Theresa Clair Wossler

In South Africa, clinical signs of American foulbrood (AFB) are limited to the province of the Western Cape, infecting Apis mellifera capensis. Currently, colony-level virulence of AFB field strains and overall resistance of A. m. capensis colonies to AFB are unknown. We evaluated hygienic behaviour and colony AFB resistance in 15 full-sized A. m. capensis colonies. Eight colonies originated from a population previously exposed to AFB and seven colonies were from an AFB-unexposed population. Firstly, hygienic behaviour of all colonies was assessed by the freeze-killed brood assay. Twenty percent of all colonies removed more than 95% of frozen brood in 24 h, while a further 26.67% removed more than 95% of dead brood in 48 h. There were no differences between the two populations in the level of hygienic behaviour. Secondly, we infected the same A. m. capensis colonies with the ERIC I subtype Ab field strain of P. larvae with a dose of 90 CFU/larva. We monitored colonies for 6 months, quantifying brood production, brood patchiness, and the number of brood cells infected with AFB. The P. larvae field strain had high virulence for all colonies regardless of previous AFB exposure or level of hygienic behaviour. The disease progressed slower in the AFB-unexposed population than in the AFB-exposed population. Colonies that removed 95% or more dead larvae within 48 h showed lower proportions of AFB infection than colonies expressing poor hygienic behaviour, which suggests that hygienic A. m. capensis colonies are more resistant to AFB.

American foulbrood (AFB) poses a serious threat to honey bees worldwide. Clinical signs of AFB were first detected in South Africa in 2008 and are currently confined to the Western Cape, an area inhabited by A. m. capensis. The virulence of isolated AFB field strains and the resistance of A. m. capensis larvae to these field strains were investigated. We individually infected larvae in full-sized A. m. capensis colonies with different doses of the ERIC I, subtype Ab field strain of P. larvae identified from colonies in the Western Cape and assessed larval mortality over 14 days. We compared larval mortality in colonies from a previously AFB-exposed A. m. capensis population to larval mortality in colonies from a non-AFB exposed population. The field strain tested was highly virulent, with the LD₅₀ found to be less than a single spore per larva in both populations, with there being no statistical difference between the populations in larval mortality rates. Our results indicate that once infected with AFB, both A. m. capensis populations responded similarly to the infection and the larvae from both populations showed low resistance to AFB. This indicates that the limited impact of AFB throughout Africa is not due to the direct resistance of larvae to AFB infection, but rather to other factors such as colony-level resistance resulting from highly developed hygienic behaviour, the dispersed nature of beekeeping in Africa, and the swarming/absconding nature intrinsic in African honey bees.

American foulbrood (AFB) is a serious and near-global disease of honey bees and was recently discovered in South Africa. The causative pathogen, Paenibacillus larvae, comprises various strains. It is currently unknown which of these are present in South Africa and what their distribution is. We address this issue by genotyping P. larvae isolates using repetitive element fingerprinting (rep-PCR) markers and microfabricated chip technology. A total of 71 brood, honey and wax samples were collected opportunistically in South Africa. Twenty-three samples tested positive for P. larvae (32.4%). Diagnostic rep-PCR fingerprinting using ERIC, BOX A1R and MBO REP1 primers found all P. larvae isolates in South Africa to correspond to the ERIC I genotype, with two subtypes revealed, Ab (13 samples) and ab (10 samples). These results are in agreement with the global prevalence of the ERIC I AFB genotype among P. larvae-infected honey bee colonies.

Invasive 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.

Invasive ants threaten biodiversity, ecosystem services and agricultural systems. This study evaluated a prey‐baiting approach for managing Argentine ants in natural habitat invaded by Argentine ants. Blackmound termites (Amitermes hastatus) were topically exposed to fipronil and presented to Argentine ants (Linepithema humile). In laboratory assays, L. humile colonies were offered fipronil‐treated termites within experimental arenas. The termites were readily consumed, and results demonstrate that a single termite topically treated with 590 ng fipronil is capable of killing at least 500 L. humile workers in 4 days. Field studies were conducted in natural areas invaded by L. humile. Fipronil‐treated termites scattered within experimental plots provided rapid control of L. humile and ant densities throughout the treated plots declined by 98 ± 5% within 21 days. Results demonstrate that the prey‐baiting approach is highly effective against L. humile and may offer an effective alternative to traditional bait treatments. Furthermore, prey‐baiting offers environmental benefits by delivering substantially less toxicant to the environment relative to current control methods which rely on commercial bait formulations and may offer greater target specificity.

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 Eumeninae (basal to eusocial vespid wasps), alternates between behavioral states characterized as queenlike 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, 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 queenlike 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 progresses faster compared to that of females attending brood. Yet contrary to the OGP hypothesis, neither juvenile hormone nor ecdysteroids is 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.

The Argentine ant, Linepithema humile, is a globally known invasive ant species responsible for widespread biodiversity and economic loss, thus there is a growing need to control and preferably locally eradicate these ants from invaded environments and households. We evaluated the attractiveness and toxicity of six commercial baits containing hydramethylnon, imidacloprid and pyriproxyfen targeting Argentine ants, and differing in bait formulation. Hydramethylnon granular baits were most effective, killing workers (85–100% worker mortality) and queens (63–75 %) in the laboratory within 24 h. Workers were most attracted to and consumed the most of the imidacloprid gel bait, but, contrary to previous studies, mortality on this bait was low. The pyriproxyfen bait was least effective in killing workers, as was expected, and was the least consumed of all baits.We advocate the use of a fine granular hydramethylnon formulation for the effective control of Argentine ants. The attractiveness and consumption of the gel formulation was encouraging, therefore increased concentrations of the toxicant imidacloprid in gel formulation should be tested for improved bait efficacy. Combinations of toxicants that act on multiple levels, such as the larvicide pyriproxyfen and the respiratory toxicant hydramethylnon, should be tested in order to maximise colony eradication from brood to queens.