Recording and reproducing the diurnal oviposition rhythms of wild populations of the soft- and stone- fruit pest Drosophila suzukii

Abstract

Drosophila suzukii is a horticultural pest on a global scale which causes both yield and economic losses on a range of soft- and stone-fruit. Tackling this pest is problematic but exploiting behavioral rhythms could increase the impact of control. To do this, a better understanding of behavioral patterns is needed. Within this study we aimed to investigate rhythms in reproductive behavior of wild D. suzukii under natural conditions in the field. Environmental parameters were also recorded to decipher how they influence these rhythms. Assays were then performed on laboratory cultures, housed under artificial conditions mimicking the temperature and light cycles, to see if these patterns were reproducible and rhythmic. We were able to promote field like oviposition patterns within the laboratory using realistic temperature and light cycles regardless of variations in other factors including substrate, humidity, and lighting type. Locomotion activity was also recorded under these mimicked conditions to identify how this behavior interacts with oviposition rhythms. Both our field and laboratory assays show that oviposition behavior is likely under the control of the circadian clock and primarily occurs during the day. However, consistent with prior reports we observed that these patterns become crepuscular when day-time temperature peaks exceeded 30°C. This was also found within locomotion rhythms. With an increased understanding of how these behaviors are influenced by environmental conditions, we highlight the importance of using realistic temperature and light cycles when investigating behavioral patterns. From an increased understanding of D. suzukii behavior we increase our ability to target the pest in the field.

Fig 1. Correlation of the number of eggs laid and adult emergence.

Flies were subjected to 12:12 L:D cycles in a constant 23°C within the reproductive oviposition confirmation assay in the laboratory. Measurements during the day are indicated by an open circle, those laid during the night indicated by a closed triangle.

Fig 2. Average oviposition rate per hour in either the day or night.

a-d. Average oviposition rates (+SE) collected under (a)12:12 L:D in 23°C, (b) 17:7 17/11°C in the laboratory or reproductive oviposition rate per hour (+SE) in either the day or night under (c) August and (d) October in the field. * indicates significant difference between day and night counts within each environmental condition.

Fig 3. Average oviposition of laboratory strains under recreated June conditions within the laboratory.

Average reproductive oviposition (+SE) collected in 2 hour ‘oviposition windows’ over three days. Average temperature (black solid line) and relative humidity (RH) (dashed grey line at x 0.5) cycled through-out. Note that relative humidity was kept constant at 65% in laboratory assays. Light is indicated by the colour of average D. suzukii bars. Black = darkness, grey = half-light and white = light.

Fig 4. Normalised counts of D. suzukii oviposition in June conditions within the laboratory.

Normalised oviposition rates (+SE) in relation to time (a) and temperature (b).

Fig 5. Average D. suzukii oviposition of wild and laboratory strains under August conditions within the field and laboratory.

Average reproductive oviposition (+SE) of (a) wild D. suzukii in the field and (b) average oviposition (+SE) of laboratory strains in recreated August conditions within the laboratory (bars) in 2 hour ‘oviposition windows’ over three days. Average temperature (black solid line) and relative humidity (RH) (dashed grey line at x 0.5) cycled through-out. Note that relative humidity was kept constant at 65% in laboratory assays. Light is indicated by the colour of average D. suzukii bars. Black = darkness, grey = half-light and white = light.

Fig 6. Normalised D. suzukii oviposition under August conditions in relation to time and temperature.

Normalised counts of D. suzukii reproductive oviposition from (a) field assay (+SE) (black bars) and (b) laboratory oviposition (+SE) (grey bars) in August conditions and (c) field vs. laboratory (+SE) in relation to time. Normalised counts of D. suzukii reproductive oviposition from (d) field assay (+SE) and (e) laboratory oviposition (+SE) in August conditions and (f) field vs. laboratory (+SE) in relation to temperature. Different letters identify significant differences between time points within each setting.

Fig 7. Average D. suzukii oviposition of wild and laboratory strains under October conditions within the field and laboratory.

Average reproductive oviposition (+SE) of (a) wild D. suzukii in the field and (b) average oviposition (+SE) of laboratory strains in recreated October conditions within the laboratory (bars) in 2 hour ‘oviposition windows’ over three days. Average temperature (black solid line) and relative humidity (RH) (dashed grey line at x 0.5) cycled through-out. Note that relative humidity was kept constant at 65% in laboratory assays. Light is indicated by the colour of average D. suzukii bars. Black = darkness, grey = half-light and white = light.

Fig 8. Normalised D. suzukii oviposition under October conditions in relation to time and temperature.

Normalised counts of D. suzukii reproductive oviposition from (a) field assay (+SE) (black bars) and (b) laboratory oviposition (+SE) (grey bars) in October conditions and (c) field vs. laboratory (+SE) in relation to time. Normalised counts of D. suzukii reproductive oviposition from (d) field assay (+SE) and (e) laboratory oviposition (+SE) in October conditions and (f) field vs. laboratory (+SE) in relation to temperature. Different letters identify significant differences between time points within each setting.

Fig 9. Mean locomotion counts/minute of mix sex groups in relation to average oviposition.

Standard error of mean range of locomotion (counts per minute) of mix sex groups (grey area) in relation to average oviposition (+SE) (bars) and temperature (dash grey line) in the laboratory. Collected under recreated (a) June, (b) August and (c) October conditions. Light is indicated by the colour of average counts bars: Black in darkness, grey in half-light and white in full-light. Oviposition was assessed during the light phase (04:00–00:00 under June conditions, 05:00–21:00 under August and 06:45–18:45 under October).