Reproductive activity and diapause induction in Ips typographus
Abstract
Numerous insects evolved diapause to cope with seasonally re-occurring adverse conditions, affecting multiple life-history traits, including reproduction, survival, and voltinism. The spruce bark beetle Ips typographus – a major disturbance agent in spruce-dominated forests of Eurasia – enters reproductive diapause to survive harsh winters. Induction of facultative diapause is mainly regulated by short daylengths, but modified by warm temperatures, potentially postponing entry into diapause. Knowledge on the interplay of these cues under natural conditions is still lacking despite its importance for phenology and management in a changing climate. We conducted a comprehensive field study over three years along an elevational gradient in South-West Germany to quantify diapause expression in I. typographus under a broad range of natural photoperiod and temperature conditions. Most individuals entered diapause in mid-August (daylengths < 14 hours), regardless of temperature. However, some individuals still reproduced at warm temperatures (> 22-26 °C) in late October (daylengths ~10 hours), even following cold nights below 5 °C. However, fecundity of these late-breeding individuals was reduced. In comparison to previous findings, we revealed a later diapause induction in I. typographus due to warm temperatures. Within-population variability in the timing of diapause induction is an effective strategy to increase the amount of late-breeding individuals and thus voltinism in a warming climate. Bark beetle phenology models should hence (i) include temperature as diapause-modifying cue in addition to photoperiod, and (ii) consider potential differences between populations from diverse geographic origins.
https://doi.org/10.5061/dryad.p8cz8wb0f
Description of the data and file structure
In a multi-year field study along an elevation gradient, we recorded the reproduction of Ips typographus in experimental logs in order to assess its diapause induction. To this end, logs were successively exposed to incoming beetles for one week to subsequently debark them and record multiple factors, to infer diapause induction.
Files and variables
File: data.csv
Description: Data recorded using experimental logs. "NA" refers to values that are not available.
Variables
- log_id: Unique ID of the respective log
- site_name: Site at which the sample was taken
- year: Year in which the sample was taken
- calendar_week: Calender week in which the sample was taken
- surface area: surface area of the experimental log in square centimeters
- adults_alive: number of living adults found in the sample
- adults_dead: number of dead adults found in the sample
- adults_total: total number of adults found in the sample
- teneral_beetles: number of teneral beetles found in the sample
- pupae: number of pupae found in the sample
- larvae_big: number big larvae found in the sample
- larvae_small: number of small larvae found in the sample
- larval_tunnels: number of larval tunnels found in the sample
- eggs: number of egg-niches without larval tunnel found in the sample
- start_infestation: starting date of the period, during which the sample was exposed to incoming beetles
- end_infestation: end date of the period, during which the sample was exposed to incoming beetles
- total_offspring: the total amount of offspring found in the sample
- mother_tunnel_count: number of mother tunnels found in the sample
- mother_tunnel_length: combined length of all mother tunnels found in the sample
- mating_chamber_count: number of mating chambers found in the sample
- t_max: maximum air temperature during sampling week in °C
- t_min: minimum air temperature during sampling week in °C
- t_mean: mean air temperature during sampling week in °C
- daylength: daylength during sampling week in hours
Code/software
R-Studio