Accounting for overwintering life-histories in an online pest risk assessment tool

The OPRAM (Online Pest Risk Analysis Model) project is developing an open source web application, which will be used in guiding risk assessment and surveillance of high priority plant pests across Ireland. Current models predict the timing of adult emergence during the year using an accumulative growing degree day model, but overwintering is not typically included (for example : https://www.usanpn.org/vis-tool). The inclusion of overwintering is particularly important when predicting a plant pest’s end-of-year phenology and for making predictions across multiple years.

We developed template models for the three main overwintering life-histories for insects. Quiescence implies that an insect may be present all year round if temperatures are high enough;e.g.  Spodoptera frugiperda may not reach the required threshold.. In addition, the inclusion of the fractional number of generations per year is especially important as it indicates regions which maybe close to completing a generation based on the threshold rather than presenting a null value.

The inclusion of obligate and facultative diapause imply the season will end earlier due to the decrease in photoperiod or because of the combined effects of photoperiod and temperature for species like Leptinotarsa decemlineata and Oulema melanopus. This would impact the overall risk assessment depending on how many generations of a species may appear during the year and the mitigative measures undertaken. For instance, Ips typographus, has greater damage if a second generation were to emerge. If diapause were not ncluded in these models then this variation in year-to-year seasonal length may not be captured. 

We give examples for six template species: Agrilus anxius, Spodoptera frugiperda, Leptinotarsa decemlineata, Oulema melanopus, Ips typographus and Halyomorpha halys. We used mean temperature and photoperiod from the Republic of Ireland from 1961 until present. Future climate scenarios were incorporated using projections across three RCP scenarios (RCP 26, 45 & 85) across two future periods : 2021 – 2050 and 2041 – 2070. 

Future climate scenarios indicate that more generations will occur; where for instance, Agrilus anxius would increase from three generations to four generations as its season is solely temperature based. Whereas, other such as Leptinotarsa decemlineata that undergo obligative diapause may not have an increase in generations as a decrease in photoperiod serves as a limiting factor for their length of season. While for Halyomorpha halys, no generations would appear despite the warmer conditions. 

The goal of this project is to have an open access web application that could then be developed further in the future. This readily could serve as a template for initiatives in other countries. This online tool will provide the decision support to allow actions to be taken in the event of high risk of the modelled pest and can be expanded to if a new pests that may emerge over time in the Republic of Ireland.