Seasonal cues induce phenotypic plasticity of Drosophila suzukii to enhance winter survival

Abstract

BackgroundAs global climate change and exponential human population growth intensifies pressure on agricultural systems, the need to effectively manage invasive insect pests is becoming increasingly important to global food security. Drosophila suzukii is an invasive pest that drastically expanded its global range in a very short time since 2008, spreading to most areas in North America and many countries in Europe and South America. Preliminary ecological modeling predicted a more restricted distribution and, for this reason, the invasion of D. suzukii to northern temperate regions is especially unexpected. Investigating D. suzukii phenology and seasonal adaptations can lead to a better understanding of the mechanisms through which insects express phenotypic plasticity, which likely enables invasive species to successfully colonize a wide range of environments.ResultsWe describe seasonal phenotypic plasticity in field populations of D. suzukii. Specifically, we observed a trend of higher proportions of flies with the winter morph phenotype, characterized by darker pigmentation and longer wing length, as summer progresses to winter. A laboratory-simulated winter photoperiod and temperature (12:12 L:D and 10 °C) were sufficient to induce the winter morph phenotype in D. suzukii. This winter morph is associated with increased survival at 1 °C when compared to the summer morph, thus explaining the ability of D. suzukii to survive cold winters. We then used RNA sequencing to identify gene expression differences underlying seasonal differences in D. suzukii physiology. Winter morph gene expression is consistent with known mechanisms of cold-hardening such as adjustments to ion transport and up-regulation of carbohydrate metabolism. In addition, transcripts involved in oogenesis and DNA replication were down-regulated in the winter morph, providing the first molecular evidence of a reproductive diapause in D. suzukii.ConclusionsTo date, D. suzukii cold resistance studies suggest that this species cannot overwinter in northern locations, e.g. Canada, even though they are established pests in these regions. Combining physiological investigations with RNA sequencing, we present potential mechanisms by which D. suzukii can overwinter in these regions. This work may contribute to more accurate population models that incorporate seasonal variation in physiological parameters, leading to development of better management strategies.Electronic supplementary materialThe online version of this article (doi:10.1186/s12898-016-0070-3) contains supplementary material, which is available to authorized users.

Baseline susceptibility of spotted wing Drosophila (Drosophila suzukii) to four key insecticide classes

“…Probit analysis on these data was conducted using SAS version 9.4 26 to determine the LC 50 and LC 90 values and the 95% fiducial limits. The slopes of the probit lines and standard errors were also determined for each insecticide for each tested colony.…”

“…Origin ® (OriginLab, Northampton, MA, USA) was used to plot the mortality data for the four insecticides when tested against the susceptible population collected from the untreated site (Site 1). Resistance ratios (RR 50 and RR 90 ) were calculated for the LC 50 and LC 90 levels as a ratio of the mortality of each collection relative to the untreated standard site (Site 1). Comparisons across the 3 years were made using analysis of variance (ANOVA) followed by Fisher's Least Significant Difference (LSD) test for post-hoc comparisons.…”

“…Non-normal data were log (X + 1) transformed to achieve normality and heteroscedastic data were 1/X transformed to achieve homogeneous variances. For the comparison between 2 years for zeta-cypermethrin, LC 50 and LC 90 data were log (X + 1) transformed and analyzed using a two-sample t-test. A comparison of spray intensity was conducted by categorizing sites into one of two groups, high or no/low spray.…”

“…These approaches will be important for future testing of whether resistance is developing in field populations. Smirle et al 14 tested several insecticides and determined LC 50 and LC 90 values for male and female D. suzukii collected from British Columbia, Canada. In addition, they attempted to accelerate resistance to malathion in the laboratory through selection pressure, but no resistance was evident after 30 generations.…”

The Phenology of Infestations and the Impacts of Different Varieties of Cold Hardy Red Raspberries on <i>Drosophila suzukii</i>

“…A better understanding of the biology and ecology of this species is critical in refining current management practices for this pest. Spatial optimization of control may be particularly important when early season infestations are likely to occur due to the emigration of overwintering individuals from other areas [14] [17] [18]. Dispersal and movement from crop and non-crop hosts remains one of the most challenging variables to characterize, particularly for insects of small size in natural settings [9] [16] [19]- [21].…”