Voltinism

The variation in response to photoperiod and temperature of different populations of the peacock butterfly, Inachis io (L.) (Lepidoptera: Nymphalidae), was investigated to test the extent to which species can adjust their response to the environment, and therefore maximise their reproductive potential. The photoperiodic (adult) diapause induction response varies between populations, and appears to be finely tuned to the local conditions. There is however variation within populations and the response can be adjusted in a population by selective breeding. The developmental rate is not significantly different between three latitudinally distinct populations, over the range of temperatures tested, and pupal weights are similar at given temperatures. However, pupal weights increase with decreasing development temperature. The implications of these findings are discussed with reference to modelling life history strategies.

In most temperate insects, diapause strategies and voltinism generally exhibit latitudinal clines, supporting the concept that they represent adaptations to climate. In contrast, in the satyrine butterfly Ypthima multistriata Butler, local populations with different voltinism patterns are geographically intermingled, suggesting that life-history traits related to diapause may differ even between geographically and phylogenetically close populations. In this study, we experimentally examined the critical photoperiod for diapause induction and the larval developmental period in two univoltine and two bivoltine populations of Y. multistriata, all of which inhabit virtually the same latitude (34.652-34.750°N). We found that the critical photoperiod for diapause induction was longer in the univoltine populations than in the bivoltine populations. Moreover, the larval period under the long day length treatment was different among populations in both sexes, although significant differences were also detected between populations with the same voltinism. These results indicate that in Y. multistriata, life-history traits related to diapause can not be attributed merely to climatic conditions such as temperature or day length, which depend largely on latitude. Therefore, we suggest that biotic elements, such as leaf toughness, as well as abiotic elements should be taken into account in attempts to explain the enigmatic pattern of geographic variation in the diapause strategies of Y. multistriata.

SEASONAL CYCLES OF MAYFLIES IN A FOOTHILL STREAM OF CORDOBA PROVINCE
Abundance change during an annual cycle of four species of mayflies (Insecta,Ephemeroptera) in a Sierras de los Comechingones stream (Córdoba, Argentina) have been
surveyed. The study area was located in Piedras Blancas stream. Surber net samples were taken monthly in a stretch of runs and riffles. The first right femur of 30 individuals, from each sample, was measured to carry out a size frequency analysis. Body size and biomass were measured in each organism. Americabaetis sp., Tricorythodes popayanicus and Leptohyphes eximius were multivoltine with an early spring generation, two fast growth summer and autumn generations and a slowly developing winter generation. Camelobaetidius penai was bivoltine with a spring and a summer generation. Baetidae species had longer developmental times and larger body sizes than Leptohyphidae species. All species, except Camelobaetidius penai, were present along the year in the study site. Torrential stream regime, with strong rainfalls and scouring floods concentrated in
the summer, seems to determine the selection of species of small size, high density, short life cycles and multivoltine generations.Key words: Baetidae, Leptohyphidae, body sizes, voltinism

Climate change induces an alteration in the life cycle of many poikilothermic organisms, resulting in changes in the structure and function of communities. Changes in voltinism in the pine moth Dendrolimus spectabilis (Butler), which is known to be univoltine in South Korea, were studied to elucidate the effects of climate change on their voltinism. The developmental stages of the pine moth were evaluated through field surveys, and the developmental rate was estimated at five different temperatures: 17, 20, 25, 28, and 32°C. Field surveys showed that the moths completed two generations per year, indicating that the phenology of the pine moth in this area had changed from univoltinism to bivoltinism. Laboratory experiments showed that increasing the temperature could induce a change in voltinism in the pine moth population. Generations of the bivoltine population displayed phenotypic plasticity: the fitness of the first generation was greater than that of the second generation with regard to size and fecundity. The difference in fitness between the first and second generations could be due to the influence of factors such as low food quality and heat stress on the second generation. Therefore, changes in thermal conditions due to climate change have offered this species the chance to develop a bivoltine population, but they have also exerted ecological costs, especially for the second generation of the pine moth. Keywords Climate change Á Dendrolimus spectabilis Á Pitch pine Á Temperature Á Voltinism W.I. Choi, Y.-K. Park contributed equally to the article.

Geographic range expansion is one of the best documented macroecological consequences of climate change. A concomitant change in morphology has been demonstrated in some species. The relationship between latitudinal variation in morphology (e.g. Bergmann’s rule) and the morphological consequences of microevolutionary pressures at expanding range margins have received little attention in the literature. Here we compare morphology of males of two Palaearctic damselfly (Odonata: Zygoptera) species, Coenagrion puella (Linnaeus, 1758) and Pyrrhosoma nymphula (Sulzer, 1776). C. puella has recently expanded its range from the north of England into Scotland. P. nymphula does not exhibit a range margin in the United Kingdom and has established populations in northern Scotland. We demonstrate evidence for spatially correlated variation in body size across the sampling sites between the two species but a deviation in patterns of dispersal-related morphology. P. nymphula exhibited very weak relationships between dispersal-related morphology (wing loading and thorax : abdomen mass ratio) and latitude. However, the more southerly distributed C. puella exhibited strong relationships between mass investment in dispersal-related morphology and latitude. These
trends appear to indicate compensatory growth patterns in cooler environments like those demonstrated for other species. The limits of this compensation for conditions that are close to the limits of a species’ tolerance may contribute to the determination of the range margin. Greater variation in morphology towards the range margin has been observed in previous studies in Odonata. As such, the location of the sampling sites relative to the range margin of each species (closer in C. puella than P. nymphula) is highlighted as a potential contributing factor to the variation observed.

The seasonal cycle of Picromerus bidens L. (Heteroptera: Pentatomidae) is usually considered to be univoltine with an obligatory winter egg diapause. Seasonal adaptations of the species were studied in the laboratory and in field experiments. When reared under short-day photoperiodic conditions (L12:D12 and L14:D10), all females began to lay eggs synchronously soon after their emergence. However, in the females reared under long-day conditions (L18:D6 and L20:D4) and outdoors in June-July, oviposition was significantly delayed. This delay in reproduction induced by photoperiodic conditions and then spontaneously terminated was considered to be aestivation. Egg batches laid by females in the laboratory and in the field were kept at 25 • C for two months. From 30.8 to 93.8% of batches contained eggs which hatched without cold treatment between day 14 and 60 after oviposition. The proportion of eggs hatched was 17.7 to 20.9% in the short-day regimes, while it was significantly less (5.7 to 6.0%) under long-day conditions. It is concluded that in some eggs diapause is of low intensity and that if under natural conditions the first batches had been laid at the end of June, nymphs would have hatched at least from some eggs during the same season even without cold treatment. Such untimely hatching would have resulted in the death of nymphs and adults unprepared for overwintering. A photoperiodic response which induces aestivation in the early emerging adults in June-August may prevent early oviposition and occurrence of a second generation and thus maintains univoltinism in P. bidens.

... Juha Pöyry1*, Reima Leinonen2, Guy Söderman1, Marko Nieminen3, Risto K. Heikkinen1 and Timothy R. Carter1 ... had been interpolated across a regular 10 ¥ 10 km grid over Finland on the basis of records from active climato-logical stations (Venäläinen & Heikinheimo, 2002 ...

The phytophagous bug Riptortus clavatus (Thunberg) (Heteroptera: Alydidae) produces two or three generations per year in Central Japan and overwinters in the adult stage. In bugs from the Kyoto population (35 • 00 N, 135 • 45 E), we studied (1) the effects of day-length on the nymphal and preoviposition periods under constant photoperiod at 20.5 • C, and (2) photoperiodic induction of adult diapause at 20.5 • C and under a combination of constant photoperiod and natural daily rhythm of temperature in the forest-steppe zone of Russia (50 • 38 N, 35 • 58 E). Then, we examined (3) the timing of diapause induction under quasi-natural conditions in the same region, far outside the species' natural geographical range. At 20.5 • C, the nymphal period in both males and females was significantly longer under regimes with shorter photophases than under those with longer photophases. The preoviposition period in females was significantly longer under the near-critical long-day regime L14:...

The effect of day-length and temperature on the duration of the egg to adult period and reproductive diapause in Orius strigicollis (Poppius) (Heteroptera: Anthocoridae) from central Japan (36°N; 140°E) was studied in the laboratory. At 20°C, the egg to adult period tended to increase with lengthening of photoperiod from short day [10:14 (L:D) h] to long day [14:10 (L:D) h], but slightly decreased with further lengthening of photoperiod, whereas at 24°C, an opposite trend was recorded. At 28°C, the developmental period was much shorter and there were no obvious trends. It is assumed that photoperiod-mediated acceleration of nymphal growth takes place in autumn when ambient temperature and natural day-length are decreasing, thus promoting earlier emergence of adults prior to the deterioration of environmental conditions. The species showed a long-day photoperiodic response of reproductive diapause induction: at 20 and 24°C, 83-100% females entered diapause under short-day conditions [10:14 (L:D), 11:13 (L:D), and 12:12 (L:D) h], whereas 82-91% of females were reproductive under long-day conditions [14:10 (L:D), 15:9 (L:D), and 16:8 (L:D) h]. The critical day-length was close to 13 h at 20°C and to 12.5 h at 24°C. Diapause induction was strongly suppressed at 28°C: its incidence did not exceed 50% even at 10:14 (L:D) h. It is estimated that O. strigicollis produces four or five generations in central Japan. The seasonal cycle and tendency to enter diapause are compared with other Orius species and other geographical populations of O. strigicollis. Implications of diapause-related traits for biological control are discussed.

Abstract.  1. Good conservation management is underpinned by a thorough understanding of species' historical and contemporary dispersal capabilities along with the possible adaptive or neutral processes behind any spatio-temporal genetic structuring. These issues are investigated with respect to the rare damselfly Coenagrion mercuriale (Charpentier) – the only odonate species currently listed in the U.K.'s Biodiversity Action Plan – in east Devon where its distribution has become fragmented.2. The two east Devon C. mercuriale populations, only 3.5 km apart, have accumulated strong differences in frequencies of alleles at 14 microsatellite loci as a consequence of poor adult dispersal and drift. There is no contemporary migration between sites.3. A genetic signature of population decline at both sites corresponds with known demographic reductions. Coenagrion mercuriale in east Devon are now significantly genetically less diverse than those from a population stronghold in the Itchen Valley.4. Colonies would benefit from improved connectivity between areas and possibly by a transfer of individuals from other ecologically similar areas.5. Because C. mercuriale has a semivoltine life cycle throughout the U.K., the possibility that alternate-year cohorts are reproductively isolated is explored. Genetic differentiation among cohorts is an order of magnitude less than between sites, suggesting that some larvae delay their development into adults for a year and recruit to a different cohort.6. To our knowledge, this is the first study to document migration and gene flow between alternate-year cohorts in a species of odonate. From a conservation standpoint, the cohorts do not require separate management.

Abstract: Ips typographus is the main spruce pest of European forests. In most areas of the Italian Alps there are two generations per year; overwintering adults fly in May looking for trees suitable for breeding, their offspring emerge in summer, 7–8 weeks after tree colonization, and the adults of the second generation emerge in spring of the following year after overwintering under the bark or in the litter. A long-term population monitoring was carried out in north-east Italy with the aim at developing a prediction model able to estimate the population density of the following year. Between 1996 and 2004, pheromone traps monitored populations of I. typographus annually. Monitoring lasted 4 months (May–August), with replacement of pheromone dispensers after 8 weeks. Insects trapped before dispenser change were called ‘spring captures’ (May–June), and included both overwintering and re-emerging adults. Beetles caught after dispenser change were called ‘summer captures’ (July–August), and included the adults of the first generation. The results show a high positive correlation between the ratio of summer and spring captures of one year (Summerx/Springx), and the ratio of total captures of the following year (Yx+1) and those of the current year (Yx) (Yx+1/Yx). Summerx/Springx lower than 0.62 indicate decreasing populations in the following year (Yx+1/Yx <1), whereas Summerx/Springx higher than 0.62 indicate increasing populations (Yx+1/Yx >1). The applicability of the model in the study of I. typographus risk of outbreak and in the forest management is discussed. The prediction of the short-time trend of the population allows assessing its density in the following year, and therefore the risk of outbreak.

During 1992 and 1993, we studied the life cycle ofLambdina athasaria(Walker) developing on eastern hemlock,Tsuga canadensis(L.) Carrière, in Connecticut. The geometrid was univoltine, overwintering as a pupa. Adults emerged during 4 weeks in May and June after hemlock budbreak. Males emerged significantly earlier than females, and both sexes emerged earlier in 1993 than in 1992. Males flew for 4–5 weeks annually. Based on measurements of head capsule width, larvae had five or six instars, which fed from June to October. Early instars ate new growth, and older ones fed on old growth. Until mid-August, larval development was more advanced in 1993 than in 1992. Larvae descended from trees in September and October to pupate in the duff beneath trees.Lambdina athasariacan be distinguished from congeneric species that feed on conifers by its overwintering stage, flight period, larval size, and host.

... This result shows that our classification of butterfly species into generalist and specialist groups based on their voltinism (seasonal time dimension) and ... Fig. 4. Rank (species sequence)–abundance (mean annual density) diagrams for five grassland butterfly communities ...

Summer drought associated with high temperatures recorded in the last few years has given rise to outbreaks of bark beetles developing in weakened host trees. The aim of this study was to investigate the possible weather effect on the biology of and damage caused by Ips typographus L. in the southeastern Alps. The study was carried out recording temperature (1962Ð2007), precipitation (1922Ð2007), and the damage caused by I. typographus (1993Ð2007). In addition, data from pheromone-baited traps (1996 Ð2005) provided information on the main periods of ßight activity of I. typographus. From 1922 to 2007, precipitation during MarchÐJuly has decreased Ϸ200 mm (Ϫ22%), whereas since 1962Ð2007, mean temperatures during MarchÐJuly increased Ϸ2ЊC (ϩ13%). Damage caused by I. typographus was inversely correlated with MarchÐJuly precipitation from the previous year but not correlated with temperature. Increases in spring temperature did not affect the development timing of the Þrst generation, but only changed its onset. Earlier swarming of both overwintering beetles and Þrst-generation offspring (Ϸ20 d sooner over 10 yr), and the early start of the second generation permitted more complete development of the second brood. Voltinism in this species is discussed in relation to thermal and photoperiodic thresholds, indicating that the occurrence of a third generation is limited by the summer photoperiod rather than by temperature. In conclusion, results suggest that spring drought increases damage caused by I. typographus in the following year, whereas warmer spring affects insect phenology. KEY WORDS precipitation, temperature, damage, phenology, voltinism Environmental disturbances or extreme weather conditions usually give rise to outbreaks of forest pests developing in weakened host trees. In recent years, high temperature coincided with periods of drought inducing a global change "type drought" (Breshears et al. 2005): increases in high temperatures reduce developmental time, increase voltinism, and increase infestation pressure (Wermelinger and Seifert 1998), whereas drought reduces tree resistance to pests (Mattson and Haack 1987, Larsson 1989, Croisé and Lieutier 1993). This can often increase the likelihood of an insect outbreak, as recently observed in several bark beetle spp. (Coleoptera: Curculionidae) in Europe (

The form and variability of temperature-dependent development responses were measured for the braconid parasitoid Meteorus trachynotus (Vier.), developing in Choristoneurafumiferana (Clem.) and C. rosaceana (Harr.). It was found that parasitism reduces the duration and variability of postdiapause development in C. rosaceana larvae, and that the development of the parasitoid does not resume until its host emerges from diapause. M. trachynotus development and entry into diapause are controlled by the host. In large, nondiapausing hosts, the parasitoid can complete one generation in about 348 degree-days above 5.9 ~ Male and female adults live an average of 22.0 and 23.8 days at 20 ~ and the preoviposition period is 1.7 days. Total fecundity averages 194.2 eggs per female and is reduced considerably by low host density. Under our experimental conditions, female M. trachynotus lay a maximum of 14.3 eggs per day, with a maximum of 3.7 eggs per host, on average. Simulations based on degree-day accumulation in 13 locations in eastern Canada showed that the parasitoid was well synchronized with its two alternative hosts, that M. trachynotus could complete three generations in most locations, and that voltinism was essentially determined by entry of C. rosaceana larvae into diapause. Overlap between adult parasitoids and larvae of the spruce budworm is incomplete, and inadequate synchrony seems to be an important aspect of the ecological interactions between these two organisms.

1. Voltinism may be conceptualised as the product of development rate and the timing of diapause -two components that together translate gradual environmental variation, through periods of growth and development, into 'generational units'. This may result in very different selection pressures on diapause induction and development time in populations with different numbers of generations per year.