Fruit flies, berries and climate change
February 17, 2019
Climate change could facilitate the spread of invasive species by warming northern regions and making them suitable habitat for species that would otherwise be excluded due to cold temperatures. Langille et al. (2017) examined the prospect of this scenario playing out for an invasive species of fruit fly called the spotted wing drosophila (Drosophila suzukii).
Spotted wing drosophila is native to Japan but has expanded its range over the past 35 years to include every continent except Antarctica. Female spotted wing drosophila will lay eggs into ripe or ripening fruit, leading to loss of the fruit through spoilage. When environmental conditions favour an infestation, spotted wing drosophila can cause important yield losses of fruit crops. Some of the female’s preferred host fruit for laying eggs include strawberries, blueberries, cherries, blackberries, and raspberries.
Temperature is a critical factor in determining the size of many insect populations and this also holds true for spotted wing drosophila. In order to make predictions about the spatial extent and population sizes of spotted wing drosophila in the US and southern Canada under climate change, Langille et al. (2017) developed population models based on temperature. The authors drew on four recently developed Global Circulation Models (GCMs) that offer climate projections. One of the challenges associated with predicting climate has to do with the vast array of complex environmental interactions and processes that influence climate. GCMs offers projected climate estimates based on modeled assumptions of these environmental factors. For their study, projections of daily temperatures were averaged over time and space giving three time periods: 2020s (2010-2039), 2050s (2040-2069), and 2080s (2070-2099).
The population models were built using a number of additional components. Langille et al (2017) chose four potential future trajectories for the main drivers of climate change (e.g., greenhouse gas emissions) called Representative Concentration Pathways or RCPs. Key simulations were also chosen and included: a fruit development/ripening index, a maximum fruit quality of 50 days, a starting point of 10 fecund females, as well as diapause initiation date and the temperature at which diapause ended. The authors acknowledge that their models are missing some important factors that could influence spotted wing drosophila population sizes such as evolutionary adaptations to changing temperatures.
Since it is impossible to know which of the four GCMs will be the best predictor of future climate, the authors combined them to obtain simulated spotted wing drosophila population totals for each of the three time periods and four RCP scenarios. The simulated results were presented as consensus maps which show the most extensive high populations corresponding to the 2020s time period. Into the 2050s, populations are lowered in central US as temperature increases beyond what is favourable for spotted wing drosophila while some areas of Canada see increases in populations due to a shift from cool to warmer temperatures. In the 2080s, central and northern US become too warm and the most favourable conditions are in northeastern and western US and some southern regions of Canada. Only one RCP scenario was markedly different from the others showing relatively lower populations by 2080.
The authors aggregated the models further by combining the RCPs to yield one consensus map per time period. These maps demonstrate a general reduction in spotted wing drosophila populations over time with the exception of some more northern regions. When compared against population size projections presented in Langille et al. (2016) that are based on historical (1993-2013) measured temperatures, more than half the locations examined have historic populations that are greater than projected estimates, indicating that populations may be on the decline in these areas.
Overall, Langille et al. (2017) conclude that the models point to a drop in spotted wing drosophila population levels in fruit-crop regions as a result of increasing temperatures. Alternatively, some northern regions may see an increase in populations with warming temperatures however, these are not currently important fruit-crop producing areas. The authors also stress that their model results are best considered in combination with other similar models in order to create a more complete picture of the mechanisms driving population levels under rapid climate change.
Read full article (open access):
Langille AB, Arteca EM, and Newman JA. 2017. The impacts of climate change on the abundance and distribution of the Spotted Wing Drosophila (Drosophila suzukii) in the United States and Canada. PeerJ. doi: 10.7717/peerj.3192.
Langille AB, Arteca EM, Ryan GD, Emiljanowicz LM, and Newman JA. 2016. North American invasion of Spotted-Wing Drosophila (Drosophila suzukii): a mechanistic model of population dynamics. Ecological Modelling. 336:70–81 doi: 10.1016/j.ecolmodel.2016.05.014.