Impact of Climate Change on Voltinism and Prospective Diapause Induction of a Global Pest Insect – Cydia pomonella (L.)

Global warming will lead to earlier beginnings and prolongation of growing seasons in temperate regions and will have pronounced effects on phenology and life-history adaptation in many species. These changes were not easy to simulate for actual phenologies because of the rudimentary temporal (season) and spatial (regional) resolution of climate model projections. We investigate the effect of climate change on the regional incidence of a pest insect with nearly worldwide distribution and very high potential for adaptation to season length and temperature – the Codling Moth, Cydia pomonella. Seasonal and regional climate change signals were downscaled to the hourly temporal scale of a pest phenology model and the spatial scale of pest habitats using a stochastic weather generator operating at daily scale in combination with a re-sampling approach for simulation of hourly weather data. Under future conditions of increased temperatures (2045–2074), the present risk of below 20% for a pronounced second generation (peak larval emergence) in Switzerland will increase to 70–100%. The risk of an additional third generation will increase from presently 0–2% to 100%. We identified a significant two-week shift to earlier dates in phenological stages, such as overwintering adult flight. The relative extent (magnitude) of first generation pupae and all later stages will significantly increase. The presence of first generation pupae and later stages will be prolonged. A significant decrease in the length of overlap of first and second generation larval emergence was identified. Such shifts in phenology may induce changes in life-history traits regulating the life cycle. An accordingly life-history adaptation in photoperiodic diapause induction to shorter day-length is expected and would thereby even more increase the risk of an additional generation. With respect to Codling Moth management, the shifts in phenology and voltinism projected here will require adaptations of plant protection strategies to maintain their sustainability

Induction and inhibition of diapause by the same photoperiod: Experimental evidence for a "double circadian oscillator clock"

Spieth H, Xue FS, Strauss K. Induction and inhibition of diapause by the same photoperiod: Experimental evidence for a "double circadian oscillator clock". JOURNAL OF BIOLOGICAL RHYTHMS. 2004;19(6):483-492.On the southern Iberian Peninsula, the seasonal life history of the large white butterfly, Pieris brassicae, comprises 2 different photoperiodically induced developmental arrests: a hibernation diapause at photophases 14 h. At intermediate photophases (12 h to 13 h), the butterfly responds with a nondiapause. Combined with the experimental setup to determine photosensitivity in insects, the different photoperiodic responses at long-, intermediate-, and short-night conditions were examined to gain more insight into the time measurement mechanism in R brassicae. The study reveals evidence for a "double circadian oscillator clock" mechanism that is based on 2 submechanisms, a "short-night determining system" and a separate "long-night determining system." This conclusion was drawn from the facts that an LD 9:15 long-night induces a hibernation diapause but inhibits an estivation diapause and, conversely, that an LD 16:8 short-night inhibits a hibernation diapause but induces an estivation diapause. This opposite effect of the same photoperiod supports the argument for the existence of 2 independent targets for light-dark cycles, interpreted as 2 antagonistic time measurement systems. The existence and independence of 2 systems was further shown by differences in long-night versus short-night responses regarding photosensitivity, temperature dependence, and heritable factors. The long-night measurement system is most effective in the 5th larval stage, is highly affected by temperature, and is easy to manipulate by selective inbreeding. The short-night measurement system is most effective in the 4th larval stage, is largely temperature compensated, and is not affected by experimental manipulation of the long-night measurement system

Latitudinal clines:An evolutionary view on biological rhythms

Properties of the circadian and annual timing systems are expected to vary systematically with latitude on the basis of different annual light and temperature patterns at higher latitudes, creating specific selection pressures. We review literature with respect to latitudinal clines in circadian phenotypes as well as in polymorphisms of circadian clock genes and their possible association with annual timing. The use of latitudinal (and altitudinal) clines in identifying selective forces acting on biological rhythms is discussed, and we evaluate how these studies can reveal novel molecular and physiological components of these rhythms

Diapause decision in the small tortoiseshell butterfly , Aglais urticae

Insects in temperate areas spend the inhospitable winter conditions in a resting stage known as diapause. In species that diapause in the larval or pupal stage, the decision whether to diapause or develop directly is customarily taken during the late instars, with long days (i.e., long light phases) and high temperatures promoting direct development. Among butterflies that overwinter as adults, data are rare and variable, but imply that the larval daylength conditions can affect the pathway decision. We studied the small tortoiseshell, Aglais urticae L. (Lepidoptera: Nymphalidae, Nymphalini), which is partially bivoltine from Central Scandinavia and southwards, and tested whether the pathway decision is taken in the larval or adult stage. We reared larvae under long-day (L22:D2) or short-day (L12:D12) photoperiods, and recorded the pathway taken by the eclosing adults by scoring their propensity to mate and produce eggs. We also tested whether the larval photoperiod influenced adult ability to diapause by assessing adult survival. The results clearly indicate that (1) there is no detectable effect of larval photoperiod treatment on the pathway decision taken by adults whether to enter diapause or to develop directly, (2) some individuals are obligately univoltine and insensitive to photoperiod during adulthood, whereas (3) other individuals can facultatively enter diapause or direct development, depending on the photoperiod experienced after adult eclosion