally and thus have the potential for ge...

PLoS ONE, 2012

Parasitoid diversity in terrestrial ecosystems is enormous. However, ecological processes underpi... more 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 nonpollinating 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.

Journal of Heredity, 2008

When workers of the thelytokous Cape honeybee, Apis mellifera capensis, come into contact with co... more When workers of the thelytokous Cape honeybee, Apis mellifera capensis, come into contact with colonies of the neighboring arrhenotokous subspecies Apis mellifera scutellata, they can become lethal social parasites. We examined the inheritance of 3 traits (number of ovarioles, number of basitarsal hairs, and size of spermatheca) that are thought to be associated with reproductive potential in A. m. capensis workers. To do so, we produced hybrid A. m. scutellata/A. m. capensis queens and backcrossed them to either A. m. capensis or A. m. scutellata drones. We then measured the 3 traits in parental, hybrid, and backcross offspring. We show that the 3 traits are phenotypically correlated. We also show that the expression of ovariole number, basitarsal hairs, and size of spermatheca is influenced by the genotype of the individual and the rearing environment but that the influence of the rearing environment is less important to the number of ovarioles. We hypothesize a single recessive allele (l), present at high frequency in natural A. m. capensis populations, which when homozygous causes larvae to elicit more food. This increased feeding as larvae causes resulting adult workers to develop more queen like morphology and increased reproductive potential. The number of ovarioles, in contrast, appears to be under independent genetic control.

Insectes Sociaux, 2005

Anarchistic honey bees are a line developed by recurrent selection in which workers frequently la... more Anarchistic honey bees are a line developed by recurrent selection in which workers frequently lay eggs. In unselected colonies, workers refrain from reproduction in response to pheromonal signals that indicate the presence of brood and a queen. We show that queen type (anarchistic or wild type) has no effect on rates of ovary activation of anarchistic or wild type workers. In addition, we show that an important component of the queen's signalling system, the queen mandibular gland pheromone, is similar in wild type and anarchistic queens. Anarchistic larvae do not inhibit worker ovary development to the same degree as wild type larvae, however all colonies in this experiment contained only wild type larvae. Anarchistic workers had greater rates of ovary activation than wild type workers in colonies headed by either queen type. We therefore conclude that there must be differences in the transmission or reception of queen pheromones, or worker sensitivity to these compounds. These results clearly demonstrate that anarchy is a complex syndrome, not simply the result of reduced pheromone production by anarchist queens and larvae.

The invasive Argentine ant, Linepithema humile, is widespread and has been introduced into the Ca... more The invasive Argentine ant, Linepithema humile, is widespread and has been introduced into the Cape Floristic Region (CFR) of South Africa. It has successfully established and spread into both urban and natural environments. Even with its potential negative effects on the CFR, a biodiversity hotspot, very few studies have focused on this ant in South Africa. Even less is known about the indigenous ants to the CFR highlighting the paucity in our knowledge of resident ant community structure and the threat of L. humile on our native ants and ultimately the CFR. In the Fynbos biome, L. humile occupies distributions mutually exclusive to those of many of the dominant native ants, as well as to Pheidole megacephala which occupies the eastern escarpment of the country. We investigated resource exploitation: i) under controlled laboratory conditions, ii) floral nectar utilisation in the field and iii) diet switching in response to levels of L. humile invasion, as well as interspecific inte...

Background: The Argentine ant, Linepithema humile, is a widespread invasive ant species that has ... more Background: The Argentine ant, Linepithema humile, 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. Results: Both the aggression assays and chemical data revealed that the Western Cap...

Apidologie, 2020

The Cape honey bee (Capensis) is unusual in that workers can produce viable female offspring via ... more The Cape honey bee (Capensis) is unusual in that workers can produce viable female offspring via thelytokous parthenogenesis. In contrast, mated queens never reproduce thelytokously, even though they could benefit from doing so when generating daughter queens. Nonetheless, virgin Capensis queens induced to lay without mating by CO 2 narcosis produce a high proportion of thelytokous eggs, and instrumentally inseminated queens produce triploid offspring as the result of the fusion of two egg pronuclei and a sperm nucleus. We show here that thelytoky/triploidy in Capensis queens is not a consequence of CO 2 narcosis per se because narcosis of laying queens does not induce thelytokous or triploid progeny. We also show that in artificially inseminated queens, the frequency of thelytoky/triploidy declines with age and is absent 10 months post-insemination. We confirm that the presence of semen in the spermatheca is not the mechanism that prevents thelytoky/triploidy in mated queens.

Apidologie, 2017

Haplodiploid insects reproduce both sexually and asexually; haploid males arise from unfertilized... more Haplodiploid insects reproduce both sexually and asexually; haploid males arise from unfertilized eggs, while diploid females arise from fertilized eggs. Some species can also produce female offspring by thelytokous parthenogenesis. For example, queenless workers of the Cape honey bee, Apis mellifera capensis , of South Africa can produce diploid female offspring from unfertilized eggs. Genetic evidence suggests that in A. m. capensis , diploidy is restored in zygotes by the fusion of two maternal pronuclei, the haploid descendants of the two alternate products of meiosis I. Here, we confirm this genetic evidence by direct cytological observation of pronucleus fusion. We also provide a description of how the fusion occurs at 4.5-5 h post oviposition and describe the meiotic events that lead up to and follow the fusion. Finally, we document numerous departures from the typical meiotic patterns, which likely explain some of the anomalous A. m. capensis individuals that have been previously identified genetically.

Journal of Apicultural Research, 1999

ABSTRACT

Behavioral Ecology, 2014

Eusocial insects undoubtedly evolved from solitary ancestors, but how this occurred is not well e... more Eusocial insects undoubtedly evolved from solitary ancestors, but how this occurred is not well established. The Ground Plan hypothesis suggests that gene networks that once regulated the oviposition and foraging phases of an ancestral solitary insect's life cycle have been co-opted to establish the queen-worker dimorphism in extant eusocial insects; queens permanently express genes that were once expressed during the oviposition phase, whereas workers express genes that were once associated with foraging. An extension of the Ground Plan hypothesis, the Reproductive Ground Plan-forager hypothesis, proposes that foraging specialization by worker honey bees for either pollen or nectar is controlled by the same reproductive gene networks. According to the Reproductive Ground Plan-forager hypothesis, workers with more ovarioles forage early in life and specialize in pollen collection. Here we find that among workers of a highly reproductive honey bee subspecies, Apis mellifera capensis, there is a positive correlation between ovariole number and age at onset of foraging, and no association between ovariole number and foraging preference, thus contradicting key aspects of the Reproductive Ground Plan-forager hypothesis. We also find a negative association between ovariole number and ovary activation, suggesting that high ovariole number is not directly related to reproductive potential as previously assumed.

Apidologie, 1999

The inhibitory effects of honeybee queen tergal gland secretion on worker ovarian development was... more 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 (χ 2 = 8.28; df = 1; P = 0.004). These results indicate that the secretion from the tergal glands can operate as a primer pheromone. ©

Apidologie, 2007

Note scientifique sur la période de vol des mâles d'Apis mellifera capensis et d'A. m. scutellata... more Note scientifique sur la période de vol des mâles d'Apis mellifera capensis et d'A. m. scutellata. Eine wissenschaftliche Notiz über die Drohnenflugzeit von Apis mellifera capensis und A. m. scutellata

Fire potentially plays an important role in minimising the impact of biological invasions through... more Fire potentially plays an important role in minimising the impact of biological invasions through its ability to change habitat structure, particularly resource availability; generating unsuitable environments that may prevent the spread of invasive species. The invasive Argentine ant, Linepithema humile has been introduced into the Cape Floristic Region (Fynbos) of South Africa and has negative impacts on this biodiversity hotspot. Understanding both the abiotic and biotic factors that reduce its spread into pristine areas are important. Fires may limit the invasion of L. humile and play an important role in controlling its population dynamics, and consequently be a potential mechanism that prevents the spread of L. humile into pristine Fynbos environments. Short and long term effects of fire on L. humile abundance and distribution were measured using a combination of bait surveys and pitfall trap sampling pre-and four years post-fire that swept through the Jonkershoek Nature Reserve, South Africa in 2009. The fire changed the plant community structure and soil condition along the distribution range of L. humile dominated by large stands of nectar producing Protea nitida and Protea repens. Native ant species, especially the displaced dominant ants Pheidole capensis and Anoplolepis custodiens, recolonised burnt areas soon after the fire while 80% fewer L. humile workers were sampled four years post-fire. The invasion front receded by 92 m after the fire owing most likely to a deficiency in floral carbohydrate resources and drier soil conditions , limiting L. humile currently to areas dominated by P. nitida stands. More studies are needed to understand the role of fire in regulating invasion success of introduced species.

Invasive ants opportunistically form mutualistic associations with plants and arthropods that pro... more Invasive ants opportunistically form mutualistic associations with plants and arthropods that produce carbohydrate exudates such as nectar and honeydew. Argentine ants, Linepithema humile, shows ecological plasticity in resource use and behaviour which is thought to enhance its invasion success. The ability of L. humile, to utilise temporarily available floral nectar was compared to that of the dominant native ant, Anoplolepis custodiens, within the Cape Floristic Region (CFR), South Africa. The abundance and species composition of ground foraging ants as well as floral arthropod visitors in inflorescences of two Proteacea species were assessed, as well as comparing the foraging activity of the two ant species on the Proteacea nectar, during different flowering periods. Elemental Stable-isotope analysis of Carbon and Nitrogen, as well as the ratio of Carbon to Nitrogen (C:N), was used to investigate patterns of resource assimilation in L. humile and A. custodiens, and how they respond to increased carbohydrate resource availability. Compared to A. custodiens, L. humile showed strong dietary flexibility, showing a trophic position similar to that of herbivores during the flowering period, and a higher trophic position when floral nectar was depleted. Linepithema humile presence altered the composition of floral visitors by 29% compared to the dominant native ant A. custodiens, and negatively affected species abundance and composition of epigaeic native ant species. The CFR is rich in floral resources, providing ample opportunity for L. humile to spread further in this biodiversity hotspot. Through the effective utilisation of this fluctuating and temporarily available carbohydrate resource abundant in the CFR, coupled with the lack of competition from native ant species, L. humile has the potential to expand into more pristine areas, which may exacerbate its negative impacts in this biodiversity hotspot.

Apidologie, 2011

We artificially inseminated queens of Apis mellifera scutellata and A. m. capensis with equal num... more We artificially inseminated queens of Apis mellifera scutellata and A. m. capensis with equal numbers of drones of both subspecies to determine the effects of sperm genotype on rates of sperm utilization. Contrary to a previous study we did not find a consistent overrepresentation of workers sired by A. m. scutellata males in the first four months after insemination. Interestingly, our study does suggest that there is a significant interaction between drone and queen genotype in both subspecies, with queens of each subspecies producing more workers sired by drones of the same subspecies. Apis mellifera scutellata / Apis mellifera capensis / sperm competition / Africanization / hybrid zone

Entomologia Experimentalis et Applicata, 2014

Argentine ants, Linepithema humile (Mayr) (Hymenoptera: Formicidae), are a significant pest in va... more Argentine ants, Linepithema humile (Mayr) (Hymenoptera: Formicidae), are a significant pest in various agricultural systems around the world, and are often associated with outbreaks of phloem-feeding hemipteran insects. Previous research has evaluated a number of active ingredients and management approaches for controlling Argentine ant populations in agricultural systems, but various regulatory and economic issues have limited the development of effective management tools. Current chemical controls rely on residual sprays or toxic baits, each one posing unique disadvantages that limit their usefulness and efficacy. This study evaluated the potential of water-storing crystals to effectively deliver liquid baits to Argentine ants. The efficacy of bait crystals containing 0.007% thiamethoxam was first evaluated in laboratory colonies. In addition, field studies were performed in a commercial plum orchard to determine the efficacy of the bait crystals. Protein marking was used within the orchard to examine the distribution of the bait in Argentine ant populations when delivered via water-storing crystals. Results of laboratory tests showed that water-storing crystals containing 0.007% thiamethoxam are highly attractive and effective against Argentine ants and require ca. 3-5 days to kill all castes and life stages. Results of the protein-marking study demonstrated that the percentage of ants carrying protein-labeled sugar water decreases sharply with increasing distance from the bait station. Bait movement was limited to within 17 m of the bait dispenser. Furthermore, bait efficacy tests in the field showed that Argentine ants can be effectively controlled using liquid thiamethoxam baits deployed via water-storing crystals. The bait was highly effective and ant densities throughout the baited plots declined by 94 AE 2% within 14 days. The results of this study demonstrate that (1) thiamethoxam is highly effective for Argentine ant control in fruit orchards when used in low concentrations (0.007%), and (2) water-storing crystals are an effective tool for delivering liquid baits to Argentine ants in agricultural settings.

Apidologie, 2011

Honey bee colonies are characterised by well-developed reproductive division of labour between th... more Honey bee colonies are characterised by well-developed reproductive division of labour between the queen and workers. Here, we test whether this reproductive division of labour is evident in both the socially parasitic workers that invade a colony as well as in their offspring generation. We infected six Apis mellifera scutellata host colonies with pseudo-clonal socially parasitic Cape honeybee workers (Apis mellifera capensis). We show that the first generation of socially parasitic workers can monopolize reproduction within host colonies. Of the initially invading parasites, 94.4% became reproductive pseudoqueens with activated ovaries and produced queen-like pheromones. Their offspring, however, had much lower levels of ovary activation (3.1%), yet 89% showed fatty acid synthesis typical of the queen substance (9-oxo-2(E)-decenoic acid) biochemical pathway. However, in these second-generation workers, the last oxidation step from the precursor (9-hydroxy-2(E)-decenoic acid) to the queen substance was interrupted and appears to be required for reproductive dominance in honeybee workers. Our data show that despite the absence of genetic diversity, residual queen mandibular pheromone (QMP) variation is sufficient to establish reproductive dominance hierarchies among parasitic workers. Consequently, QMP produced by a group of workers can maintain reproductive division of labour in queenless honeybee colonies.

Apidologie, 2002

Thelytokous Apis mellifera capensis workers recently brought into regions occupied by the arrkeno... more Thelytokous Apis mellifera capensis workers recently brought into regions occupied by the arrkenotokous African bee A. m. scutellata, parasitise these colonies, causing colony death. These capensis workers are genetically almost identical and are referred to as a 'pseudo-clone'. We surveyed 120 scutellata colonies, 27 in detail, at various stages of usurpation by the pseudo-clone. The scutellata queen could co-exist with egg-laying pseudo-clones for 50+ days in one case but disappeared 1-15 days in three other cases. Despite the presence of emerged queen cells no new adult queens of either race were observed in usurped colonies. Only 11 ± 13% of the pseudo-clone population had fully active ovaries, suggesting ovarian development is inhibited in the majority of the pseudo-clones. Only 2.7 ± 1.7% of the foraging force were pseudo-clones. The data were modelled and showed the rapid (56-105 days) growth of the pseudo-clone population and colony death over a wide range of initial conditions.

Proceedings of the Royal Society B: Biological Sciences, 2008

The Cape bee ( Apis mellifera capensis ) is unique among honeybees in that workers can lay eggs t... more The Cape bee ( Apis mellifera capensis ) is unique among honeybees in that workers can lay eggs that instead of developing into males develop into females via thelytokous parthenogenesis. We show that this ability allows workers to compete directly with the queen over the production of new queens. Genetic analyses using microsatellites revealed that 23 out of 39 new queens produced by seven colonies were offspring of workers and not the resident queen. Of these, eight were laid by resident workers, but the majority were offspring of parasitic workers from other colonies. The parasites were derived from several clonal lineages that entered the colonies and successfully targeted queen cells for parasitism. Hence, these parasitic workers had the potential to become genetically reincarnated as queens. Of the daughter queens laid by the resident queen, three were produced asexually, suggesting that queens can ‘choose’ to produce daughter queens clonally and thus have the potential for ge...

PLoS ONE, 2012

Parasitoid diversity in terrestrial ecosystems is enormous. However, ecological processes underpi... more 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 nonpollinating 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.

Journal of Heredity, 2008

When workers of the thelytokous Cape honeybee, Apis mellifera capensis, come into contact with co... more When workers of the thelytokous Cape honeybee, Apis mellifera capensis, come into contact with colonies of the neighboring arrhenotokous subspecies Apis mellifera scutellata, they can become lethal social parasites. We examined the inheritance of 3 traits (number of ovarioles, number of basitarsal hairs, and size of spermatheca) that are thought to be associated with reproductive potential in A. m. capensis workers. To do so, we produced hybrid A. m. scutellata/A. m. capensis queens and backcrossed them to either A. m. capensis or A. m. scutellata drones. We then measured the 3 traits in parental, hybrid, and backcross offspring. We show that the 3 traits are phenotypically correlated. We also show that the expression of ovariole number, basitarsal hairs, and size of spermatheca is influenced by the genotype of the individual and the rearing environment but that the influence of the rearing environment is less important to the number of ovarioles. We hypothesize a single recessive allele (l), present at high frequency in natural A. m. capensis populations, which when homozygous causes larvae to elicit more food. This increased feeding as larvae causes resulting adult workers to develop more queen like morphology and increased reproductive potential. The number of ovarioles, in contrast, appears to be under independent genetic control.

Insectes Sociaux, 2005

Anarchistic honey bees are a line developed by recurrent selection in which workers frequently la... more Anarchistic honey bees are a line developed by recurrent selection in which workers frequently lay eggs. In unselected colonies, workers refrain from reproduction in response to pheromonal signals that indicate the presence of brood and a queen. We show that queen type (anarchistic or wild type) has no effect on rates of ovary activation of anarchistic or wild type workers. In addition, we show that an important component of the queen's signalling system, the queen mandibular gland pheromone, is similar in wild type and anarchistic queens. Anarchistic larvae do not inhibit worker ovary development to the same degree as wild type larvae, however all colonies in this experiment contained only wild type larvae. Anarchistic workers had greater rates of ovary activation than wild type workers in colonies headed by either queen type. We therefore conclude that there must be differences in the transmission or reception of queen pheromones, or worker sensitivity to these compounds. These results clearly demonstrate that anarchy is a complex syndrome, not simply the result of reduced pheromone production by anarchist queens and larvae.