Project datasets and thesis

Abstract Invasive pests have become a significant research topic worldwide due to the damage caused when these pests are established in new environments. Invasive shot hole borers (ISHB) are a good example of these invasive pests causing significant damage to urban trees, forests, and agricultural ecosystems worldwide. Ambrosia beetles are from the subfamily Scolytinae, are minute in size, can infest multiple host tree species, and have a symbiotic relationship with different fungal species that can cause branch dieback and lead to tree death. For Euwallacea fornicatus (Polyphagous Shot Hole Borer, PSHB), female beetles are the main dispersers. Realized dispersal can be strongly influenced by biotic and abiotic factors, including temperature, wind, photoperiod, and humidity. Among other factors, body size and wing morphology (wing shape, wing size, and wing structure) can also influence the flight performance and dispersal of insects. This study therefore aimed to estimate PSHB dispersal ability under controlled laboratory conditions and assess the environmental (temperature) dependence thereof to inform risk management of this invasive species in South Africa. To achieve this, I determined the effects of time-ofday patterns and five experimental temperatures on the proportion of individuals in the population that flew. I also tested if there was performance variation among the experimentally controlled temperatures for the major flight parameters obtained from automated flight mills. Lastly, I compared the wing morphology of those that flew and those that did not by looking at the potential morphological variation associated with dispersal-prone beetles. First, the results indicated that PSHB female beetles fly better in cooler conditions, with peak flight activity occurring in the afternoon, between 12:00 and 15:00. Secondly, there were little to no temperature effects on the flight parameters obtained from the flight mills, except perhaps on the number of flight bouts which showed a significant negative interaction with body mass. Lastly, the results showed that dispersal-prone beetles had smaller wings at cooler temperatures and therefore that wing morphology might be negatively correlated with the flight ability of PSHB. In conclusion, I argue that time-of-day and environmental conditions will greatly mediate flight responses of PSHB thus potentially impacting their invasiveness. Furthermore, thermal and time-of-day effects will need to be accounted for when assessing population abundances based on trap catches in the field for management decisions.