THE VECTOR POTENTIAL OF THE MOSQUITO AEDES KOREICUS Silvia Ciocchetta BVSc, Masters Animal Health, Animal Farming & Animal Production Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) School of Biomedical Sciences Faculty of Health Queensland University of Technology 2018 Keywords Aedes koreicus, invasive mosquito species, laboratory colonisation, hatching percentage, embryo dormancy, embryo development, fecundity index, pupae differentiation, mosquito reproductive biology, mosquito mating biology, autogeny, interspecific mating, mosquito sperm, competitive displacement, satyrization, Wolbachia, fluctuating temperature, arbovirus, chikungunya, chikungunya virus (CHIKV), vector competence, arthropod-borne disease, public health. The vector potential of the mosquito Aedes koreicus i Abstract The introduction and establishment of exotic mosquitoes have facilitated outbreaks of arthropod-borne disease in new areas of the world. There is an urgent need to understand the risk of disease outbreaks posed by invasive mosquitoes. Aedes (Finlaya) koreicus [1] is an invasive mosquito species from South-East Asia recently discovered in Europe. It has now colonised six European countries, including Italy (Belluno province), where it was first reported in 2011. Between 2011 and 2012, Ae. koreicus doubled its distribution in the Belluno province from 33.3% to 65.2% of municipalities (n= 65) and increased its presence in the Treviso province from 2.1% to 18.9 % of municipalities (n= 95). This invasive behaviour is similar to that of Aedes albopictus, a major vector of chikungunya (CHIKV) and dengue (DENV) viruses, that has become endemic in 22 European countries since introduction in 1991. Despite the rapid spread and establishment of Ae. koreicus, the impact of this mosquito on native ecosystems and public health remains unknown. This thesis provides the first detailed insights into the biology of Ae. koreicus and its capacity to transmit CHIKV. Field and laboratory work was conducted in Italy to evaluate trapping and surveillance techniques for Ae. koreicus, along with the propensity of this species to bite humans. None of the traps used returned high numbers of Ae. koreicus, either in rural or urban settings. However, host-seeking Ae. koreicus were found to feed on humans during late afternoon and evening. Field-collected material was used to establish laboratory colonies of Ae. koreicus, first in Italy, and then at QIMR Berghofer in Australia, and to confirm the absence of the endosymbiont Wolbachia pipientis in specimens from field. Despite few Ae. koreicus eggs (10.4 ± 2.1%) hatching and relatively long gonotrophic cycles The vector potential of the mosquito Aedes koreicus ii (blood-feeding to oviposition interval = 11.5 ± 3.5 days) the species proved suitable for colonisation in the laboratory, providing an ideal opportunity to further study its biology. Mosquitoes reared under artificial conditions were used to calculate a fecundity-size relationship (Y = 88.51 * X – 239.6, P ˂ 0.0001, r2 = 0.6051; n=51) for evaluating Ae. koreicus population fitness, to explore the species’ reproductive behaviour and to determine the lack of autogeny in the colony. The possibility of mating interference between Ae. albopictus and Ae. koreicus was explored using a small-scale behavioural study. Ae. albopictus’ ability to disrupt other mosquitos’ behaviours and to sterilise mosquito females of different species through sperm transfer is well documented [2-6]. Repeated attempts of interspecific mating of Ae. albopictus males with Ae. koreicus female were recorded, suggesting that disruption/interference could occur in the field. The Ae. koreicus colony proved highly suitable for laboratory-based vector competence experiments, providing the first evidence to evaluate the risk of CHIKV transmission by this species. The mosquitoes had high feeding rates on artificially infected blood delivered via membranes (65.5%) and almost all (96.8%) of the colony mosquitoes survived at day 14 post feeding. Infection rates post challenge with CHIKV were low at two temperature regimes examined (13.8% at 23°C; 6.2% under fluctuating temperature close to climatic conditions in the Ae. koreicus Italian range). Dissemination of the virus to wings and legs occurred only in 6.1% mosquitoes and only in those maintained at 23°C. Salivary infection occurred in just two of the blood fed mosquitoes (n=129). No dissemination of the virus to the wings and legs or saliva of mosquitoes occurred when they were maintained under fluctuating temperatures. The vector potential of the mosquito Aedes koreicus iii These findings deliver novel insights into the biology of Ae. koreicus and help to elucidate the public health risk posed by this species in regards to the transmission of arboviruses. The vector potential of the mosquito Aedes koreicus iv Table of Contents Keywords .................................................................................................................................. i Abstract .................................................................................................................................... ii Table of Contents .................................................................................................................... vi List of Figures ......................................................................................................................... ix List of Tables ........................................................................................................................... xi List of Abbreviations .............................................................................................................. xii Statement of Original Authorship ......................................................................................... xiv Acknowledgements ................................................................................................................ xv Conference abstracts............................................................................................................. xvii Publications arising from candidature .................................................................................. xvii Publications included in this document ............................................................................... xviii Chapter 1: Introduction ...................................................................................... 1 1.1 Background .................................................................................................................... 1 1.2 Context ........................................................................................................................... 7 1.3 Purposes ......................................................................................................................... 7 1.4 Significance, Scope and Definitions .............................................................................. 8 1.5 Thesis Outline ................................................................................................................ 9 Chapter 2: Literature review ............................................................................ 11 2.1 Introduction .................................................................................................................. 11 2.2 Major arboviruses and their public health impact ........................................................ 11 2.3 Major vectors of arboviruses and their invasive potential ........................................... 14 2.4 Invasive mosquito species in Europe ........................................................................... 16 2.5 Ae. koreicus: native range and biology ........................................................................ 20 2.6 Vector competence of Ae. koreicus .............................................................................. 20 2.7 Distinguishing Ae. koreicus from Ae. japonicus: morphological and genetic features 22 2.8 Ae. koreicus in Europe ................................................................................................. 26 2.9 Ae. koreicus monitoring: ECDC guidelines for invasive mosquito species ................. 27 2.10 Interspecies competition between invasive and native species: current knowledge .... 33 Chapter 3: Evaluation of mosquito traps for the field collection of adult Ae. koreicus in a variety of physiological states ........................................................... 36 3.1 Introduction .................................................................................................................. 36 3.2 Methods ........................................................................................................................ 37 3.2.1 Evaluation of the field performance of four trapping methods .......................... 37 3.2.2 Human landing ................................................................................................... 44 3.3 Results .......................................................................................................................... 46 The vector potential of the mosquito Aedes koreicus vi 3.3.1 Evaluation of the field performance of four trapping methods ..........................46 3.3.2 Human landing ...................................................................................................48 3.4 Discussion and conclusion ............................................................................................51