Effect of temperature, humidity and wind on the dispersal capacity of the Asian citrus psyllid

The Asian citrus psyllid (ACP) (Diaphorina citri) vectors the bacterium Candidatus Liberibacter asiaticus, the causal agent of Huanglongbing (HLB) which is a lethal disease of citrus with no known cure. Identifying the effect of environmental conditions on the flight capacity of the ACP is critical to predict its dispersion in citrus production zones. While flight capacity has been explored under tropical and subtropical conditions (high temperatures, high humidity), this has not been investigated for the Mediterranean climate, high temperatures like those experienced in southern California, where the insect and pathogen are currently under quarantine. Additionally, southern California experiences high speed winds called the “Santa Ana Winds” throughout the year and it is not yet understood how this may influence the dispersion of ACP from their host plants. Here, by using a novel, temperature-controlled flight mill and a high-speed wind tunnel, we studied the effect of high temperatures and humidity and high-speed wind on ACP flight capacity and propensity and wind-assisted dispersion. Overall, ACP flight capacity was affected by temperature but not by humidity. Specifically, there was a negative correlation between temperature and flight capacity with no long flights above 43 °C. Humidity had an effect on flight distance with long flights happening more commonly in low humidity. Strong winds (30 - 40 mph) significantly increased the percentage of insects that were wind-dispersed. In conclusion, moderate temperatures, low humidity and strong wind are likely to favor ACP dispersion.