Featured Researcher
Steffan Hansen
PhD student, Department Conservation Ecology and Entomology, Stellenbosch University, South Africa
BScAgric in Crop Protection, Stellenbosch University, South Africa-2019
Research Interests
Systematics and biology of pestiferous Entiminae taxa, and the application to biological pest control, specifically through the use of entomopathogenic nematodes-and-fungi.
I completed my undergraduate studies (with honours included) in BScAgric at the beautiful Stellenbosch University in the Western Cape province of South Africa, double majoring in Plant Pathology and Entomology. The combination of these two fields of study inevitably led to an interest in entomopathogenic fungi and their use in biological control, which was the focus of my honours thesis. Around this time Dr Julien Haran, a CIRAD weevil taxonomist at Montpellier University (France) was working at Stellenbosch for two years. His observations of the genus Phlyctinus Schönherr while co-supervising a Master thesis on pestiferous Entiminae at the department of Conservation Ecology and Entomology led to taxonomic investigation into the genus.
Phlyctinus callosus Schönherr, or the banded fruit weevil, was long considered a monotypic taxon, and is a key Entiminae pest on some deciduous fruit and grapevine in South Africa. It was subsequently shown to be a complex of cryptic species, with five new species named and the P. callosus s.s. concept revised in a first integrative taxonomic investigation of the complex. Of these, P. callosus is the most widespread pest on deciduous fruit and grapevine in its native range, and the newly named Phlyctinus xerophilus Haran is apparently restricted to several inland valleys of the Western Cape region of South Africa. The other four Phlyctinus species (and some undescribed ones) seem to be limited to coastal distributions and native host-plants (Asteraceae). Together with Dr Haran, Prof Pia Addison and Prof Antoinette Malan at Stellenbosch (the latter two who have been extensively involved in the biological control research and efforts against banded fruit weevil), my own project came into being, and would focus on further taxonomical investigation into Phlyctinus, and the potential impact that the closely related but similar species Phlyctinus callosus and Phlyctinus xerophilus have on the biological control (with entomopathogenic fungi-and-nematodes) of these pests. This work has since gained so much scope and co-researchers (including a passionate team of taxonomical researchers at Montpellier University) that the project has rolled into a PhD. I look forward on spending a minimum of two more years in close contact with Phlyctinus and splendid colleagues.
Context
Entiminae (broad-nosed weevils) are a large and economically significant subfamily of Curculionidae. The number of species in Entiminae, the cosmopolitan distribution of the subfamily as a whole, and the ease with which many native species are able to undergo host-plant shifts due to the loose host plant associations cause some genera and species to rank amongst the most important and notorious insect pests of agriculture in many regions of the world. While the ectophagous soil-living larvae damage plant roots and crowns, the adults gnaw notches out of leaves, stems and fruit.
Proper taxonomy and identifications of taxa under study is the key cornerstone to any applied work, and can significantly impact research ranging from the reliability of diagnostic tools such as COI barcoding to disease vector investigation to biological control. Cryptic or closely related species in arthropod taxa may play a subtle to significant role in behaviors, host-plant range or preference, and biological control. Good case studies from Curculionidae include matching the correct Crytobagous weevil species with the aquatic fern Salvinia molesta for successful biological control of the weed, subtle differences in behaviour between the virtually indistinguishable pest palm weevil species Rhynchophorus ferrugineus and R. vulneratus, and the presence of cryptic species in the eucalypt weevil Gonipterus scutellatus complex that may potentially contribute to erratic results observed in the biological control of these pests with a hymenopteran egg parasitoid.
Dissertation abstract
The genus Phlyctinus has been shown to consist of multiple cryptic species, some of which still await description. The genus seems to be restricted natively to the biodiversity hot-spot of the Cape Floristic Region (CFR) biome of South Africa. While the majority of these species are coastal in distribution and feed mostly on native Asteraceae hosts, two of these species, Phlyctinus callosus s.s. and Phlyctinus xerophilus are pests of economic significance. Proper taxonomy and the recognition of cryptic species in insect pest taxa are of vital importance to any applied work on these taxa, including biological control efforts.
Several native and exotic Entiminae taxa co-occur with Phlyctinus, and are potential or sporadic pests of agriculture. The sporadic pest nature of many species, and the presence of pest complexes and cryptic species presents an identification challenge to non-specialists. Furthermore no comprehensive identification tools to identify immature stages that may be found in crops/soil exist. A curated barcoding database with 70 COI sequences from 40 species (38 Entiminae, two Cyclominae) was initiated in the course of this work, to assist with the complexity of identification of species in this group. The genus Phlyctinus itself was comprehensively sampled over a 3 year period, and host-plant record obtained for the majority of the specimens. These samples will be subject to thorough taxonomical investigation, through morphological (geometric morphometrics) and molecular means (RAD-seq of multiple gene regions), to determine true species richness, and start inferring speciation processes. This will be the first study to investigate drivers of speciation in a Curculionidae taxa native to the CFR.
South African native strains of the entomopathogenic nematodes (EPNs) Heterorhabditis indica and Steinernema yirgalemense, and the entomopathogenic fungus (EPF) Beauveria bassiana PPRI 5339 have shown a high virulence against different life stages of Phlyctinus callosus s.l. As the taxonomical revisions of the genus took place after this research, a distinction between the pest species P. callosus s.s. and P. xerophilus was not possible at the time. As differences in susceptibility to entomopathogens may be shown even by closely related arthropod species, it is necessary to screen different target live-stages of accurately identified P. callosus s.s. and P. xerophilus against these entomopathogens Apart from genetically and physiologically linked susceptibility or resistance, insect behaviour in a host-plant environment under natural conditions may determine levels of infection by entomopathogens. Screening of the adults of P. callosus and P. xerophilus show differences in susceptibility to B. bassiana PPRI 5339 and H. indica, while clear results could not be obtained for S. yirgalemense. Larvae and pupae of both weevil species will be screened against the two EPNs, and a semi-field trial conducted under natural conditions, while shelter site preference of adult weevils will be determined for both Phlyctinus pest species under semi-field conditions, and this information used to develop a targeted application approach for the EPF in a semi-field trial.
Professional Experience
2017. Assistant in Bagrada bug (Bagrada hilaris Burmeister) sampling and maintenance for USDA/ARC bio-control study
2017. Leading investigator and consultant into true bug damage of a commercial apple orchard, Picketberg, Western Cape, South Africa for Dept. Conservation Ecology and Entomology IPM initiative, Stellenbosch University/Nexus
2020-2021. Student demonstrator for the module Entomology 418, Stellenbosch University
2020-2021. Consultant for Dept. Genetics, Stellenbosch on study of sucking insect damage on pears.
Publications
Haran, J.M, Hansen, S., Benoit, L. and Addison, P. 2020. Description of five new species in the genus Phlyctinus Schoenherr (Coleoptera, Curculionidae): a first step in deciphering the P. callosus complex. European Journal of Taxonomy 669: 129. doi: 10.5852/ejt.2020.669
Hansen, S., Addison, P., Benoit, L. and Haran, J.M. 2021. Barcoding pest species in a biodiversity hot-spot: the South African polyphagous broad-nosed weevils (Coleoptera, Curculionidae, Entiminae). Biodiversity Data Journal 9: e66452. doi: 10.3897/BDJ.9.e66452